The partial molar volumes of some tetra- and pentapeptides in aqueous solution:: a test of amino acid side-chain group additivity for unfolded proteins

Ten new peptides with the amino acid sequences glycyl-X-Y-glycine and glycyl-X-Y-Z-glycine, where X, Y and Z are amino acids with neutral side-chains, have been synthesized and the partial molar volumes at infinite dilution, V(2)degrees, have been determined for all these peptides in aqueous solution at 298.15 K. For several of the peptides, V(2)degrees data have also been obtained over the temperature range 283.15 to 363.15 K using a scanning densimetric method. The V(2)degrees results obtained are compared with those calculated using the principle of group additivity and the group partial molar volumes we have derived in earlier work. We have shown that our group partial molar volumes can be used to reliably predict the partial molar volumes over a wide temperature range of polypeptides that have neutral amino acid side-chains.