Volumetric properties of some oligopeptides in aqueous solution: partial molar expansibilities and isothermal compressibilities at 298.15 K for the peptides of sequence Ala(gly)(n), n=1-4

The partial molar isentropic compressibilities at infinite dilution, K-S,2( 0), have been determined for the two peptides alanylglycylglycylglycine and alanylglycylglycylglycylglycine in aqueous solution at 298.15 K. These res ults were combined with those obtained previously for the peptides alanylgl ycine and alanylglycylglycine to derive the partial molar isentropic compre ssibility of the glycyl group of a polypeptide. The partial molar volumes a t infinite dilution, V-2(0), have also been determined for these peptides a t temperatures over the range 291.15 to 313.15 K. These results were used t o derive the partial molar expansibilities, E-2(0), of the peptides at 298. 15 K which were combined with the K-s,2(0) data to obtain the isothermal co mpressibilities, K-T,2(0), of the peptides. Using new V-2(0) data for tetra - and pentaglycine, we have also derived E-2(0) and K-T,2(0) values for som e oligoglycines. The K-T,2(0) results for both sets of peptides were used t o derive the isothermal compressibilities of the glycyl group.