Density functional theory calculations on two glycosides, namely, n-octyl-β-D-glucopyranoside (C(8)O-β-Glc) and n-octyl-β-D-galactopyranoside (C(8)O-β-Gal) were performed for geometry optimization at the B3LYP/6-31G level. Both molecules are stereoisomers (epimers) differing only in the orientation of the hydroxyl group at the C4 position. Thus it is interesting to investigate electronically the effect of the direction (axial/equatorial) of the hydroxyl group at the C4 position. The structure parameters of X-H∙∙∙Y intramolecular hydrogen bonds were analyzed, while the nature of these bonds and the intramolecular interactions were considered using the atoms in molecules (AIM) approach. Natural bond orbital analysis (NBO) was used to determine bond orders, charge and lone pair electrons on each atom and effective non-bonding interactions. We have also reported electronic energy and dipole moment in gas and solution phases. Further, the electronic properties such as the highest occupied molecular orbital, lowest unoccupied molecular orbital, ionization energy, electron affinity, electronic chemical potential, chemical hardness, softness and electrophilicity index, are also presented here for both C(8)O-β-Glc and C(8)O-β-Gal. These results show that, while C(8)O-β-Glc possess- only one hydrogen bond, C(8)O-β-Gal has two intramolecular hydrogen bonds, which further confirms the anomalous stability of the latter in self-assembly phenomena.
Density functional theory calculations on α/β-D-mannose (α/β-D-Man) and the corresponding glycosides of n-octyl-α/β-D-mannopyranoside (C 8 O-α/β-D-Man) were carried out for geometrical optimisation and stability predictions at the B3LYP/6-31G level of theory. These compounds are related anomerically, since they differ by only the orientation of the hydroxyl group at the C1 position. The aim of this study is to investigate the effect of the hydroxyl group's orientations (axial vs. equatorial) at the C1 position on the intra-molecular interactions and the conformational stability of these isomers. The structural parameters of X-H•••Y intra-molecular hydrogen bonds were analysed, while the nature of these bonds was considered using the atoms-in-molecules (AIM) approach. Natural bond orbital (NBO) analysis was used to determine bond orders and the effective non-bonding interactions. We have also reported thermodynamic properties and the electronic properties, such as the highest occupied molecular orbital, lowest unoccupied molecular orbital, ionisation energy, electron affinity, electronic chemical potential, chemical hardness, softness and electrophilicity index in the gas phase for all compounds. These results showed that while α-anomers possess only one intra-molecular hydrogen bond, β-anomers possess two intra-molecular hydrogen bonds, which further confirms the anomalous stability of the latter in the selfassembly phenomena.
The unusual monosaccharaides such as deoxy‐hexose sugars, including methyl‐pentose and aldo‐pentose, are promising and important sugars in life science. However, little research on H‐bond interactions in these systems has been reported. The aldo‐pentose has a proton instead of the CH2OH group on C5; conversely, methyl‐pentose has a CH3 group on C5. The aim of the present study is to investigate the role and nature of intramolecular H‐bonds on acidity of CH3‐pentose sugars (L‐fucose and L‐rhamnose) and aldo‐pentose sugars (D‐xylose, L‐lyxose, D‐ribose, and L‐arabinose) using B3LYP/6‐311++G (d, p) level. The calculated acidity values (ΔHacid) of these Dexoy‐hexose were found to be from 343 to 369 kcal.mol−1, indicating they are stronger acid than ethanol and 2‐propanol with the acidity values of 378.3 and 375.1 kcal.mol−1, respectively. This is related to the stabilization of the conjugate bases of these sugar through intramolecular H‐bonds, which were analyzed in this study using atoms in molecules (AIM) and natural bonding orbital (NBO) methods. AIM and NBO analyses indicate the presence of one bifurcated intramolecular H‐bond in the conjugate bases of L‐lyxose and L‐arabinose and two bifurcated H‐bonds in conjugate base of D‐ribose, whereas the conjugate bases of L‐fucose, L‐rhamnose, and D‐xylose present one normal intramolecular H‐bond. According to the topological parameters and charge transfer data, existence of normal and bifurcated intramolecular H‐bonds could greatly increase acidity of deoxy‐hexose sugars. The H‐bond strength in the conjugate bases of aldo‐pentose sugars is higher than that in the conjugate bases of methyl‐pentose sugars including CH3 group on C5, making aldo‐pentose sugars stronger acid than methyl‐pentose sugars.
This report present the results of natural energy decomposition analysis (NEDA), natural bond orbital (NBO), and quantum theory of atoms in molecules (QTAIM) calculations of three derivatives of biphenyl-1-aza-18-crown-6 ether and their 1:1 complexes with Cd(2+). All calculations used the B3LYP density functional theory in combination with the 6-311G and WTBS basis sets for ligands and Cd(2+) ion, respectively. Ligands 1 and 3 have a single 1-aza-18-crown-6, substituent; ligand 2 has two such substituents. The results show that, in the optimized geometries of the complexes, the distance between N and Cd(2+) is greater than the distance between O and Cd(2+). NBO and QTAIM data confirm these results. There was no stabilization energy or bond critical point for N · · · Cd(2+) in NBO or QTAIM, respectively. Data show that the O · · · Cd(2+) interaction is a kind of closed shell interaction. The trend of the calculated stabilization energy was similar to the experimental data. Different contributions of interaction energies for complex formation were analyzed by NEDA, and the results show that the main component of the interactions is accounted for by polarization.
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