Ultrasonic absorption in glycyltyrosine solutions and its relevance to the ultrasonic absorption of protein solutions at physiological pH

Abstract

Excess ultrasonic absorption has been investigated in solutions of the dipeptide glycyltyrosine at 37 °C and in the pH range 6.8–8.8. A mechanism involving both intra- and inter-molecular proton transfer is proposed to account for the changes in acoustic absorption with concentration and pH. Broad bandwidth measurements of absorption vs. frequency have been made for 0.05 and 0.1 mol dm^–3 solutions, using a novel pulse transmission technique, and estimates have been derived for a number of the proton-transfer reaction rate constants. The relevance of this absorption mechanism to the acoustic absorption of proteins at neutral pH is discussed.