ENTHALPIES OF INTERACTION OF SOME AMINO-ACIDS AND PEPTIDES WITH CROWN-ETHERS IN WATER AT 25-DEGREES-C

Enthalpies of dilution of ternary aqueous solutions containing glycine , diglycine, triglycine, L-alpha-alanine, L-alpha-alanyl-L-alpha-alani ne and 12-crown-4, 15-crown-5, 18-crown-6, 1,10-diaza-18-crown-6 at 29 8.15 K have been determined. The results have been analysed in terms o f the McMillan-Mayer formalism to obtain the enthalpic virial coeffici ents for heterotactic interactions. It is concluded that the solvation state and the macrocycle size of the crown ethers do not determine th e entire change of the cross enthalpic coefficients h(xy) for the pept ide-crown interaction. On the contrary, the influence of specific cont ributions to the host-guest interaction leads to linearity of the depe ndence of h(xy) values for 18-crown-6/peptide interaction versus the h eat capacity of solution Delta(sol)C(p) of glycyl peptides. The effect of the solvent on the selectivity of the peptide-crown interaction is also discussed.