RESEARCH
In the presence of an electrical field perpendicular to the light beam, the mesomorphic phase spreads a beam of light perpendicular to the axis of the field (left). In absence of a field, no such spreading is observed ( right ). Studies of the mesomorphic state now under way at the University of Cincinnati may bring greater understanding of the theory of liquids and of some natural products which exhibit this "liquid |crystalliiiity"
Shedding Light on Liquid Crystals Studies of the optical properties of the meso morphic phase may throw light on the theory of liquids T J ELATIVELY
FEW
STUDIES
ΟΠ
the
" • mesomorphic or "liquid crystal line" phase have been undertaken since the 1930's, but interest is being revived by a research group at the University of Cincinnati. Using a specially constructed instrument, G. H. Brown, J. F. Dreyer, W. H. H. Middendorf, and R. H . Lubowitz h a v e studied the optical properties of this phase. Their work, they feel, will shed light on the theory of liquids and lead to a better understanding of some natural products which show liquid crystallinity, such as tobacco, mosaic virus, beeswax, and the pigments of bittersweet root. Some substances when "melting" d o not go directly from the solid state to the isotropic liquid state but pass through a fluid phase ( t h e mesomor phic phase) which exhibits the prop erty of double refraction (a character istic of anisotropic crystals). T h e r e are some substances which can be con verted to the mesomorphic phase at room temperatures by solvents through solvation—methylene blue with alco hol, for example. T h e mesomorphic phase has been classified into two major types—nematic, with one axis of symmetry and smectic, with two. Investigations have given a clearer physical picture of the mesomorphic phase. Compounds studied most ex tensively have been p-azoxyanisole and its homologs. T h e rectilinear and 2962
extended nature of the individual mol ecules and the weak dipole on the alkoxyl group restrict rotation of the in dividual molecules which associated through the strong dipole in the azoxygroup on the molecular axis. This as sociation gives rise to what may be termed a lath-shaped or ribbon-shaped chain which is similar in its stereo-con figuration to molecules of much larger molecular weights which, in turn, ex hibit a mesomorphic range. The role of the alkoxyl group seems to be quite important in the mesomor phic behavior of this homolgous series of compounds. For example, azoxybenzene and azoxytoluene have a very narrow mesomorphic range while pazoxyanisole and its homologs have a mesomorphic range in some cases as large as 40 degrees. Association of the chains results in "swarms" which have a cigar-like shape. T h e mesomorphic phase consists of swarms which are regions of anistropy in an isotropic en vironment. p-Azoxyanisole and its homologs pass through several apparently dis tinct phases during melting. From the solid crystalline phase labeled phase I, they change to what has been termed phase II, a metastable crystal line phase, existing over a range of about one-half a degree. Although crystalline p-azoxyanisole appears yel low-green, microscopic studies show the absence of color in thin layers of CHEMICAL
this phase. This phase is smectic in character and the molecules are at tracted to the glass slide in such a manner that their long axes are ori ented perpendicular to glass surface. From phase II they change to the mesomorphic phase, phase III, which possesses fluidity and anisotropy and is nematic in character. T h e swarms of the mesomorphic phase are oriented to the glass surface of the cell in such a manner that the long axes of the molecules making u p the swarms are perpendicular to the glass surface. W h e n the melt is cooled these oriented swarms serve as nuclei for crystallization. On further heating a system is formed which has a bubbly appearance, is biréfringent, and exists over a range of about one-half a degree. The substances then melt to form the isotropic liquid. Experimental measurements have shown the size of the swarm in the mesomorphic phase is of the order of the wave length of visible light and that it has an axial ratio of about two to one. Size of the swarms throughout the mesomorphic range (about 20° C. for p-azoxyanisole) remains constant. T h e mesomorphic phase, when placed under the influence of an electric field, spreads a beam of light perpendicular to the axis of an applied electric field. T h e filtering action on incident white light by the randomly distributed swarms in cells of certain thicknesses results in transmission of light which appears red when viewed in line with the incident beam. Under t h e influence of an electric field, all other conditions constant, the light transmitted shifts from red to a greenish-yellow, J. F . Dreyer points out the unusual physical changes in the mesomorphic substance that take place when the substance is under the influence of electric and magnetic fields. With Dreyer are R. H. Lubowitz (left), G. H. Brown, and W. H. H. Middendorf, all of Cincinnati University
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J^Bft&rl^ Capsules, tablets and other pharmaceuticals are delicate products, subject to moisture damage, dusting, breakage and malformation when shipped in bulk. Yet this type of shipment is a "must" with many druggists. To protect against damage and keep handling at a minimum, Lederle Laboratories Division, American Cyanamid Company, has perfected its new Century-pak in which tablets or capsules are packaged in envelopes of moisture-proof VISQXJEEN " C " film each containing 100 pieces. Bags are imprinted with the product name. This new technique not only puts tablets and capsules into the druggist's hands in superior condition, but makes his counting and bottling chores easier. I t has been a major factor in boosting Lederle sales. I m p o r t a n t ! VISQUEEN film is an polyethylene, b u t not all polyethylene is VISQUEEN. VISQUEEN film is produced by process of U. S. Patents No. 2461975 and 2 6 3 2 2 0 6 . Only VISQUEEN has the benefit of research and technical experience of The VISKING Corporation, pioneers in the development of pure polyethylene f i l m . * Trade Mark of American Cyanamid
