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 glycy l-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 solutio n 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 de nsimetric method. The V(2)degrees results obtained are compared with those calculated using the principle of group additivity and the group partial mo lar volumes we have derived in earlier work. We have shown that our group p artial molar volumes can be used to reliably predict the partial molar volu mes over a wide temperature range of polypeptides that have neutral amino a cid side-chains.