THE COMPLEXATION OF GLUCOSE AND OTHER MONOSACCHARIDES WITH CYCLODEXTRINS

Equilibrium constants of complexes between beta-cyclodextrin and gluco se, galactose, or mannose have been determined by fluorometric competi tion titrations in water to be as low as K = 1-0.5 M-1, in sharp contr ast to recently published values for glucose around K = 400 M-1. The p entoses ribose, xylose, and arabinose show association constants betwe en 6.3 and 1.5 M-1, in agreement with published values. Preliminary co mputer-aided molecular modelling studies suggest that the small values observed for the hexoses are not due to steric hindrance of an intrac avity inclusion but to a smaller number of intermolecular hydrogen bon ds and to some strain as a result of cyclodextrin deformation. Calorim etric measurements of the glucose-beta-cyclodextrin complex show, agai n in contradiction with the literature, an endothermic reaction, or a free enthalpy value close to zero.