Apparent molar volume and adiabatic compressibility studies of aqueous solutions of some drug compounds at 25 °C

Abstract

Apparent molar adiabatic compressibilities and volumes of aqueous solutions of the following drugs (sodium salicylate, methyl orange, L-tryptophan, phenol, and the hydrochloride salts of propranalol, procaine, pilocarpene, and ephedrine) have been calculated from high precision density and sound velocity measurements at 25 °C. These drugs are considered important in several biochemical phenomena such as anomalous protein binding, anesthesia, or unique structure–activity relationship and this study is part of a comprehensive investigation of drug–protein interactions in biological systems. The data are qualitatively interpreted in terms of solute–solvent and solute–solute interactions. Some plausible modes of drug hydration are discussed with particular reference to the structure of the drug molecules. The adiabatic compressibility shows a strong correlation with the hydrational behaviour of the solute molecule and appears to be sensitive to the structural features of the solute, such as shape, size, branching, and presence of aromatic rings. It is argued that these aspects are important in terms of considering the geometrical fit of the solute into the ordered form of the aqueous solvent surrounding these solutes. Keywords: apparent molar adiabatic compressibilities, apparent molar volumes, hydration of drugs.