Enthalpies of interaction of some amino acids and peptides with crown ethers in water at 25°C

Abstract

Enthalpies of dilution of ternary aqueous solutions containing glycine, diglycine, triglycine, l-α-alanine, l-α-alanyl- l-α-alanine and 12-crown-4, 15-crown-5, 18-crown-6, 1,10-diaza-18-crown-6 at 298.15 K have been determined. The results have been analysed in terms of the McMillan-Mayer formalism to obtain the enthalpic virial coefficients for heterotactic interactions. It is concluded that the solvation state and the macrocycle size of the crown ethers do not determine the entire change of the cross enthalpic coefficients h xy for the peptide-crown interaction. On the contrary, the influence of specific contributions to the host-guest interaction leads to linearity of the dependence of h xy values for 18-crown-6/peptide interaction versus the heat capacity of solution Δ sol C p of glycyl peptides. The effect of the solvent on the selectivity of the peptide-crown interaction is also discussed.