Calculation of the structure and IR spectrum of methyl-β-D-glucopyranoside by density functional theory

Abstract

539.194 Structural-dynamic models of methyl-β-D-glucopyranoside have been constructed by a density functional method using a B3LYP functional in bases 6-31G(d) and 6-31+G(d,p). Energies have been minimized. Structures, dipole moments, polarizabilities, frequencies of normal modes in the harmonic approximation, and the intensity distribution in the molecular IR spectrum have been calculated. The calculation results have been compared with both the experimental spectra of methyl-β-D-glucopyranoside in the region 400-3700 cm -1 and data obtained within the framework of an approach that uses the classical valence-force method to calculate normal mode frequencies and the quantum-chemical CNDO/2 technique to calculate the electronic structure.Introduction. The construction of structural-dynamic models of molecules and molecular systems based on quantum-mechanical methods has become an essential part of research on the structure, optical spectra, and properties of compounds. The accuracy of quantum-mechanical calculations has risen significantly during the last three decades. This made it possible to use them in molecular spectroscopy. The satisfactory agreement of theoretical and experimental spectra provides indirect confirmation that the selected quantum-mechanical methods and approximations are correct and precise. The discrepancy between calculated harmonically and measured fundamental vibration frequencies is less than 4-5%. This enables the results of such calculations to be used to interpret measured vibrational spectra. The absolute error within the limits of this uncertainty turns out to be different for frequencies of normal vibrations. It is 150-200 cm -1 in the high-frequency range (2850-3750 cm

Calculation of the Structure and IR Spectrum of 2,3-di-O-Nitromethyl-β-D-Glucopyranoside by the Density Functional Method

“…The current state of these methods and the algorithms and computing programs gave hope that using them would be successful. Explicit consideration of the H-bond in the modeling reproduced the IR spectrum, which was closer to the experimental one [1][2][3]. This problem as applied to 2,3-di-O-nitromethyl-β-D-glucopyranoside was solved before [13].…”

“…The results indicated that the geometries of the pyranose rings in the monosaccharides differed little. The dipole moment (3.697 D) was approximately one third greater than that of methyl-β-D-glucopyranoside (2.807 D) [1].…”

“…1, fragment R1). They corresponded to medium and strong maxima at 1030 and 1222 cm -1 in the spectrum of methyl-β-D-glucopyranoside [1]. These frequencies practically did not change whereas the intensity of mode ν 44 doubled and that of mode ν 53 was halved on going from methyl-β-D-glucopyranoside to 2,3-di-O-nitromethyl-β-D-glucopyranoside.…”

“…The cores (vicinity of the H bridges) of H-bonded complexes II, IIa, III, and IIIa were identical. The calculated IR spectra of H-bonded complexes IIa and IIIa and dimeric H-bonded complexes of methyl-β-D-glucopyranoside [1][2][3] enabled the effect of the H-bond on the spectrum of 2,3-di-O-nitromethyl-β-D-glucopyranoside to be rather fully explained.…”

“…The non-planar pyranose rings had the chair conformation. Its C-C bonds were slightly longer (by ~0.01 Å) than the corresponding pyranose bonds in methyl-β-D-glucopyranoside [1] and methyl-β-D-glucopyranoside tetranitrate [24] that were determined by x-ray crystal structure analyses. The exception was C 5 -C 7 , which was lengthened by 0.03 Å because of the replacement of two hydroxyl H atoms by nitro groups.…”