Acoustic absorption in L-cysteine solutions at physiological pH and temperature measured using a novel technique

Abstract

Absorption of ultrasound in L-cysteine has been measured at 37 °C for the pH range 6.8–8.0 for 0.2 and 0.5 mol dm^–3 solutions. A new pulse-transmission technique has been used which produces continuous absorption spectra for the range 2–50 MHz, enabling accurate determination of relaxation frequency (f₀) within this range. The variation of f₀ with concentration and pH is explained in terms of a mechanism involving both intra- and inter-molecular proton transfer. For the first time, values have been determined for the volume change of the intramolecular proton-transfer reaction and for a number of the individual ionization rate constants for cysteine.