Constructing and Evaluating Energy Surfaces of Crystalline Disaccharides

French, A. D.; Kelterer, A.-M.; Johnson, G. P.; Dowd, M. K.; Cramer, C. J.
J. Mol. Graph. Model. 2000, 18, 95.

Experience with making, manipulating and evaluating Ramachandran plots for several disaccharides based on molecular mechanics (MM) and quantum mechanics (QM) energies pointed out the need for very careful construction of such surfaces. Care is also important in the quantitative validation of these energy surfaces with linkage conformations by crystallography. Especially important concerns include accounting for stereoelectronic effects, the techniques used to scan the range of conformations, starting geometries, finding the zero of relative potential energy and the strength given to hydrogen bonding (studied with varied dielectric constants). The distributions of observed conformations on energy maps of sucrose, maltose, and laminarabiose at dielectric constants of 1.5 and 7.5 illustrate the importance of an elevated dielectric constant. At dielectric constants of 3.5 and 7.5, the overall average energies of observed conformations of sucrose and seven disaccharides of glucose were less than 1.0 kcal mol^-1. The distribution of corresponding energies of the various crystalline conformations conformed well to a Boltzmann-like equation.

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