Click for next page ( 22


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 21
CHAPTER III Human Needs Through Chemistry In this chapter, we will see how chem- istry is essential in our eternal struggle for survival, freedom from toil, and, finally, for comfort. All of the tangible human needs will be considered: food, energy, materials, health, products that raise the quality of life, and economic vitality. We will begin with the most fundamental of these needs, adequate food supply for an ever-increasing world population. 2

OCR for page 21
1 Whipping a Wicked Weed The plant Stnga asiatica is one of the most devastating destroyers of grain crops in the world. This wicked weed restricts the food supply of more than 400 million people in Asia and Africa. It is a parasite that nourishes itself by latching onto and draining the vitality of a nearby grain plant. The results are stunted grain, a meager harvest, and hungry people. Basic research on Striga asiatica by chemists and biologists has revealed one of the plant world's incredible host-parasite adaptations. The parasite seed lies in wait until it detects the proximity of the host plant by using an uncanny chemical radar. ED ~0 The give-away is provided by specific chemical compounds exuded by the host.~` Striga asiatica can recognize the exuded compounds and use them to trigger its own growth cycle. Then the parasite has an independent growth period of 4 days, ding which it must locate the nearby host. Researchers trying to solve the mystery of this recognition system faced forrn~dable obstacles; they were seeking unknown, complex molecules produced only in tiny amounts. But, by extending the sensitivity of the most modern instruments, chemists have been able to deduce the chemical structures of these host-recognition substances, even though the agricultural scientist could accumulate the active chemicals in amounts no larger than a few bits of dust (a few micrograms). One method used, nuclear magnetic resonance (NMR), depends upon the fact that the nuclei of many atoms have magnetic fields that respond measurably to the presence of other such nuclei nearby. Thus precise NMR measurements reveal molecular geometries, even of ornate molecules. A second, equally sophisticated approach is high-resoluiion mass a/ (:JA IT spectometry. In a high vacuum, molecules are given an electric charge, then acceler- ated with a known energy. By measuring the velocities at which these molecules and fragments from them are traveling (or their curved paths in magnetic fields), chemists can measure the masses and decide the atomic groupings present. These He critical clues to the molecular identities. Now, the complex host-recogli~tion (xenogistic) substances have been identified and their detailed structures are known. With this information in hand, we may be able to beat this wicked weed at its own game. Chemists can now synthesize the substances and give agricultural scientists enough material for field tests designed to tnck the parasite into begging its today growth cycle. It will die out never having found its host. A few days later, grain can be planted safely. With this success for guidance, similar host-parasite relationships are being sought and foun~here In the United States. 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. ~ 4~ HO ~ At. ~

OCR for page 21
III-A. MORE FOOD IlI-A. More Food Agriculture, discovered 12,000 years ago, was the beginning of man's attempt to enhance survival by increasing the food supply. The human population at that time was about 15 million, but agriculture helped it rise to 250 million 2,000 years ago. By 1650, it had doubled to 500 million. But then it took only 200 years, until 1850, for the world population to double again, to one billion. Eighty years later, in 1930, the 2 billion level was passed. The acceleration has not abated: by 1985, the number of humans to be fed had reached 5 billion. If the growth were to continue at the 1985 level of 2 percent per year, the world population in 2020 would be about 10 billion. The rate of natural increase in population seems to be slowing worldwide (Table IlI-A-1), with the industnal countries adding only 80 million up to the year 2000. This is not the case for Africa, however, where population Table III-A-1 Population Growth-Rate, 1960-1980 growth has been accelerating at an alarming pace. In 1983, about 20 million hu- man beings starved to death- about 0.5 percent of the worId's population. Moreover, an additional 500 million were severely malnourished. Esti- mates indicate that by the end of the century, the number of severely undernourished people will reach 650 million. Plainly, one of the major and increasing problems facing the human race will be providing itself with adequate food and nourishment and, ultimately, to limit its own population growth. And whose problem is this? In the most elemental way, it is the problem of those who are hungry, those who are undernourished, those who are least able to change the course of events on more than a personal and momentary scale. But human hunger is also the problem, indeed, the responsibility, of those who can affect the course of events. Any attempt to fulfill that responsibility will surely need the options that can come from science, and among the sciences that can generate options, chemistry is seen to be one of the foremost. It can do so, first, by increasing food supply and, second, by providing safe methods by which individuals can limit population growth (see Section ITI-E). Food production cannot be significantly increased simply by cultivating new land. In most countries, the farmable land is already in use. In the heavily populated developing countries, expansion of cultivated areas requires huge capital investments and endangers the local ecology and wildlife. 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. We are developing an understanding at the molecular level of the factors Annual Percent Increase Area 1960-1965 1975-1980 World 1.99 1.81 Industrialized 1.19 0.67 Asia 2.06 1.31 Latin America 2.77 2.66 -4.0 Africa 2.49 2.91 ~ 16.9 SOURCE: W.P. Mauldi. 1980. Science 209:148-157. Percent Change -9.0 43.7 -33.5 23