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RESEARCH the color of the isotropic liquid- However, under the same conditions of the applied electric field, the light observed at an angle of 15 degrees from the incident beam appears red. The speed with which the swarms can be oriented by an electric field and the speed with which the oriented swarms will relax have been studied. Relaxation studies were carried out by orienting the swarms in an electric field and then allowing them to relax in "no field" or in a magnetic field. Relaxation time of the swarms is slowed down by the magnetic field. The orientation studies were carried out by orienting the swarms in an electric field, or in an electric field with a superimposed magnetic field. The orientation time is speeded up by a magnetic field. Results show that the orientation and relaxation times are of the order of Vas of a second. Relaxation and orientation times of the swarms are influenced by the "wall-effects" of the glass cells in which t h e measurements were made. Studies of wall-effects have shown that the thinner the cell used the slower the orientation time and the faster the relaxation time. Future work will b e directed along such lines as continued study of the bubbly system, an estimation of the concentration of the swarms in the mesomorphic phase, relationship of molecular constitution and liquid crystallinity, interpretation of data in an effort to throw some light on the theory of liquids, and a study of natural products which show liquid crystallinity. A technological importance of the work at the present time might be attached to possibility of the construction of a light valve. Application of an electric and /or magnetic field alters the transmission pattern of light which passes through the nematic phase. Since the swarms have higher magnetic and electric susceptibilities than most molecules, an external field of lesser strength than is currently employed in some light valves can be used conveniently. The research is being supported by Aeronautical Research Lab of the physics branch, Wright Air Development Center, Dayton. In the future, the scope of the study is to b e expanded through support from the Dreyer Foundation. Instrument Construction. A special instrument has been constructed and used to study optical properties of this phase. Important parts of the instrument consist of a special glass cell, a light source, a collimator, light filters, a light integrating sphere, a light de2964
tec tor with amplifying system, a strong adjustable magnetic field, and a power supply which provides a strong electric field. Uniqueness of the instrument is that all parts are movable with respect to each other. Thus it is possible to apply magnetic and electric fields to the liquid crystalline materials in the cell at various angles relative to the light source. The instrument is constructed so that the fight detector can be swept through an arc of 135 degrees. A special mounting makes it possible to replace the light detector with a microscope so that study of the optical properties of the mesomorphic phase under the influence of strong magnetic fields up to 3000 gauss can be carried out. Ethylmercapto Compounds Show Antituberculosis Activity Over 50 ethylmercapto compounds have been found to afford protection to mice infected with human type tuberculosis. One of them—S-ethylcysteine ( L and D L ) — is at least as effective as pyrazinamide and several times more effective than p-aminosalicylic acid, both widely used in tuberculosis therapy» generally in combination with isoniazid drugs. Another—S-ethyl-L-cysteine—was equally effective against isoniazid-resistant strains. Some may b e used to enhance the activity of isoniazid or streptomycin. The present tests grew out of previous work by J. H. Quastel, biochemist at the Research Institute, Montreal General Hospital. While studying nitrification in the soil, he observed that growth of certain nitrifying bacteria was inhibited by several alkyl mercapto acids. A research team of five chemists and three bacteriologists at Merck are now testing these acids against various bacteria. Activity against tuberculosis provides the most promising lead. Of 350 compounds tested to date, 50 are effective in mice when 0.2% or less is added to the diet. Clinical tests are now under way to determine their value in treatment of human tuberculosis. S-ethylcysteine, evaluated early in the program, is worthy of practical consideration on the basis of efficacy and acute and chronic toxicity studies. The investigators have also undertaken a systematic investigation of the relationship of structure to in vitro antituberculosis activity of derivatives of /3-ethylmercaptopropionic acid. Substitution of various terminal alkyl groups (methyl through octadecyl) on the sulfur atom gives activity only with the C 2 H 5 -homolog. Aryl and heterocyclic moieties are also disappointing. Varying the distance between sulfur and carboxyl to give mercaptoacetic CHEMICAL
through mercaptovaleric acids indicates the yS-relationship between sulfur and carboxyl is essential. Replacing carboxyl b y — C H 2 O H , — C H O , — C O O R does not destroy activity. In general, structural modifications which decreased the tendency for cleavage of the C 2 H 5 —S—R homolog decreased antituberculosis activity. Quastel and t h e Merck research team (H. D . Brown, A. R. Matzuk, H . J. Becker, J. P . Conbere, J. M . Constantin, M. Solotorovsky, S. Winsten, a n d E. Ironson) report their work in the July 20 issue of J. Am. Chem. Soc. Poison Ivy T r e a t e d w i t h Zirconium-Containing O i n t m e n t Parke, Davis has developed an ointment for treatment and prevention of poison ivy and poison oak. Called Ziradryl Cream, it consists of 2% benadryl hydrochloride and 4 % zirconium oxide (as zirconium carbonate) in a watermiscible base. In contact with zirconium, the toxic agent in poison ivy— urushiol, a n o-dihydroxybenezene derivative—combines to form a nonirritating salt, according t o P-D. T h e benadryl provides antihistaminic benefits for topical application. T h e ointment helps protect against the dermatitis resulting from exposure if applied before contact with t h e plants or as soon as possible after contact.
• AEC is u r g i n g university groups to
get into basic research of uranium and its alloys. Many fundamental projects can be performed on an unclassified basis, according to A E C . A E C is also willing to provide financial support or necessary small amounts of uranium free of charge in return for information developed. Inquiries should b e m a d e to AEC's division of research, Washington 25, D . C. • Treatment
of
heart
disease
and
bronchial asthma with Choledyl gives good to excellent results, according to the May issue of International Record of Medicine and General Practice Clinics. Clinical trials of the drug— Nepera Chemical's brand of oxytrimethylline—shows it produces fewer side reactions and provides longer lasting therapeutic benefit than aminophylline. • Twenty-seven fellowships are being offered b y t h e American Association of University Women. Fellowships are open to American women for advanced study or research during the academic year 1955-56. Information is available from: Secretary, Committee on Fellowship Awards, AAUW, 1634 Eye St., N. W., Washington 6, D . C. AND
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