Partial Molar Isentropic Compressions of Some Tetra- and Pentapeptides in Aqueous Solution: Implications for Group Additivity Schemes for Unfolded Proteins.

Sound speeds have been measured for aqueous solutions of five tetrapeptides and five pentapeptides at T=298.15 K. The partial molar isentropic compressions at infinite dilution, $K_{S,2}^{\circ}$, were derived for the peptides using conventional methods. The results were compared with those calculated using group additivity methods, with the amino acid side-chain contributions derived using $K_{S,2}^{\circ}$ data reported previously for some tripeptides of sequence gly-X-gly, where X represents an amino acid, and also for some N-acetyl amino acid amides. The tripeptides are the preferred model compounds for the estimation of the side-chain contributions to $K_{S,2}^{\circ}$ of a polypeptide. Our study also confirms that simple group additivity schemes are not feasible for the estimation of $K_{S,2}^{\circ}$ values for polypeptides and unfolded proteins. [ABSTRACT FROM AUTHOR]