OCR for page 21
24 HUMAN NEEDS THROUGH CHEMISTRY that can be controlled to aid in the fight for more food. These factors include the hormones, pheromones, self-defense structures, and nutrients at work in our animal and plant food crops and also those of their natural enemies. We can best address these problems by using our present understanding of living systems. Pest control, for example, is an essential element of efficient food production. The emphasis in this area has been on the use of chemicals that attempt to eliminate insects or other pests by killing them (biocidal agents). This method risks upsetting nature's balance and introduces foreign substances into the envi- ronment. But we want to control insect pests, not exterminate them. Then we can avoid the potentially devastating ejects that may accompany profound ecological disturbances. By understanding the biochemistry of the organisms themselves, we can limit the impact of pests on food production in ways that can be used indefinitely without harmful effects on nature. Increasingly, such fundamental questions about biological systems have become questions about molecular struc- tures and chemical reactions. 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. They include natural compounds produced within the organism and also some natural products that come from the environment. However, many similar compounds (analogs) that have been synthesized in the laboratory have been found to function as growth regulators. They are usually patterned after compounds found in nature, and some of them work just as effectively but without undesired side effects. The chemicals already present in plants or animals that exert regulatory actions are called hormones (e.g., growth hormones and sex hormones). A hormone can be said to be a chemical message sent between cells. The so-called plant hormones include growth substances (e.g., auxins, gibberellins, and cytokinins) and growth inhibitors (e.g., abscisic acid and ethylene) that seem to be structurally unrelated. These growth regulators are surely of immense social (and economic) importance for the worId's future because they influence every phase of plant development. Unfortunately, even though we know the structures of many plant growth regulators, we have little insight concerning the molecular basis for their activity. Since chemical interactions and reactions are involved, chemistry must play a central and indispensable role in the development of this insight. Below are some typical growth regulators. Notice the variety of molecular structures nature has developed for this function. By establishing the exact makeup of these structures, scientists have taken an essential step toward understanding and controlling the growth processes being regulated. Indole Acetic Acid (lAA), an Auxin (1) This compound was the first plant hormone to be characterized. It promotes plant growth, the rooting of cuttings, and the formation of fruit without fertilization.

OCR for page 21
III-A. MORE FOOD The synthesis of numerous lAA analogs led to the first commercial herbicide, 2,4-dichiorophenoxya- cetic acid, or 2,4-D. Gibberellic Acid (GA) (2) 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. Commercially produced by large-scale cultures of this fungus, GA has extensive use in agnculture. Its applications range from trigger- ing formation of flower buds to growing seedless GIBBERELLIC ACID(GA) grapes and manufacturing malt in the beer industry. Triggers flowenng (I) o A ~ HO go OH COOH Cytokinins (3) The first cytokinin that was isolated is a compound that enhances cell division. Many analogs, including trans-zeatin, have since been isolated from DNA, transfer RNA, and other sources, and quite a number have been synthesized. They promote cell division, en- hance flowering and seed germination, and inhibit aging. H ~ CH2 OH C=C NHCH2 ACHE Nit NO H Ethylene (4) This simple gas behaves like a hormone since it encourages fruit ripening, leaf-drop, and gelmina- lion, as well as growth of roots and seedlings. TRANS-ZEATIN Currently, a substance that generates ethylene Promotes seed germination above pH 4 is used widely as a fruit ripener. It is suggested that ethylene regulates the action of the growth hormones auxin, GA, and cytokinin. Strigol (5) The seeds of witchweed (Striga) lie in the soil for years and will only sprout when a particular chemical substance is released by the root of another plant. The weed then attaches itself to the root of the plant and lives off of it (as a parasite). The active substance stngol now has been isolated from the root area of the cotton plant and its structure identified. Now it has been synthesized. Strigol and its synthetic analogs are proving effective in removing these parasitic weeds by causing them to sprout and die off before a crop is planted. HA OH C=C H' 'H ETHYLENE Ripens fruit G2 Factor or Trigonelline (6) H o o STRIGOL Initiates weed growth This compound was discovered to be involved in one stage of a four-step cycle in plant cell reproduction. This stage, called G2 or "gapZ," is characterized by a 25 (2) (3) (4) (5)

OCR for page 21
26 (6) AN} CH3 HUMAN NEEDS THROUGH CHEMISTRY pause in growth activity. In isolating this compound, the "first leaves" or cotyledons of 15,000 garden pea seedlings provided r~~ only one quarter of a milligram of the G2 factor. This compound may be of particular importance because of a link between the G2 stage and the formation of root bumps (caDed nitrogen nodules) that have the power to convert elemental nitrogen from the soil to nitrate, which enriches the soil. TRIGONELLINE G2 FACTOR Influences nitrogen fixation Glycinoeclepin A (7) Nematodes are tiny worms that inflict huge damage on such crops as soybean and potato. The nematode eggs can rest unchanged in the soil for many years until H ' t~ (7) I It ~L~ COOH GLYCINOECLEPIN A Promotes worm egg hatching the root of a nearby host plant releases a substance that will promote hatching. The first such hatching COOH initiator was isolated and understood recently. Dur- ing a span of 17 years, a total area corresponding to 500 football fields was planted with soybeans to give 1.5 mg of the active substance, glycinoeclepin A, which was then shown to have the unusual structure (7~. Synthetic analogs may someday be applied agriculturally to force nematode eggs to hatch be- fore a crop is planted. Hundreds of natural plant products are now known to exert growth regulatory activity of one sort or another. These compounds represent a surprising range of structural types. Recognition of these structures is the first step toward their systematic use to increase the worId's food supply. We are only at the beginning of this important process. 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. The desire to reduce maInourishment and starvation around the globe is not incompatible with the strong element of environmental concern in our society. Pests can be controlled without being exterminated. Furthermore, with the sensitivity of detection meth- ods constantly improving, we can be assured that pest control can eventually be monitored to give ample early warning of unexpected side effects. Certainly, knowledge of the basic chemistry involved in the growth and increase of insect populations should be extended to provide options that may be needed to save human lives. Molting Hormones (MH) (~) Two types of hormones are directly involved in the development of insects (known as metamo~phosisKmolting hormones and juvenile hormones. The molt- ing hormones cause insects to shed their skins; an example is 20-hydroxyec~ysone

