Volumetric properties of the glycyl group of proteins in aqueous solution at high pressures

Sound speeds have been measured for aqueous solutions of alanine and the peptides alanylglycine (alagly), alanylglycylglycine (ala(gly)(2)), alanylglycylglycylglycine (ala(gly)(3)) and alanylglycylglycylglycylglycine (ala(gly)(4)) at T = 298.15 K and at the pressures p = 0.1, 5.0, 10.0, 20.0, 40.0, 60.0, 80.0 and 100.0 MPa. A method is described whereby reliable partial molar volumes at infinite dilution, V-2(o), partial molar isentropic compressions at infinite dilution, K-S, 2(o), and partial molar isothermal compressions at infinite dilution, K-T,2(o), for the solutes can be derived from the sound speed data. These results were used to obtain partial molar volumes, isentropic and isothermal compressions for the backbone glycyl group of proteins, CH2CONH, over the pressure range p = 0.1 to 100.0 MPa. The variations of these properties with pressure are discussed in terms of the likely glycyl-group-water interactions.