stituted by Indira Ghandi's govern- possible for the farmer to survive by ment in India. Under the program, reducing the risks he incurs to a barethe Indian government is fostering bones minimum. He simply cannot local industries in rural areas, even afford to experience a crop failure though there may be some operational induced by an innovation that may be penalties involved. pushed upon him by a well-meaning An observer of the symposium, Dr. but ignorant advocate. Any innovaSamuel M. Weisberg, executive di- tion terrifies the farmer because it rector of the League for International represents the prospect of going into Food Education, notes that the philos- debt or even the potential loss of his ophy of the program seems to be land. And his land is all that he has that, while industry must be profit- to fortify his family against disaster. able, it must also provide employFostering innovation in such an atment, goods, and services to the popu- mosphere obviously is an activity that lace wherever it happens to be. requires more than enthusiasm. The Rather than displace people to the best way, in Dr. Matthews' opinion, is urban areas where it is more con- to perform, and maintain an acceptvenient for industry to make a profit, able performance over a long period the industry will have to go to the of time. Only in this way will the people, even if it means lower returns farmer see for himself that innovaon the investment. He also notes tions can be productive and an imthat some of the most desperate ex- provement over his present operaamples of overurbanization are in the tions. Philippines and in South America. Chemical companies control two of Extension. Since the greatest prob- the three commodities—fertilizers, inlems in improving agriculture and the secticides, and seeds—that farmers marketing of products are sociological must have to operate. Fertilizers and and political, it follows that govern- insecticides, because they are manument programs should take these as- factured products, present the chemipects into account. One approach has cal industry with opportunities to parbeen the promotion of the agricultural ticipate in extension activities. Howextension concept that has been so ever, Dr. Matthews notes, to apprecisuccessful in the United States. The ate the ultimate profitability of new general idea is to make available to markets a sustained development profarmers the benefits of agricultural gram must be supported by industry research through a local extension as well as by government. representative who can demonstrate the beneficial effects on the scene. In developing countries this usually means that foreign advisers are sent in to do the job. According to Dr. J. L. Matthews, PHYSICAL—Wrist watches, televiassistant administrator for the intersion screens, and readout national extension programs of the U.S. Department of Agriculture, the displays are still much on liquid crysresults to date indicate that the trans- tal chemists' minds. But the mood of ferability of the extension concept is participants in the symposium on liqpossible, but there have been both uid crystals was directed toward seeksuccesses and failures in practice. He ing new knowledge before proceeding attributes the failures to three major to new applications of that fourth causes. The first is the fact that many state of matter. advisers attempting to apply the exChemists described expanding the tension concept really don't under- temperature ranges and lowering the stand it. The second is the unrealistic temperatures of liquid crystal—mesoexpectations with which programs are phase—availability to permit operaoften begun. Finally, there is the fail- tions at room temperature and lower. ure of U.S. and other governments to Liquid crystal display devices opersustain a program long enough to per- able at room temperature presently mit a reasonable chance for success. exist, however, indicating that this In Latin America during the period problem has found at least partial of 1962-68, for example, only 1.3% of solution. the U.S. foreign assistance funds for Display devices also need more agriculture were expended in support stable mesophases. Repeated elecof extension services. trical signals, leakage of air, and A major problem encountered by photolysis of liquid crystal sandthe extension representative, Dr. wiched between plates shorten the Matthews says, is the extreme con- life of devices. Beyond present applications, disservatism with which a farmer approaches any change in the status quo. covery that cholesterol deposits in This very conservatism has made it arteries are mesophasic hints at un-
Liquid crystals get improved properties
42
C&EN SEPT. 27, 1971
expected connections between liquid crystal physics and medicine. Just as mixtures of solids have melting points depressed from the melting points of the pure components, so mixtures of some liquid crystal substances have melting points depressed —but to a considerably greater extent than predicted from simple thermodynamics. However, temperatures of change to isotropic liquids—normal liquids, with randomly oriented molecules—vary linearly with molar average composition between the temperatures for the pure components. Impressive. The most impressive nematic mesophase in the work of Dr. John B. Flannery, Jr., of Xerox Corp., Webster, N.Y., is a 55 mole% p-methoxybenzylidene-p-n-butylaniline with 45 mole°/o p-butoxybenzylidene-p-n-butylaniline. Working with Werner Haas, James E. Adams, and Bela Mechlowitz, he finds a —20° C. melting point for the mixture, with a nematic
Molecular order determines liquid crystal class
Nematic
Smectic
Cholesteric
