Internal proton transfer and ultrasonic absorption by proteins

Abstract

The measured pH and frequency dependence of ultrasonic absorption in aqueous solutions of proteins and model compounds are reported and compared with an estimate of the contribution of internal charge‐transfer processes to the acoustic relaxation spectrum of protein solutions based on the approximate method employed by Kirkwood and Shumaker [J. G. Kirkwood and J. B. Shumaker, Proc. Nat. Acad. Sci. 38, 855 (1952)] to compute the contribution of the fluctuation dipole moment to the dielectric relaxation spectrum. The agreement with experiment is quite good and there appears to be a reasonable case for perturbation of internal proton‐transfer equilibria as a major or principal to ultrasonic absorption in protein solutions at physiological pH.