World of Chemistry

Base Of Organic Chemistry

noreply@blogger.com (Unknown) — Tue, 2 Jun 2015 09:31:00 -0700

Brief History :

Jöns Jacob Berzelius, a physician by trade, first coined the term "organic chemistry" in 1807 for the study of compounds derived from biological sources. Up through the early 19th century, naturalists and scientists observed critical differences between compounds that were derived from living things and those that were not.

Chemists of the period noted that there seemed to be an essential yet inexplicable difference between the properties of the two different types of compounds. The vital force theory (sometimes called "vitalism") was therefore proposed (and widely accepted) as a way to explain these differences. Vitalism proposed that there was something called a "vital force" which existed within organic material but did not exist in any inorganic materials.

Synthesis of Urea

Friedrich Wöhler is widely regarded as a pioneer in organic chemistry as a result of his synthesizing of the biological compound urea (a component of urine in many animals) utilizing what is now called "the Wöhler synthesis."

Wöhler mixed silver or lead cyanate with ammonium nitrate; this was supposed to yield ammonium cyanate as a result of an exchange reaction, according to Berzelius's dualism theory. Wöhler, however, discovered that the end product of this reaction is not ammonium cyanate (NH4OCN), an inorganic salt, but urea ((NH2)2CO), a biological compound. (Furthermore, heating ammonium cyanate turns it into urea.) Faced with this result, Berzelius had to concede that (NH2)2CO and NH4OCN were isomers. Until this discovery in the year 1828, it was widely believed by chemists that organic substances could only be formed under the influence of the "vital force" in the bodies of animals and plants. Wöhler's synthesis dramatically proved that view to be false.

Urea synthesis was a critical discovery for biochemists because it showed that a compound known to be produced in nature only by biological organisms could be produced in a laboratory under controlled conditions from inanimate matter. This "in vitro" synthesis of organic matter disproved the common theory (vitalism) about the vis vitalis, a transcendent "life force" needed for producing organic compounds.

Organic vs Inorganic Chemistry:

Although originally defined as the chemistry of biological molecules, organic chemistry has since been redefined to refer specifically to carbon compounds — even those with non-biological origin. Some carbon molecules are not considered organic, with carbon dioxide being the most well known and most common inorganic carbon compound, but such molecules are the exception and not the rule.

Organic chemistry focuses on carbon and following movement of the electrons in carbon chains and rings, and also how electrons are shared with other carbon atoms and heteroatoms. Organic chemistry is primarily concerned with the properties of covalent bonds and non-metallic elements, though ions and metals do play critical roles in some reactions.

The applications of organic chemistry are myriad, and include all sorts of plastics, dyes, flavorings, scents, detergents, explosives, fuels and many, many other products. Read the ingredient list for almost any kind of food that you eat — or even your shampoo bottle — and you will see the handiwork of organic chemists listed there.

Major Advances in the Field of Organic Chemistry:

Of course no description of a text should be without at least a mention of Antoine Laurent Lavoisier. The French chemist is often called the "Father of Modern Chemistry" and his place is first in any pantheon of great chemistry figures. Your general chemistry textbook should contain information on the specific work and discoveries of Lavoisier — they will not be repeated here because his discoveries did not relate directly to organic chemistry in particular.

Berzelius and Wöhler are discussed above, and their work was foundational to the specific field of organic chemistry. After those two, three more scientists are famed for independently proposing the elements of structural theory. Those chemists were August Kekulé, Archibald Couper and Alexander Butlerov.

Kekulé was a German, an architect by training, and he was perhaps the first to propose that the concept of isomerism was due to carbon's proclivity towards forming four bonds. Its ability to bond with up to four other atoms made it ideal for forming long chains of atoms in a single molecule, and also made it possible for the same number of atoms to be connected in an enormous variety of ways. Couper, a Scot, and Butlerov, a Russian, came to many of the same conclusions at the same time or just a short time after.

Through the nineteenth century and into the twentieth, experimental results brought to light much new knowledge about atoms, molecules and molecular bonding. In 1916 it was Gilbert Lewis of U.C. Berkeley who described covalent bonding largely as we know it today (electron-sharing). Nobel laureate Linus Pauling further developed Lewis' concepts by proposing resonance while he was at the California Institute of Technology. At about the same time, Sir Robert Robinson of Oxford University focused primarily on the electrons of atoms as the engines of molecular change. Sir Christopher Ingold of University College, London, organized what was known of organic chemical reactions by arranging them in schemes we now know of as mechanisms, in order to better understand the sequence of changes in a synthesis or reaction.

The field of organic chemistry is probably the most active and important field of chemistry at the moment, due to its extreme applicability to both biochemistry (especially in the pharmaceutical industry) and petrochemistry (especially in the energy industry). Organic chemistry has a relatively recent history, but it will have an enormously important future, affecting the lives of everyone around the world for many, many years to come.

Organic chemistry :-

Organic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of hydrocarbons and their derivatives. These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens as well as phosphorus, silicon and sulfur. Because of their unique properties, multi-carbon compounds exhibit extremely large variety and the range of application of organic compounds is enormous. They form the basis of, or are important constituents of many products (paints, plastics, food, explosives, drugs, petrochemicals, to name but a few) and (apart from a very few exceptions) they form the basis of all earthly life processes.

Organic chemistry, like all areas of science, evolves with particular waves of innovation. These innovations are motivated by practical considerations as well as theoretical innovations. The area is however underpinned financially by the very large applications in polymer science, pharmaceutical chemistry, and agrichemicals.

Properties :

Physical properties of organic compounds typically of interest include both quantitative and qualitative features. Quantitative information include melting point, boiling point, and index of refraction. Qualitative properties include odor, solubility, and color.

Melting and boiling properties

In contrast to many inorganic materials, typical organic compounds typically melt and boil. In earlier times, the melting point (m.p.) and boiling point (b.p.) provided crucial information on the purity and identity of organic compounds. The melting and boiling points correlate with the polarity of the molecules and their molecular weight. Some organic compounds, especially symmetrical ones, sublime, that is they evaporate without melting. A well known example of a sublimable organic compound is para-dichlorobenzene, the odiferous constituent of mothballs. Organic compounds are usually not very stable at temperatures above 300 °C, although some exceptions exist.

Color

Organic compounds are typically colorless or white. The situation is quite different for organic compounds that contain several adjacent multiple bonds. These compounds, where the double bonds are "conjugated" can be deeply colored. The biological pigments carotene and heme illustrate the relationship between "conjugation" and color. Impure organic compounds, as well as many biological materials, often are yellow or brownish owing to the presence of trace amounts of intensely colored impurities.

Solubility

Neutral organic compounds tend to be hydrophobic, that is they are less soluble in water than in organic solvents. Exceptions include organic compounds that contain ionizable groups as well as low molecular weight alcohols, amines, and carboxylic acids where hydrogen bonding occurs. Organic compounds tend to dissolve in organic solvents. Solvents can be either pure substances like ether or ethyl alcohol, or mixtures, such as the paraffinic solvents such as the various petroleum ethers and white spirits, or the range of pure or mixed aromatic solvents obtained from petroleum or tar fractions by physical separation or by chemical conversion. Solubility in the different solvents depends upon the solvent type and on the functional groups if present.

Solid state properties

Various specialized properties are of interest depending on applications, e.g. thermo-mechanical and electro-mechanical such as piezoelectricity, electrical conductivity (see organic metals), and electro-optical (e.g. non-linear optics) properties. For historical reasons, such properties are mainly the subjects of the areas of polymer science and materials science.

Toxicity :

Living matter including food, drugs are collections organic compounds, so the potential beneficial and harmful aspects of organic compounds span the entire range required for life to some of the most dangerous materials known. Indicative of the power of organic chemistry, the biomolecule called botulism toxin ("Botox") is lethal at the level of less than a microgram.

Nomenclature?:

The names of organic compounds are either systematic, following logically from a set of rules, or nonsystematic, following various traditions. Systematic nomenclature is stipulated by recommendations from IUPAC. Systematic nomenclature starts with the name for a parent structure within the molecule of interest. This parent name is then modified by prefixes, suffixes, and numbers to unambiguously convey the structure. Given that millions of organic compounds are known, rigorous use of systematic names can be cumbersome. Thus, IUPAC recommendations are more closely followed for simple compounds, but not complex molecules. To use the systematic naming, one must know the structures and names of the parent structures. Parent structures include unsubstituted hydrocarbons, heterocycles, and monofunctionalized derivatives thereof.

Nonsystematic nomenclature is simpler and unambiguous, at least to organic chemists. Nonsystematic names do not indicate the structure of the compound. Nonsystematic names are common for complex molecules, which includes most natural products. Thus, the informally named lysergic acid diethylamide is systematically named (6aR, 9R)-N, N-diethyl-7-methyl-4, 6, 6a, 7, 8, 9-hexahydroindolo-[4, 3-fg] quinoline-9-carboxamide.

With the increased use of computing, other naming methods have evolved that are intended to be interpreted by machines. Two popular formats are SMILES and InChI.

Structural drawings :

Organic molecules are described more commonly by drawings or structural formulas, combinations of drawings and chemical symbols. The line-angle formula is simple and unambiguous. In this system, the endpoints and intersections of each line represent one carbon, and hydrogen atoms can either be notated explicitly or assumed to be present as implied by tetravalent carbon. The depiction of organic compounds with drawings is greatly simplified by the fact that carbon in almost all organic compounds has four bonds, oxygen two, hydrogen one, and nitrogen three.

Arrhenius Definition: Hydroxide and Hydronium Ions:

The first and earliest definition of acids and bases was proposed in the 1800's by Swedish scientist Svante Arrhenius, who said that an acid was anything that dissolved in water to yield H+ ions (like stomach acid HCl, hydrochloric acid), and a base was anything that dissolved in water to give up OH- ions (like soda lye NaOH, sodium hydroxide). Acids and bases were already widely used in various occupations and activities of the time, so Arrhenius' definition merely attempted to explained well-known and long-observed phenomenon.

Although simple, at the time this definition of the two types of substances was significant. It allowed chemists to explain certain reactions as ion chemistry, and it also expanded the ability of scientists of the time to predict certain chemical reactions. The definition left a great deal wanting, however, in that many types of reactions that did not involve hydroxide or hydronium ions directly remained unexplained.

Many general chemistry classes (especially in the lower grades or introductory levels) still use this simple definition of acids and bases today, but modern organic chemists make further distinctions between acids and bases than the distinctions provided under Arrhenius's definition.

Author : Kirti Niralwad

Documented Dangers of Gas Chambers and Carbon Monoxide Poisoning

noreply@blogger.com (Unknown) — Wed, 29 Jun 2011 10:55:00 -0700

Documented Dangers of Gas Chambers and Carbon Monoxide Poisoning

Four state and local agencies of North Carolina government have documented hazards of faulty gas chambers and supply cylinders at public animal shelters since 2004. Leaks and malfunctions were recorded by the North Carolina Department of Labor, North Carolina Department of Health and Human Services, North Carolina Department of Agriculture, and local fire marshals in Reidsville and Stokes County. The findings of these agencies were obtained through public record requests.

Most gas chambers in our state had reportedly never been formally inspected prior to 2004. Since that time, complaints from thousands of residents to government officials and the media have brought the controversial euthanasia method to the forefront. One of the most compelling documents is a North Carolina Department of Labor inspection for Sampson County Animal Control in 2004.

