Conformational analysis of aqueous pullulan oligomers: an effective computational approach

Three rotational isomeric state (RIS) models for pullulan, a polysaccharide defined as [--> 6)-alpha -D-glucopyranosyl-(1 --> 4)-alpha -D-glucopyranos yl-(1 --> 4)-alpha -D-giucopyranosyl-(1 -->](n), are presented. These RIS m odels are based upon simple molecular mechanics and solvation calculations and differ in the complexity of the energy evaluations used to determine Bo ltzmann weighting factors for each isomeric state. Each model is evaluated for its ability to predict correctly experimental small angle X-ray scatter ing data and the radius of gyration (R-g) for the hexameric pullulan oligom er (G(3))(2). A simple model based upon only disaccharide conformational en ergies in conjunction with a correction for solvation energies, as determin ed using a continuum Poisson-Boltzmann solvation method, was best and gave an excellent fit to experimental measurements. (C) 2001 Elsevier Science Lt d. All rights reserved.