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

Abstract

ABSTRACT: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.

Oligosaccharide analysis using anion attachment in negative mode electrospray mass spectrometry

“…B3LYP/6-31G* was chosen because it has been used previously to study the minimum energy conformation of monosaccharides [44 -49], and it is a higher level calculation compared to the HF/6-31G* level. The HF/6-31G* level of theory was employed elsewhere to calculate relaxed potential energy surfaces for 12 analogs of disaccharides [50]. In the latter study, analogs were made by replacing glucose with tetrahydropyran; thus, hydrogen bonding effects were ignored.…”

Ab initio Computational Modeling of Glyphosate Analogs: Conformational Perspective

“…Thus, the generated CESs can clearly explain the effect of substitution of various chemical moieties on the structure of the parent compound and hence dictate the way of identifying the potency of modelled systems [14][15][16].…”

Conformational properties of glucose-based disaccharides investigated using molecular dynamics simulations with local elevation umbrella sampling

“…For simplicity, however, the eight reducing disaccharides are only simulated in their b-anomeric form at the reducing end, which accounts for about 60% of the total anomeric population. 82,83 All of these disaccharides have been subjected to previous investigations, both experimentally by X-ray crystallography, 2,84-90 NMR spectroscopy, 83,[91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106] or circular dichroism 92,107 (CD), as well as theoretically by quantum mechanics [108][109][110][111][112][113][114][115][116] (QM), molecular mechanics 117-125 (MM), or MD simulation. 58,59,95,[101][102][103][104] The 11 + 2 new simulations with LEUS sampling enhancement (all disaccharides with LEUS applied to / and w, plus I and G with LEUS applied to /, w, andx) are analyzed in terms of (i) calculated free-energy maps G(/, w), as well as Gð/; w;xÞ for the (1?6)-linked disaccharides, in the subspace of the glycosidic dihedral angles; (ii) relative free energies of the identified conformational states (free-energy basins); (iii) interconversion barriers between these states (and transition timescales estimated using the TST approximation 75 ); (iv) occurrences of intramolecular H-bonds in these states; (v) estimates for the single molecule configurational entropies (QH analysis plus correction terms 69,<...>…”