1. The inspector's worksheet reads,

"The animal begins to struggle because it cannot breathe...They wait approximately 10 minutes until the animal stops making sounds and then turn on a fan that is supposed to evacuate the CO from the chamber."
Gas monitor readings showed employee overexposure to carbon monoxide, which the officer believed "is occurring when the chamber door is opened to remove the animal." No respiratory protection was provided for employees.
Reidsville Fire Marshal John Harris inspected a gas chamber at Rockingham County Animal Control in 2004, on the property of Reidsville Veterinary Hospital, after repeated attempts to repair gas leaks (2). An inspection from August 2004 recounts:
"Harris checked the chamber finding that the door seals to the chamber were in disrepair and damaged in several locations. Harris also observed where attempts to repair the seals were made with what appeared to be caulking. Also noted that the integral safety systems for monitoring carbon monoxide levels has been DISABLED. Vent pipe from the top portion of the chamber is poorly fitted and sealed with what appears to be adhesive tape. During operation of the euthanasia chamber carbon monoxide monitors were used to test levels present adjacent to the chamber....carbon monoxide levels exceeded 984 ppm in the area of the chamber....After the purge cycle during removal of animals a reading of 460 ppm still remaining in the chamber as officers removed dead animals."
Not only can gas chambers leak and malfunction, but gas cylinders provided by carbon monoxide suppliers have also been documented as a potential hazard. North Carolina Department of Labor inspections revealed faulty gas cylinders at Columbus County Animal Control (3) and Davidson County Animal Control in 2006 (4). The Davidson County inspection notes that National Welders Supply does not formally test the cylinders for leaks. The Columbus County inspection says, "It was determined the overexposure occurred whenever the valve on the CO cylinder was initially opened, so the feasible engineering control would be to have the cylinder and valves checked for leaks." Animal control supervisor Rossie Hayes replied to the NCDOL, asking "for any suggestion on how to check the unit for leaks." He asked if employees should wear some type of respirator.
Stokes County Fire Marshal inspected a rusty dump-truck gas chamber at Stokes County Animal Control in January 2007 (5). A letter from the Marshal to shelter supervisor Sarah Shumate documented high levels of gas at the supply tank as well as the gas chamber door. Marshal Bradley Cheek warned:
"During the euthanasia process, levels of carbon monoxide in excess of 1000 ppm were detected on the exterior of the chamber loading door. It is not known what the exact readings were; this is due to the monitor having a maximum reading of 1000 ppm....Carbon monoxide is immediately dangerous to life and health at 1200 ppm."
Yet another jaw-dropping inspection was performed for Montgomery County Animal Control by North Carolina Department of Agriculture inspector Shelly Swaim in 2007 (6). Swaim writes,
"It was reported to me by Mr. Beane that the chamber is leaking and that there were visible cracks as well as an insufficient gasket around door. There is also no mechanism to facilitate venting of this unit. Inmates were on property and addressing chamber issues at 12:17. It appears that this CO chamber even with corrections employed at this time will pose a significant risk to the safety and life of the operator."
Industrial hygienist Marilyn Parker of the North Carolina Department of Health and Human Services has performed gas monitor readings for two animal shelters, Granville County Animal Control in 2006 (7) and Randolph County Animal Control in 2007 (8). Both inspections revealed high level leaks of carbon monoxide around the edges of the gas chamber doors. Chambers at both facilities are modern, commercially manufactured units. Concerning the Randolph County inspection, Parker wrote, "While the chambers were in operation the monitor was placed in various locations around the door seals. Levels of CO were detected in excess of 500 ppm around the door seal....It was determined that the seals did not prevent carbon monoxide (CO) from escaping while the chambers were in operation." Ms. Parker requested in both letters that she be called for follow up inspections after corrections were made. As of October 2008, Parker said that she was not aware of any correspondence with county officials since the inspections.
CO levels above 10% are explosive, as affirmed by the gas chamber explosion at Iredell County Animal Control of Statesville in 2008. No inspection record for the machine was available, but an invoice shows that the unit had been purchased only months prior from Cutting Edge Fabrication, after originally being sold to Union County Animal Control in Monroe. In a Statesville News and Record article (9), Cutting Edge owner Stephen Whitesell is quoted: "Whitesell believes the fan somehow sparked the carbon monoxide before the gas could be purged from the chamber....Whitesell said the fan is not explosion proof." To the contrary, the AVMA 2007 Guidelines on Euthanasia include this warning about carbon monoxide chambers, "Any electrical equipment exposed to CO (eg., lights and fans) must be explosion proof."(10) Union County Sheriff Eddie Cathey told the Enquirer Journal in August 2008, (11) "the chamber that was eventually sold to Iredell was returned to Cutting Edge three years ago because it had a warped door." These are among the most expensive and hi-tech gas chambers on the market. Gas chambers from this manufacturer are reportedly still in use at Gaston, Cabarrus, and Union county animal control facilities.
Dangers to Humans
Carbon monoxide oozing from gas chambers can put shelter workers at risk of health problems, some of which can be delayed for weeks after exposure.
*The AVMA 2007 Guidelines on Euthanasia warns humans operating CO chambers: "In humans, exposure to 0.32% CO and 0.45% CO for one hour will induce loss of consciousness and death, respectively. Carbon monoxide is extremely hazardous for personnel because it is highly toxic and difficult to detect. Chronic exposure to low concentrations of carbon monoxide may be a health hazard, especially with regard to cardiovascular disease and teratogenic effects." (10)
* The National Institute for Environmental Safety and Health published an International Chemical Safety Card for Carbon Monoxide, which states,
"The gas mixes well with air, explosive mixtures are easily formed. The gas penetrates easily through walls and ceilings...Fatal if inhaled. May damage fertility or the unborn child if inhaled. Causes damage to blood if inhaled. Causes damage to blood and central nervous system through prolonged or repeated exposure if inhaled...Inhalation Risk: A harmful concentration of this gas in the air will be reached very quickly on loss of containment. Effects of Short-term Exposure: The substance may cause effects on the blood, resulting in carboxyhaemoglobinemia and cardiac disorders. Exposure at high levels may result in death. Effects of Long-term or Repeated Exposure: The substance may have effects on the cardiovascular system and central nervous system. May cause toxicity to human reproduction or development. " (12)
* The U.S. Environmental Protection Agency says, "Perhaps the most insidious effect of CP poisoning is the development of delayed neuropsychiatric impairment within 2 - 28 days after poisoning and the slow resolution of neurobehavioral consequences."(15)
* According to an article from the Journal of the American Medical Association in 2006, "Researchers discover a link between severe carbon monoxide poisoning and death years later from heart disease."(14)
* A materials safety data sheet from National Welders Supply, a leading supplier of bottled carbon monoxide to animal shelters, says that carbon monoxide is "Harmful if inhaled. Causes damage to the following organs: Blood, Lungs, Cardiovascular System, Central Nervous System. Vapor may cause flash fire...Extremely flammable. Gas may accumulate in confined areas, travel considerable distance to source of ignition and flash back causing fire or explosion." (18)
* A study by Ramona Hopkins and Fu Lye M. Woon states, "It is estimated that as high as 50% of individuals with carbon monoxide poisoning will develop neurologic, neurobehavioral, or cognitive sequelae." (17)
* A study of patients poisoned by carbon monoxide, from LDS Hospital in Salt Lake City, Utah in 1999 concluded, "Ninety-three per cent of the patients exhibited a variety of cognitive impairments, including impaired attention, memory, executive function, and mental processing speed. Ninety-five per cent of the patients experienced affective changes including depression and anxiety." (18)
* Yona Amatai studied the effects of low-level CO exposure on higher cognitive function. The study concluded, "The lower scores on neuropsychological tests indicate dysfunctions in memory, new learning ability, attention and concentration, tracking skills, visuomotor skills, abstract thinking, and visuospatial planing and processing. These dysfunctions correspond with previous reports of carbon monoxide neurotoxic effects in patients with moderate carbon monoxide poisoning. Low-level exposure to carbon monoxide results in impairment of higher cognitive functions." (19)
* A 1925 study by William C. Stadie and Kirby Martin of Yale University School of Medicine says, "Occasionally the blood becomes free of carbon monoxide and the coma terminates, but the patient subsequently sinks into a coma again and dies, probably as a result of central nervous system damage." (20)
* A 2006 study by Christopher Henry and Daniel Satran, M.D. states, "Myocardial injury is a frequent consequence of moderate to severe CO poisoning." (21)
* The Department of Health and Human Services, Center for Disease Control and Prevention says, "Red blood cells pick up CO quicker than they pick up oxygen. If there is a lot of CO in the air, the body may replace oxygen in blood with CO. This blocks oxygen from getting into the body, which can damage tissues and result in death." (22)
* Science Daily reported in 2004, "Brain damage occurs – days to weeks later – in half of the patients with a serious case of CO poisoning." (23)
* A 1983 article from Archives of Neurology detailed delayed neurologic effects of CO: "The most frequent symptoms were mental deterioration, urinary or fecal incontinence, gait disturbance, and mutism." (24)
* Dr. David G. Penney, author of several books on the subject of carbon monoxide, lists nervous system damage caused by CO exposure: causes seizure disorders, multiple-sclerosis-type disorders, speech impairments, forms of aphasia; effects on learning, decrements in intellectual capacity, judgment, ability to concentrate, memory, executive functioning, multi-tasking, emotion; effects on short- to long-term memory and limbic system, ataxia, and slurring of speech. (25)
Ineffectiveness of Gas Chambers
Several mishaps have been reported by North Carolina media, showing that gas chambers are not always effective. Leaking carbon monoxide can keep the machines from reaching or maintaining a lethal level of 6%-10% for animals inside the chamber. The result can be a slower death, or mere unconsciousness and assumed death before the animal is placed in a freezer, dumpster, landfill, or incinerator. Some animals do not die the first time, whether due to inadequate gas levels, age of animal, or health issues.
Kerry Prichard of the Charlotte Observer reported a leaking gas chamber at Cabarrus County Animal Control in March 1998. "The gas chamber used to euthanize the animals was in clear view of visitors and, some critics say, it didn't always work well. Critics say it killed the animals too slowly or not at all, because of leaks or overcrowding....The gas chamber has been reconditioned and moved to the new shelter." The same chamber is still in use, complete with patching compound. (26)
A September 2003 article from Charlotte Observer reporter Hannah Mitchell uncovered problems with a gas chamber used at Alexander County Animal Control. "League volunteers heard a dog barking in a freezer after it went through the shelter's gas chamber and was assumed to be dead. The county's gas chamber used for euthanizing animals is sealed with duct tape. Campbell worried that the makeshift sealer lengthened the time it takes for animals to die." (27)
The Charlotte Observer's "Death at the Pound" series in June 2003 reported the same problem in other county shelters : "In Union, as many as 10 dogs are gassed together in a 4-by-4-foot steel container. It replaced a cinder-block chamber that leaked, causing some animals to survive the gassing." In the same article, Stanly County Animal Control Officer Randy Palmer described a situation with a newer commercially manufactured gas chamber: "After you bring them out, some of them aren't all down. Sometimes we have to put them back in." (28)
Heather Howard of the Charlotte Observer interviewed Catawba County officials in 2004. County Manager Tom Lundy said that the existing gas chamber at the animal shelter "is inefficient and outdated." Emergency Services Director David Weldon felt that a new model "would ensure that animals in the device are euthanized." (29) Instead, the county made the change to euthanasia by injection in 2008.
Doug Clark of the Sampson Independent wrote a gripping story about a litter of puppies that survived the gas chamber at the local shelter in 2004 and were later adopted, only to die the next day. Attempting to dispel rumors of parvo in the facility, former employee Dianna Williford admitted, "We had tried to euthanize those puppies a half hour earlier and it just didn't work."(30) The only method of euthanasia used by the shelter at that time was a carbon monoxide chamber.
The most well known canine gas chamber survivor in North Carolina is Davie, a dog who was found alive in a dumpster after being dumped and assumed dead by Davie County Animal Control of Mocksville in 2005. Local residents Jeff and Susan Armsworthy were discarding trash at the dump when they heard a whining noise, which turned out to be a crying puppy in a plastic bag in the dumpster. The fearless couple jumped in and rescued the pup among piles of animal carcasses. Author Mike Gunning wrote, "Apparently, one of the puppies, while knocked unconscious by the gas, didn’t inhale enough to be fatal. It appears to have become conscious while in the dumpster." (31)
Though many shelters have made the transition toward humane euthanasia in recent years, at least 22 county animal control facilities in North Carolina still kill unclaimed animals in gas chambers as of December 2009.
Sources
1. North Carolina Department of Labor Inspection, Sampson County Animal Control, March 2004.
2. Reidsville Fire Marshal inspections of Reidsville Veterinary Hospital/ Rockingham County Animal Control 2004-2006.
3. North Carolina Department of Labor Inspection, Columbus County Animal Control, 2006.
4. North Carolina Department of Labor Inspection, Davidson County Animal Control, May 2006.
5. Letter from Stokes County Fire Marshal to animal control supervisor Sarah Shumate, January 4, 2007.
6. North Carolina Department of Agriculture, Montgomery County Animal Control, inspection by Shelley Swaim, September 19, 2007.
7. Letter from North Carolina Department of Health and Human Services, Epidemiology Section, Granville County Animal Control inspection, August 21, 2006.
8. Letter from North Carolina Department of Health and Human Services, Epidemiology Section, Randolph County Animal Control inspection, April 24, 2007.
9. Statesville News and Record, July 24, 2008, author Bethany Fuller.
10. 2007 American Veterinary Medical Association Guidelines on Euthanasia
11. Enquirer Journal article, August 3, 2008, Author Billy Ball.
12. National Institute for Environmental Safety and Health, International Chemical Safety Card, Carbon Monoxide.
13. "Heart Injury Due to Carbon Monoxide Poisoning Increases Long Term Risk of Death," Journal of the American Medical Association, January 24, 2006, Timothy D. Henry, M.D.
14. "The Brain Lesion Responsible for Parkinsonism After Carbon Monoxide Poisoning," Young H. Sohn, MD; Yong Jeong, MD; Hyun S. Kim, MD; Joo H. Im, MD; Jin-Soo Kim, MD, Archives of Neurology 2000;57:1214-1218.
15. "Carbon Monoxide Poisoning- A Public Health Perspective," US Environmental Protection Agency.
16. Carbon Monoxide Materials Safety Data Sheet, National Welders Supply.
17. Neuroimaging, Cognitive, and Neurobehavioral Outcomes Following Carbon Monoxide Poisoning Ramona O. Hopkins, Fu Lye M. Woon, Brigham Young University
18. "MRI, quantitative MRI, SPECT, and neuropsychological findings following carbon monoxide poisoning," Gale, S.D., Hopkins, R.O., Weaver, L.K., Bigler, E.D., Booth, E.J., Blatter, D.D., 1999, Brain Injury, 13 (4), pgs. 229-243.
19. "Neuropsychological Impairment From Acute Low-Level Exposure to Carbon Monoxide," Yona Amitai, MD; Zoli Zlotogorski, PhD; Vered Golan-Katzav, MA; Anya Wexler, MD; Ditza Gross, PhD
Archives of Neurology. 1998;55:845-848.
20. "The Elimination of Carbon Monoxide from the Blood," William Stadie and Kirby Martin, Yale University School of Medicine, 1925.
21. "Myocardial Injury and Long-term Mortality Following Moderate to Severe Carbon Monoxide Poisoning," Journal of American Medical Association, 2006, Christopher R. Henry, BS; Daniel Satran, MD; Bruce Lindgren, MS; Cheryl Adkinson, MD; Caren I. Nicholson, RN; Timothy D. Henry, MD;295:398-402.
22. Department of Health and Human Services, Centers for Disease Control and Prevention,
23. "Long-term Effects Of Carbon Monoxide Poisoning Are An Autoimmune Reaction," Science Daily; Veena M. Bhopale, Donald Fisher, Jie Zhang, and Phyllis Gimotty.
24. "Delayed neurologic sequelae in carbon monoxide intoxication," Archives of Neurology, July 1983, I. S. Choi.
25. “Major Sites of Nervous System Damage,” Dr. David G. Penney.
26. "Happy Endings Now Possible for Strays," Charlotte Observer, March 5, 1998, Author Kerry Prichard.
27. "Animal League Told to Leave- Alexander County Resumes Control of Shelter," Charlotte Observer, September 7, 2003, Author Hannah Mitchell.
28. "Death at the Pound: Animals in the Charlotte Region..." Charlotte Observer, June 29, 2003, Authors Michelle Crouch and Scott Dodd.
29. "Needs of Animal Shelter Outlined- Catawba Official Pitches Plan," Charlotte Observer, April 28, 2004, Author Heather Howard.
30. "Inhumane Treatment Or a Doing Their Best?" The Sampson Independent, February 07, 2004, Author Doug Clark.
31."Puppy Survives Euthanasia Attempt, Trip to Dump," Davie County Enterprise Record, April 2005, Author Mike Gunning.
Electronic copies of public records referenced above are available from the author at no charge.

AUTHOR :
Michele King is a board member of the North Carolina Coalition for Humane Euthanasia http://NCCHE.com. Members of this organization advocate for an end to gas chambers and other inhumane killing in animal shelters.

Chemistry Dealing With the Study of Chemical Compounds Containing Bond Between Carbon and Metal

noreply@blogger.com (Unknown) — Fri, 27 Nov 2009 06:30:00 -0800

The branch of chemistry that deals with the study of chemical compounds containing bonds between carbon and a metal is called as Organometallic chemistry. It combines the aspects of inorganic chemistry with organic chemistry, so such compounds are also known as organo-inorganic compounds.

Including all the traditional metals; lanthanides, actinides and semi-metals are considered to form organometallic compounds. There are many complexes also that feature the coordination bonds between a metal and an organic ligands, as organic ligands would always bind a metal through a heteroatom such as nitrogen or oxygen, and such compounds are then considered as coordination compounds. But, if any of the ligands would form a direct metal-carbon bond, then it would usually be considered as organometallic compound. In case of lipophilic and metal alkoxides it would be termed as metalorganics.

There are many organic coordination compounds that occur naturally in nature like hemoglobin which simply contain an iron centre that is coordinated to nitrogen atoms. When speaking of chlorophyll, magnesium acts as centre of a chlorine ring. The study of such inorganic compounds is termed as bioinorganic chemistry. The status of such compounds may vary with the nature of anionic moiety, and they may not usually be considered as organometallic.

Depending on the nature of the organic compound, the nature of the bond may also vary from ionic or covalent type. So the organic compounds that are bonded to sodium are ionic while those bonded to lead or tin are usually covalent whereas the ones bonded to lithium may have bonds with intermediate properties.

Such compounds also find their practical uses as stoichiometric and catalytic active compounds, like the use of ferrocene instead of tetraethyl lead as an anti knock agent. Organometallic compounds of reactive metals are extremely basic and are used as reductants. The act as superbases in organic synthesis, but their flammability reduces their industrial uses severely. The Monsanto process utilizes rhodium-carbonyl complex to manufacture acetic acid industrially. Also the Wacker process is used in the oxidation of olefins. Another titanium based organometallic compound called Ziegler-Natta catalyst is used in the production of polyethylene and other polymers.

The key to understand the chemical bonding in such compounds the isobal principle is used. NMR and infrared spectroscopy techniques are commonly used to determine the structure and bonding. Organometallics play an important role in other branches of chemistry such as biological and analytical. So, chemists sometimes refer to a particular molecule as organometallic making it more convenient to understand that molecules has reaction chemistry that derives from an organometallic molecule.

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Author: lalit sharma

Antioxidants: Chemistry and Their Impact on Health

noreply@blogger.com (Unknown) — Sun, 13 Sep 2009 08:24:00 -0700

1. Introduction.

In the aerobic environment, the most dangerous by product are the species of reactive oxygen. The role of antioxidants is to detoxify reactive oxygen intermediates (ROI) in the body. Over the past several years, nutritional antioxidants have attracted considerable interest in the popular press as potential treatment for a wide variety of disease states, including cancer and other causes e.g. cancer, chronic inflammatory diseases and aging (Delany L. 1993).

Naturally occurring inhibitors of oxidation in food generally originate from plant-based materials. The active components, namely phenolics and polyphenolics, including tocopherols, are secondary plant metabolites and are first derived from phenylalanine and in certain cases and in some plants from tyrosine. The resultant phenylpropanoids may then undergo further transformation to yield benzoic acid derivatives as well as flavonoids, isoflavons, and other complex polyphenols. Thus, natural food phenolics are present as a complex mixture of compounds that provide a cocktail of many active components present in the free, esterified, glycosylated and bound forms (Shahidi and Naczk, 1995). The potency of preparations is therefore dictated by their chemical structures and governed by the hydrophilic-lipophilic balance (HLB) of the participating molecules in a concentration- and system-dependent manner. Thus, the mode of action of natural antioxidants may involve multiple mechanisms, depending on the source material and possible presence of synergists and antagonists.

In order to use any antioxidant preparation in food, it must be safe, easy to incorporate, effective at low concentrations, with no undesirable odour, flavour or colour, heat stable, nonvolatile and with good carry through properties and cost-effective. In addition, presence and possible effects of antagonists must be carefully considered, as an antioxidant may become a prooxidant in the presence of certain other molecules. As an example, chlorophylls may overwhelm the antioxidant effect of phenolics due to photosensitized oxidation and transition metal ions such as those of iron and copper may render conditions that favour oxidation. Synergism among different phenolic antioxidants and between phenolics and non-phenolics should be considered in all application areas. Definition
Free radicals are atoms or groups of atoms with an odd (unpaired) number of electrons and can be formed when oxygen interacts with certain molecules. Once formed these highly reactive radicals can start a chain reaction. Their chief danger comes from the damage they can do when they react with important cellular components such as DNA, or the cell membrane. Cells may function poorly or die if this occurs. To prevent free radical the body has a defence system of antioxidants.

An antioxidant is a substance that when present in low concentrations relative to the oxidizable substrate significantly delays or reduces oxidation of the substrate (Halliwell, 1995).
Antioxidants get their name because they combat oxidation. They are substances that protect other chemicals of the body from damaging oxidation reactions by reacting with free radicals and other reactive oxygen species within the body, hence hindering the process of oxidation. During this reaction the antioxidant sacrifices itself by becoming oxidized. However, antioxidant supply is not unlimited as one antioxidant molecule can only react with a single free radical. Therefore, there is a constant need to replenish antioxidant resources, whether endogenously or through supplementation.