mesophase persisting to 58° C , when the melt converts to isotropic liquid. Nematic liquid crystals are charac terized by domains of parallel ellipsoi dal molecules. When a thin nematic liquid crystal film sandwiched between two conducting plates is pulsed by an electric signal, migration of trace ions disrupts the molecular order. The film appears to light up as ambient light is scattered from the disordered array of molecules. At the isotropic transition temperature, the mesophase changes to an ordinary liquid without liquid crystal ordering. Dr. Juel P. Schroeder of University of North Carolina, Greensboro, has sought lower melting points and ex tended mesophasic ranges by varying dissimilar alkyl groups of a series of nematic 1,4-phenylene bis-4-rc-alkoxybenzoates. Dr. Schroeder, Stephen A. Haut, and Dr. Dorothy C. Schroeder find that 4-rc-hexyloxy-4'-rc-octyloxy diester has the lowest melting point of the compounds examined, melting at 106° C. and remaining anisotropic to 202° C. To problems of Schiff base instabil ity, nonplanar stilbenes are the answer of Dr. William R. Young and Arieh Aviram of International Business Machines Corp., Yorktown Heights, N.Y., and Robert J. Cox of IBM in San Jose, Calif. DL-4-Ethoxy-4'-(2-methylhexyl)-^-chloro-ir*ms-stilbene, for ex ample, is nematic from 22° to 35° C. Nematic clearing points—isotropic transition temperatures—are predict able, according to Dr. Herbert M. Rosenberg and Dr. Lawrence E. Knaak of Wright-Patterson Air Force Base, and Dr. M. Paul Serve of Wright State University, Dayton, Ohio. Their find ing helps understanding of isotropic transitions and suggests that chemists may be able to design liquid crystals on paper for intended applications. For nematic diphenyl derivatives of some group Y, substituted in positions 4 and 4% by two groups X and Z, they find that adding values for X, Y, and Ζ gives clearing points for almost 10,000 possible combinations of groups. Artherosclerosis. Transitions of mes omorphic substances may be involved in artherosclerosis, Dr. Roger S. Porter, University of Massachusetts, Amherst, thinks. Most cholesterol in ^-lipoprotein complexes is in the form of esters, he says. In previous work, he found that mixtures of complexes with several unsaturated esters of cholesterol form liquid crystals near body temperature. Cholesteric mesophases have layers of parallel-oriented molecules. From one layer to the next, the direction of parallel orientation is shifted, so that a curve joining similar parts of mole
cules in successive layers would form a spiral. Because of the striking op tical properties that result from this structure, cholesteric liquid crystals have attracted much attention as temperature-measuring films, chang ing colors with temperature over se lected temperature ranges, which can vary from 1° C. to greater than 10° C. Speaking on work with Charles W. Griffen, supported by the National In stitutes of Health, Dr. Porter described construction of phase diagrams of cholesteryl ester mixtures. He sees in formation on possible mechanics of arterial cholesterol deposits coming out of this work. "The low transition temperatures of cholesteryl ester complexes and their soft mechanical properties should lead to deposits that will form in arteries in positions most favored by thermo dynamics and hydrodynamics," Dr. Porter explains. "It is possible that under certain conditions, such de posits might be reduced by dissolution back into the blood."
Moving molecules built with computers ORGANIC—Molecular modeling with the computer has entered the era of the dynamic display. The visual appeal of the cathode ray tube (CRT) is the latest advantage to be appended to machine computation of molecular geometries and thermody namic properties. But, although the advantages of machine computation and display are undeniable, they are achieved at considerable cost and are not without some undesirable side ef fects, such as misuse of computer languages. According to Dr. John Fritsch, most chemists have difficulty in grasping the three-dimensional nature of their subject. They depend on physical models that often are cumbersome to manipulate and often are too compli cated to extend beyond the simpler molecules. Dr. Fritsch and his associates at Washington University, St. Louis, have developed a computer modeling sys tem for application to a wide variety of research problems. Molecules are entered piecewise as chemical frag ments, such as methylene groups, hydroxyl radicals, amine groups, and indole groups. Each of these groups is assumed to have a standard ge ometry, with standard bond angles, bond lengths, and the like. Via coded keyboarding, using a standard (LAP6) program, the fragments may be as sembled into a molecule and displayed on the CRT. The molecules also can
Utah's Breitling (left) and Boyd record atom positions with stylus for computer
be plotted automatically on paper as a single image or as a pair of images, each in a different color, for stereo scopic viewing. A most useful feature of the CRT display is the manual control of the image with a pair of orthogonal po tentiometers called the "twister." The twister permits translation and/ or rotation of the molecule on the CRT. The model displayed can also be rotated about a fixed axis, or any part of the molecule can be rotated about a single bond. It also is pos sible to monitor van der Waals col lisions between pairs of atoms. A dotted line appears on the display when the distance between the pair of atoms is less than the sum of the van der Waals radii for the pair. A number of other subroutines permit a variety of similar manipulations to be performed, and the results dis played on the CRT may be stored on magnetic tape for reference. All rotations performed by the com puter are based on matrix formula tions for the equilibrium positions of the atoms in the molecules. The formulations were developed inde pendently by Dr. C. D. Barry of the laboratory of molecular biophysics at Oxford University, but originally were formulated by Prof. Josiah Willard Gibbs. An even more elaborate system of computerized molecule building has been reported by Dr. R. H. Boyd and Dr. S. M. Breitling of the University of Utah. Dr. Boyd notes that pre dicting or estimating molecular prop erties traditionally has been de pendent on the fact that bonds or SEPT. 27, 1971 C&EN
43
