Amino acid derivatives as protein side-chain model compounds:: The partial molar volumes and heat capacities of some N-acetyl-N′-methyl amino acid amides in aqueous solution

The partial molar heat capacities, C-p2(o), and partial molar volumes, V-2(o), at infinite dilution have been determined for the compounds N-acetyl-N'-methylglycinamide, N-acetyl-N'-methylalaninamide, N-acetyl-N'-methylvalinamide, and N-acetyl-N'-methylleucinamide in aqueous solution at the temperatures 15, 25, 40, and 55 degreesC. The C-p,2(o) and V-2(o) results have been used to calculate amino acid side-chain contributions to the thermodynamic properties. These side-chain contributions are compared with those derived in previous work using thermodynamic data for the corresponding acetylated primary amides and with results reported using peptide model compounds.