Opportunities in Chemistry Today and Tomorrow (1987) / Chapter Skim
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III. Human Needs Through Chemistry
III. Human Needs Through Chemistry
Pages 21-114
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We will begin with the most fundamental of these needs, adequate food supply for an ever-increasing world population.
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In addition to grains, bean crops have similar parasite enemies. Thus in collaboration with agricultural and biological scientists, chemists play a crucial role in our efforts to increase the world's food supply and eliminate hunger.
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To increase the world food supply, we need improvements in food production; food preservation; conservation of soil nutnents, water, and fuel; and better use of solar energy through photosynthesis. Science is providing such improvements and chemistry is playing a central role by clarifying the actual chemistry involved in biological life cycles.
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The following examples vividly display the key role chemistry plays in our current attempts to expand the world food supply. PLANT HORMONES AND GROWTH REGULATORS Growth regulators are chemical compounds that work in small concentrations to regulate the size, appearance, and shape of plants and animals.
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COOH H INDOLE ACETIC ACID (IAA) Promotes plant growth More than 65 compounds related to gibberedic acid have been characterized from plants and lower orga n~sms since their landmark discovery in the fungus Gibberella fujikuroi.
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INSECT HORMONES AND GROWTH REGULATORS Insects that attack food-beanng plants reduce crop yields and, thereby, limit food supplies. The ability to understand and control these natural enemies provides another dimension by which the worId's food supply can be increased.
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It was discovered that molting hormones are widely distnbHO OH "% ~ HO, ~ HO ~ O 20-HYDROXYECI) YSONE INSECT MOLTING H-ORMO-NE Causes insects to shed their skins POOH uted in plants and are probably produced as a defense against insects.
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The isolation and full identification always involve handling extremely small quantities. Characterization of the four pheromones for cotton boll weevil pheromones (1SA-D)
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~ ~ CHO OHC ~ C H H D ~CH2OH Am,, POOH ': (15) FOUR COTTON BOLL WEEVIL PHEROMONES A tiny bit is enough ~0 PESTICIDES Pesticides insecticides, herbicides, and fungicides are essential to our attempts to improve food and fiber production and to control insect-transmitted diseases in humans and livestock.
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Chemical synthesis aIld testing programs have led to other novel structures that act as nerve poisons, inhibitors of chitin synthesis, and growth disruptors (e.g., (20~. This new range and vanely of insecticide classes has helped immensely in the pest control battle.
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Hence, a fundamental aspect of increasing the worId's food supply is to deepen our knowledge of plant chemistry. Because of special promise, two frontiers deserve special mention nitrogen fixation and photosynthesis.
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Since all of our food supply ultimately depends upon the growth of plants, we see that photosynthesis is also the key to the world's food supply. Photosynthesis is the process in nature by which green plants, algae, and photosynthetic bacteria use the energy from sunlight to stimulate chemical reactions in plants.
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Chromatography and electrophoresis techniques fill this need. None of the molecular structures displayed in this section could have been determined without the use of the most modern spectroscopic methods.
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These powerful instruments have played a central role in the advances already mentioned in this section; they are essential to our continued progress in the science that underlies modern methods of food production. CONCLUSION Food supply and efficient use of energy are rapidly emerging as major concerns for the wodd's future.
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When methanol and carbon monoxide meet in the gas phase, they won't even give each other the time of day. But because of the special environment provided by that thin layer of surface atoms on the rhodium catalyst, methanol and carbon monoxide react so rapidly that 500,000 tons of commercial acetic acid are made every year this way!
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A stereoselective catalyst not only controls the end product, it also favors a particular molecular shape, often with remarkable effects on the physical properties (such as tensile strength, stiffness, or plasticity) and, for biologically active substances, on the potency.
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Hence, when two reactants A and B meet in this two-dimensional reaction zone, their chemistry can differ greatly from when they meet in solution or in the gas phase. To understand this different chemistry, we must know the molecular structures for A and B as they exist on the reactive catalyst surface.
