Additivity of the partial molar heat capacities of the amino acid side-chains of small peptides:: Implications for unfolded proteins

The partial molar heat capacities at infinite dilution, C-p,2(0), for eight tetrapeptides of sequence glycyl-X-Y-glycine and four pentapeptides of sequence glycyl-X-Y-Z-glycine, where X, Y and Z are amino acids with neutral side-chains, have been determined in aqueous solution over the temperature range 283.15 to 373.15 K using high sensitivity scanning microcalorimetry. The results are compared with those calculated by group additivity using the partial molar heat capacities for the constituent groups of unfolded proteins that we reported in previous work. The comparison verifies that the heat capacity of a polypeptide with neutral side-chains can be reliably estimated using the principle of group additivity and our published group heat capacities.