Partial molal heat capacity of the peptide group in aqueous solutions

Abstract

Integral enthalpies of solution at very high dilution of sodium salts of N-acetyl amino acids, N-acetyl peptides, and N-benzoyl glycine have been measured in water at 298.15 and 308.15 K. Standard heat capacities of solution at 303.15 K have been derived from the enthalpy of solution data. The peptide backbone-unit (CH₂CONH) contribution toward the limiting partial molal heat capacities derived from these experimental results is compared with those obtained from C_p2 of other model compounds, viz. oligopeptides, pyrrolidones, piperidones, diketopiperazine, and amides. C_p2 of the peptide backbone unit observed in the sodium salts of the Nu-substituted amino acids and peptides is also correlated with the structural details of the compounds and it is concluded that C_p2 contribution of the whole CH₂CONH group, rather than that of CONH group, should be used for predicting the heat capacities of polypeptides and proteins in aqueous solution.