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; coal to hydrocarbons (for fuels) ; and one-carbon compounds, like carbon monoxide, carbon dioxide, methane, and methanol, to two-carbon compounds, like ethylene, ethanol, acetic acid, and ethylene glycol (for industnal feedstocks)
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The process uses salts of cobalt and manganese dissolved in acetic acid at 215°C as the catalyst system. Most of the product is then copolymerized with ethylene glycol to give us polyester clothing, tire cord, soda bottles, and a host of other useful articles.
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With our new preparative methods, we will be able to answer these questions. Many metal cluster compounds consist of several metal atoms bound to each other in the "core" of the molecule with carbon monoxide molecules chemically attached on the outside.
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These are of special interest because heterogeneous catalysts are presumed to consist only of metal atoms. Still other cluster compounds are called "cubanes." These are molecules built around a unit of four metal atoms and four sulfur atoms at the eight corners of a cube.
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. This rapidly moving field depends upon our knowledge of homogeneous catalysis, heterogeneous catalysis, and semiconductor behavior.
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ARTIFICIAI`-ENZYME CATALYSIS A striking outcome of our expanding chemical knowledge has been the development or our ability to deal with molecular systems ot extreme complexity. Using such modern instrumentation as nuclear magnetic resonance, X-ray spectroscopy, and mass spectroscopy, we can now synthesize and control the structure of molecules that come close to the complexity of biological molecules.
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When the reaction partner arrives, the scene is set for the desired reaction to take place in the desired geometry. Organic chemists who are trying to make artificial enzymes are making notable progress.
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SUPPLEMENTARY READING Chemical & Engineering News '~Stereospecific Routes to Silyl Enol Ethers" by S Stinson (C.& E.N.
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13, 1982. "Metal Clusters: Bridges Between Molecular and Solid State Chemistry" by E.L.
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They must start the human machine every morning without fail, and the hyenas lights and radio are running all the time. Yet many, many people are adding healthy years to life by betting on the chemical reactions that occur In these batteries to generate~ay in, day out the electnc current that drives their pacemakers.
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Complex chemical processing is required to convert the raw natural product into chemical forms that meet the demands of modern, high-compression engines.
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Refining Crude oil, as it is pumped out of a well, is a liquid solution containing mostly hydrocarbons. The largest component is made up of compounds containing only single bonds; these are called alkanes.
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After that, the large molecules must be broken down into smaller, lower-boiling molecules by catalytic cracking. Then, catalytic reforming can be used to change the molecular structures to forms that burn better (high octane number)
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H7DROGENO LT S I S , 1E I NEED ( 1 0,8.7 ) ~ CHIC HC`~ ITCH 2 CH aromatic _ H2C`c J. CH3 ~ H2 2 cyclic alkane CH3 1 TIC ACHE ~2 H branched all~anes CH2 H3C CH3 CH CH2 propane DIFFERENT SURFACES FAVOR DIFFERENT PRODUCTS TABLE IlI-C-1 Heterogeneous Catalysis in the Petroleum Industry Feedstocks Catalyst Product Used for C~6-C24 oils Zeolite C7-Cg alkanes, alkenes "Cracking,' to high molecular sieves octane fuels (aluminosilicates)
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Fortunately, the area of chemical kinetics currently offers great promise. Such optimism comes because of an array of new, sophisticated instrumental techniques that allows us to understand the basic chemical behaviors at work (see Section IVA)
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The ethane and propane can be catalytically changed to ethylene, C2H4; propylene, C3H6; and acetylene, C2H2, all valuable raw materials for products needed by our society. Natural gas is an important resource as it is easily transported in pipelines and has many applications.
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, which is a mixture of carbon monoxide and hydrogen. The use of synthesis gas has enormous potential, but so far it is not economically competitive.
