KINETICS OF PROTON-TRANSFER REACTIONS OF AMINO ACIDS AND SIMPLE POLYPEPTIDES

The velocity and attenuation of 3-100-MHz ultrasonic waves propagating in aqueous solutions of glycine, diglycine, triglycine, β3-alanine, and σ-aminobutyric, aspartic, and glutamic acids have been measured as a function of pH. No dispersion is observed but excess acoustic absorption characterized by a relaxation time between 2.8 × 10-9 sec (for σ-aminobutyric acid) and 3.2 × 10-8 sec (for triglycine) is found. From the dependence of the absorption on pH it is deduced that perturbation of the proton-transfer equilibrium, R-NH3+ + OH- ═ R-NH2 + H2O, is the process responsible, and values of kf, kb, and the standard volume change are determined. © 1968, American Chemical Society. All rights reserved.