SOLVENT-INDUCED AND SALT-INDUCED COIL HELIX TRANSITION OF ALKALI-METAL SALTS OF POLY(L-GLUTAMIC ACID) IN AQUEOUS ORGANIC-SOLVENTS

The coil-helix transition has been studied for alkali metal salts of poly (L-glutamic acid) (PLG), i.e., PLGLi, -Na, -K, and -Cs, in aqueous organic solvent systems. Dependence of the transition on the solvent composition has been qualitatively discussed in terms of the solvent dielectric constant D, Gutmann's acceptor number AN, and water activity a(w). The helix formation induced by addition of alkali chlorides has also been studied. The sharpness of the transition has been interpreted as a measure of reduction of electrostatic energy of helical PLG through contact ion-pair formation between a counterion and carboxyl anion.