OCR for page 21
III-A. MORE POOD all. Nine milligrams of this complex substance (a steroid) were painstakingly extracted from one ton of silkworm pu- pae (a cocoon-like stage of in- sect development). It was also shown to be the active molting hormone of crustaceans, using two milligrams isolated from one ton of crayfish waste. It was discovered that molting hormones are widely distnb- HO 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. Approximately 50 such steroids with insect MH activity have been identified. Juvenile Hormone (JH) (9) These hormones tend to keep insects in the juvenile state. The first OH (9) was identified using 0.3 milligrams of sample isolated from the butterfly T.epidoptera. Several OH analogs are now known, the most universal be- ing ~H-~l with three methyl groups on carbons 3, 7, and 11. Their importance has stimu- lated syntheses of thousands of related compounds, one of which is methoprene (101. This biodegradable compound imi- tates (mimics) the natural hor- mone, and therefore, insects will not readily become resistant to it; it is widely used to kill the larval stage of fleas, flies, and mosquitoes. Because it produced oversized larvae and pupae by prolonging the juvenile stage in silkworm, it has been widely used in China to increase silk production. (a) o JUVENILE HORMONE JH-I Prolongs juvenile state COOCH3 (9) H3 CO~COO ~ (10) METHOPRENE Biodegradable insecticide Anti-Juvenile Hormones These are substances, both natural and man-made, that somehow interfere with normal juvenile development. Systematic screening of plants has led to the identification of a number of compounds with anti- ~H activities. They are called precocenes (111. MeO BOW Some insects develop prematurely into tiny sterile ~ ~! -I (~) adults when they are treated with precocenes. Natural Defense Compounds: Antifeedants R:4W PRECOCENES R=H OR OCH3 Causes early maturation Plants produce and store a number of chemical substances used in defense against insects, bacteria, fungi, and viruses. One 27

OCR for page 21
28 HUMAN NEEDS THROUGH CHEMISTRY category of such defense substances is made up of chemical compounds that interfere with feeding. Many antifeedants have been characterized and show a wide variety of structure. Among them, azadirachtin (12) is probably the most potent antifeedant isolated to date. It is found in the seeds of the neem tree Azadirachta indica, which is known for its use in folk medicine. An amount of only 2 ng/cm2 (2 x 10-9 g/cm2) is enough to stop the desert locust from eating. Although (12) is far too complex for commercial synthesis, it might be possible to isolate it in useful amounts from cultivated trees. It is known that (12) is not poisonous because twigs from the neem tree have been commonly used for brushing teeth, its leaves are used as an antimalarial agent, and the fruit is a favorite food of birds. H ~ ~` MeOOC ~ (12) (13) (14) ,CC- CO CH3COO' J~.,O H MeOOC '` O \ OH AZADIRACHTIN Causes locusts to stop eating ECHO /\ WARBURGANAL Causes worms to stop feeding H Warburganal (13) seems to be specifically active against the African army worm. An insect kept for 30 minutes on corn leaves sprayed with war- burganal will permanently lose its ability to feed. The plant from which warburganal has been isolated is also commonly used as a spice in East Africa and therefore cannot be highly poisonous to humans. Practically all antifeedants are isolated from plants that are resistant to insect attack. While no antifeedant has yet been developed commercially, they offer an intriguing new avenue for control of insect pests. INSECT PHEROMONES Pheromones are chemical compounds released by organisms in order to trigger specific behaviors from other individuals of the same species. Pheromones function as communication signals in mating, alarm, territonal display, raiding, nest mate recognition, and marking. They have attracted great interest as a means to monitor and perhaps control pest insects. The first insect pheromone to be identified was from the female silkworm, and it was shown to be an unbranched Cue alcohol containing two double bonds, structure (14~. Since then, hundreds of pheromones have been identified, including those for most major agIicultura1 and forest pests. The isolation and full identification always involve handling extremely small quan- tities. Characterization of the four pheromones for cotton boll weevil pheromones (1SA-D) required over 4 million weevils and 215 pounds of waste material (feces). It took over 30 years to cianfy the structure that SILKWORM PHEROMONE First insect attractant identified

OCR for page 21
III-A. MORE FOOD stimulates mating in the American cockroach (16~. It required processing of 75,000 female cockroaches, which fi- nally resulted in 0.2 mg of one compour~d and 0.02 mg of an- other. Special methods for collect- ing and analyzing these com- pounds had to be developed to cope with the tiny quantities being investigated. It is now possible to extract a single fe- male moth gland, remove the intestines of a single beetle, AMERICAN COCKROACH PHEROMONE collect airborne pheromones Stimulates mating on glass wool, and analyze the pheromone from a single insect. One of the most important developments in this area is the electroantennogram technique, in which a single sensory unit from an olfactory antenna hair (used for smell by the insect) is used by researchers to detect the presence of these compounds. In addition to natural pheromones, chemists continue to synthesize artificial pheromones. Pheromone-baited traps have been used worldwide to monitor and survey pest populations. They assist in precise timing of insecticide application, thus reducing the amount of spray, and in insect trapping operations. For example, more than one million traps have been recently deployed for a period of 4 years in the Norwegian and Swedish forests, resulting in spruce bark beetle captures of 4 billion a year. Another commercial use is pheromone distribution throughout an area to confuse the insects. In 1982, pheromones were used on 130,000 acres of cotton to control pink bollworms, on 2,000 acres of artichokes to control plume moths, and on 6,000 acres of tomato to fight pinworms. Many questions about the basic chemistry and biology of pheromones remain to be answered. In the long run, it is clear that research on pheromones will yield useful benefits to agnculture and to health. B H. ~ ~ 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 at- tempts to improve food and fiber production and to control insect-transmitted diseases in humans and livestock. Although major changes have recently occurred in pesticide use, environmental concerns make it increasingly difficult to introduce better pesticides into practical use in this country. The time and cost of developing a new compound currently run about 10 years and $30 million. Over 10,000 new compounds normally have to be synthesized and tested before a single acceptably safe and therefore marketablepesticide is found. 29 (16)

