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, Cop,2, and partial molar volumes, Vo2, 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°C. The Cop,2 and Vo2 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.