Partial molal heat capacity of the peptide group in aqueous solutions

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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 Cp2 of other model compounds, viz. oligopeptides, pyrrolidones, piperidones, diketopiperazine, and amides. Cp2 of the peptide backbone unit observed in the sodium salts of the N‐substituted amino acids and peptides is also correlated with the structural details of the compounds and it is concluded that Cp2 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.

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