2. Review of Literature

Qin Yan Zhu et. al.(2001) studied antioxidant property of oolong tree. Inhibitory effect on FeCl2/ H2O2 – induced damage and the inhibitory effect on erythrocyte hemolysis of an oolonge tea extract (OTE) were evaluated. The OTE was found to have strong antioxidant activity in all model system. When OTE was separated into fractions according to molecular weight it was found that fraction with higher amount of phenolic compound (with low molecular weight) have strong antioxidative activity.
Yi Fang Chu and Xianzona Wu (2002) reported that increased consumption of fruits and vegetables containing high levels of phytochemicals have been recommended to prevent chronic diseases related to oxidative stress in human body. 10 common vegetables were selected. The study showed that Red peeper had highest total antioxidant activity followed by Broccoli, Carrot, Spinach, Cabbage, Onion, Potato etc.

Jie Sun and Yi Fang (2002) reported that consumption of fruit & vegetable associated with reduced risk to Chronic disease due to present of antioxidant. According to them vitamin C is the major antioxidant in fruit.

Jeong- Chae Lee (2002) assessed an ethanol extract of stem of opuntia to determine the mechanism of its antioxidant activities. The ethanol extract exhibited a concentration dependent inhibition of linoleic acid oxidation.

Keni Chi Ya na Gimoto et. al. (2002) investigated the antioxidant activity of column chromatographic fractions obtained from brewed coffee to find antioxidant and to assess benefits of coffee drinking. Coffee contain many antioxidant and consumption of antioxidant rich brewed coffee may inhibit disease caused by oxidative damage.

Anaberta Cardadose et.al. (2003) showed that fraction extracted with ethyl acetate have antioxidant activity with potent free radical scavenging activity.

Joon Hee Lee et. al. (2003) reported that Muscadine Grapes and its winary bi product have antioxidant capacity.

Kizhiyedathu et. al. (2003) reported that extract obtained from sesame cake and oil have free radical scavenging capacity i.e. antioxidant property.

K.S. Shivashankara and Seiichiro Isobe (2004) reported that if greenhouse- grown tree ripe ( TR) and mature green ( MG) mangoes (cv. Irwin) were exposed to high electric field treatment before 20 and 30 days of storage at 5O C. MG fruits were allowed to ripen at room temperature after low- temperature storage and antioxidant capacity were estimated before and after the storage period. Antioxidant capacity of fruits remained unchanged up to 20 days of storage period and decreased thereafter. Antioxidant capacity of fruits was significantly correlated only to ascorbic acids.

Joseph O. Kuti et.al. (2004) reported that total phenolics and antioxidant capacity were higher in raw that in cooked leaf extracts. Cooking reduced antioxidant activity. The results of their study indicate that tree spinach leaves are a rich source of natural antioxidants.

Mahinda Wella singh and Kirk Parkin (2004) studied a broad range of antioxidant activities in crude extract of beet root tissues. Betalain pigment have been shown to posses various antioxidant function.

3. Classification of antioxidants

Table 1. Classification of antioxidants based on their roles
Enzymes
Antioxidant
Role
Remarks
Superoxide dismutase (SOD)
Mitochondrial
Cytoplasmic
Extracellular
Dismutates O2· to H2O2
Contains Manganese (Mn.SOD)
Contains Copper & Zinc (CuZnSOD)
Contains Copper (CuSOD)
Catalase
Dismutates H2O2 to H2O
Tetrameric hemoprotein present in peroxisomes
Glutathione peroxidase (GSH.Px)
Removes H2O2 and lipid peroxides
Selenoproteins (contains Se2+)
Primarily in the cytosol also mitochondria
Uses GSH
Vitamins
Alpha tocopherol
Breaks lipid peroxidation
Lipid peroxide and O2· and ·OH scavenger
Fat soluble vitamin
Beta carotene
Scavenges ·OH, O2·and peroxy radicals
Prevents oxidation of vitamin A
Binds to transition metals
Fat soluble vitamin
Ascorbic acid
Directly scavenges O2·, ·OH, and H2O2
Neutralizes oxidants from stimulated neutrophils
Contributes to regeneration of vitamin E
Water soluble vitamin

Table 2.Classification Of antioxidants based on their sources
Source Material
Example
Antioxidant
Vegetable Oils
Soybean oil
Tocopherols
Tropical Oils
Palm oil
Tocotrienols
Plant Oils
Palm oil
Carotenoids
Herbs and Spices
Rosemary and Sage
Complex phenolics
Cereals
Wheat and buckwheat
Flavenoids
Legumes
Soybean
Isoflavones
Oil Seeds
Canola and Mustard
Phenolic acids & Phenylpropanoids
Teas
Green Tea
Catechins and Polyphenols
Fruit skin and seeds
Grape seed and skin
Polyphenols and Tannins

4. Antioxidant chemistry of some vitamins

4.1 Alpha tocopherol (vitamin E) Vitamin E -2D structure - C26H44O2

4.1.1 Nomenclature It is the major lipid soluble antioxidant found in cells.

The name originated in the early 1920s when vegetable oil was discovered to restore fertility in rats. This unknown substance was designated vitamin E by Sure in 1924.The term tocopherol was first used by Evans. Because this compound permitted an animal to have offspring, he named it tocopherol from the Greek word tokos, meaning childbirth, and added the verb phero, meaning to bring forth. To indicate the alcohol nature of the molecule, ol was added to the ending.

Vitamin E is a generic term that includes all entities that exhibit the biological activity of natural vitamin E, d-alpha-tocopherol. In nature, eight substances have been found to have vitamin E activity: d-alpha-, d-beta-, d-gamma- and d-delta-tocopherol (which differ in methylation site and side-chain saturation (Kellof et al. 1996); and d-alpha-, d-beta-, d-gamma- and d-delta-tocotrienol. Also, the acetate and succinate derivatives of the natural tocopherols have vitamin E activity, as do synthetic tocopherols and their acetate and succinate derivatives.

Of all these, d-alpha-tocopherol has the highest biopotency, and its activity is the standard against which all the others must be compared. It is the predominant isomer in plasma.

4.1.2 Source and Nature

Vitamin E is an essential nutrient that functions as an antioxidant in the human body. It is essential, by definition, because the body cannot manufacture its own vitamin E and thus it must be provided by foods and supplements.

Tocopherols are present in oils, nuts, seeds, wheat germ and grains. Absorption is believed to be associated with intestinal fat absorption. Approximately 40% of the ingested tocopherol is absorbed. Most tocopherols enter the blood via lymph where they are associated with chylomicrons. Vitamin E was shown to be stored in adipose tissue. Phospholipids of the mitochondria & endoplasmic reticulum & plasma membranes possess affinities for alpha tocopherol & the vitamin tends to concentrate in these sites.

4.1.3 Mechanisms of Action

Vitamin E is more appropriately described as an antioxidant than a vitamin. This is because, unlike most vitamins, it does not act as a co-factor for enzymatic reactions.

Also, deficiency of vitamin E does not produce a disease with rapidly developing symptoms such as scurvy or beriberi. Overt symptoms due to vitamin E deficiency occur only in cases involving fat mal absorption syndromes, premature infants and patients on total parenteral nutrition. The effects of inadequate vitamin E intake usually develop over a long time, typically decades, and have been linked to chronic diseases such as cancer and atherosclerosis.

Hence, its main function is to prevent the peroxidation of membrane phospholipids, and avoids cell membrane damage through its antioxidant action. The lipophilic character of tocopherol enables it to locate in the interior of the cell membrane bilayers (Halliway and Getteridge, 1992; Borg, 1993). Tocopherol-OH can transfer a hydrogen atom with a single electron to a free radical, thus removing the radical before it can interact with cell membrane proteins or generate lipid peroxidation. When tocopherol-OH combines with the free radical, it becomes tocopherol-O·, itself a radical. When ascorbic acid is available, tocopherol-O· plus ascorbate (with its available hydrogen) yields semidehydroascorbate (a weak radical) plus tocopherol-OH (Halliway and Gutteridge, 1992). By this process, an aggressive ROI(Reactive Oxygen Intermediate) is eliminated and a weak ROI (dehydroascorbate) is formed, and tocopherol-OH is regenerated. Despite this complex defence system, there are no known endogenous enzymatic antioxidant systems for the hydroxyl radical.
Vitamin E also stimulates the immune response. Some studies have shown lower incidence of infections when vitamin E levels are high, and vitamin E may inhibit cancer initiation through enhanced immunocompetence.

Vitamin E also has a direct chemical function. It inhibits the conversion of nitrites in smoked, pickled and cured foods to nitrosamines in the stomach. Nitrosamines are strong tumour promoters.
Alpha-tocopherol has been shown to be capable of reducing ferric iron to ferrous iron (i.e. to act as a pro-oxidant). Moreover, the ability of alpha-tocopherol to act as a pro-oxidant (reducing agent) or antioxidant depends on whether all of the alpha-tocopherol becomes consumed in the conversion from ferric to ferrous iron or whether, following this interaction, residual alpha-tocopherol is available to scavenge the resultant ROI (Yamamoto and Nike, 1988).

4.1.4 Possible therapeutic effects

Ø Vitamin E decreases the incidence of ischaemic heart disease (Gey et al. 1991).
Ø Decreases the incidence of cataract (Packer, 1991; 1992).
Ø Decreases the incidence of osteoarthritis (Blankenhorn, 1986).
Ø Decreases the incidence of rheumatoid arthritis (Kheir El-dein et al. 1992).

4.2 Ascorbic acid (vitamin C) Vitamin C -2D structure C6H8O6

4.2.1 Source and Nature

Ascorbic acid (vitamin C) is a water-soluble, antioxidant present in citrus fruits, potatoes, tomatoes and green leafy vegetables.
Humans are unable to synthesize l-ascorbic acid from d-glucose due to absence of the enzyme L-gulacolactone oxidase (Ensimnger et al.1995). Hence, humans must therefore obtain ascorbic acid from dietary sources.

4.2.2 Mechanism of Action

The chemopreventive action of vitamin C is attributed to two of its functions. It is a water-soluble chain breaking antioxidant (Ishwarial et at 1991). As an antioxidant, it scavenges free radicals and reactive oxygen molecules, which are produced during metabolic pathways of detoxification. It also prevents formation of carcinogens from precursor compounds (Block and Menkes, 1988). The structure of ascorbic acid is reminiscent of glucose, from which it is derived in the majority of mammals.

One important property is its ability to act as a reducing agent (electron donor). Ascorbic acid is a reducing agent with a hydrogen potential of +O.08V, making it capable of reducing such compounds as a molecular oxygen, nitrate and cytochromes a and c. Donation of one electron by ascorbate gives the semi-dehydroascorbate radical (DHA). Ascorbate reacts rapidly with O2·⁻and even more rapidly with ·OH to give DHA. DHA, itself can act as a source of vitamin C.
Ascorbic acid + 2O2· + 2H ® H2O2 + DHA

It has also been shown that ascorbate is more potent than a-tocopherol in inhibiting the oxidation of LDL (Low Density Lipoprotein) in a cell free system (Jialal et at 1990). Co-incubation of LDL with ascorbate during similar oxidative condition inhibited LDL oxidation and resulted in preservation of the endogenous antioxidant in the LDL particle (Ishwarial et at, 1991). The concentration of ascorbate used to inhibit LDL oxidation (40-60 mm) is well within the normal plasma range (23-85 pm).

Vitamin C also contributes to the regeneration of membrane bound oxidized vitamin E. It will react with the a -tocopheroxyl radical, resulting in the generation of tocopherol in this process itself being oxidized to dehydroascorbic acid (Ward & Peters 1995). Vitamin C supplementation in animals leads to increased plasma and tissue levels of vitamin E.
In vitro studies suggest that the antioxidant properties of ascorbic acid may not increase linearly as ascorbic acid concentrations rise (Frei et al. 1989). Moreover, ascorbic acid alone can act as a "pro-oxidant" or reducing agent to react with copper or iron salts. Ferric iron (Fe3+) formed by the reaction, Fe2+ + H2O2 ® HO + ·OH + Fe3+, is converted by ascorbic acid to ferrous (Fe2+) ion. Ferrous iron is therefore recycled to promote the conversion of more H2O2 to ·OH (Halliway et al. 1992).

4.3 Beta Carotene Me 2-D Structure of Beta Carotene

4.3.1 Source and Nature

Carotenoids are pigmented micronutrients present in fruits and vegetables.
Carotenoids are precursors of vitamin A and have antioxidant effects. While over 600 carotenoids have been found in the food supply, the most common forms are alpha-carotene, beta-carotene, lycopene, crocetin, canthaxanthin, and fucoxanthin. Beta-carotene is the most widely studied. It is composed of two molecules of vitamin A (retinol) joined together. Dietary beta-carotene is converted to retinol at the level of the intestinal mucosa.

4.3.2 Mechanisms of Action

The antioxidant function of beta-carotene is due to its ability to quench singlet oxygen, scavenge free radicals and protect the cell membrane lipids from the harmful effects of oxidative degradation (Krinsky and Deneke, 1982; Santamaria et al. 1991). The quenching involves a physical reaction in which the energy of the excited oxygen is transferred to the carotenoid, forming an excited state molecule (Krinsky, 1993). Quenching of singlet oxygen is the basis for beta-carotene's well known therapeutic efficacy in erythropoietic protoporphyria (a photosensitivity disorder) (Matthews-Roth, 1993). The ability of beta-carotene and other carotenoids to quench excited oxygen, however, is limited, because the carotenoid itself can be oxidized during the process (autoxidation). Burton and Ingold (Burton and Ingold, 1984) and others have shown that beta-carotene autoxidation in vitro is dose-dependent and dependent upon oxygen concentrations. At higher concentrations, it may function as a pro-oxidant and can activate proteases.

In addition to singlet oxygen, carotenoids are also thought to quench other oxygen free radicals. It is also suggested that beta carotene might react directly with the peroxyl radical at low oxygen tensions; this may provide some synergism to vitamin E which reacts with peroxyl radicals at higher oxygen tensions (Cotgreave et al. 1988).

Carotenoids also have been reported to have a number of other biologic actions, including immuno-enhancement; inhibition of mutagenesis and transformation; and regression of premalignant lesions

5. Antioxidant chemistry of some enzymes
This includes superoxide dismutase, catalase, and peroxidases.

5.1 Superoxide dismutase (SOD) 5.1.1 Source and Nature

SOD is an endogenously produced intracellular enzyme present in essentially every cell in the body.Cellular SOD is actually represented by a group of metalloenzymes with various prosthetic groups.The prevalent enzyme is cupro-zinc (CuZn) SOD, which is a stable dimeric protein (32,000 D). SOD appears in three forms: (1) Cu-Zn SOD in the cytoplasm with two subunits, and (2) Mn-SOD in the mitochondrion (Mayes, 1993; Warner, 1994). A third extracellular SOD recently has been described contains Copper (CuSOD).

2O2· + 2H + SOD ® H2O2 + O2

5.1.2 Mechanism of action

SOD is considered fundamental in the process of eliminating ROI by reducing (adding an electron to) superoxide to form H2O2. Catalase and the selenium-dependent glutathione peroxidase are responsible for reducing H2O2 to H2O.

The respective enzymes that interact with superoxide and H2O2 are tightly regulated through a feedback system. Excessive superoxide inhibits glutathione peroxidase and catalase to modulate the equation from H2O2 to H2O (see Fig.5). Likewise, increased H2O2 slowly inactivates CuZn-SOD. Meanwhile, catalases and glutathione peroxidase, by reducing H2O2, conserve SOD; and SOD, by reducing superoxide, conserves catalases and glutathione peroxidase. Through this feedback system, steady low levels of SOD, glutathione peroxidase, and catalase, as well as superoxide and H2O2 are maintained, which keeps the entire system in a fully functioning state (Fridovich, 1993).

SOD also exhibits antioxidant activity by reducing O2·⁻ that would otherwise lead to the reduction of Fe3+ to Fe2+ and thereby promote ·OH formation. When the catalase activity is insufficient to metabolize the H2O2 produced SOD will increase the tissue oxidant activity. Hence, it was found that the antioxidant enzymes function as a tightly balanced system, any disruption of this system would lead to promotion of oxidation .

5.2 The catalase enzyme

This enzyme is a protein enzyme present in most aerobic cells in animal tissues. Catalase is present in all body organs being especially concentrated in the liver & erythrocytes. The brain, heart, skeletal muscle contains only low amounts.

Catalase and glutathione peroxidase seek out hydrogen peroxide and convert it to water and diatomic oxygen. An increase in the production of SOD without a subsequent elevation of catalase or glutathione peroxidase leads to the accumulation of hydrogen peroxide, which gets converted into the hydroxyl radical. Indeed research in the pathogenesis of Down’s syndrome has revealed that the existence of trisomy 21 leads to the overproduction of SOD, the gene for which is located also on chromosome 21. This finding is intriguing in that it reveals the possibility of a genetic link to the increased activity of free radicals. (Krinsky, 1992)

2 H2O2 ® 2 H2O + O2

5.3 Glutathione peroxidase enzyme

The glutathione redox cycle is a central mechanism for reduction of intracellular hydroperoxides.
5.3.1 Source and Nature
It is a tetrameric protein 85,000-D. it has 4 atoms of selenium (Se) bound as seleno-cysteine moieties that confers the catalytic activity. One of the essential requirements is glutathione as a cosubstrate.
Glutathione peroxidase reduces H2O2 to H2O by oxidizing glutathione (GSH) (Equation A). Rereduction of the oxidized form of glutathione (GSSG) is then catalysed by glutathione reductase (Equation B). These enzymes also require trace metal cofactors for maximal efficiency, including selenium for glutathione peroxidase; copper, zinc, or manganese for SOD; and iron for catalase (Halliwell, 1995).

