Isentropic and isothermal compressibilities of the backbone glycyl group of proteins in aqueous solution

The partial molar isentropic compressibilities at infinite dilution, KS,2o, have been determined for the peptides serylglycine, serylglycylglycine and serylglycylglycylglycine in aqueous solution at 25 °C. The partial molar volumes at infinite dilution, V2o, have also been determined for these peptides in aqueous solution at the temperatures 15, 30 and 40 °C. These results, along with those obtained previously at 25 °C, were used to derive the partial molar exansibilities, E2o, of the peptides at 25 °C, which in turn were used to convert the isentropic compressibilities into the partial molar isothermal compressibilities at infinite dilution, KT,2o. These KS,2o and KT,2o results were used to obtain the partial molar compressibilities of the glycyl group CH2CONH at 25 °C. The results are compared with those obtained using data for other series of peptides of sequence ala(gly)n, n = 1-4, and (gly)n, n = 2-5.