OCR for page 21
30 HUMAN NEEDS THROUGH CHEMISTRY Insecticides Most potent insecticides discovered recently are modeled on natural products and act on the nervous system of insects. They include deltamethrin (17) and cartap (18), which are based on compounds found in chrysanthemum flow- ers and marine worms. Another compound still on the drawing board is pipercide (19), which includes an unusual cyclic di- ether unit. Chemical synthesis aIld testing programs have led to other novel structures that act as nerve poisons, inhibitors of chitin synthesis, and growth dis- ruptors (e.g., (20~. This new range and vanely of insecticide classes has helped immensely in the pest control battle. Br (17) (18) (19) o_, (20) (21) '0 B: O H CN OELTAMETHRIN An insecticide from chrysanthemum CH3. o 11 rSCNH2 NO CH3 ~ ~ SCNH2 D o CARTAP An insecticide from marine worms W ~~'~ O / PIPERCIDE A synthetic insecticide o HN I H l Cl F IF A growth disrupter \ / Fungicides ~~ - so BUTY LATE A weed control agent Herbicides These are substances that work to control weed pests. Highly novel structures de- rived through chemical synthe- sis have provided a variety of new herbicides in recent years. The butylates (21) work on the weed before it emerges from the soil, while atrazine (22) blocks photosynthesis by the weed. Still others interfere with seed germination or block formation of chlorophyll. Her- bicide resistance in weeds is an increasingly impor- tant problem. Genetic research currently directed toward improved crop tolerance suggests that we should transfer to the crop the gene that a weed has developed to make itself herbicide resistant. Major advances have been made in fungicides and antibiotics to control plant diseases caused by fungal and bacterial microorganisms. Some fungicides, such as triadimefon (23), work by slowing RNA synthesis. Other compounds block cell division or formation of cell walls, as in benomyl (241. New fungicides are needed

OCR for page 21
Ill-A. MORE FOOD that are not only highly selective of their targets but that may also disrupt more than one biological function so that resistance is less likely to develop. Special Techniques Specialized techniques, instrumentation, and fa- cilities are required to solve the multidisciplinary problems encountered in pesticide chemistry. The quantities of pesticide that can be used on crops are restncted so that crops will be free of hazardous leftover chemicals. The chemical by-products of pesticide use are also being evaluated for environ- mental impact and safety levels. Some hazardous impurities have been placed under strict control, such as tetrachIorodibenzodioxin ("dioxin,~' an im- purity in the herbicide 2,4,5-T) and nitrosamines (25) that occur in some other useful herbicides. The fact that pesticide research involves many scientific disciplines requires increased cooperation on a lo- cal, national, and international basis between indus- tnal, government, and university scientists. Research into pesticide chemistry can provide farmers and public health officials with safe and effective means to control pests. The research per- mits replacement of compounds that may be highly toxic or that have unfavorable long-tenn effects with better and environmentally safe pesticides. Because pest control problems are complex, but of extreme importance to society's well-being, long-term commit- ments to pesticide research are necessary and will be rewarding. c] NOUN 1NJ:N4NJ (22) 1 ! H H ATRAZINE Blocks photosynthesis Cl~o~ /N: \'N 0~' TRIADIMEFON '\ Slows fungus growth \ - NHCOCH ~ OCNH' BENOMYL Blocks fungus cell division DIPROPYLNITROS~ INK A herbicide impurity FIXATION OF NITROGEN AND PHOTOSYNTHESIS All of our food supply ultimately depends upon the growth of plants. 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. Nitrogen Fixation Nitrogen is a crucial element in the chemistry of all living systems and one that can limit food production. Since nitrogen is drawn from the soil as the plant grows, restoring nitrogen to the soil is a primary concern in agriculture. This concern accounts for the centunes-old practice of crop rotation, and it figures importantly in the choice and amounts of fertilizers used by farmers. Ironically, nitrogen is abundantair is 80 percent nitrogen but it is present in the elemental form that is difficult to convert into useful compounds. Some plants know how to convert this 31 (23) (24) (25)

OCR for page 21
104 NUMAN NEEDS THROUGH CHEMISTRY IIl-G. Economic Benefits INTRODUCTION The chemical industry has enormous scope. It encompasses inorganic and organic chemicals used in industry, plastics, drugs and other biomedical products, rubber, fertilizers and pesticides, paints, soaps, cosmetics, adhesives, inks, explo- sives, and on and on. The value of U.S. chemical sales in recent years has been in the neighborhood of $175 billion-$~80 billion, with a favorable balance of exports over imports of about $8 billion-$12 billion. Employment in U.S. chemical and allied product industries is over a million people, includ- ing over 150,000 scientists and engineers. The numbers are large, and the effect on the economy is important. And even they do not adequately indicate the far-reaching pres- ence and impact of chemistry throughout our society. Chem- ical products are supplied to countless other industries to be processed and resold. Addi- tionally, chemical processes are abundant and growing in modern manufacturing. Me- chanical operations, such as cutting, bending, drilling, and riveting, are being replaced by etching, plating, polymenza- tion, cross-linking, sintering, etc. For example, electronic microcircuits are produced through a sequence of perhaps 100 chemical process steps. Finally, chemistry is the science on which our understanding of living systems is based. Heredity is now understood in terms of the chemical structure of genetic material. Disease and its treatment are chemical processes. 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. Here in the United States the situation is particularly difficult due to many diverse factors that are unique to our society. Antitrust law in the United States strongly discourages cooperative actions on the part of U.S. corporations. Abroad, coop- erative partnerships between foreign corporations and the government are encour- aged. Governmental policies in regard to science-based industnes are frequently more favorable abroad than in the United States. International activity in the petrochemical arena is increasing as nations control- ling cheap and abundant feedstocks establish their own manufacturing complexes ~ 965 ~ 970 ~ 975 _ _ _ i,, AS IOB C: he J a: S OB a A: A: ~ - S lOB of o - He -S2 OB be - Cal As cD -S30B _ Chemicals ~ | art ~65 '70 \41~: - ~74 \~ ; ~76 All Merchandise f 1 980 1 985 _ _ 1 ~ 1 _ ~ 1 1 . ~ 1 .. ~ 1.... ~74 \~ 6 CHEM ~ CA LS: A MU CH N BED ED POSITIVE TRADE BALANCE