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Research on both synthesis and catalytic activity of metalorganic compounds, artificial enzymes, and natural enzymes should help us weigh the potential of biomass as a source of hydrocarbon fuels or chemical feedstocks. Of course, there is tremendous appeal in the prospect of producing useful energy from garbage, sewage, and plant waste disposal.
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To halt this trend, we should be seeking new energy sources that do not release CO2. Solar energy is such an alternative.
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This observation has led to the idea that the center of photoreaction is a pair of parallel chIorophyI} rings held closely together by hydrogen bonding between amino acid groups. Another promising approach to the use of solar energy is the direct conversion of sunlight to electrical or chemical energy with the aid of electrochemical devices.
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Whatever course society ultimately chooses, it will rely heavily upon the ingenuity of chemists and chemical engineers to reduce those risks. Indeed, chemical research is essential to practically all phases of nuclear energy generation and the subsequent management of radioactive waste.
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An enormous energy release would result from this fusion- more than 100 million kilocalories of heat would be released for every gram of helium formed. Thus, nuclear fusion competes with nuclear fission as a possible future source of energy, but it does not produce the myriad of radioactive fission products that present such a troublesome radioactive waste problem.
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Fortunately, chemistry is ready to respond to these challenges. SUPPLEMENTARY READING Chemical & Engineering News "Photovoltaic Cells" by K
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III-C. MORE ENERGY with Molecular Reagents" by M.S.
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One of these, poly~para-phenylene terephthalamide) , has a tensile strength slightly higher than that of steel.
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By clever manipulation of these factors, chemists can design polymers with tailored properties such as plasticity or hardness, tensile strength, flexibility or elasticity, thermal softening or thermal stability, chemical inertness or solubility, attraction or repulsion of solvents (wetting properties) , permeability to water, responsiveness to light (photodegradability)
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The resulting progress is shown in Table IlI-D-1, which compares the tensile strengths of two organic polymer fibers to those of both aluminum alloy and drawn steel. The two polymers significantly outperform both of the conventional structural metals in a crucial measure, strength per unit weight.
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It is just this control that lies behind the production of fibers of exceptionally high tensile strength which can replace steel in products ranging from airframe construction to bullet-proof vests.
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. BLOCK POLYMERS CAN SELF-ORGANIZE of such molecular design are shown dramatically by companug the tensile strengths of the two types of triblock polymers that can be made from butadiene (B)
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The critical development that made this optical technology possible was the production of highly transparent silica fibers through a new process known as chemical vapor deposition (CVD)
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The reason is that entirely new families of electrically conducting solids are being discovered families susceptible to a chemist's ability to control local structures and molecular properties. As will be seen, some of these new families are inorganic solids and some are organics.
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Organic chemists can use their creative skills to fashion compounds that combine electrical conductivity with the various beneficial properties of polymers, such as structural strength, thermoplasticity, or flexibility. Electrostudy that make polyacetylene photovoltaic cells light can be designed to match the solar spectrum, for cheap organic photovoltaic cells with which to
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GERMAN I UM SILICON SODIUM CHLOR I DE IODINE GLASS Dl AMOND : —- ~ -~.r~ ~ Late in 1986, however, an enormous breakthrough was made when certain copper oxide solids were found to become superconducting at temperatures above 90K. These solids have layers of copper oxide with various metal atoms sandwiched between in the so-called perovskite crystal structure.
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The mobile charge carriers might be small ions like lithium ion or hydrogen ion. Substances with layered molecular structures like graphite provide excellent crystal hosts for such manipulations.
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. Such a short-lived, high-temperature pulse can cause significant chemical and physical changes, modifying the surface, forming surface alloys, and promoting specific chemical reactions when coupled with vapor deposition.
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That is why more chemists are being attracted to research in the matenals sciences. SUPPLEMENTARY READING Chemical & Engineering News "The Organic Solid State" by D.O.
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"Liquid Crystals" pp. 8-11, December 1983.
