Partial molar isentropic and isothermal compressibilities of some N-acetyl amino acid amides in aqueous solution at 298.15 K

Abstract

The partial molar isentropic compressibilities at infinite dilution, K^°_S,2, have been determined for eight N-acetyl amino acid amides and four N-acetyl-N′-methyl amino acid amides in aqueous solution at 298.15 K. The partial molar isothermal compressibilities at infinite dilution, K^°_T,2, were derived from the K^°_S,2 results using partial molar expansibilities and heat capacities determined in previous work. The K^°_T,2 and K^°_S,2 results were used to calculate the contributions to the compressibility of the amino acid side-chains. These results are compared with those derived using alternative small solutes that have been proposed as models for the amino acid side-chains in proteins. The applicability of the various side-chain contributions in group additivity schemes for the calculation of the compressibilities of poylpeptides and proteins is discussed.