OCR for page 21
111~. ECONOMIC BENEFITS to refine crude of! and produce polymers and other products higher up the value scale. It seems probable that this foreign effort will be concentrated in commodities with the largest established markets (e.g., ethylene glycol, polyethylene). The chemical industry must also respond to an active public concern for health and safety connected with possible exposure to toxic chemicals. This movement is most advanced in the United States, where concerns range from sensibly prudent to panicky. Economically, these responses must lead to higher costs to achieve the desired environmental protection, worker safety, proof of safety and effectiveness of new products, and protection against product liability. Of course, these costs are always paid for by the consumer, but they are significantly affecting the ability of U.S. industry to compete when the same industnes abroad do not feel the fud impact of these pressures. 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. Preservation of this quality of life depends to no small extent upon whether the United States can remain a strong and leading participant in chemistry-based technologies. A key factor responsible for past success has been the strength of U.S. university research and the effective use of its new discoveries to develop new products needed by society. Vigorous support of this academic research community is a critical first requirement for maintaining the ongoing health of the U.S. chemical industry. ENERGY AND FEEDSTOCKS Energy and chemical feedstocks are tied together through their overwhelming dependence on petroleum. Energy uses account for most of the consumption of these organic materials. Burning of petroleum goes on at an ever-increasing pace, and the future supply crisis is directly related to this fact. Throughout much of the world, people take petroleum-denved heat and transportation for granted. Thus, the inevitable depletion of the earth's petroleum resources will strongly affect the style and standard of living of people everywhere. The effects of de- pletion should become evident within two decades and severe within four. Hubbert has estimated that 80 percent of the worId's ultimate production of of! and gas will be consumed between 1965 and 2025. This estimate, made in 1970, seems to be consistent with current discovery and consumption rates. Its alarming implications are not fully recognized by the public. Petrochemical uses of petroleum account for only a few percent of the total 3 to 5 percent by most estimates. Thus, the chemical industry is not the cause of the approaching era of depletion, but the effects will be felt within the industry as feedstocks and processes change. However, petrochem- ical uses are charactenzed by higher retail prices, and they can withstand the 105 - a 0 0` en: . 1 1 1 1 . it, ~ OOJSU~ED . u' 1965.... 2025 C , . ,,., .,., ,.,.,.- c Jo ~ 9 so 2000 2050 2 100 YEAR An Estimate: Worldwide Production of Gas and O i 1 =_. <__,

OCR for page 21
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. Therefore, it is expected that the impact of petroleum depletion on chemical feedstocks will be much less damaging than its impact on energy production. RENEWING OUR INDUSTRIES International competition is a general problem for U.S. industry. Steel, automo- biles, communications, textiles, and machine tools are examples of industries that have encountered significant problems. It is instructive to consider the response to these pressures in the automobile industry. It shows the central role of chemistry in maintaining and improving the U.S. position. The U.S. automobile industry evolved into a gigantic business during the first half of this century. In the 1950s and 1960s American products enjoyed great success. The vehicles were large, heavy, and powerful. Fuel was abundant and inexpensive. There was no reason to conserve, so fuel economy of the American car was not considered by buyers. Furthermore, few foreign-built cars made their way to North America. By the mid-1960s, however, Volkswagen had entered the U.S. market with sales of more than half a million small economy cars per year. During the 1970s the market was further affected by cars manufactured in Japan. Pursuing an aggressive policy of collecting design, technology, engineering, and assembly information from other countries, the Japanese developed the most automated and efficient car-building facilities in the world. These facilities, and a commitment to quality, yielded the worId's most fuel-efficient and low-cost cars at a time when gasoline prices began to soar. At the same time, antismog legislation was passed in the United States that required better fuel economy and placed strict limits on air pollution from automobile emissions. The American car was required to change dramatically, and the investment required by the manufacturers was very high, approximately $80 billion. The antismog objectives are being achieved through many developments involving chemistry: new and lighter materials, better combustion control and engine efficiency, catalytic exhaust treatment, lowered corrosion, reduced size, . . . transmission Improvements, etc. Polymers, aluminum, and high-strength alloy steels are used to reduce the weight of the car. New chemicals for of! additives and improved rubber formulations for tubes and hoses are solving problems of engine compartment temperature brought on by aerodynamic designs featuring sloping hoods. The ride quality of the smaller cars is being improved through the use of vibration-damping busy} rubber. Tire tread compounds are being reformulated to reduce rolling resistance. New, high-solid paints are being developed to reduce air pollution from automobile painting. Chemically based rust-proofing systems are being introduced to prolong life. Contemporary U.S. cars each contain over 500 pounds of plastics, rubbers, fluids, coatings, sealants, and lubricants, all products of the chemical industry. Further uses of plastic materials are sure to come. Reaction injection molding is a recently introduced process for making large parts such as fenders and hoods.

