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

Abstract

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 , were derived for the peptides using conventional methods. The results were compared with those calculated using group additivity methods, with the amino acid sidechain contributions derived using K • S,2 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 of a polypeptide. Our study also confirms that simple group additivity schemes are not feasible for the estimation of K • S,2 values for polypeptides and unfolded proteins.

Volumetric Properties at High Pressures of the Nucleosides Inosine, 2′-Deoxyinosine, and 2′-Deoxyguanosine and the Volumetric Properties of Guanosine Derived Using Group Additivity Methods

“…The application of simple group additivity methods to the thermodynamic properties K S ,2 o and K T ,2 o has not been universally successful. In our previous work, the prediction of K S ,2 o values for polypeptides using a peptide-based group additivity scheme was not quantitative, primarily because of specific interactions between adjacent functional groups and their associated solvent cospheres. On the other hand, K S ,2 o data in aqueous solution for a selection of 31 small amphiphilic molecules that have no vicinal polar functional groups were successfully analyzed recently using a group additivity model.…”