• RESEARCH Flexing fhe Muscles Frosn changes in muscle length to running heat engines, it's a matter of phase transition M ANY KEYS fit many doors. Only problem is to find the right key for the right door. Chemically speaking, this may mean t h e investigation of many theories. At present, one of the latest keys uncovered may explain dimensional changes in living muscle. The theory, says Paul J. Flory of Cornell University, is concerned with phase transition of proteins. Similarly, if the crystal-liquid transition be applied to high polymers, it may be a key to conversion of chemical to mechanical energy, adds the Cornell chemist. Flory made these comments at t h e 11th annual Harrison Howe lecture in Rochester recently. The award is given in memory of the Rochester ACS section founder and former editor of IÙ-EC. • A Matter of Properties. Continuing, Flory explains that the physical properties of high polymers combine t h e capacity for high deformation with high strength. In bulk states, polymer molecules are brought close together, and there is a tendency to w h a t may be called "random" configuration. Hence, each molecule becomes entangled hopelessly with its neighbors. X-ray diffraction, infrared adsorption spectra, and density determinations of polymeric materials reveal, according to the Cornell chemist, that many polymers are anywhere from 30 to 90% crystalline. T h e remaining portion is in the amorphous state. Failure of crystallization to pervade the entire system may b e d u e to the intractibility of the long polymer chains. • Careful Melting. But, crystallinity disappears at the melting point, Flory a d d s . This is accompanied by a latent volume change, a latent heat, increased transparency, and decrease in elastic modulus and strength. Contrary to opinions of many investigators, this change from a semicrystalline to a completely liquid state is truly a phase transition. (Objections stem mainly from submicroscopic studies and the b r o a d range of polymer melting points.) T h e range of melting can b e reduced b y sample uniformity and by very slow heating which assures time for anneal5366
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ing before completion of the melting process. T h e final disappearance of crystallinity then occurs abruptly at a reproducible temperature. Also, the melting point is depressed by diluents, in accordance with the dictates of thermodynamic equilibrium. Finally, crystallization of the supercooled melt proceeds spontaneously or may b e developed about foreign bodies. Hence, Flory stresses, amorphous crystalline transition and its reverse are really a phase transition. Transformation between amorphous and crystalline states can exert a marked effect on the elastic properties of polymers. Stretching—for example of vulcanized rubber— will promote crystal growth; conversely, crystallization diminishes stress. In addition, melting point is increased by elongation. Hence, various degrees of crystallization can b e induced in molecular structure. > Energy Converter. Crystal-liquid phase transition could, in principle, be used to convert thermal into mechanical energy in a heat engine in which the working substance is a crystallizing polymer, Flory adds. T h e substance would contract at high temperature because of melting and would lengthen because of oriented crystallization as the temperature is lowered. The
Flory is no newcomer to the ranks of ACS medalists, having won the 1947 Baekeland Award of the New Jersey Section. H e was cited for his outstanding achievement in the field of high polymers [C&EN, 25 1502 (1947)]. In 1948 he went to Cornell as the George Fisher Baker lecturer. Later in 1948, he abandoned an illustrious industrial career that included Goodyear Tire, Esso Research and D e velopment, and D u Pont to become professor of chemistry at Cornell. Since then, his time has been divided between teaching and continuing his research in high polymers. H e has also received the Colwyn Medal of Great Britain's Institution of the Rubber Industry for his work in synthetic rubber.