OCR for page 21
III-G. ECONOMIC BENEFITS High-performance composite materials, i.e., stiff fibers in a polymer matrix, have already appeared as drive shafts and leaf springs. Some advanced models have frames and bodies made of composite polymers. For automobiles, the use of composite polymers may lead to new design-fabncation methods which will greatly reduce the number of parts that must be assembled. Furthermore, new designs for light aircraft have airframes that are almost entirely composites. Advances such as these will tend to reduce the problems faced by the automobile and other basic U.S.industries, problems that arise from a complex mixture of historical prefer- ences, social pressure, legislation, and vigorous outside competition. NEW HORIZONS The chemical industry is changing, and chemical science is becoming importantly intertwined with other areas of science and technology. To an increasing degree chemists must be skilled at dealing with subjects in interrelated technologies. Chemistry is critical in providing materials and processes for American industry, meeting their wide range of needs from established industries (new electrode materials for aluminum production, decaffeinated coffees, sweeteners for the food industry, etc.) to rapidly growing, high-technology areas (composites for aircraft, ceramics for electronics and engines, protein pharmaceuticals, etc.~. Each of these areas requires development of chemical products that respond to markets outside of chemistry. Representative examples are given below. Biotechnology Biotechnology is not new. The ancients knew how to bake arid brew thousands of years ago. The processes of fermentation, separation, and purification have long been familiar. But as the molecular structure and basic chemistry of genetic matenal became known, a new era of biotechnol- ogy has opened up. (See Section IlI-F.) It led to gene splicing procedures that allow biochem- ists to cause bacteria to produce complex molecules with biolog- ical activity. Enzymes have been found that wid break chemical bonds in DNA chains at specific points and allow for- eign DNA to be inserted with new chemical bonds. The al- tered DNA wiD then produce proteins according to its revised code. The protein products can be hormones, antibodies, or other desired complex chemical compounds with specific prop- e~ties and functions. Interferon, 107 ~ ._ <$~! A'' + ~ ~ t ~ BIOTEC~C ~ 1~--~ L4> J ~ BI OTECH I Nc \/ ANYONE FOR DESIGNER GENES?

OCR for page 21
108 . HUMAN NEEDS THROUGH CHEMISTRY produced by bacteria with a human gene spliced in place, is expected to be valuable in treating a variety of diseases. Human insulin produced through gene splicing tech- n~ques is already being marketed. Activity is intense and commercial enterprises are emerging rapidly. The area of biotechnology is an exciting and optimistic one for scientists, engineers, and investors. Although some of the expectations may be extravagant, there can be no doubt that this area win give us many important economic developments in the coming decades. The United States is at present the world leader, with basic chemical and molecular biological research feeding an effective commercial community. Europe has strong, relevant research, and Japan has a leading position in fermentation processes. 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. High-Technology Ceramics Ceramics are materials with high-temperature stability and hardness; they tend to be brittle and therefore are difficult to shape in manufactunng. Ceramics are now of major commercial interest for components of electrical devices, engines, tools, and a wide range of other applications in which hardness, stiffness, and stability at high temperatures are essential. Major advances in their use can be anticipated because of new chemical compositions and novel fabrication techniques. For many, many centunes, ceramic pieces have been made from fine particles suspended in a liquid (a slurry) or a paste of a finely ground natural mineral. The slurry is formed or cast in the desired shape and then "fired," i.e., heated to a high enough temperature to burn away the added slurry components and to melt and join the mineral particles where they touch. We now know that the strength of the final object is cntically limited by small imperfections. A number of new chemical techniques are now being developed to synthesize new ceramic starting materials that will produce more defect-free final products. These techniques depend upon control of reaction kinetics and tailoring of molecular properties. For instance, controlled hydrolysis of organometallic com- pounds is used to generate highly uniform ceramic particles ("sol-ge! technology". Organometallic polymers can be spun into fibers, and then all but the polymer skeleton is burned away to produce high-temperature materials like silicon carbide. Highly uniform temperature-resistant coatings in desired shapes can be produced using high-temperature reactions of volatile compounds followed by controlled deposit of the products onto a preformed solid object. For example, jet engine parts might be made this way. Addition of suitable impurities ("doping agents,') can change properties dramatically. For example, alumina ceramics can be significantly toughened by the addition of zirconia, solid ZnO2. Advanced Composites and Engineering Plastics The discovery of ultra-high-strength fibers based upon graphite embedded in an organic polymer has led to development of a new class of materials now referred to as "advanced composites." A fiber, such as a graphitic carbon chain, a mineral

OCR for page 21
III-G. ECONOMIC BENEFITS fiber, or an extended hydrocarbon polymer, is suspended in a conventional high polymer such as epoxy. The resulting composite can exhibit tensile strength nearly equal to that of struc- tural steel but at a much lower density. Because of this high strength-to-weight ratio, such composites are finding abun- dant applications in the aero- space industry. Significant weight reductions are achieved in commercial and military a~r- craft that use airframes and other aircraft components made of composites. Other applica- tions include space hardware, sporting goods, automotive components (e.g., Unve shafts and leaf springs), and boat hubs. There has also been a rapid development in designing 5000 30 21 ~ o ! ill 20 I=` Hi ~1 ICI All I 1 0 1_3 1_ 1~ . , _ ~ : ADDITION OF -ElTRA5- MEETING REGULATIONS FOR SAFETY, POLLUTION r C^R WEIGHT/ it, J GA S M I LEAGEI V 1 INTRODUCTION OF LIGHT WEIGHT - hIATERIALS /- \ / . , ~ ~ 950 1 960 1 970 1 960 1 990 YEAR HIGH STRENGTH-TO-WEIGHT MATERIALS DOUBLED AUTO MILEAGE- 1975 TO 1985 polymer mixtures to obtain particular properties or behavior. Success with these polymer "alloys'' or "blends" has required a high degree of chemical under- standing of the molecular interactions at phase boundaries between two polymers that are not soluble in each other. An example is the commercial polymer blend called Zyte! Y.T.@, a nylon toughened with an elastic hydrocarbon. The development of this high-performance plastic was based upon extensive studies of interactions at interfaces between different polymers. Plastics are also being developed for high-temperature applications such as engine blocks for automobiles. A prototype '~plastic engine'' based on reinforced polyamide and polyimide resins has been demonstrated in an actual racing car. An engine weight reduction of 200 pounds can be achieved, with obvious benefit to fuel economy. All of these technologies are moving forward rapidly around the world. Carbon fiber production has been well developed in Japan, while the United States is showing the way in high-strength polymeric fibers. The nature of the bonding region between the fiber and its composite environment is an important factor in structural performance but is poorly understood chemically. Research will figure importantly in the evolution of the field. sooo :~ 3000 c: 5 2000 Photoimaging The aim of photography is to produce an accurate and lasting record of the image of an object or a scene. 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