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This story began 30 years ago when scientists discovered the chemical mechanisms by which blood pressure is elevated in humans. Chemical techniques isolated two closely related substances, angiotensin ~ and angiotensin II.
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Of particular importance have been molecular structure determinations through computer-a~ded high-resolution X-ray crystallography. Combining knowledge about how enzymes accelerate chemical reactions with knowledge about the coiling of proteins (tertiary structure)
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They then recognize and bind biologically active molecules. This has the effect of catalyzing and controlling reactions with these molecules, as they are "held" by the receptors in a strategic manner.
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Norepinephrine, the chemical messenger for the part of the nervous system that controls adrenalin flow, has been shown to bind to at least four types of receptors assisting in several types of biological responses. Compounds that act as specific antagonists have already proven their value in treating cardiovascular disease, cancer, disorders of the central nervous system, and endocrine disorders.
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CARDIOVASCULAR DISEASE Diseases of the heart and blood vessels are presently the major cause of death in the United States. Therefore, high blood pressure (hypertension)
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Their biological properties are now being investigated to decide their possible usefulness in the creation of new therapeutic agents. We already know that these compounds tend to increase urine discharge, to relax blood vessels, and to lower blood pressure.
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Drugs that inactivate the sodium ion channel (quinidine, procainamide, lidocaine) , depress the calcium ion channel (verapamil)
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Ten years ago, only eight or nine monoamine or amino acid compounds were known that seemed to be neurotransmitters. Now over 40 more small peptides have been added to the list, each of which has a possible messenger function.
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Cancer is characterized by uncontrolled cell growth in the body. It is gratifying that cancer research has entered a fruitful phase.
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the amino acid sequence of the proteins made from these genes. Changing only a single nucleotide in a gene from a bladder, colon, or lung cell can replace a particular amino acid by another in the gene product, and thereby make an otherwise normal cell malignant.
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There remains a pressing need for more effective and less toxic anticancer drugs, in particular for treating siowgrowing solid tumors, lung cancer, and brain tumors. Immunologists and cell biologists are discovering differences between the surfaces of normal cells and tumor cells which may provide new directions for drug design.
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From this has emerged a picture of nature's design of these molecules. They have a "variable region," in which the amino acid sequence varies according to which foreign substance the antibody is attacking, and a "constant region," which stays essentially the same for most antibodies.
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It stimulates the pituitary gland to release a wide range of hormones involved in the reproductive system. Many compounds similar to GnRH (a 10-amino acid polypeptide)
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Determination of its molecular structure in 1956 by X-ray crystallographic and chemical studies showed it to be by far the most complex of any of the known vitamins. Its synthesis in 1976 was a landmark of organic chemistry.
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Science is starred with examples of unanticipated breakthroughs that prove to be more important than the advances we can foresee. SUPPLEMENTARY READING Chemical & Engineering News "Synthetic Antiviral Agents" by R.K.
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From page 91... ...
_ , Am,, 0 CH 2 CH3 ~ ~'CH3 Down the cellular cholesterol factory, the cell produces more lipoprotein receptors, and the blood cholesterol level drops. The importance of this advance is shown by the fact that the average person with double the normal blood level of cholesterol can expect to live only 45 to 50 years.
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Today, we have a basic understanding of the chemical structures and functions of the molecules and macromolecules that are involved in these chemical factones. The blueprints are called DNA molecules (DNA means a~eoxynbonucleic acid)
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Thus, the covalent strands of two complementary DNA molecules are held together in the helix shape by the much weaker hydrogen bonds. Because the bonding between these amino bases is so specific, the helix can form only if the sequence of bases on the first string is perfectly matched to the sequence on the second string.
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From page 94... ...
Thus, these 20 amino acids make up a molecular alphabet + H2O containing 20 letters. The order in which these amino acid letters link up "speDs out" and determines the molecular structure of the protein and therefore its biOlogical function.
