ELECTROCHEMICAL PROPERTIES OF PERMEABLE MULTICHAIN POLYAMINO ACIDS

Several electrochemical properties (the titration curve, Donnan distribution of counterions, and osmotic properties) of permeable multichain polyelectrolyte molecules at finite polymer concentration, in the presence and absence of salt, have been computed. The model used for the calculation of the electrostatic potential, ψ, is a permeable cylinder with a uniform distribution of the fixed charges. The Poisson-Boltzmann equation was solved numerically, with the boundary conditions that the potential and gradient of the potential, respectively, are equal on both sides of the surface of the macromolecule. The dimensions of the cylinder correspond to those for a multichain polymer in which the polyamino acid chains are either in the α-helical or fully stretched conformations, respectively. The model is thus applicable for evaluation of the electrochemical properties of multichain polyamino acids in which a helix → fully stretched transformation may occur as the degree of ionization of the charged groups increases. The computed titration curvss are in agreement with those obtained by Goldstein2 for a multichain poly-L-glutamic acid, taking cognizance of the effect of conformation on pK0. The theory may also be applicable to proteins and nucleic acids. © 1969, American Chemical Society. All rights reserved.