Publication
Title
Ab-initio-MIA and molecular mechanics studies of the distorted sucrose linkage in raffinose
Author
Abstract
A conformational energy map for a tetrahydropyran-tetrahydrofuran analogue of sucrose was calculated with ab initio quantum mechanics. Geometries were optimized at the HF/4-21G level, using the MIA approximation. The highest energy (with the exception of trichlorogalactosucrose) corresponding to a conformation of an observed crystal structure was for the sucrose moiety in crystalline raffinose. It was less than 1.5 kcal/mol above the local minimum occupied by sucrose, and calculations with larger HF basis sets converged at an energy difference of 2.9 kcal/mol. On the other hand, MM3(92) energies for the raffinose conformation are improbably high, 7 or 8 kcal/mol above the global minimum, whether or not the galactose residue is included in the calculation. Intra- and intermolecular MM3 forces in a miniature model of crystalline raffinose pentahydrate were unable to account for the observed conformation. Also, other observed crystalline sucrose conformations correspond poorly to low-energy regions on MM2, MM3, and other molecular mechanics surfaces. About 6 kcal/mol of the 8 kcal/mol difference in conformational energies comes from the torsion angles involving the anomeric center on the furanose ring. This suggests that even MM3, which has been very successful in modeling other disaccharides, miscalculates the energies of compounds that have overlapping anomeric sequences.
Language
English
Source (journal)
Journal of the American Chemical Society. - Washington, D.C.
Publication
Washington, D.C. : 1994
ISSN
0002-7863
Volume/pages
116:21(1994), p. 9590-9595
ISI
A1994PN45200025
Full text (Publishers DOI)
UAntwerpen
Faculty/Department
Research group
Publication type
Subject
Affiliation
Publications with a UAntwerp address
External links
Web of Science
Record
Identification
Creation 08.10.2008
Last edited 21.03.2017
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