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. Chemists also learned how to assemble amino acids in a desired sequence so they could make polypeptides in the laboratory and even small proteins identical in structure and function to those isolated from natural sources.
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RECOMBINANT DNA TECHNOLOGIES A recent development in biotechnology is caned recombinant DNA technology or genetic eng~neenng. It combines nucleic acid chemistry, protein chemistry, microbiology, genetics, and biochemistry.
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Separations technology has been developed to isolate such DNA fragments. Other analytical techniques have been developed to identify the genetically engineered cells in which the desired DNA has been introduced as wed as those within which the DNA (through the inte~ediary rnRNA)
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Perhaps the most important contribution that recombinant DNA technology can achieve will be the expansion of knowledge about the regulation of genes within ceils. Naturally occumng molecules are often found that are biologically active and thus medically useful.
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Further progress in the chemical modification of proteins may remove these limitations. Often, a protein produced using recombinant DNA technology requires modification before its biological activity can be realized.
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cold have been immobilized and used to catalyze the chemical conversion of fumaric acid and ammonia into aspartic acid, one of the amino acid building blocks of proteins. In addition, immobilized yeast cells can be used in the fermentation by which we produce alcohol (ethanol)
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SUPPLEMENTARY READING Chemical & Engineering News "Biomaterials in Artificial Organs" by lI.E. Kambic, S
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18, 1986. "Automated Chemical Synthesis of a Protein Growth Factor for Hemopoietic Cells, Interleukin-3" by I
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This combats the van der Waals force by keeping the particles at a distance from each other. One of the first practical magnetic fluids was made from a mixture of iron oxide particles (FeO and Fe2O3)
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Every medicine that a doctor prescribes is a chemical compound whose effectiveness depends upon the chemical reactions it stimulates or controls. The business climate of the chemical industry is complex and changing.
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It is not surprising that the viability of chemical companies in the United States has become a cause for national concern. The advanced standard of living in the United States owes a great deal to the innovations and productivity of the nation's chemical businesses.
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106 HUMAN NEEDS THROUGH CHEMISTRY coming price increases brought on by decreases in oil and gas reserves better than uses involving combustion. Further, processes are already known for the conversion of coal to suitable forms for use as feedstocks, and coal deposits are more abundant.
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The protein products can be hormones, antibodies, or other desired complex chemical compounds with specific prope~ties and functions. Interferon, 107 ~ ._ <$~!
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The advances that win determine the future of this field win come through a deep understanding of biology at the molecular level. Basic research on the molecular structure and chemistry of biological molecules wid be a crucial ingredient as we bring biotechnology into practical use.
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From page 109... ...
With a history of 150 years, the silver halide process has evolved from complex procedures conducted by specialists with a working knowledge of photochemistry into a pastime expertly pursued by a large chunk of the population. The camera owner presides over remarkable feats of optics and chemistry to produce pictures on the spot, usually without having the faintest 109
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From page 110... ...
Physical chemical factors such as solubility and diffusion are critical, as are the chemical reactions occurring in the various layers dunug processing. The sophistication of the chemistry of instant color photography is difficult to comprehend considering how simple the camera is to use.
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From page 111... ...
What is not generally appreciated is that this solubility is achieved through carefully designed polymer photochemistry. Existing organic photoresists were able to achieve the spacing between circuit elements needed in the early 1970s when individual circuit features were in the size range of 3-10 microns.
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Many new types of chemical reactions and polymers are involved, and the advances in integrated circuit complexity could not have occurred if these new materials had not been available. Virtually none of them existed in 1970.
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SUPPLEMENTARY READING Chemical & Engineering News `'Engineering Plastics: More Products, More Competition" by David Webber (C.& E.N. stab, vol.
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114 HUMAN NEEDS THROUGH CHEMISTRY Scientific American `'Advanced Materials and the Economy" by J.P. Clark and M.C.
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