Dielectric properties of macromolecular solutions of synthetic polypeptides in strong organic acids

Abstract

In the frequency range of an external electric field of f =5 kc/s−5 Mc/s the dielectric constant ϵ′ and conductivity G f of solutions were measured for eight synthetic polypeptides (SPP) with a varying lateral radical of different degrees of polymerization z in strong organic acids-dichloroacetic (DCA) and trifluoroacetic (TFA) acids. In all cases a sole range of dispersion was detected with a specific dielectric increment Δϵ o ′ C 2 ( C 2 -polymer concentration in solution) and critical frequency f cr dependent on z of the sample. Values of Δδ o ′ C 2 of solutions and their dependence on the degree of polymerization indicate that charges fixed on the polypeptide chain, formed as a result of interaction with acid (mainly protonization of the N-terminal amino-group NH 3 + ) have a significant effect on the mean square of the dipole moment of the macro-molecule This effect is determined by the strength of acid, the dielectric constant of the solvent and depends on z. A comparison of absolute values of Δϵ′ C 2 and f cr for solutions of SPP studied enables the existence of an undecomposed secondary structure to be established for macromolecules, some in DCA.