Enthalpic interaction coefficients of some dipeptides dissolved in N,N-dimethylformamide

Abstract

Enthalpies of dilution of the N-acetyl-N′-methyl-amino acid amides of glycine, L-alanine, L-valine, L-leucine, L-isoleucine, L-phenylalanine, L-proline and the N-acetyl-amino acid amides of L-isoleucine and L-proline dissolved in N,N-dimethylformamide (DMF) have been measured calorimetrically at 25 °C. Using the formalism of the McMillan–Mayer theory of solutions, enthalpic interaction coefficients have been calculated. The pair interaction coefficients, B^h₂, are negative in the solvent DMF, whereas they are generally positive in water. The influence of methylation of the acid amide group on the magnitude and sign of the pair interaction coefficients in both solvents is discussed. Finally, it is shown that a correlation exists between the pair interaction coefficients of several peptides in DMF and affinity parameters of amino acid residues in globular proteins.