H2O2 + 2 GSH ® GSSG + 2 H2O (equation A)

GSSG + NADPH + H+ ® 2 GSH + NADP+ (equation B)

6. Mode of action of antioxidants

There are four routes:
1.Chain breaking reactions, e.g. alpha-tocopherol which acts in lipid phase to trap "ROD" radical.
2.Reducing the concentration of reactive oxygen species e.g. glutathione.
3.Scavenging initiating radicals e.g. superoxide dismutase which acts in aqueous phase to trap superoxide free radicals.
4.Chelating the transition metal catalysts: A group of compounds serves an antioxidant function by sequestration of transition metals that are well-established pro-oxidants. In this way, transferrin, lactoferrin, and ferritin function to keep iron induced oxidant stress in check and ceruloplasmin and albumin as copper sequestrants.

7. Antioxidant System in our body

The body has developed several endogenous antioxidant systems to deal with the production of ROI. These systems can be divided into enzymatic and nonenzymatic groups.
The enzymatic antioxidants include superoxide dismutase (SOD), which catalyses the conversion of O2·⁻ to H2O2 and H2O; catalase, which then converts H2O2 to H2O and O2; and glutathione peroxidase, which reduces H2O2 to H2O.

The nonenzymatic antioxidants include the lipid-soluble vitamins, vitamin E and vitamin A or provitamin A (beta-carotene), and the water-soluble vitamin C and GSH. Vitamin E has been described as the major chain-breaking antioxidant in humans (Packer, 1992). Because of its lipid solubility, vitamin E is located within cell membranes, where it interrupts lipid peroxidation and may play a role in modulating intracellular signalling pathways that rely on ROI (Kagan et al. 1990; Azzi et al. 1993). Vitamin E can also directly quench ROI, including O2·, ·OH, and (Algayer et al. 1992) O2.

8. Commercial Sources of Natural Antioxidants

The most common natural antioxidant preparations in the market are mixed tocopherols, which are by-products of vegetable oil refining. In addition, spices or their oleoresins and extracts, such as those of rosemary and sage, green tea extracts, other plant-based mixtures, such as those of mustard and certain unsaponifiables of edible oils, and, of course, carotenoids are also important (Table 2) ( Ho et al., 1994; Shahidi, 1997).

9. Efficacy of anti oxidants in different systems

The chemical composition and structures of active extract components are important factors governing the efficacy of natural antioxidants in different foods. Thus, phenolic compounds with ortho- and para- dihydroxylation or a hydroxy and a methoxy group are more effective than simple phenolics. In addition, phenylpropanoids with extended conjugation are more effective than benzoic acid derivatives. Furthermore, hydrophilicity and lipophilicity of the active components is dictated by the appropriateness of antioxidants in systems. In general, more hydrophilic antioxidants are better in stabilizing bulk oil than oil-in-water emulsions while the activity of lipophilic antioxidants follows the opposite trend. There are also many other factors that must be taken into account when considering and selecting antioxidants and extracts for food application. Specifically, attention should be paid to the photosensitizing effect of chlorophylls in natural extracts. In addition, the level of incorporation of antioxidants in foods should be optimized and the use of chelating agents considered, when and where appropriate. Many antioxidants behave prooxidatively at high concentrations or when present together with ions of transition metals; such effects are also important when considering the in-vivo activity of antioxidants ( Shahidi and Ho, 2000). Some chelators, such as polyphosphates, in addition to metal sequestration, may also exert other beneficial effects such as to improve the cooking yield and juiciness of meat and poultry products or keeping quality of fresh seafoods. The role of natural antioxidants in foods is expected to rise over the years to come.

10. Summary

Antioxidant are molecules that can safely interact with the free radicals and terminate the chain reactions before the vital molecules are damaged.Although there are several enzyme system and vitamins that scavenges free radicals the principle antioxidant in the body are Vitamin E, Vitamin C,beta carotene, catalase enzyme, super oxide dismutase enzyme,glutathion peroxidase enzyme etc.Vitamin E ,a lipid soluble antioxidant prevent peroxidation of phospholipid.Vitamin C is a water soluble chain breaking antioxidant. Beta carotene protect cell membrane lipid from harmful effect of antioxidant damage.Catalase ,glutathion peroxidase ,super oxide dismutase etc. enzyme systems also prevent our body oxidative damage by free radicals.

11. Conclusion

Antioxidant plays an important role to prevent cancer,and other disease.They also have role in slowing ageing process and preventing heart disease.So antioxidant are very much necessary for our body .But our body can’t manufacture these chemicals ,so they must be supplied through diet.Although there is a little doubt that antioxidant are necessary component for good health , no one knows if supplements should be taken or not and if so how much is optimum.Though antioxidant supplement were thought to be harmless but as we are becoming more aware of this chemicals we come to know that antioxidant may be harmful for our body in some cases.In normal concentration vitamin C and beta carotene are antioxidant but at higher concentration they are pro oxidant and thus harmful .Also very little is known about the long term consequences of megadoses of antioxidant .the body’s finely tuned mechanism are carefully balanced to withstand a variety of insults.Taking chemicals without understanding of all their effect may disrupt this balance. So we should follow the following recommendations.

1. It will be helpful for us to follow a balanced training program that emphasizes regular exercise and to eat 5 servings of fruit or vegetables per day. This will ensure that we are developing our inherent antioxidant systems and that our diet is providing the necessary components.
2. Weekend warriors should strongly consider a more balanced approach to exercise. Failing that, consider supplementation.
3. For extremely demanding races (such as an ultra distance event ), or when adapting to high altitude, it will be helpful to take a vitamin E supplement @ 100 to 200 IU per day for several weeks up to and following the race.
4. We should look for upcoming FDA recommendations, but we should be wary of advertising and media hype.
5. We should not over supplement.

12. Future Scope of Research

Antioxidant are necessary for our health but we do not know the exact dose and the way how to supplement it. So further research are required to know more about antioxidant. There are so many flora and fauna in our environment which may contain antioxidant chemicals. So there is a huge scope to conduct research work in this interesting topic to know
1) How much antioxidant supplementation is required.
2) Natural sources of different antioxidant.
3) To discover antioxidant property of different chemicals.
4) To know whether they have any other pharmacological and toxicological effect.
Bibliography

Anaberta Cardadose et.al. (2003). Antioxidant Activity In Common Beans. Journal of Agricultural and Food Chemistry. pp. 6975-80.

Jeong- Chae Lee (2002). Antioxidant Property of An Ethanol Extract of the Stem of Opuntia fiscus. Journal of Agricultural and Food Chemistry. pp. 6490-6496.

Jie Sun and Yi Fang (2002). Antioxidant and Antiprofilactive Activities of Common Fruits. Journal of Agricultural and Food Chemistry. pp. 7449-7454.

Joon Hee Lee et. al. (2003). Antioxidant Polyphenolics in Muscadine Grapes Journal of Agricultural and Food Chemistry. pp 480-485.

K.S. Shivashankara and Seiichiro Isobe (2004). Fruit Antioxidant Activity of Irwin Mango Fruits Stored at Low Temperature. Journal of Agricultural and Food Chemistry. pp. 1281-1286.
Kagan et al. 1990; Azzi et al. (1993).

Keni Chi Ya na Gimoto et. al. (2002). Antioxidative Activities of Fractions Obtained From Brewed Coffee. Journal of Agricultural and Food Chemistry. pp 1281-1290.

Mahinda Wella singh and Kirk Parkin (2002). Phase II Enzyme Inducing Activities of Beet Root From Phenotypes of Different Pigmentation. Journal of Agricultural and Food Chemistry. pp. 6704-09.

Qin Yan Zhu et. al.(2001). Antioxidant Activities of Oolong Tea. Journal of Agricultural and Food Chemistry. pp. 1280-1286.

Shahidi and Ho. (2000).Valcic, S; Burr ,J.A. Timmermann BN, Liebler DC. Department of Pharmacology and Toxicology, College of Pharmacy, The University of Arizona, Tucson, Arizona 85721, USA.

Yi Fang Chu and Xianzona Wu (2002). Antioxidant and Antiprofilactive Activities of Common Vegetables. Journal of Agricultural and Food Chemistry. pp. 381-385.

Author: Md. Wasim Aktar

Carbon and Organic Chemistry

noreply@blogger.com (Unknown) — Wed, 8 Jul 2009 09:04:00 -0700

The phrase "carbon-based life forms," is often used in science-fiction books and movies by aliens to describe the creatures of Earth, the only planet known to support life. Not only all living things contain carbon but also carbon is in plenty of things that were once living and now are the source for living, which makes it useful for dating the remains of past settlements on Earth. Of even greater usefulness is petroleum, a substance containing carbon-based forms that died long ago, became fossilized, and ultimately changed chemically into fuels. Then again, not all materials containing carbon were once living creatures; yet because carbon is a common denominator to all living things on Earth, the branch of study known as organic chemistry is devoted to the study of compounds containing carbon. Though among the most important organic compounds are the many carboxylic acids that are vital to life, carbon is also present in numerous important inorganic compounds, most notably its small but unavoidable compounds such as carbon dioxide, carbon monoxide and carbonates.

Carbon's name comes from the Latin word carbo, or charcoal which, indeed, is almost pure carbon. Its chemical symbol is C is generally crowned with its atomic number of 6, meaning that there are six protons in its nucleus. Its two stable isotopes are 12C, which constitutes 98.9% of all carbon found in nature, and 13C, which accounts for the other 1.1%. The mass of the 12C atom is the basis for the atomic mass unit (amu), by which mass figures for all other elements are measured: the amu is defined as exactly 1/12 the mass of a single 12C atom. The difference in mass between 12C and 13C, which is heavier because of its extra neutron, account for the fact that the atomic mass of carbon is 12.01 amu: were it not for the small quantities of 13C present in a sample of carbon, the mass would be exactly 12.00 amu.

Carbon makes up only a small portion of the known elemental mass in Earth's crust, oceans, and atmosphere (just 0.08%, or 1/1250 of the whole) yet it is the fourteenth most abundant element on the planet. In the human body, carbon is second only to oxygen in abundance, and accounts for 18% of the body's mass. Thus if a person weighs 100 lb (45.3 kg), he/she is carrying around 18 lb (8.2 kg) of carbon, interestingly the same material from which the cherished and much valued diamonds are made. Present in the inorganic rocks of the ground and in the living creatures above it, carbon is everywhere. Combined with other elements, it forms carbonates, most notably calcium carbonate (CaCO3), which appears in the form of limestone, marble, and chalk. In combination with hydrogen, it creates hydrocarbons, present in deposits of fossil fuels: natural gas, petroleum, and coal. In the environment, carbon, in the form of carbon dioxide (CO2), is taken in by plants, which undergo the process of photosynthesis and release oxygen for sustenance of animals that breathe in oxygen and release carbon dioxide to the atmosphere.

We know that carbon forms tetravalent bonds, and makes multiple bonds with a single atom. In addition, we have mentioned the fact that carbon forms long chains of atoms and varieties of shapes. But how does it do these things, and why? These are so good questions that an entire branch of chemistry, organic chemistry, is devoted to answering these theoretical questions, as well as to determining solutions to a host of other, more related and practical problems. Organic chemistry is the study of carbon, its compounds, and their properties. At one time, chemists thought that “organics” were synonymous with "living," and even as recently as the early nineteenth century, they believed that organic substances contained a supernatural "life force." Then, in 1828, German chemist Friedrich Wöhler cracked the code that distinguished the living from the nonliving species, and the organic from the inorganic.

Wöhler took a sample of ammonium cyanate (NH4OCN), and by heating it, converted it into urea (H2N-CO-NH2), a waste product in the urine of mammals. In other words, he had turned an inorganic material into an organic one, and he did so, as he observed, "without benefit of a kidney, a bladder, or a dog." It was almost as though he had created life. In fact, what Wöhler had glimpsed—and what other scientists who followed came to understand, was this: ‘what separates the organic from the inorganic is the manner in which the carbon chains are arranged’.

Ammonium cyanate and urea have exactly the same numbers and proportions of atoms, yet they are different compounds. They are thus isomers: substances which have the same formula, but are different chemically. In urea, the carbon forms an organic chain, and in ammonium cyanate, it does not. Thus, to reduce the specifics of organic chemistry even further, it can be said that this area of the field constitutes the study of carbon chains, and ways to rearrange them in order to create new substances.

Rubber, vitamins, cloth, and paper are all organically based compounds we encounter in our daily lives. In each case, the material comes from something that once was living, but what truly make these substances organic in nature is the common denominator of carbon, as well as the specific arrangements of the atoms. We have organic chemistry to thank for any number of things: aspirins and all manner of other drugs; preservatives that keep food from spoiling; perfumes and toiletries; dyes and flavorings, and so on.

It may not be out of context to mention that radiocarbon dating is used to date the age of charcoal, wood, and other biological materials as when an organism is alive, it incorporates a certain ratio of carbon-12 in proportion to the amount of the radioisotope (that is, radioactive isotope) carbon-14 that it receives from the atmosphere. As soon as the organism dies, however, it stops incorporating new carbon, and the ratio between carbon-12 and carbon-14 will begin to change as the carbon-14 decays to form nitrogen-14. Carbon-14 has a half-life of 5,730 years, meaning that it takes that long for half the isotopes in a sample to decay to nitrogen-14. Therefore a scientist can use the ratios of carbon-12, carbon-14, and nitrogen-14 to guess the age of an organic sample. The problem with radiocarbon dating, however, is that there is a good likelihood the sample can become contaminated by additional carbon from the soil. Furthermore, it cannot be said with certainty that the ratio of carbon-12 to carbon-14 in the atmosphere has been constant throughout time.

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Carbon and Organic Chemistry

Author: Dr.Badruddin Khan

Chemistry and Goals of Chemists

noreply@blogger.com (Unknown) — Thu, 9 Apr 2009 09:39:00 -0700

Chemistry is a science of substances, their properties, and how and why materials combine or separate to form different substances. Atoms, molecules and compounds are the involved ones in the study of Chemistry. In other words, it is how atoms interact to form molecules and how molecules interact with each other. It also looks into the composition of substances and their properties. The outer electron orbits or shells primarily determine the chemical characteristics of a material and whether materials will chemically combine. Thus Chemistry is the study of the composition of matter and the changes that take place in that composition. If we place a bar of iron outside our window, the iron bar will soon begin to rust. If we pour vinegar on baking soda, the mixture fizzes. If we hold a sugar cube over a flame, the sugar begins to turn brown and give off steam. The goal of chemistry is to understand the composition of substances such as iron, vinegar, baking soda, and sugar and to understand what happens during the changes described here.

The term chemistry has grown out of an earlier field of study known as alchemy. Alchemy has been described as a kind of pre-chemistry, in which scholars studied the nature of matter but without the formal scientific approach that modern chemists use. The term alchemy is probably based on the Arabic name for Egypt, al-Kimia, or the "black country." Ancient scholars learned a great deal about matter, usually by trial- and-error methods. For example, the Egyptians mastered many technical procedures such as making different types of metals, manufacturing colored glass, dying cloth, and extracting oils from plants. Alchemists of the Middle Ages discovered a number of elements and compounds and perfected other chemical techniques, such as distillation and crystallization. The modern subject of chemistry did not appear, however, until the eighteenth century. At that point, scholars began to recognize that research on the nature of matter had to be conducted according to certain specific rules. Among these rules was one stating that ideas in chemistry had to be subjected to experimental tests. Nowadays keeping in view the overall significance and versatility of chemistry, we can say that:

Chemistry is a science: There is only one sanctioned procedure for determining whether a statement about matter is really chemistry: the exhaustive, inefficient, but highly successful scientific method. Chemists often arrive at new results by nonscientific means (like luck or sheer creativity), but their work isn't chemistry unless it can be reproduced and verified scientifically.

Chemistry is a systematic study: Chemists have devised several good methods for solving problems and making observations. For example, analytical chemists often use protocols (thoroughly tested recipes) for determining the concentrations of substances in a sample. Chemists use well-defined techniques like spectroscopy and chromatography to study new or unknown substances.

Chemistry is the study of the composition and properties of matter: Chemistry is the study of the composition and properties of matter as it answers questions like, "What kind of stuff is a sample made of? What does the sample look like on a molecular scale? How does the structure of the material determine its properties? How do the properties of the material change when we increase temperature, or pressure, or some other environmental variable?"

