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

Abstract

The partial molar isentropic compressibilities at infinite dilution, K_S,2⁰ , have been determined for the two peptides alanylglycylglycylglycine and alanylglycylglycylglycylglycine in aqueous solution at 298.15 K. These results were combined with those obtained previously for the peptides alanylglycine and alanylglycylglycine to derive the partial molar isentropic compressibility of the glycyl group of a polypeptide. The partial molar volumes at infinite dilution, V₂⁰, have also been determined for these peptides at temperatures over the range 291.15 to 313.15 K. These results were used to derive the partial molar expansibilities, E₂⁰, of the peptides at 298.15 K which were combined with the K_s,2⁰ data to obtain the isothermal compressibilities, K_T,2⁰, of the peptides. Using new V₂⁰ data for tetra- and pentaglycine, we have also derived E₂⁰ and K_T,2⁰ values for some oligoglycines. The K_T,2⁰ results for both sets of peptides were used to derive the isothermal compressibilities of the glycyl group.