HF/6-31G* energy surfaces for disaccharide analogs

The HF/6-31G level of theory was used to calculate relaxed potential energy surfaces for 12 analogs of disaccharides. The analogs were made by replacing glucose with tetrahydropyran and fructose with 2-methyltetrahydrofuran. Molecules had zero, one or two anomeric carbon atoms, and di-axial, axial-equatorial, and di-equatorial linkages. Despite the absence of hydroxyl groups, the surfaces account well for conformations that are observed in crystals of the parent disaccharides. Thus, torsional energy and the simple bulk of ring structures are major factors in determining disaccharide conformation. The contour shapes around the global minima depend on the number of anomeric carbons involved in the linkage, while the presence of alternative minima that have relative energies less than 4 kcal/mol mostly requires equatorial bonds. However, molecules with two adjacent anomeric centers gave exceptions to these rules. Flexibility values related to a partition function show that the di-axial trehalose analog is the most rigid. The di-equatorial pseudodisaccharide analog with no anomeric centers is most flexible. Reproduction of these surfaces is proposed as a simple test of force fields for modeling carbohydrates. Also, these surfaces can be used in a simple hybrid method for calculating disaccharide energy surfaces. c © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 65–78, 2001 Dedicated to the memory of Professor Georgy A. Jeffrey, deceased February 13, 2000 Correspondence to: A. D. French; e-mail: [email protected]. usda.gov or to: A.-M. Kelterer; e-mail: [email protected] This article includes Supplementary Material available from the author upon request or via the Internet at ftp.wiley.com/ public/journals/jcc/suppmat/22/65 or http://journals.wiley. com/jcc Journal of Computational Chemistry, Vol. 22, No. 1, 65–78 (2001) c © 2000 John Wiley & Sons, Inc. ∗This article is a US Government work and, as such, is in the public domain in the United States