Chemistry is the study of the reactivity of substances: Chemistry is the study of the reactivity of substances as one material can be changed into another by a chemical reaction. A complex substance can by made from simpler ones. Chemical compounds can break down into simpler substances. For example, fuels burn, food cooks, leaves turn their colors in the fall, cells grow, medicines cure and it is both their chemistry and the chemistry which is concerned with the essential processes that make these changes happen. Today, the science of chemistry is often divided into four major areas: organic, inorganic, physical, and analytical chemistry. Each discipline investigates a different aspect of the properties and reactions of matter.

Organic chemistry: Organic chemistry is the study of carbon compounds. That definition sometimes puzzles beginning chemistry students because more than 100 chemical elements are known. How does it happen that one large field of chemistry is devoted to the study of only one of those elements and its compounds? The answer to that question is that carbon is a most unusual element. It is the only element whose atoms are able to combine with each other in apparently endless combinations. Many organic compounds consist of dozens, hundreds, or even thousands of carbon atoms joined to each other in a continuous chain. Other organic compounds consist of carbon chains with other carbon chains branching off them. Still other organic compounds consist of carbon atoms arranged in rings, cages, spheres, or other geometric forms. The scope of organic chemistry can be appreciated by knowing that more than 90 percent of all compounds known to science (more than 10 million compounds) are organic compounds. Organic chemistry is of special interest because it deals with many of the compounds that we encounter in our everyday lives: natural and synthetic rubber, vitamins, carbohydrates, proteins, fats and oils, cloth, plastics, paper, and most of the compounds that make up all living organisms, from simple one-cell bacteria to the most complex plants and animals.

Inorganic chemistry: Inorganic chemistry is the study of the chemistry of all the elements in the periodic table except for carbon. Like their cousins in the field of organic chemistry, inorganic chemists have provided the world with countless numbers of useful products, including fertilizers, alloys, ceramics, household cleaning products, building materials, water softening and purification systems, paints and stains, computer chips and other electronic components, and beauty products. The more than 100 elements included in the field of inorganic chemistry have a staggering variety of properties. Some are gases, others are solid, and a few are liquid. Some are so reactive that they have to be stored in special containers, while others are so inert (inactive) that they virtually never react with other elements. Some are so common they can be produced for only a few cents a pound, while others are so rare that they cost hundreds of dollars an ounce. Because of this wide variety of elements and properties, most inorganic chemists concentrate on a single element or family of elements or on certain types of reactions.

Physical chemistry: Physical chemistry is the branch of chemistry that investigates the physical properties of materials and relates these properties to the structure of the substance. Physical chemists study both organic and inorganic compounds and measure such variables as the temperature needed to liquefy a solid, the energy of the light absorbed by a substance, and the heat required to accomplish a chemical transformation. A computer is used to calculate the properties of a material and compare these assumptions to laboratory measurements. Physical chemistry is responsible for the theories and understanding of the physical phenomena utilized in organic and inorganic chemistry.

Analytical chemistry: Analytical chemistry is that field of chemistry concerned with the identification of materials and with the determination of the percentage composition of compounds and mixtures. These two lines of research are known, respectively, as qualitative analysis and quantitative analysis. Two of the oldest techniques used in analytical chemistry are gravimetric and volumetric analysis. Gravimetric analysis refers to the process by which a substance is precipitated (changed to a solid) out of solution and then dried and weighed. Volumetric analysis involves the reaction between two liquids in order to determine the composition of one or both of the liquids.

In the last half of the twentieth century, a number of mechanical systems have been developed for use in analytical research. For example, spectroscopy is the process by which an unknown sample is excited (or energized) by heating or by some other process. The radiation given off by the hot sample can then be analyzed to determine what elements are present. Various forms of spectroscopy are available (X-ray, infrared, and ultraviolet, for example) depending on the form of radiation analyzed. Other analytical techniques now in use include optical and electron microscopy, nuclear magnetic resonance (MRI; used to produce a three-dimensional image), mass spectrometry (used to identify and find out the mass of particles contained in a mixture), and various forms of chromatography (used to identify the components of mixtures).

Other fields of chemistry: The division of chemistry into four major fields is in some ways misleading and inaccurate. In the first place, each of these four fields is so large that no chemist is an authority in any one field. An inorganic chemist might specialize in the chemistry of sulfur, the chemistry of nitrogen, the chemistry of the inert gases, or in even more specialized topics. Secondly, many fields have developed within one of the four major areas, and many other fields cross two or more of the major areas. For an example of specialization, the subject of biochemistry is considered a subspecialty of organic chemistry. It is concerned with organic compounds that occur within living systems. An example of a cross-discipline subject is bioinorganic chemistry. Bioinorganic chemistry is the science dealing with the role of inorganic elements and their compounds (such as iron, copper, and sulfur) in living organisms. At present, chemists explore the boundaries of chemistry and its connections with other sciences, such as biology, environmental science, geology, mathematics, and physics. A chemist today may even have a so-called nontraditional occupation. He or she may be a pharmaceutical salesperson, a technical writer, a science librarian, an investment broker, or a patent lawyer, since discoveries by a traditional chemist may expand and diversify into a variety of fields that encompass our whole society.

Chemists have two major goals. One is to find out the composition of matter in order to learn what elements are present in a given sample and in what percentage and arrangement. This type of research is known as analysis. A second goal is to invent new substances that replicate or are different from those found in nature. This form of research is known as synthesis. In many cases, analysis leads to synthesis. That is, chemists may find that some naturally occurring substance is a good painkiller. That discovery may suggest new avenues of research that will lead to a synthetic (human-made) product similar to the natural product, but with other desirable properties (and usually lower cost). Many of the substances that chemistry has produced for human use have been developed by this process of analysis and synthesis.

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About the Author:

Dr.Badruddin Khan teaches Chemistry in the University of kashmir, srinagar, India. His E.mail is:khanbudr@yahoo.co.in

Article Source: http://www.articlesbase.com/science-articles/chemistry-and-goals-of-chemists-570403.html

Importance of Functional Groups in Organic Chemistry

noreply@blogger.com (Unknown) — Thu, 9 Apr 2009 09:31:00 -0700

While organic chemistry is considered as the branch of chemistry in which the compounds of carbon are studied, the name organic goes back to a much earlier time in history when chemists thought that chemical compounds in living organisms were fundamentally different from those that occur in nonliving things. Their belief was that the chemicals that could be extracted from or that were produced by living organisms had a special "vitalism" or "breath of life" given to them by some supernatural being. As such, they presented fundamentally different kinds of problems than did the chemicals found in rocks, minerals, water, air, and other nonliving entities. The chemical compounds associated with living organisms were given the name organic to emphasize their connection with life. In 1828, German chemist Friedrich Wöhler, who found a very simple way to convert chemical compounds from living organisms into comparable compounds from nonliving entities, proved that this theory of vitalism was untrue. Consequently, the definition of organic chemistry changed as a result of Wöhler's research. The new definition was based on the observation that every compound discovered in living organisms had one property in common; they all contained the element carbon. As a result, the modern definition of organic chemistry, as the study of compounds of carbon, was adopted.

One important point that Wöhler's research showed was that the principles and techniques of chemistry apply equally well to compounds found in living organisms and nonliving things. Nonetheless, some important differences between organic and inorganic (not organic) compounds exist. These include the following:

1. The number of organic compounds vastly exceeds the number of inorganic compounds. The ratio of carbon-based compounds to non-carbon-based compounds is at least ten to one, with close to 10 million organic compounds known today. The reason for this dramatic difference is a special property of the carbon atom: its ability to join with other carbon atoms in very long chains, in rings, and in other kinds of geometric arrangements. It is not at all unusual for dozens, hundreds, or thousands of carbon atoms to bond to each other within a single compound—a property that no other element exhibits.

2. In general, organic compounds tend to have much lower melting and boiling points than do inorganic compounds.

3. In general, organic compounds are less likely to dissolve in water than are inorganic compounds.

4. Organic compounds are likely to be more flammable but poorer conductors of heat and electricity than are inorganic compounds.

5. Organic reactions tend to take place more slowly and to produce a much more complex set of products than do inorganic reactions.

The huge number of organic compounds requires that some system be developed for organizing them. The criterion on which those compounds are organized is the presence of various functional groups. A functional group is an arrangement of atoms that is responsible for certain characteristic physical and chemical properties in a compound. For example, one such functional group is the hydroxyl group, consisting of an oxygen atom and hydrogen atom joined to each other. It is represented by the formula —OH. All organic compounds with the same functional group are said to belong to the same organic family. Any organic compound that contains a hydroxyl group, for instance, is called an alcohol. All alcohols are similar to each other in that: (1) they contain one or more hydroxyl groups, and (2) because of those groups, they have similar physical and chemical properties. For example, alcohols tend to be more soluble in water than other organic compounds because the hydroxyl groups in the alcohol form bonds with water molecules.

The simplest organic compounds are the hydrocarbons, compounds that contain only two elements: carbon and hydrogen. The class of hydrocarbons can be divided into subgroups depending on the way in which carbon and hydrogen atoms are joined to each other. In some hydrocarbons, for example, carbon and hydrogen atoms are joined to each other only by single bonds. A single bond is a chemical bond that consists of a pair of electrons. Such hydrocarbons are known as saturated hydrocarbons. In other hydrocarbons, carbon and hydrogen atoms are joined to each other by double or triple bonds. A double bond consists of two pairs of electrons, and a triple bond consists of three pairs of electrons. The symbols used for single, double, and triple bonds, respectively, are —, =, and ?. Hydrocarbons containing double and triple bonds are said to be unsaturated. Hydrocarbons can also be open-chain or ring compounds. In an open-chain hydrocarbon, the carbon atoms are all arranged in a straight line, like a strand of spaghetti. In a ring hydrocarbon, the carbons are arranged in a continuous loop, such as a square, a pentagon, or a triangle.

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About the Author:

Dr.Badruddin Khan teaches Chemistry in the University of Kashmir, Srinagar, India

Article Source: http://www.articlesbase.com/college-and-university-articles/importance-of-functional-groups-in-organic-chemistry-623415.html

Organic Chemistry

noreply@blogger.com (Unknown) — Fri, 20 Mar 2009 03:32:00 -0700

Organic chemistry is the chemistry of carbon compounds. All organic compounds contain carbon; however, there are some compounds of carbon that are not classified as organic. For example, salts such as carbonates (e.g., Na₂CO₃, CaCO₃) and cyanides (e.g., NaCN, KCN) are usually designated as inorganic. Perhaps a more useful description might be: Organic compounds are compounds of carbon that usually contain hydrogen and that may also contain other elements such as oxygen, nitrogen, sulfur, phosphorus, or halogen (F, Cl, Br, or I). In any case, there are very few carbon compounds that are not organic, while there are millions that are.

History

Prehistoric civilizations obtained many useful chemicals from plants and animals. They were familiar with sugar, which they learned to ferment to make wine. Then they found that the wine could turn into vinegar. Ancient Egyptians used blue dye made from the indigo in madder root, and a royal purple dye extracted from a rare kind of mollusk. Soap was made by heating animal fat with base from wood ashes.

During the Middle Ages dry distillation of wood yielded mixtures of methyl alcohol, acetone, and acetic acid. Alchemists isolated cholesterol from gallstones, morphine from opium, and drugs such as quinine, strychnine, and brucine from various plants. Two hundred years ago chemists such as Antoine Lavoisier determined the elemental composition of many of these substances and noted that they all contained carbon and hydrogen, and that many also contained oxygen and nitrogen. It also appeared that there were two classes of materials: the mineral type (generally hard, high-melting, and noncombustible), and the organic type (often soft, liquid or low melting solids, and frequently easily combustible materials). Most organic chemicals could be burned to produce carbon dioxide; and any hydrogen present was converted to water (H₂O). Because organic compounds had for centuries been isolated only from plants and animals, it was commonly believed that some "vital force" in living things was necessary to produce them. This belief persisted until 1828, when Friedrich Wöhler was able to make urea, a chemical found in the urine of animals, from the inorganic salt ammonium cyanate.

Since that time organic chemistry has grown into a vast and ever expanding field that encompasses millions of chemical compounds.

Scope of Organic Chemistry

The field of organic chemistry includes more than twenty million compounds for which properties have been determined and recorded in the literature. Many hundreds of new compounds are added every day. Much more than half of the world's chemists are organic chemists. Some new organic compounds are simply isolated from plants or animals; some are made by modifying naturally occurring chemicals; but most new organic compounds are actually synthesized in the laboratory from other (usually smaller) organic molecules. Over the years organic chemists have developed a broad array of reactions that allow them to make all kinds of complex products from simpler starting materials.

Singular Attributes of Carbon

When one considers the millions of chemical compounds that are known and notes that more than 95 percent of them are compounds of carbon, one realizes that carbon is unique. Why are there so many carbon compounds? It turns out that atoms of carbon are quite remarkable in a number of ways.

Carbon atoms form very strong bonds with other carbon atoms. The bonds are so strong that carbon can form long chains, some containing thousands of carbon atoms. (Carbon is the only element that can do this.)

A carbon atom forms four bonds, therefore carbon not only can form long chains, but it also forms chains that have branches. It is a major reason why carbon compounds exhibit so much isomerism. The simple compound decane (C₁₀H₂₂), for example, has 75 different isomers .

Carbon atoms can be bonded by double or triple bonds as well as single bonds. This multiple bonding is much more prevalent with carbon than with any other element.

Carbon atoms can form rings of various sizes. The rings may be saturated or unsaturated. The unsaturated 6-membered ring known as the benzene ring is the basis for an entire subfield of "aromatic" organic chemistry.

Carbon atoms form strong bonds not only with other carbon atoms but also with atoms of other elements. In addition to hydrogen, many carbon compounds also contain oxygen. Nitrogen, sulfur, phosphorus, and the halogens also frequently occur in carbon compounds.

Various kinds of functional groups occur widely among carbon compounds, and many different kinds of isomers are possible.

Hydrocarbons

Compounds of carbon and hydrogen only are called hydrocarbons. These are the simplest compounds of organic chemistry. The most basic group of hydrocarbons are the alkanes, which contain only single bonds. The simplest member of the alkane series is methane, CH₄, the main component of natural gas. The names of some alkanes are listed in Table 1. Alkanes sometimes

ALKANES
Formula		Name
CH₄	CH₄	methane	gases
C₂H₆	CH₃CH₃	ethane
C₃H₈	CH₃CH₂CH₃	propane
C₄H₁₀	CH₃CH₂CH₂CH₃	butane
C₅H₁₂	CH₃(CH₂)₃CH₃	pentane	liquids
C₆H₁₄	CH₃(CH₂)₄CH₃	hexane
C₇H₁₆	CH₃(CH₂)₅CH₃	heptane
C₈H₁₈	CH₃(CH₂)₆CH₃	octane
C₉H₂₀	CH₃(CH₂)₇CH₃	nonane
C₁₀H₂₂	CH₃(CH₂)₈CH₃	decane
C₁₁H₂₄	CH₃(CH₂)₉CH₃	undecane
C₁₂H₂₆	CH₃(CH₂)₁₀CH₃	dodecane
C₁₃H₂₈	CH₃(CH₂)₁₁CH₃	tridecane
C₁₄H₃₀	CH₃(CH₂)₁₂CH₃	tetradecane
C₁₅H₃₂	CH₃(CH₂)₁₃CH₃	pentadecane
C₁₆H₃₄	CH₃(CH₂)₁₄CH₃	hexadecane
C₁₇H₃₆	CH₃(CH₂)₁₅CH₃	heptadecane
C₁₈H₃₈	CH₃(CH₂)₁₆CH₃	octadecane	solids
C₁₉H₄₀	CH₃(CH₂)₁₇CH₃	nonadecane
C₂₀H₄₂	CH₃(CH₂)₁₈CH₃	eicosane

have ring structures. Since a 4-carbon chain of the alkane series is called butane, a ring of 4 carbon atoms is called cyclobutane.

Simple hydrocarbons that contain one or more double bonds are called alkenes. They are named like alkanes, but their names end in " –ene." The simplest alkene has two carbon atoms and is called ethene. A 3-carbon chain that has a double bond is called propene.

A 5-carbon hydrocarbon chain with a double bond is called pentene, and if the double bond links the second and third carbons, it is 2-pentene. Like cycloalkanes, alkenes have the general formula C_nH_2n. Alkenes having ring structures are called cycloalkenes. A 5-carbon ring with a double bond is called cyclopentene.

Hydrocarbons that contain one or more triple bonds are called alkynes, and is the name ending is "–yne." A 2-carbon alkyne is therefore named ethyne. (However, the compound is often referred to by its common name, which is acetylene. )

Compounds that contain double or triple bonds are said to be "unsaturated"—because they are not "saturated" with hydrogen atoms. Unsaturated compounds are reactive materials that readily add hydrogen when heated over a catalyst such as nickel. The reverse reaction also occurs. Heating ethane with steam is an important commercial process for making ethene (or ethylene). This is an important commercial process called "steam cracking."

