Sugar-salt and sugar-salt-water complexes: Structure and dynamics of glucose-KNO₃-(H₂O)_n

Molecular dynamics (MD) simulations are carried out for the complex of glucose with KNO₃ and for complexes of the type glucose-KNO ₃-(H₂O)_n, for n ≤ 11. Structure and dynamic properties of the systems are explored. The MD simulations are carried out using primarily the DL-POLY/OPLS force field, and global and local minimum energy structures of some of the systems are compared with ab initio calculations. The main findings include: (1) complexation with KNO₃ leads to an "inverse anomeric effect", with the β-glucose complex more stable than the α-glucose by ∼1.74 kcal mol^-1; (2) as temperature is increased to 600 K, the KNO₃ remains undissociated in the 1:1 complex, with the K⁺ hooked to the equilibrium site, and the NO ₃^- bound to it, undergoing large-amplitude bending/torsional motions; (3) for n ≥ 3 water molecules added to the system, charge separation into K⁺ and NO₃^- ions takes place; (4) for the sugar-water system with n = 11 water molecules all hydroxyl groups are hydrated with the glucose adopting a surface position, indicative of a surfactant property of the sugar; and (5) comparison of DL-POLY with MP2/TZP structure predictions indicates that the empirical force field predicts global and local minimum structures reasonably well, but errs in giving the energy rankings of the different minima. The implications of the results on the effects of salts on saccharides are discussed.