Interactions between small molecules of biological interest. Excess enthalpies of ternary solutions of oligomers of glycine and isomeric pentoses in water at 25°C

Enthalpies of dilution of ternary aqueous solutions containing an oligomer of glycine (glycyl-glycine and glycyl-glycyl-glycine) and one of the pentoses: L-arabinose, D-lyxose, D-ribose, D-xylose, were experimentally determined. The cross coefficients of the virial expansion of the excess enthalpies were evaluated and compared with those relative to the solutions containing the same pentoses and other structure breaking solutes (glycine, urea, thiourea, biuret). The trend of these coefficients seems to depend very little on the particular pentose, with the exception of a pronounced minimum for D-ribose. Also, the cross coefficients for each of the four pentoses studied do not seem to depend on the nature of the oligomers of glycine. The results were interpreted in terms of a prevailing release of water from the hydration cosphere of the sugars. These last substances show, once more, a behavior in water more complex than that commonly thought.