When a 6-carbon ring contains 2 double bonds, it is called cyclohexadiene, but when it has 3 double bonds, it is not called cyclohexatriene; this is because a 6-carbon ring with three double bonds takes on a special kind of stability. The double bonds become completely conjugated and no longer behave as double bonds. The ring, known as a "benzene ring," is said to be aromatic.

The removal of a hydrogen atom from a hydrocarbon molecule leaves an alkyl group that readily attaches to a functional group, or forms a branch on a hydrocarbon chain. The groups are named after the corresponding hydrocarbons. For example, CH₃– is named methyl; CH₃CH₂–, ethyl; CH₂= CH–, ethenyl; CH₃CH₂CH₂–, propyl; and so on. A benzene ring from which a hydrogen atom has been removed is often referred to as a phenyl. The branched molecules shown here would be given names as follows

Theoretically there is no limit to the length of hydrocarbon chains. Very large hydrocarbon molecules (polymers) have been made containing as many as 100,000 carbon atoms. However, such molecules are hard to make and very difficult to melt and to shape into useful products.

Hydrocarbons are obtained primarily from fossil fuels—especially petroleum and natural gas. Natural gas is a mixture that is largely methane mixed with varying amounts of ethane and other light hydrocarbons, while petroleum is a complex mixture of many different hydrocarbons. Coal, the other fossil fuel, is a much more complicated material from which many kinds of organic compounds, some of them hydrocarbons, can be obtained.

Functional Groups

Alkane molecules are rather unreactive (except for being very flammable), but alkenes react with many other substances. When a drop of bromine is added to an alkene, for example, the deep orange color of the bromine immediately disappears as the bromine adds across the double bond to form a dibromo derivative. The double bond is called a "functional group" because its presence in a molecule causes reactivity at that particular site. There are a dozen or so functional groups that appear frequently in organic compounds. Some of the most common ones are listed in Table 2. The same molecule may contain several functional groups. Aspirin, for example, is both a carboxylic acid and an ester , and cholesterol is an alkene as well as an alcohol.

Isomerism

Isomers are molecules with the same molecular formula but different structures. There is only one structure for methane, ethane, or propane; but butane, C₄H₁₀, can have either of two different structure:

The linear molecule (1) is called butane, or normal butane (n -butane), whereas the branched molecule (2) is methylpropane (rather than 2-methylpropane, as the methyl group has to be in a 2-position). If the methyl group of (2) were attached to a terminal carbon, the resultant molecule would be the same as (1). Methylpropane (2) is also called iso butane.

In a conjugated system, there are alternating double and single bonds, allowing electrons to flow back and forth. Molecules that contain such conjugated systems are said to be stabilized by "resonance." In the benzene ring every other bond is a double bond, all the way around the ring. This results in a special kind of stabilization called "aromaticity," in which the electrons are delocalized and free to travel all around the ring. Certain ring compounds, like benzene, that contain such a conjugated system of double and single bonds are described as "aromatic."

Pentane has 3 isomers: pentane (or n -pentane), methylbutane (or iso- pentane), and dimethyl propane (or neo pentane). Hexane has 5 isomers: hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane. Heptane has 9 different isomers, octane has 18, nonane has 35, and decane has 75. An increase in the number of carbon atoms greatly increases the possibilities for isomerism. There are more than 4,000 isomers of C₁₅H₃₂ and more than 366,000 isomers of C₂₀H₄₂. The formula C₃₀H₆₂ has more than 4 billion. Of course, most of them have never been isolated as pure compounds (but could be, if there were any point in doing it).

For molecules other than hydrocarbons, still other kinds of isomers are possible. The simple formula C₂H₆O can represent ethyl alcohol or dimethyl ether; and C₃H₆O could stand for an alcohol, an ether, an aldehyde , or a ketone (among other things). The larger a molecule is, and the greater the variety of atoms and functional groups it contains, the more numerous its isomers.

There is still another kind of isomerism that stems from the existence of "right-" and "left-handed" molecules. It is sometimes referred to as optical isomerism because the molecules that make up a pair of these isomers usually differ only in the way they rotate plane polarized light.

Nomenclature

There are so many millions of organic compounds that simply finding names for them all is a major challenge. It was not until the late nineteenth century that chemists developed a logical system for naming organic compounds. Compounds had often been named according to their sources. The 1-carbon carboxylic acid, for example, was first obtained from ants, and so it was called formic acid, from the Latin word for ants (formicae ). The 2-carbon acid was obtained from vinegar (acetum in Latin), and was called acetic acid.

To bring some order to the naming process an international meeting was held in 1892 at Geneva, Switzerland. The group later became known as the International Union of Pure and Applied Chemistry (IUPAC). Its objective was to establish a naming process that would provide each compound with a unique and systematic name. An initial set of rules was adopted at that first meeting in Geneva, and IUPAC has continued that work. Its systematic naming rules are used by organic chemists all over the world. The names of the alkanes form the basis for the system, with functional groups usually being indicated with appropriate suffixes. Some examples are given in Table 2.

Organic Reactions

Organic chemistry is concerned with the many compounds of carbon, their names, their isomers, and their properties, but it is mostly concerned with their reactions. Organic chemists have developed a huge array of chemical reactions that can convert one organic compound to another. Some reactions involve addition of one molecule to another; some involve decomposition of molecules; some involve substitution of one atom or group by another; and some even involve the rearrangement of molecules, with some atoms moving into new positions. Some reactions require energy in the form of heat or radiation; and some require a special kind of catalyst or some sort

NAMING ORGANIC COMPOUNDS
Functional Group		Type Compound	Example	IUPAC Name	Common Name
C=C	double bond	alkene	H₂C=CH₂	ethene	ethylene
C≡C	triple bond	alkyne	HC≡CH	ethyne	acetylene
–OH	hydroxyl	alcohol	CH₃OH	methanol	methyl alcohol
–O–	oxy	ether	H₃COCH₃	methoxymethane	methyl ether
	carbonyl	aldehyde	H₂C=0	methanal	formaldehyde
	carbonyl	ketone	CH₃COCH₃	propanone	acetone
	carboxyl	carboxylic acid	HCOOH	methanoic acid	formic acid
	carboxyl	ester	HCOOCH₂CH₃	ethyl methanoate	ethyl formate
–NH₂	amino	amine	CH₃NH₂	aminomethane	methylamine
–CN	cyano	nitrile	CH₃CN	ethanenitrile	acetonitrile
–X	halogen	haloalkane	CH₃Cl	chloromethane	methyl chloride

of solvent. Of course, not all organic reactions are highly successful. One reaction might be a very simple one giving essentially 100 percent of the desired product; but another might be a complex multistep process yielding less than 5 percent overall of the wanted product.

Organic reactions can often give remarkable control as to what products should be formed. Adding water to propene for example, produces 2-propanol in the presence of acid, but it yields 1-propanol if treated first with B₂H₆ and then H₂O₂ in the presence of base.

Future Sources of Organic Chemicals

Fossil fuels have been our primary natural source for many organic chemicals for more than a century, but our fossil fuel resources are finite, and they are being rapidly depleted (especially oil and gas). What will be our sources of organic materials in the future? Since fossil fuels are nonrenewable resources, it is believed that the twenty-first century will see a shift toward greater dependence on renewable raw materials. The largest U.S. chemical company has a goal of becoming 25 percent based on renewable resources by 2010. It is already producing 1,3-propanediol from cornstarch using a gene-tailored E. coli bacterium. This diol is used in Du Pont's fiber Sorona, which is said to combine the best features of both polyester and nylon fibers. Succinic acid and polyhydroxybutyrate are also obtainable from renewable crops, and the list of such renewable raw materials is destined to grow. For example, ethylene (or ethene), CH₂=CH₂, which is a highly important commercial chemical used in making many industrial chemicals and polymers, is presently made by steam cracking of ethane obtained from oil or natural gas; but ethylene can also be made by dehydration of ethyl alcohol made by fermentation of sugar. Efforts are even being made to use biowaste materials, such as corn husks, nutshells, and wood chips as industrial raw materials.

Analytical Tools

Organic chemists often need to examine products for identification, purity analysis, or structure determination. There are some marvelous tools available to help them do these things. Chromatography , spectroscopy , and crystallography are especially widely used in organic chemistry.

Column chromatography, gas chromatography, and liquid chromatography are all important methods for separating mixtures of organic compounds. Spectroscopic tools include ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR), and mass spectroscopy (MS), each capable of providing a different kind of information about an organic compound. Although it is limited to substances that can be prepared as pure crystals, x-ray crystallography is probably the ultimate tool for determining molecular structure.

Careers in Organic Chemistry

Some organic chemists are involved in basic research at government or academic institutions, but most have careers in industry. The industries vary from oil and chemical companies to industries producing food, pharmaceuticals, cosmetics, detergents, paints, plastics, pesticides, textiles, or other kinds of products. Many organic chemists work in laboratories, where they do various kinds of analysis or research, but many others do not. Some are teachers, or writers, or science librarians. Some study law and become patent attorneys; some study medicine and become medical researchers; and some study business and become administrators of companies, colleges, or other institutions. Organic chemistry is an enormous field full of many kinds of career possibilities.

Kenneth E. Kolb

Bibliography

Atkins, Robert C., and Carey, Francis A. (2002). Organic Chemistry: A Brief Course, 3rd edition. Boston: McGraw-Hill.

Bailey, Philip S., Jr., and Bailey, Christina A. (2000). Organic Chemistry: A Brief Survey of Concepts and Applications, 6th edition. Upper Saddle River, NJ: Prentice Hall.

Brown, William H., and Foote, Christopher S. (2002). Organic Chemistry, 3rd edition. San Diego: Saunders.

Fessenden, Ralph J.; Fessenden, Joan S.; and Logue, Marshall (1998). Organic Chemistry, 6th edition. Pacific Grove, CA: Brooks/Cole.

Solomons, T. W. Graham (1997). Fundamentals of Organic Chemistry, 5th edition. New York: Wiley.

www.encyclopedia.com

Curie

noreply@blogger.com (Unknown) — Thu, 12 Mar 2009 18:33:00 -0700

Curie , family of French scientists. Pierre Curie, 1859-1906, scientist, and his wife, Marie Sklodowska Curie, 1867-1934, chemist and physicist, b. Warsaw, are known for their work on radioactivity and on radium. The Curies' daughter Irène (see under Joliot-Curie , family) was also a scientist.

Pierre Curie's early work dealt with crystallography and with the effects of temperature on magnetism; he discovered (1883) and, with his brother Jacques Curie, investigated piezoelectricity (a form of electric polarity) in crystals. Marie Sklodowska's interest in science was stimulated by her father, a professor of physics in Warsaw. In 1891 she went to Paris to continue her studies at the Sorbonne. In 1895 she married Pierre Curie and engaged in independent research in his laboratory at the municipal school of physics and chemistry where Pierre was director of laboratories (from 1882) and professor (from 1895).

Following A. H. Becquerel 's discovery of radioactivity, Mme Curie began to investigate uranium, a radioactive element found in pitchblende. In 1898 she reported a probable new element in pitchblende, and Pierre Curie joined in her research. They discovered (1898) both polonium and radium, laboriously isolated one gram of radium salts from about eight tons of pitchblende, and determined the atomic weights and properties of radium and polonium. The Curies refused to patent their processes or otherwise to profit from the commercial exploitation of radium. For their work on radioactivity they shared with Becquerel the 1903 Nobel Prize in Physics.

The Sorbonne created (1904) a special chair of physics for Pierre Curie; Marie Curie was appointed his successor after his death in a street accident. She also retained her professorship (assumed in 1900) at the normal school at Sèvres and continued her research. In 1910 she isolated (with André Debierne) metallic radium. As the recipient of the 1911 Nobel Prize in Chemistry she was the first person to be awarded a second Nobel Prize. She was made director of the laboratory of radioactivity at the Curie Institute of Radium, established jointly by the Univ. of Paris and the Pasteur Institute, for research on radioactivity and for radium therapy.

During World War I, Mme Curie devoted her energies to providing radiological services for hospitals. In 1921 a gram of radium, a gift from American women, was presented to her by President Harding; this she accepted in behalf of the Curie Institute. A second gram, presented in 1929, was given by Mme Curie to the newly founded Curie Institute in Warsaw. Five years later she died from the effects of radioactivity. In 1995 Marie and Pierre Curie's ashes were enshrined in the Panthéon, Paris; she was the first woman to be honored so in her own right.

Bibliography: Among the numerous and valuable writings of the Curies are Marie Curie's doctoral dissertation, Radioactive Substances (1902, 2 vol.; tr. 1961); Traité de radioactivité (1910); Radioactivité (1935); and her biography of Pierre Curie (1923, tr. 1923). Pierre Curie's collected works appeared in 1908. A biography of Marie Curie was written by a daughter, Ève Curie (tr. 1937). See also biographies by R. W. Reid (1974), F. Giroud (tr. 1986), S. Quinn (1995), and B. Goldsmith (2004).
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adapted from: "Curie." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. 12 Mar. 2009 <http://www.encyclopedia.com>.

Contributions of Ancient Arabian and Egyptian Scientists on Chemistry

noreply@blogger.com (Unknown) — Thu, 12 Mar 2009 18:30:00 -0700

Contributions of Ancient Arabian and Egyptian Scientists on Chemistry
Md. Wasim Aktar* and M. Paramasivam
Deptt. of Agril. Chemicals, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India.

Abstracts
The modern chemistry is based on the findings and thinking of the people of historical age. If no one knows the base and work of the previous on a subject, he or she could mere develop a new thought or findings. For, a civilization must know its past. Hence, the present work is a small effort to find out the contribution of ancient Arabian and Egyptian scientists in the field of Chemistry. Different scientists of different school of thought, correlating different streams of science being Chemistry as a main subject, are described in the present work.
Chemistry deals with the composition and properties of substances and the changes of composition they undergo. It has been divided into Inorganic and Organic. The conception of this in modern Chemistry came from al-Rãzi’s classification of chemical substances into mineral, vegetable and animal. Inorganic Chemistry, deals with the preparation and properties of the elements, and their compounds, originally arose from the study of minerals and metals, whereas Organic Chemistry, which deals with carbon compounds, developed through the investigation of animal and plant products.
Prior to 1828 it was not possible to synthesize organic substances from their elements and, therefore, it was supposed that there existed fundamental difference between Organic and Inorganic Chemistry. In 1828 F. Wohler synthetically prepared urea, an organic substance; thereby revealing that there was no fundamental difference between these two branches of Chemistry. Since carbon compounds were numerous, their study separately made under Organic Chemistry, and study of elements and non-carbon compounds included in Inorganic Chemistry’. (1)
The earliest discoveries in Inorganic Chemistry were made in metallurgy, Materia Medica, painting, enameling, glazing, glass-making, arts, etc. These arts, and many metals, compounds and alloys were known to the Arabs. Similarly, the discoveries in Organic Chemistry were made in the arts of dyeing, tanning, the manufacture of paper, in the study of fats, both of plant and animal origin, in medicine, etc. Thus Chemistry had its sources in photo techniques, mineralogy, metallurgy, Materia Medica and decorative arts. It is the product of transmutation of baser metals into gold
and philosophical thoughts of practical or theoretical interest. Finally, it is the result of the study of the properties of the substances.
A Greek philosopher, Empedocles, held the view that all the four elements, air, water, earth and fire, were the primal elements, and that the various substances were made by their intermixing. He regarded them to be distinct and unchangeable. Aristotle considered these elements to be changeable i.e., one kind of matter could be changed into another kind. (2)
Jábir ibn Hayyãn (Liatinized as Geber), a great Arabian Chemist of the 8th century A.C., modified the Aristotelian doctrine of the four elements, and presented the so-called sulphur-mercury theory of metals. According to this theory metals differ essentially because of different proportions of sulphur and mercury in them. He also formulated the theory of geologic formation of metals.
Unlike his Greek predecessors, he did not merely speculate, but performed experiments to reach certain conclusions. He recognized and stated the importance of experimentation in Chemistry. He combined the theoretical knowledge of the Greeks and practical knowledge of the craftsmen, and himself made noteworthy advance both in the theory and practice of Chemistry.
Jâbir’s contribution to Chemistry is very great. He gave a scientific description of two principle operations of Chemistry. One of them is calcinations which is employed in the extraction of metals from their ores. The other is reduction which is employed in numerous chemical treatments. He improved upon the methods of evaporation, melting, distillation, sublimation and crystallization. These are the fundamental methods employed for the purification of chemical substances, enabling the chemist to study their properties and uses, and to prepare them. The process of distillation is particularly applied for taking extract of plant material.
In the opinion of Jàbir the cultivation of gold was not the only object of a chemist. The preparation of new chemical substances was also regarded by him as the chief object of Chemistry. We owe to him for the first preparation of such substances as arsenic and antimony from their sulphides, and basic lead carbonate. He also did important work in the preparation of steel, and the refinement of metals. Jàbir also deals with such applications as the use of manganese dioxide in glass-making, varnishes to water-proof cloth and protect iron use of iron pyrites for writing in gold and distillation of vinegar to concentrate acetic acid.
The most important discovery made by Jabir was the preparation of sulphuric acid. The importance of this discovery can be realized by the fact that in this modern age the extent of the industrial progress of a country is mostly judged by the amount of. sulphuric acid consumed in that country. Another important acid prepared by him was nitric acid which he obtained by distilling a mixture of alum (of Yemen) and copper sulphate (of Cyprus). Then by dissolving ammonium chloride into this acid, he prepared aqua regia which, unlike acids, could dissolve gold in it.
Jabir classified chemical substances, on the basis of some distinctive features, into bodies (gold, silver, etc.) and souls (mercury, sulphur, etc.) to make the study of their properties easier.
Jãbir is the author of a large number of books on chemistry and a book on astrolabe. About one hundred chemical works ascribed to him are extant. His fame chiefly rests on his chemical books preserved in Arabic. (3)
We find that the author recognized and stated clearly the importance of experimentation more clearly than any other early chemist. He remarkably sound views on methods of chemical research. It is impossible to reach definite conclusions regarding the extent of his contributions until all the Arabic writings ascribed to him have been properly edited and studied. But on the basis of our present knowledge, Jabir appears to be one of the greatest scientist whose influence can be traced throughout the whole period of the historical development of the Arabian and European chemistry. In the light of these facts it would not be improper to call Jãbir as the father of Chemistry.
Some of the chemical writings to which Jãbir’s name is attached were translated into Latin. The first such version, the Book of the Composition of Alchemy was made by Robert of Chester in 1144. The Kitab al-Sab’in (the book of the seventy) was translated by Gerard of Cremona in the 12th century’. The translation of the Sum of Perfection was made by Richard Russell. One of his books has been translated into French by Berthelot. (4)
Several technical terms have passed from Jãbir’s Arabic writings through Latin into the European languages. Among these are realgar (red sulphide of arsenic), tutia (zinc oxide), alkali, antimony, and alembic for distillation Vessel. The Arabic equivalents for the last three words are alqali, ithmad, and al-’anbiq respectively. (5)
Before Jãbir Ibn Hayyan, the Umayyad prince Khalid Ibn Yazid, who was a philosopher, poet and chemist, encouraged Greek philosophers in Egypt to translate Greek scientific works into Arabic. These were among the earliest translations in Arabic from other languages. He was himself deeply interested in medicine, astrology and chemistry. Many chemical works are ascribed to him. One of them is entitled Firdaus al-Hikmah fi’Ilm al-Kimiya. This work was in verse, and contained 2,315 couplets. (6)
An encyclopaedic scientist, and philosopher, Abu Yusuf Ya’qub al-Kindi considered the art of transformation of one metal into the other as an imposture. A few of ‘his numerous works dealing with many sciences are extant. One of his works is on pharmacy, a branch of applied chemistry. (7)

