The helix-coil transition in charged macromolecules

Abstract

Starting from the Grand Partition Function and using matrix methods introduced previously, a formulation of the theory of helix-coil transitions in charged macromolecules is given. The theory is compared with experimental data for the system polyglutamic acid-dioxane-water-NaCl. If the parameter describing the extra difficulty associated with initiating a helical configuration is assigned the same value as for polybenzylglutamate, the calculations are in excellent agreement with experiment. An analysis of the physical significance of the Grand Partition Function leads to methods for determining the fraction of polymer in helical form, the equilibrium constant for the addition of a residue to an already formed helix, as well as the initiation parameter mentioned above. The value of the initiation parameter deduced from titration data on polyglutamic acid is in rough agreement with the value for polybenzylglutamate. The nature of the approximations used is discussed briefly.