Chemistry....

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Chemistry....

帖子 由 Giraffe 于 周二 七月 28, 2009 7:02 am

Chemistry
Chemistry is the science that studies why materials have their characteristic properties, how these particular qualities relate to their simplest structure, and how these properties can be modified or changed. The term chemistry is derived from the word alchemist which finds its roots in the Arabic name for Egypt or the " black country," al-Kimia. The Egyptians are credited with being the first to study chemistry. They developed an understanding of the materials around them and became very skillful at *** different types of metals, manufacturing colored glass, dying cloth, and extracting oils from plants. Today, chemistry is divided into four traditional areas: organic, inorganic, analytical, and physical. Each discipline investigates a different aspect of the properties and reactions of the substances in our universe. The different areas of chemistry have the common goal of understanding and manipulating matter.
Organic chemistry is the study of the chemistry of materials and compounds that contain carbon atoms. Carbon atoms are one of the few elements that bond to each other. This allows vast variation in the length of carbon atom chains and an immense number of different combinations of carbon atoms from which to form the basic structural framework of millions of molecules. The word organic is used because most natural compounds contain carbon atoms and are isolated from either plants or animals. Rubber, vitamins, cloth, and paper represent organic materials we come in contact with on a daily basis. Organic chemistry explores how to change and connect compounds based on carbon atoms in order to synthesize new substances with new properties. Organic chemistry is the backbone in the development and manufacture of many products produced commercially, such as drugs, food preservatives, perfumes, food flavorings, dyes, etc. For example, recently scientists discovered that chlorofluorocarbons (CFCs), are depleting the ozone layer around the earth. One of these CFCs is used in refrigerators to keep food cold. Organic chemistry was used to make new carbon atom containing compounds that offer the same physical capabilities as the chlorofluorocarbons in maintaining a cold environment, but do not deplete the ozone layer. These compounds are called hydrofluorocarbons (HFCs) and are not as destructive to the earth's protective layer.
Inorganic chemistry is the study of the chemistry of all the elements in the periodic table except for carbon. Inorganic chemistry is a very diverse field because it investigates the properties of many different elements. Some materials are solids and must be heated to extremely high temperatures to react with other substances. For example, the powder that is responsible for the light and color of fluorescent light bulbs is manufactured by heating a mixture of various solids to thousands of degrees of temperature in a poisonous atmosphere. An inorganic compound may alternatively be very unreactive and require special techniques to change its chemical composition. Inorganic chemistry is used to construct electronic components such as transistors, diodes, computer chips, and various metal compounds. In order to make a new gas for refrigerators that does not deplete the ozone layer, inorganic chemistry was used to make a metal catalyst that facilitated the large scale production of HFCs for use throughout the world.
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 chemistry studies both organic and inorganic compounds and measures 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. The 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 phenomenon utilized in organic and inorganic chemistry. In the development of the new refrigerator gas, physical chemistry was used to measure the physical properties of the new compounds and determine which one would best serve its purpose.
Analytical chemistry is that area of chemistry that develops methods to identify substances by analyzing and quantitating the exact composition of a mixture. A material is identified by a measurement of its physical properties, such as the boiling point (the temperature where the physical change of state from a liquid to a gas occurs) and the refractive index (the angle which light is bent as it shines though a sample), and the reactivity of the material with various known substances. These characteristics that distinguish one compound from another are also used to separate a mixture of materials into their component parts. If a solution contains two materials with different boiling points, then they can be separated by heating the liquid until one of the materials boils out and the other remains. By measuring the amount of the remaining liquid, the component parts of the original mixture can be calculated. Analytical chemistry develops instruments and chemical methods to characterize, separate, and measure materials. In the development of HFCs for refrigerators, analytical chemistry was used to determine the structure and purity of the new compounds tested.
Chemists are scientists who work in the university, the government, or the industrial laboratories investigating the properties and reactions of materials. These people research new theories and chemical reactions as well as synthesize or manufacture drugs, plastics, and chemicals. The chemist of today may have many "non-traditional" occupations such as 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 related fields which encompass our whole society.

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帖子 由 Giraffe 于 周二 七月 28, 2009 7:03 am

Combinatorial Chemistry


Combinatorial chemistry is a sophisticated set of techniques used to synthesize, purify, analyze, and screen large numbers of chemical compounds, far faster and cheaper than was previously possible. The direct precursor of combinatorial chemistry was the solid-phase synthesis of polypeptides developed by American biochemist Robert Bruce Merrifield in the 1960s, followed by the advances in laboratory automation since then. Initial development of the field has been led by the pharmaceutical industry in the search for new drugs, but its applications are spreading into other fields of chemistry. Other terms associated with this field are parallel array synthesis and high-throughput chemistry.

Whereas classical synthetic chemistry involves the stepwise synthesis and purification of a single compound at a time, combinatorial chemistry makes it possible to synthesize thousands of different molecules in a relatively short amount of time, usually without the intermediate separation of compounds involved in the synthetic pathway, and with a high degree of automation. Such procedures result in the production of new compounds faster and in greater numbers than is possible with standard synthetic methods. The first and still the most common type of combinatorial synthesis involves attaching a molecular species onto a macroscopic substrate such as a plastic bead and performing one or several well-characterized chemical reactions on the species. After each reaction, the product mixture can be split among several reaction containers and then recombined after the reaction (a procedure called mix and split), or else carried out in parallel containers. The resulting mixture of compounds is referred to as a molecular library and can contain many thousands of individual compounds. The analysis, or screening, of these libraries to identify the compounds of interest, along with their subsequent isolation and identification, can be completed by a variety of methods. One example is iterative deconvolution; it involves the successive identification of each of the units backward along the chain of synthesized units. Another, called positional scanning, requires the multiple synthesis of a library, each time varying the location of a known unit along the chain and comparing the activities of the resulting libraries. More recent advances in library screening involve the "tagging" of a substrate with tiny radio frequency transmitters or unique two-dimensional barcodes. Another important recent advance by researchers allows combinatorial syntheses to be carried out in solution, which further extends the scope and utility of this field.

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