The Study of the Helix-Coil Transition of Polyglutamic Acid in the Presence of the Cupric Ion

Abstract

Since Pauling and Corey (1) proposed the well ordered helix conformation of polyamino acids, great interest has been shown concerning their behavior in solvent systems. Doty et. al,, (2) in 1957 showed evidence that solvent conditions, including pH, could effect this helical structure. There was strong evidence that the helical structure, if its environment were changed enough, would undergo a conformational change to a random coil, the random coil being a considerably less ordered structure. It was evident that when this conformational change took place, the physical properties of this system also changed. | It is an interesting study in itself to examine and evaluate the different methods of measuring or observing this helix-coil transition. Probably the most obvious indication of the conformational change is the viscosity. (2) While this physical property shows the transition well, it does not enable one to calculate what percent of the total number of polymer residues is involved in the helix, and what part is involved in the coil. Such a method was proposed (3), however, which correlates the helix content with the optical rotatory dispersion (ORD). At the present time, the ORD method is taken as the standard procedure for determining helix content. By use of the ORD, the percent helicity has been related to other physical properties and their changes for systems undergoing the transition.