Chemistry was usually mixed up with mineralogy and geology. The oldest Arabian lapidary which may serve as an important source of chemistry was written by ‘Utärid Ibn Muhammad al-Hãsib who flourished in the ninth century. It deals with the properties of precious stones. (8)
In the same century Jãbir’s work was further advanced by al-Räzi who wrote many chemical treatises, and described a number of chemical instruments. One of his treatises consists of 25 pieces of chemical apparatus. He made investigations on specific gravity. One of his important works is on the art of transformation of baser metals into the noble ones. He applied his chemical knowledge for medical purposes, thus laying the foundation of Iatrochemistry. (9)
Other important chemists of this century were Dhu’l-Nün and al-Jàhiz. The former mostly dealt with the art of transmutation of metals. (10) The latter prepared ammonia from animal offals by dry distillation. (11)
In the tenth century Ibn Wahshiyah wrote on chemistry, His work may help to understand chemical symbolism. Maslamah Ibn Ahmad, an astronomer, mathematician and oculist of this century wrote two chemical works entitled, Rutbat al-Hakim and Ghãyat al-Hakim. The second is well known in the Latin translation made in 1252 by the order of King Alfonso under the title Picatrix. (12)
A Persian pharmacologist Abü Mansür Muwaffaq Ibn ‘Ali al-Harawi who flourished in Herat in the tenth century, was apparently the first to think of compiling a treatise on Materia Medica in Persian. He travelled extensively in Persia and India to obtain necessary information. He wrote, between 968 and 977, a book entitled Kitab al-Abniyah ‘an Haqã’iq al-Adwiyah. It contains Greek, Syrian, Arabian, Persian, and Indian knowledge. It deals with 585 remedies (of which 466 are derived from plants, 75 from minerals, and 44 from animals). He classified them into four groups according to their action, and gave the outline of a general pharmacological theory.
Abu Mansür distinguished between sodium carbonate (natrum) and potassium carbonate (qali). He had some knowledge of arsenious oxide, cupric oxide, silicic acid, antimony and so on. He knew the toxicological effects of copper and lead compounds, the depilatory virtue of quicklime, the composition of plaster of Paris and its surgical use. (13)
The greatest Arabian surgeon, Khalaf Ibn ‘Abbäs al-Zahrãwi (d. 1013) wrote a great medical encyclopaedia, al-Tasrif in 30 sections, which contains interesting methods of preparing drugs by sublimation and distillation, but its most important part is the surgical one. (14)
Abü Rayhan Muhammad al-Birüni (973—1048) took a great interest in the determination of the specific gravity of eighteen precious stones and metals. A voluminous unedited lapidary by al- Biruni is extant in unique manuscript in the Escorial Library. It contains a description of a great number of stones and metals from the natural, commercial, and medical point of view. Moreover, he composed a pharmacology (saydalah).Important information could certainly be obtained from his unedited works, on the origin of Indian and Chinese stones and drugs, which appeared in early Arabic scientific works. (15)
Ibn Sinà wrote a treatise on minerals, which was very important and one of the main sources of geological knowledge, also a source of chemistry in Western Europe until the Renaissance.
As mentioned before, mineralogy stood in close relation to chemistry. Nearly fifty Arabic lapidaries have been named. The best known of them is. the ‘Flowers of Knowledge of Stones’, by Shihàb al-Din al-Tifãshi (died in Cairo in 1154). It gives in 25 chapters extensive information on the subject of the same number of precious stones, their origin, geography, examination, purity, price, application for medicinal and magical purposes, and so on. Except for Pliny and the superior Aristotelian lapidary, he quotes only Arabic authors. (16)

The output of the books on Chemistry was very great after the eleventh century. Thus, there are known books of about forty Arabic and Persian chemists. Ibn Khaldun, (d. 1406) the talented Arabian philosopher of history and the greatest intellect of his century, was a violent opponent of the idea of transmutation of metals by chemical means. (17)
Some chemists thought that one metal can be transformed into another by artificial methods. For such transformation they followed different procedures depending on the character and form of the chemical treatment and the substance chosen for this purpose; the substance being called the ‘Noble Stone’ or ‘Philosopher’s Stone’. This may be excrements, or blood, or hair, or eggs, or anything else. After the substance has been specified, it is treated along certain lines mentioned in their books. The result is an earthen or fluid substance which is called Elixir. These chemists think that if Elixir is added to silver which has been heated in a fire, the silver turns into gold. If added to copper which had been heated in a fire, the copper turns into silver.
The question arises whether the metals are of specific differences, each constituting a distinct species, or whether they differ in certain properties and qualities and constitute different kinds of one and the same species?
Abü Nasr al-Färabi and his followers held the opinion that the difference in metals is caused by certain conditions such as humidity and dryness, softness and hardness, and colours such as yellow, white and black. According to him the metals are different kinds of one and the same species.
On the other hand, Ibn Sina and his followers believed that metals have specific differences and belong to different species, each of which has its own differential and genus, like all other species.
According to Abü Nasr al-Färãbi, it is possible to transform one metal into another, because it is possible to change their conditions.
“Ibn Sinà thought that such transformation was impossible. His assumption is based on the fact that specific differences in metals cannot be changed by artificial means. He believed that since the metals are created by the Creator and Determiner of things, God Almighty, and the mystery of their real character was utterly unknown and could not be perceived, any attempt for transformation would be meaningless”. (18)
Ancient Arabs’ art of transformation of metals was based upon Hellenistic and Iranian traditions, but apparently the main principles and the main operations were already established long before the 12th century. Before this century the Arabs had not only made many experiments, and produced several works on this art, but they had begun to doubt and criticise the most advanced theories concerning it. This proves that the standard of their chemical thinking was advanced.
The 12th and 13th centuries added very little to their knowledge about the transformation of metals, but their research continued in various fields. The main chemical writer of this age was Abu‘l-Qãsim Muhammad al-Iraqi who flourished in the second half of the 13th century. He was an experimenter and a theorist. His works represent the full development of the Arabic doctrine. (19)
The 14th century was an enlightened period when a group of intelligent writers began to reject the idea of transformation of metals by chemical means. One of such person was a historian, Rashid al-Din who described such chemical practice in Mongol Persia and expressed his distrust of such chemists. The large encyclopaedic work Nukhbat al-Dahr of al-Dimashqi contains, in part second, much information on metal, their properties, and influences. (19) As usual in Arabic treatises, chemistry is mixed up with mineralogy and geology. (20)
Even in their purely chemical researches on transformation of metals, the Arab chemists achieved by no means unimportant results. In their efforts to discover Elixir they often discovered new chemical processes, and hit upon the catalytic properties of various substances. The pains, which they took in the search of gold, ultimately resulted in their great contribution to the development of modern chemistry.
The last important chemist of the 14th century was ‘Izz al-Din ‘Ali Ibn al- Jildaki. Some twenty treatises are ascribed to him. The list shows al-Jildaki’s great activity as a chemical writer. A complete study of his vast writings is necessary to know what he actually tried to establish. To some extent, this study was made by Ruska, Stapleton, Holm yard, and their disciples.
One of al-Jildaki’s important books entitled Nihâyat al-Talab fi Sharh al-Muktasab contains many quotations from the earlier works, and some novelties, as the use of nitric acid to extract silver out of the gold-silver alloy. Al- Jildaki remarked that the substances do not react except by definite weights. (21) This is one of the four fundamental laws of modern chemistry.
The ancient chemists applied their chemical knowledge to a large number of industrial arts. Only three such arts are mentioned here, which will enable the readers to estimate the extent of their knowledge of Applied Chemistry.
Paper:
Paper was invented by the Chinese who prepared it from the cocoon of the silkworm. Some specimens of Chinese paper extant date back to the second century A.C. The first manufacture of the paper outside China occurred in Samarqand (757). When Samarqand was captured by Arabs the manufacture of paper spread over the whole Arab world including the Maghrib. (Tunis, Morocco, Algiers).

By the end of the 12th century there were four hundred paper mills in Fasalone. In Spain the main centre of manufacture of paper was Shatiba which remained a ancient Arab city until 1239. Cordova was the centre of the business of paper in Spain.
The Arabs developed this art. They prepared paper not only from silk, but also from cotton, rags and wood.In the middle of the 10th century the paper industry was introduced in Spain. In Khurasan paper was made of linen.
There is an early treatise dealing with paper-making, the Umdat al-Kuttab wa ‘Uddatu dhawi’l-Albãb which is ascribed to the Amir al- Mu’izz’ Ibn Badis, a ruler of the Zayri dynasty (1015—61) in Tunis. The 11th chapter of this treatise, dealing with paper, has been edited, translated and elaborately discussed by the foremost student of Arabic paper, Josef Karabacek. This work explains how to prepare the pulp, make the sheets, wash and clean them, colour, polish and paste them, and give them an antique appearance. No text comparable to this in any other language of so early a date is known.
The preparation of pulp involves a large number of complicated chemical processes, which shows the advancement of the chemical knowledge of the Arabs and Egyptians at that time.
The manufacture of writing-paper in Spain is one of the most beneficial contributions of Arabs to Europe. Without paper the scale on which popular education in Europe developed would have not been possible. The preparation of paper from silk would have been impossible in Europe due to the lack of silk production there. The Arabs method of producing paper from cotton could only be useful for the Europeans. After Spain the art of paper-making was established in Italy (1268—76). France owed its first paper mills to ancient Spain. From these countries the industry spread throughout Europe.
Another type of paper; marbled paper, which was common upon end-papers, paper covers and edges of books, was prepared in the East, and exported to the West. About the preparation of marbled paper Roger Bacon tells us: “The Turks have a pretty art of chamoletting of paper, which is not with us in use. They take diverse oiled colours, and put them severally (in drops) upon water; and stirr the water lightly and then wet their paper (being of some thickness) with it, and the paper will be waved, and veined, like Chamolet or Marble’.
Books bound in the West towards the end of the 16th century are found with end-papers brought from the East, but it was not until about a century later that European binders began to make them themselves. Hand-made marbled papers are now rarely used, but more or less clumsily reproduced imitations still serve various purposes.

There is an Arabic word ‘rizma’ meaning a bundle of merchandise, which had been adopted in almost every Western language with slight variations to mean a bundle of paper (English: ream). This also testifies to the Arabic origin of that business in the West. (22)
Tiles :
The industry of tile-making which involves a large number of complex technical and chemical processes, was highly developed by Arabs. The earliest treatise, a Persian text, dealing with the manufacture of faience, was unique of its kind in world literature until the 16th century. It has been written by ‘Abd Allah Ibn ‘Ali Kàshàni in the 13th century. This book entitled Jawahir al-‘Arã’is Wa Aja’ib al-Nafä’is was written on precious stones and perfumes. It explains the manufacture of Faience, the ingredients (as clay, borax, feldspar, cobalt, lapis lazuli, lead, manganese, tin etc.), their mixtures, the kiln processes and implements, the methods of glazing and decorating. This treatise is similar to the various other treatises on precious stones written in Arabic and Persian. The final chapter deals with the art of enamelled pottery. This account is specially valuable because it is based on actual and traditional practice. The maker of the beautiful lustre ‘mihrab’ (arch) of the tomb of Imam Yahyã (now in the Hermitage, Leningrad), dated 1305 A.C., Yusuf Ibn ‘Ali Ibn Muhammad, was possibly a brother of the author. (23)
Ceramics:
The early history of Arabian and Egyptian ceramics has not so far been written. Many interesting specimens have been discovered in recent years which throw much light on the development of this industry in the Arab world. The centers of this industry were situated in Persia, Mesopotamia, Syria, Egypt and Valencia from where various types spread rapidly throughout the Islamic Caliphate.
Under Arabian influence the potters in these Centers revived old technical processes, developed new ones and began to experiment with decorative and ornamental schemes. The Arabian potters readily absorbed progressive ideas but at
the same time maintained great originality. Two types of pottery were in common use; enamelled and lustered. In enamelled pottery (the glazed earthenware) the Ancient s, from an early period, were expert masters. In lustered pottery also they made great progress. “In this the design is painted in a metallic salt on a glazed surface and fixed by firing in smike in a way that gives it a metallic gleam, which varies in different specimens from a bright copper-red to a greenish- yellow tint, and in some cases throws off brilliant iridescent reflections. (24)
In the last chapter of the Persian text Kitab al-Jawähir’ al-’Ara’is Wa ‘Ajã’ib al-Nafa’is, the author describes the techniques of glazing
with two fires (lustres), leaf building, over glaze decoration fired in a muffle kiln. (i.e.,
separated from the flame, the source of heat being outside), haf’t rang, a Persian term
referring to the seven colours of the planets. There may be a reference to the polychrome over glaze technique, the so called minai ware (another Persian term; mina-wash means lustre; mina coloured). The author indicates differences between the art as practiced in Kashan, Baghdad and Tabriz. In Baghdad and Tabriz other kinds of firewood and potash were used.
In the 15th century the Arabian ceramic art was followed by Italian potters, who obtained much of the mature technical knowledge from Arab sources. This technical knowledge proved to be helpful in the revival of ceramic art during the Renaissance. (25)
REFERENCES :-
1. Encyclopaedia Britannica, chicago, 1951, p.360
2. Ibid., p. 355.
3 Sarton George, Introduction to the History of Science, Washington, 1950, Vol I. p. 532.
4. Wasiti, Hakim Nayyar, Tibb al-’Arab ( ãn Urdu Translation of Arabian Medicine by Edward G. Browne), Lahore, 1954, p. 26.
5. Ibid.
6. Hãji Khalifah, Kashf al-Zunün, Istanbul, 1943. Vol., I, p. 1254.
Al-Zirakli, Khair al-Din, Al-’Alãm vol. II p. 342.
7. Sarton, op. cit., p. 559.
8. Ibid., p. 572. Al-Qifti, op. cit. p. 251.
9. Ibid., p. 271. Sarton, op. cit. p. 609.
10. lbid, p. 592.
11. lbid, p. 597.
12. Ibid., pp. 620, 668.
13. Ibid., p. 678.
14. Ibid., p. 681.
15 Ibid., p. 707.
16. Ibid, vol. II, part II, p. 650.

