Cooperative intramolecular H-bonds in quercetine: MNDO/H quantum chemical investigation
DOI:
https://doi.org/10.7124/bc.0005B6Abstract
For the first time four anticooperative intramolecular H-bonds have been determined by the semiempirical quantum chemical method MNDO/H in eight low-energy (in the energy range ΔE ≤ 1 kcal/mol) conformations of quercetine, a molecule with the wide spectrum of biological activity. Two of these H-bonds are bifurcated ones (C5OH...OC4 and C3OH...OC4) in a heterocycle, one (C6'H...OC3) – between a hetero- and a phenyl cycles, and one (C3'OH...OC4' or C4OH..OC3', depending on conformation) – in a phenyl ring. The H-bonds energies are 8.8, 2.9, 2.8 and 1.4 kcal/mol , respectively. The H-bonds parameters are conformationally insensitive. The effect of their anticooperativity, mutual weakening, reaches –1.1 kcal/mol A possibility of experimental (by vibrational spectroscopy) confirmation of the existence of these intramolecular H-bonds is discussed as well as the reasons of a propeller-like orientation of planar hetero- and phenyl cycles, which is the intrinsic characteristic of all low-energy quercetine conformations.References
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