elastic force and sample length in such a system would perform as analogs of the pressure and volume in a steam engine where the phase change is one of vaporization rather than melting. Also, crystallizing polymers having functional groups readily altered by a change in chemical environment could be used as t h e working substance of a machine for converting chemical into mechanical energy. Alteration of the chemical surroundings in such a way as to lower the melting point could cause contraction. Opposite chemical change would cause extension. Such a system, which depends upon phase transition, should be a sensitive converter of chemical to mechanical energy. • Proteins Too. Much evidence is available t o indicate that polypeptide chains of proteins occur in ordered, crystalline arrangements, according to Flory. But, t h e perfection of crystallinity is low, probably because of bulkiness of amino acid substituents. However, from phase transition studies, as applied to proteins, crystalline regions may be pictured as remaining highly ordered, although coexisting with an amorphous region where crystal order has disappeared altogether. T h e latter region therefore should be rubberlike with a length depending on the tension. If the protein is uniform throughout its length, continues the Cornell chemist, melting should take place at a sharply defined temperature. There is however, some variation of abruptness among the proteins. Collagen, for example, displays very sharp melting point characteristics, b u t others such as myosin, elastin, and keratin, do not. Nevertheless, there is evidence to indicate crystal-liquid phase transitions occur. This phase transition concept may be the key to understanding dimensional changes in fibrous proteins, including muscle, Flory explains. Active muscle is contracted as a result of melting caused by stimulation. Lengthening, on the other hand, during relaxation signifies recrystallization. It should be added that a change in chemical environment will, in general, alter the chemical potential of a protein in the liquid state. Usually the melting point range will be shifted somewhat. If the degree of crystallinity is intermediate, then the degree of crystallinity and the external dimensions will readily reflect a change in surroundings. This may account for the "razor e d g e " character of dimension changes in muscle. As for a more precise description of how chemical surroundings can affect crystal-liquid equilibrium, concludes Flory, it m a y be proposed that a re-
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agent is generated during stimulation ( probably a product of myosin ATP-ase activity ) . The chemical formed would tend to form complexes with functional groups of the protein or to ionize b y proton transfer. If formation of such complexes disrupt the crystalline order, the postulated reagent should shorten protein length. Its dissipation, on the other hand, would allow return to the initial (more crystalline) form during relaxation.
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In his laboratory at Cornell, Flory studies phase tran sition of polymers and proteins with special melting point equipment designed for very slow melting
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American Cy's Acronize gets FDA g o - a h e a d f o r poultry preservation, is first antibiotic permitted in f o o d JL HE DOOR HAS BEEN OPENED, b u t n o t
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too wide—so says the Food and Drug Admini strati on about its action per mitting use of the antibiotic chlorotetracycline as a preservative for un cooked poultry (C&EN, Dec. 5, page 5 2 3 3 ) . In permitting the first use of an antibiotic on food, F D A modifies a policy announced in 1953. Its n e w position is summarized in the amend ment t o its original policy statement declaring that foods might be harm fully adulterated by presence of any amount of antibiotics. T h e amend ment: "[The] policy will not bar the estab lishment of safe tolerances for antibi otic drugs in or on raw agricultural commodities . . . where suitable evi dence of usefulness of the antibiotic drugs and of safety of the residues is available." Other companies are working on similar processes. Each case will b e dec'ded individually on the basis of usefulness and safety, F D A says. N o petitions are now pending before F D A . • Fresher Birds. Acronize is a formulation of chlorotetracycline. ( A u reomycin), salt, and citric acid. T h e latter's function is to stabilize the active ingredient during processing of the
food. Salt is used in minute quanti ties as a diluent. Added to water in which poultry is chilled after dressing, Acronize stops bacterial growth respon sible for most food spoilage, F D A set a tolerance of 7 p.p.m. of the antibiotic remaining in tlie uncooked poultry. This tolerance cannot be exceeded in any portion of the bird. American Cy presented data showing that cooking destroys this amount so that none is left when the poultry is served. Cost of using Acronize for poultry will run about one third of a cent per pound. Company officials believe this will be more than offset by reduced processing, packaging, and shipping costs. With the bird protected by the antibiotic, it will be possible to use a higher scalding temperature with sub sequent treatment made easier. Scald ing temperatures have previously been limited because of damage to the bac terial resistance of the bird. Shelf life of the bird is extended by five to seven days, reducing frequency of deliveries. American Cyanamid calls Acronize the first giant in the field of process ing perishable foods since the advent of frozen foods 25 years ago. Besides increasing the availability of fresher foods, it can mean savings of millions of dollars b y reducing spoilage losses. It can be particularly valuable in South America where lack of refrigeration keeps meat scarce and expensive. An Acronii'.e process for beef is n o w com mercially available in Columbia. Form ulations for the red meat and fish in dustries in the U. S. are also being developed. At a press conference in N e w York last week, Cyanamid's A. B. Clow emphasized the importance of the development in countries where the time lag between slaughter and con sumption is short.
Fresher birds with Acronize
