INFLUENCE OF AQUEOUS SOLVATION ON SIDE-CHAIN BACKBONE INTERACTION IN COMB-LIKE BRANCHED BACTERIAL POLYSACCHARIDES

The solution behavior of regularly repeating branched bacterial copolysaccharides has been modeled using an approximate statistical mechanical treatment that accounts for the effects of side chain-backbone interactions on the conformational freedom of the backbone glycosidic linkages. The probability distribution for glycosidic linkage orientations is based on pseudoindependent nearest-neighbor conformational energy surfaces for each backbone linkage, perturbed by the influence of the side chain-backbone interaction. The influence of aqueous solvation has been investigated by using conformational potential energy functions that incorporate strong intrapolymeric hydrogen bonding to simulate weak solvation; stronger aqueous solvation is modeled by reducing the strength of the intramolecular hydrogen bonds. This approach recognizes the geometric specificities of aqueous hydrogen- bonded solvation more realistically than do continuum approaches to solvation but is less computationally intensive than procedures (e.g., molecular dynamics) that incorporate the solvent molecules explicitly. It is shown that variations of the strength of aqueous solvation over an energetically reasonable range can have a marked influence of the solution configuration of the polysaccharide chain. Poor solvation is predicted for one paradigmatic comblike polysaccharide chain to induce an intrinsic bending anisotropy reminiscent of the intrinsic supercoiling of regularly repeating polynucleotides.