OCR for page 21
110 HUMAN NEEDS THROUGH CHEMISTRY appreciation of what goes on in the camera and on the film. The result brings lifelike communication and pleasure to people throughout the world. The chemistry of the photographic process can be usefully divided into the inorganic photochemistry of the silver halide and the organic chemistry of sensitization, development, and dye formation. When radiation strikes a microcrys- tal of a silver halide in the film emulsion, a faint image is formed that is believed to consist of a few atoms of metallic silver. The metallic silver functions as a catalyst for the reduction of the entire microcrystalline grain under the chemical action of an easily oxidized organic substance, the "developer." The silver halide grains in a photographic film are typically about one micron in size, and control of the size and shape of the particles is important. Although silver halides are sensitive only to light at the blue end of the spectrum, the grains can be activated at longer wavelengths with sensitizing dyes on the crystal surface. These molecules are coated onto the silver halide surface in layers less than one thousandth of a millimeter thick. Color is achieved when the oxidized form of the developer reacts with another organic compound to give a dye of the required hue. By combining the 3 color primaries, 11 colors can be achieved. Conventional color photography involves several carefully controlled chemical processes, including development, bleaching, fixing, and washing. In instant color photography these steps must be combined in a single sheet that can be processed under existing light without temperature control. A typical instant film contains over a dozen separate layers with thicknesses of about one micron each. Physical chemical factors such as solubility and diffusion are critical, as are the chemical reactions occurring in the various layers dunug processing. The sophistica- tion of the chemistry of instant color photography is difficult to comprehend consid- ering how simple the camera is to use. In this important area of our economy, new technological achievements continue to appear, ranging from amateur photography to such demanding and specialized uses as photoresists for semiconductor production (see below) and infrared mapping of the Earth's resources from satellites. The United States has been the world leader in photographic technology for many years in an industry in which the connection with our traditional research strength in photochemistry is clear. Microelectronic Devices The microelectronics revolution has already had an enormous impact on the industrialized world, and it is clear that there is a great deal more to come. The best- known device is the microprocessor, a remarkably intricate and functionally integrated electrical circuit built on a tiny bit of pure silicon, called a "chip." Some microprocessors and the latest high-capacity computer memory chips contain hundreds of thousands of individual transistors or other solid-state components squeezed onto a piece of silicon about one-quarter of an inch square. These chips are currently made from highly purified silicon which contains impurities that have been deliberately implanted to form individual devices with desired electronic functions, such as amplification, rectification, switching, or storage of on-off logic information. These minute devices are then interconnected by metal "wires" on a microscopic scale. The fabrication of these exquisitely

OCR for page 21
III-G. ECONOMIC BENEFITS complex devices depends cntically on thin (less than one micron thick) organic films that are sensitive to radiation. Their technology involves organic chemistry, photochemistry, and polymer chemistry. The purpose of these films is to allow impurities or "dopants" to be added selec- tively to the silicon forming the pattern of a desired electncal circuit. Because steps in the process involve high tempera- ture, a thin layer of silicon dioxide is used to mask the underlying silicon. This mask determines whether or not the silicon below is exposed for doping. Organic materials called photoresists are used to form the pattern that is trans- fe~Ted into this silicon dioxide layer. In photolithography, chemi- cal changes in the photoresist matenal are begun by exposure to light. In these changes, co- valent chemical bonds are bro- KEY STEPS IN THE ken (or formed) at light-sensi- FABRICATION OF SILICON INTEGRATED live chemical groups attached CIRCUITS USING PHOTORESISTS to the polymer structure. These chemical bond changes result in a local increase (or decrease) of the photoresist solubility in a suitable solvent. Thus, after exposure through a mask, an image of the mask can be developed merely by washing in the solvent. 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. However, the continued desire for smaller devices has demanded smaller and smaller features. A decade ago it became apparent that new photoresists would be needed because existing materials were not capable of defining the feature sizes (1-2 microns) soon to be required. The development of these materials has been made possible by the research in polymer chemistry, photochemistry, and radiation chemistry done in the last two decades. Because these circuit elements have dimensions close to the wavelength of light normally used for conventional photographic imaging (0.4 microns), diffraction effects caused by lines and marks on the mask become important. These effects can be reduced by using shorter-wavelength radiation. Hence, lots of effort is being spent on widespread development of resist matenals that are chemically sensitive to ILLUMINATED AREAS - NEGATIVE RESIST O RENDERED I NSOLUBLE LIGHT | ~ ~ ~ ~ ~ MASK 111 ~ 11/ ~ ~ ,PHOTORESIST ~ ~ . ~ ~ at, = .., .. .., , , _ ~ ~ SILICON DIOXIDE POSITIVE RESIST ORENDERED SOl UBLE 1 rat ETCHED FILM PATTERNS RESIST REMOVED ~ E3 if, ~ 111

