Weak stereospecific interactions in water. Excess enthalpies of aqueous solutions containing aldopyranosides at 25�C

Abstract

The heats of dilution in water of methyl-β-D-galacto-, gluco-, and xylopyranosides and the heats of mixing with the respective α-isomers were determined calorimetrically at 25°C. The excess enthalpies, expressed as virial expansions as a function of the molalities, lead to the evaluation of the self- and cross-interaction coefficients. As for other saccharide derivatives, the pairwise interaction coefficients are positive and larger than those for the parent monosacharides. The cross coefficients, in turn, are smaller than the homogeneous coefficients resulting in a favorable contribution to the free energy of mixing. This indicates the existence of a weak, water-mediated, but still stereospecific recognition between pairs of solute molecules.