Abstract
The coil→helix transition in aqueous mixed solvents of alkaline metal salts of poly(L-glutamic acid) has been studied by circular dichroism (CD) as a function of solvent composition and time. Four organic solvents were used, dioxane, 2-chloroethanol (CE), 2,2,2-trifluoroethanol (TFE), and tetrahydrofuran (THF). CD spectra were taken just after the dissolution of the polypeptide, after three days and after seven days. In the water–dioxane pair, the transition is almost complete at the solubility limit of Li+ and Na+ salts (∼70% by weight of dioxane); for the K+, Rb+, and Cs+ salts, the helicity does not go over 20% even after seven days. When CE is used as organic solvent, the transition appears at a rather low CE content (25—35%) and is complete for all the salts. The transition occurs also for the salts up to their solubility limit in water–TFE but at high TFE content (∼80%). No transition takes place when THF is used as the organic solvent. A time dependent phenomenon in the helical content was found with dioxane and CE as organic solvents but none with TFE. The results are discussed in the light of the work of Morcellet and Loucheux.
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Daoust, H., St-Cyr, D. Effect of the Cation Size and of the Solvent Composition on the Conformation of Poly(L-glutamic acid) Alkaline Metal Salts. Polym J 14, 831–838 (1982). https://doi.org/10.1295/polymj.14.831
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DOI: https://doi.org/10.1295/polymj.14.831