OCR for page 21
112 HUMAN NEEDS THROUGH CHEMISTRY exposure with short-wavelength ultraviolet light, X-rays, and even electron beams, instead of the near-ultraviolet light now used. The mask itself is now made by chemically etching the desired pattern into a thin chromium film deposited on glass. The pattern is "written" into a resist film by exposure to a computer-controlled electron beam. The development of the organic resist material that is used for defining the pattern on the metal rests on relatively recent research. 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. Examples of new electron beam resists are the polymers that result from copoly- merizing various alkenes and sulfur dioxide. Their synthesis and radiation sensi- tivity were only recently discovered. A present trend in semiconductor fabrication is to use reactive gas plasmas from a glow discharge instead of liquid solutions to etch the material under the photoresist mask. Most organic materials are not sufficiently resistant to these vigorous conditions, and it has taken much research to provide a few useful materials. It is difficult to design materials having the necessary combination of physical and chemical properties. Their development will draw on continued research advances in polymer chemistry and photochemistry (including laser- induced chemistry). Molecular-Scale Computers . Miniaturization of electrical devices has been one of the most significant factors in the astonishingly rapid advances that have made modern computers possible. Circuit elements in present silicon chips have dimensions near one micron, i.e., in the range of 10,000 A. However, it may be that fabrication of microscopic devices based upon silicon and other semiconductor methods is beginning to push against natural barriers that will limit movement toward even smaller devices. Thereafter, breakthroughs will be needed. Where will we turn when existing technologies are blocked by natural limits? Irresistibly, we must contemplate molecular circuit elements that will permit us to move well inside the 10,000-A limit. We are led to think about computer devices in which information is stored in or transformed by individual molecules or assemblies of molecules i.e., molecular-scale computers. In a three-dimensional architecture, use of molecular circuit elements with lOO-A spacing would provide packing a million times more dense than now possible. The materials under discussion range from entirely synthetic, electrically conducting polymers to natural proteins. Molecular switches, the basic memory elements of the proposed computer, might be based upon charge movement in polyacetylene, photochromism, or molecular orientation in solids. Ideas on connecting the molecular elements to the outside world are still vague. As is normal, adventurous concepts generate exciting, often emotional contro- versy. However, the arguments of even the most sophisticated detractors are disarmed (contradicted?) by the obvious fact that their intelligent opposition is being generated in the human brain, a working "computer" using exactly the structure under challenge! In an age of machine synthesis of DNA segments and , . . ..

OCR for page 21
III-G. ECONOMIC BENEFITS laboratory design of artificial enzymes, it would be timid to say that we will never be able to mimic the elegant circuits that each of us depends upon to read and consider these printed words. Only a few de- cades ago, some individuals might have classified as science fiction a proposal that someday there would be a man on the Moon, that fertility could be controlled by taking a pill, or that we could learn the structure of DNA. But since we know that molec- ular computers are routine accessories in all animals ~3 ~ - ~ on ^ TV ~.~ ~- ~''--"~ Molecular Computer at Worlc from Ants to Zebras, it would be prudent to change the question from whether there will be man-made counterparts to the questions of when they will come into existence and who will be leading in their development. The question When? will be answered on the basis of fundamental research in chemistry. The question Who? will depend on which countries commit the required resources and creativity to the search. CONCLUSION The field of chemistry in the United States has great industrial and economic importance. The consistent and significant positive balance of payments is an indication of considerable strength. The continuing flow of innovations that benefit society is encouraging. U.S. universities are among the best in the world and year by year draw students from throughout the world for graduate study. We have a lot going for us. The United States must work hard and be creative to maintain its leadership in view of social values that lead to antitrust regulation, environmental restrictions, health and safety requirements, and high wage rates, all of which tend to increase the cost of U.S. chemical products. Hence, we must insist upon logical and objective justification of any restraints imposed by legislation while maintaining a balanced concern for the important social values represented in current regulations. And we must continue to stimulate the academic and industrial research that maintains the impressive knowledge base that makes our progress possible. We must attract some of the finest young minds to the field of chemistry, as only a sustained and vigorous approach will be effective in keeping pace in the essential field of chemistry, so necessary for any high-technology society. SUPPLEMENTARY READING Chemical & Engineering News `'Engineering Plastics: More Products, More Competition" by David Webber (C.& E.N. stab, vol. 64, pp. 21~6, Aug. 18, 1986. Cat Chemistry: Growing Field Despite Crude Oil Drop" by J. Haggin (C.& E.N. staff), vol. 64, pp. 7-13, May 19, 1986. "Marine Mining to Improve its Organization, Direction and Financing" by J. Haggin (C.& E.N. staff), vol. 63, pp. 63-67, Nov. 18, 1985. "High Tech Ceramics" by H. Sanders (C.& E.N. staf0, vol. 62, pp. 26-40, July 9, 1984.

OCR for page 21
114 HUMAN NEEDS THROUGH CHEMISTRY Scientific American `'Advanced Materials and the Economy" by J.P. Clark and M.C. Flemings, vol. 255, pp. 50-57, October 1986. `'Composites" by T.-W. Chou, R.L. McCul- lough, and R.B. Pipes, vol. 255, pp. 192- 203, October 1986. "Electronic and Magnetic Materials" by P. Chaudhari, vol. 255, pp. 136-145, October 1986. ``Advanced Ceramics'' by H.K. Bowen, vol. 255, pp. 168-177, October 1986.