17. Ibn Khaldun, Muqaddimah, English translation by Frenz Rosenthal, London, 1957, vol. 3, p. 267.
18. Ibid. p. 278
19. Haji. Khalifah, op. cit. p. 1936.
20. Sarton, op. cit vol. III, part I, p. 759.
21. Ibid. Vol. II, Part. II, p. 1045.
22. Sarton, op. cit., Vol. III, Part I, p. 321.
23. Sarton, op. cit vol. III , part I, p. 756.
24 Arnold and Guillaume, op. cit. p. 125.

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About the Author:
The author is now engaged in various aspects of research work mainly in the field of Analytical Chemistry with special reference to Agricultural Science. He is currently working as a Senior Research Fellow in Export Testing Laboratory under Deptt of Agril. Chemicals in BCKV. He has completed his B.Sc. (Ag.) Hons from Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India in 2004. He has got his M.Sc.(Ag. Chemicals) degree from the same university in 2006. He was awarded with Karunamoyee Gold Medal from the same university for his out standing academic performance as well as significant achievements regarding his research work during his P.G. curriculam. He has attended a no. of national and international seminars, symposiums, workshops. He has a no. of papers in various journal of national and international repute.

Article Source: http://www.articlesbase.com/science-articles/contributions-of-ancient-arabian-and-egyptian-scientists-on-chemistry-327375.html

Chemistry and Goals of Chemists

noreply@blogger.com (Unknown) — Thu, 12 Mar 2009 18:28:00 -0700

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About the Author:

Dr.Badruddin Khan teaches Chemistry in the University of kashmir, srinagar, India. His E.mail is:khanbudr@yahoo.co.in

Article Source: http://www.articlesbase.com/science-articles/chemistry-and-goals-of-chemists-570403.html

What is Chemistry and How to Tame It?

noreply@blogger.com (Unknown) — Thu, 12 Mar 2009 18:20:00 -0700

Chemistry is the study of matter and its changes. This includes everything in the universe from a simple hydrogen atom to very large replicating molecules in life processes. Chemistry is involved with the development of medicines that control and cure diseases; food production through specific and safe agricultural chemicals; consumer products such as cleaners, plastics and clothing; new methods of energy production, transfer and storage; new materials for electronic components; and new methods for protection and cleanup of the environment. Chemists are needed to help solve some of society's most difficult technological problems through research, development and teaching.

A major branch of chemistry, known as ‘Inorganic Chemistry’, is generally considered to embrace all substances except hydrocarbons and their derivatives, or all substances that are not compounds of carbon (including some of the small molecules of carbon.) It covers a broad range of subjects, among which are atomic structure, crystallography, chemical bonding, coordination compounds, acid-base reactions, ceramics, and various subdivisions of electrochemistry (electrolysis, battery science, corrosion, semi conduction, etc.). It is important to state that inorganic and organic chemistry often overlap. For example, chemical bonding applies to both disciplines, electrochemistry and acid-base reactions have their organic counterparts, catalysts and coordination compounds may be either organic or inorganic.

Regarding the importance of inorganic chemistry, R.T. Sanderson has written: "All chemistry is the science of atoms, involving an understanding of why they possess certain characteristic qualities and why these qualities dictate the behavior of atoms when they come together. All properties of material substances are the inevitable result of the kind of atoms and the manner in which they are attached and assembled. All chemical change involves a rearrangement of atoms. Inorganic chemistry (is) the only discipline within the chemistry that examines specifically the differences among all the different kinds of atoms".

Another major branch of chemistry is ‘Organic Chemistry’ which embraces all compounds of carbon except such binary compounds as the carbon oxides, the carbides, carbon disulfide, etc.; such ternary compounds as the metallic cyanides, metallic carbonyls, phosgene (COCl2), carbonyl sulfide (COS), etc.; and the metallic carbonates, such as calcium carbonate and sodium carbonate. The total number of organic compounds is indeterminate, but a huge number has been identified and named. Important areas of organic chemistry include polymerization, hydrogenation, Isomerisation, fermentation, photochemistry, and stereochemistry. There is no sharp dividing line between organic and inorganic chemistry, for the two often tend to overlap.

Application of the concepts and laws of physics to chemical phenomena is included under the heading ‘Physical Chemistry’ in order to describe in quantitative (mathematical) terms a vast amount of qualitative (observational) information. A selection of only the most important concepts of physical chemistry would include: the electron wave equation and the quantum mechanical interpretation of atomic and molecular structure, the study of the subatomic fundamental particles of matter, application of thermodynamics to heats of formation of compounds and the heats of chemical reaction, the theory of rate processes and chemical equilibria, orbital theory and chemical bonding, surface chemistry, including catalysis and finely divided particles, the principles of electrochemistry and ionization. Although physical chemistry is closely related to both inorganic and organic chemistry, it is considered a separate discipline.

Analytical Chemistry is the subdivision of chemistry concerned with identification of materials (qualitative analysis) and with determination of the percentage composition of mixtures or the constituents of a pure compound (quantitative analysis). The gravimetric and volumetric (or "wet") methods (precipitation, titration and solvent extraction) are still used for routine work and new titration methods have been introduced e.g. cryoscopic, pressure-metric (for reactions that produce a gaseous product), redox methods, and use of a F-sensitive electrode etc. However, faster and more accurate techniques (collectively called instrumental) have been developed in the recent past. Among these are infrared, ultraviolet, and x-ray spectroscopy where the presence and amount of a metallic element is indicated by lines in it's emission or absorption spectrum; colorimetry by which the percentage of a substance in soluble is determined by the intensity of it's colour; chromatography of various types by which the components of a liquid or gaseous mixture are determined by passing it through a column of porous material or on thin layers of finely divided solids; and separation of mixtures in ion exchange columns and radioactive tracer analysis. Optical and electron microscopy, mass spectrometry, microanalysis, Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) spectroscopy all fall within the area of analytical chemistry. New and highly sophisticated techniques have been introduced in recent years, in many cases replacing traditional methods.

Originally Biochemistry was a subdivision of chemistry but now an independent science, which includes all aspects of chemistry that apply to living organisms. Thus, photochemistry is directly involved with photosynthesis and physical chemistry with osmosis, two phenomena that underline all plant and animal life. Other important chemical mechanisms that apply directly to living organisms are catalysis, which takes place in biochemical systems by the agency of enzymes; nucleic acid and protein constitution and behavior, which is known to control the mechanism of genetics; colloid chemistry, which deals in part with the nature of cell walls, muscles, collagen, etc; acid-base relations, involved in the pH of body fluids; and such nutritional components as amino acids, fats, carbohydrates, minerals, lipids and vitamins, all of which are essential to life. The chemical organization and reproductive behavior of microorganisms (bacteria and viruses) and a large part of agricultural chemistry are also included in biochemistry. Particularly active areas of biochemistry are nucleic acids, cell surfaces (membranes), enzymology, peptide hormones, molecular biology, and recombinant DNA.

Nuclear Chemistry is the division of chemistry dealing with changes in or transformations of the atomic nucleus. It includes spontaneous and induced radioactivity, the fission or splitting of nuclei, and their fusion, or union; also the properties and behavior of the reaction products and their separation and analysis. The reactions involving nuclei are usually accompanied by large energy changes, far greater than those of chemical reactions; that are carried out in nuclear reactors for electric power production and manufacture of radioactive isotopes for medical use, also (in research work) in cyclotrons.

Stoichiometry is the branch of chemistry and chemical engineering that deals with the quantities of substances that enter into, and are produced by, chemical reactions. Stoichiometry provides the quantitative relationship between reactants and products in a chemical reaction. For example, when methane unites with oxygen in complete combustion, 16g of methane require 64g of oxygen. At the same time 44g of carbon dioxide and 36g of water are formed as reaction productions. Every chemical reaction has its characteristic proportions. The method of obtaining these from chemical formulas, equations, atomic weights and molecular weights, and determination of what and how much is used and produced in chemical processes, is the major concern of Stoichiometry.

Many students treat chemistry as "too difficult to understand and prefer to escape and memorize even on the expense of the realization that by doing so they are bound to harm themselves now and deprive the society of their contribution later. Henceforth they should note that although it is somewhat challenging, any reasonably intelligent and dedicated student can succeed in chemistry. They should also realize that there is no use of wasting both money and time for some thing that is either memorized before examination or forgotten thereafter or some portion of it is dropped under the pretext of selection of important topics for the purpose of preparation for examination. One must not waste his/her valuables (money and time) just for the sake of degree and literacy as both of these are bound to have detrimental consequences not only for the individual concerned but also the society for obvious reasons.

Those of the students who get their confidence shattered whenever they come across chemistry may note Some Tips (given below) from tose who have succeeded in Chemistry

Develop good study habits.
Attend all lectures and labs.
Take all lecture notes and make your own notes after understanding things properly.
Use your lecture notes as a guide to your reading in the textbook. Write your questions down if you don't understand something. Ask your teacher if you don't understand a concept.
Make flash cards of definitions, concepts, reactions, structures, and nomenclature that are in the textbook and are emphasized by your teacher in lecture.
Remember that writing something is equivalent to reading it ten times and notes are records for recollecting the material and not something to be memorized in a capsule form.
Do all the homework problems sincerely and with sincerity.
One of the best ways of learning is to find a study partner or to form a study group and work on problems independently and then together.
Keep yourself up –to- date. If you get behind or get a poor grade in class tests, either you want to drop the class or may be made to drop the class.
Try to see the ‘big picture; of the future instead of being mean and escapist.
Practice applying what you have learned in class to the world around you.
Try to foster your own scientific curiosity and wonder around ‘why things are and how they happen’.
Have a positive attitude.
Realize that science requires more self discipline, but offers more rewards.
Try to be organized and recognized.
Persevere and be determined to succeed.

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Dr.Badruddin Khan teaches Chemistry in the University of Kashmir, Srinagar, India.

Article Source: http://www.articlesbase.com/college-and-university-articles/what-is-chemistry-and-how-to-tame-it-583872.html

Atom

noreply@blogger.com (Unknown) — Mon, 9 Mar 2009 22:49:00 -0700

atom [Gr.,=uncuttable (indivisible)], basic unit of matter ; more properly, the smallest unit of a chemical element having the properties of that element.

Structure of the Atom

The atom consists of a central, positively charged core, the nucleus , and negatively charged particles called electrons that are found in orbits around the nucleus.

The Nucleus

Almost the entire mass of the atom is concentrated in the nucleus, which occupies only a tiny fraction of the atom's volume. The nucleus of an atom consists of neutrons and protons, the neutron being an uncharged particle and the proton a positively charged one. Their masses are almost equal. Atoms containing the same number of protons but different numbers of neutrons represent different forms, or isotopes , of the same element.

The Electrons

Surrounding the nucleus of an atom are its electrons; for a neutral atom, the number of electrons is equal to the atomic number. The outermost electrons of an atom determine its chemical and electrical properties. An atom may combine chemically with another atom in various ways, either by giving up or receiving electrons, thus setting up an electrical attraction between the atoms (see ion ), or by sharing one or more pairs of electrons (see chemical bond ). Because metals have few outermost electrons and tend to give them up easily, they are good conductors of electricity or heat (see conduction ).

The electrons are often described as revolving about the nucleus as the planets revolve about the sun. This picture, however, is misleading. The quantum theory has shown that all particles in motion also have certain wave properties. For a particle the size of an electron, these properties are of considerable importance. As a result the electrons in an atom cannot be pictured as localized in space, but rather should be viewed as smeared out over the entire orbit so that they form a cloud of charge. The electron clouds around the nucleus represent regions in which the electrons are most likely to be found. The shapes of these clouds can be very complex, in marked contrast to the simple elliptical orbits of planets. Surprisingly, the sizes of all atoms are comparable, in spite of the large differences in the number of electrons they contain.

Atomic Weight and Number

The atomic number of an atom is simply the number of protons in its nucleus. The atomic weight of an atom is given in most cases by the mass number of the atom, equal to the total number of protons and neutrons combined. An atom may be conveniently symbolized by its chemical symbol with the atomic number and mass number written as subscript and superscript, respectively. For example, the symbol for uranium is U (atomic number 92); the isotopes of uranium with atomic weights 235 and 238 are indicated by ²³⁵₉₂ U and ²³⁸₉₂ U.

Development of Atomic Theory

Early Atomic Theory

The atomic theory, which holds that matter is composed of tiny, indivisible particles in constant motion, was proposed in the 5th cent. BC by the Greek philosophers Leucippus and Democritus and was adopted by the Roman Lucretius. However, Aristotle did not accept the theory, and it was ignored for many centuries. Interest in the atomic theory was revived during the 18th cent. following work on the nature and behavior of gases (see gas laws ).

From Dalton to the Periodic Table

Modern atomic theory begins with the work of John Dalton, published in 1808. He held that all the atoms of an element are of exactly the same size and weight (see atomic weight ) and are in these two respects unlike the atoms of any other element. He stated that atoms of the elements unite chemically in simple numerical ratios to form compounds. The best evidence for his theory was the experimentally verified law of simple multiple proportions , which gives a relation between the weights of two elements that combine to form different compounds.

Evidence for Dalton's theory also came from Michael Faraday's law of electrolysis . A major development was the periodic table , devised simultaneously by Dmitri Mendeleev and J. L. Meyer, which arranged atoms of different elements in order of increasing atomic weight so that elements with similar chemical properties fell into groups. By the end of the 19th cent. it was generally accepted that matter is composed of atoms that combine to form molecules.

Discovery of the Atom's Structure

In 1911, Ernest Rutherford developed the first coherent explanation of the structure of an atom. Using alpha particles emitted by radioactive atoms, he showed that the atom consists of a central, positively charged core, the nucleus , and negatively charged particles called electrons that orbit the nucleus. There was one serious obstacle to acceptance of the nuclear atom, however. According to classical theory, as the electrons orbit about the nucleus, they are continuously being accelerated (see acceleration ), and all accelerated charges radiate electromagnetic energy. Thus, they should lose their energy and spiral into the nucleus.

This difficulty was solved by Niels Bohr (1913), who applied the quantum theory developed by Max Planck and Albert Einstein to the problem of atomic structure. Bohr proposed that electrons could circle a nucleus without radiating energy only in orbits for which their orbital angular momentum was an integral multiple of Planck's constant h divided by 2π. The discrete spectral lines (see spectrum ) emitted by each element were produced by electrons dropping from allowed orbits of higher energy to those of lower energy, the frequency of the photon of light emitted being proportional to the energy difference between the orbits.

Around the same time, experiments on x-ray spectra (see X ray ) by H. G. J. Moseley showed that each nucleus was characterized by an atomic number, equal to the number of unit positive charges associated with it. By rearranging the periodic table according to atomic number rather than atomic weight, a more systematic arrangement was obtained. The development of quantum mechanics during the 1920s resulted in a satisfactory explanation for all phenomena related to the role of electrons in atoms and all aspects of their associated spectra. With the discovery of the neutron in 1932 the modern picture of the atom was complete.

Contemporary Studies of the Atom

With many of the problems of individual atomic structure and behavior now solved, attention has turned to both smaller and larger scales. On a smaller scale the atomic nucleus is being studied in order to determine the details of its structure and to develop sources of energy from nuclear fission and fusion (see nuclear energy ), for the atom is not at all indivisible, as the ancient philosophers thought, but can undergo a number of possible changes. On a larger scale new discoveries about the behavior of large groups of atoms have been made (see solid-state physics ). The question of the basic nature of matter has been carried beyond the atom and now centers on the nature of and relations between the hundreds of elementary particles that have been discovered in addition to the proton, neutron, and electron. Some of these particles have been used to make new types of exotic "atoms" such as positronium (see antiparticle ) and muonium (see muon ).

Bibliography

See G. Gamow, The Atom and Its Nucleus (1961); H. A. Boorse and L. Motz, ed., The World of the Atom (2 vol., 1966); B. H. Bransden and C. J. Joachain, Physics of Atoms and Molecules (1986).

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adapted from: "atom." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. 10 Mar. 2009 <http://www.encyclopedia.com>.

Atom

noreply@blogger.com (Unknown) — Mon, 9 Mar 2009 22:38:00 -0700

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of Hydrogen-1, which is the only stable isotope with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determine the isotope of the element.

The name atom comes from the Greek ἄτομος/átomos, α-τεμνω, which means uncuttable, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was not indivisible. The principles of quantum mechanics were used to successfully model the atom.^[1]^[2]

Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom's mass is concentrated in the nucleus,^{[note 1]} with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus. Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties.

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adapted from: http://en.wikipedia.org/wiki/Atom

Chemistry

noreply@blogger.com (Unknown) — Mon, 9 Mar 2009 22:35:00 -0700

Chemistry (from Egyptian kēme (chem), meaning "earth"^[1]) is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.^[2] It is a physical science for studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination, which incorporates the concepts of energy and entropy in relation to the spontaneity of chemical processes. Modern chemistry evolved out of alchemy following the chemical revolution (1773).

Disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the energy related studies of chemical systems at macro, molecular and submolecular scales; analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system

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adapted from: http://en.wikipedia.org/wiki/Chemistry