ASPECTS OF CONFORMATIONAL MOBILITY IN CHARGED OLIGOSACCHARIDES

Three aspects of conformational mobility in charged oligosaccharides a re discussed in this paper. Statistical thermodynamics is used to prov ide a simple definition of conformational mobility, or flexibility. Th e use of the Boltzmann distribution law, including the partition funct ion, and the thermodynamic equilibrium condition is discussed in some detail, pointing out the importance of including both the enthalpic an d entropic terms when calculating relative probabilities. A simple mea sure of the entropy or number of micro-canonical states based on the c onformationally accessible space within 1/2 kT of a potential energy m inimum is suggested. The differences between and combined use of grid- search maps of the potential energy (enthalpy) surface and equilibrium MD simulations for the free energy term are described, taking a tetra saccharide glycopeptide as an example. Ring conformational mobility in a galactopyranose ring carrying both positively and negatively charge d substituents is described for a bacterial lipoteichoic acid. The eff ects of branching on glycosidic linkage conformational mobility is dis cussed with reference to a branched tetrasaccharide containing two neu raminic acid substituents. (C) 1997 Elsevier Science B.V.