BETA-LACTOSE IN THE VIEW OF A CFF-OPTIMIZED FORCE-FIELD

A recently developed force field PEF95SAC, based on Consistent Force F ield (CFF) optimized potential energy parameters for alcohols and most of the naturally occurring carbohydrates, is applied to and tested on beta-lactose. The properties of the potential energy surface of this disaccharide are compared to X-ray structures, NMR coupling constants and optical rotation data. The overall performance indicates good extr apolative power for the modeling of oligo-and polysaccharide structure s. A new glycosidic linkage geometry region is proposed for beta-lacto se as being important in both solid state and water solutions. This fi nding is supported by calculated J(H,C) coupling constants and calcula ted optical rotation values. In relation to the spectral calculations on beta-lactose, the error of the use of relative energies (Delta E) i n place of the Gibbs free energy (Delta G) as the basis for calculatin g Boltzmann distributed properties is demonstrated. In the beta-lactos e case it is shown that the conformational entropy is neither negligib le nor uniformly distributed over the potential energy surface.