Effect of temperature on the volume and compressibilities of some amphiphilic penicillins in aqueous solution

Abstract

Apparent molal volumes and adiabatic compressibilities of aqueous solutions of the amphiphilic anionic penicillins sodium cloxacillin and sodium dicloxacillin have been determined from density and ultrasound velocity measurements in the temperature range 288.15–313.15 K. Critical concentrations for aggregation of these drugs were obtained from both techniques. Positive deviation from the Debye-Hückel limiting law of the apparent molal volume of both drugs at temperatures higher than 298.15 K provides evidence of pre-association at concentrations below the critical concentration. Apparent molal adiabatic compressibilities of the aggregates formed by the drugs, calculated by combining the ultrasound velocity and density data, were typical of those for a stacked aggregate.