Theoretical Study of Intramolecular Proton Transfer in Flavonols with Density Functional Theory

Khajadpai Thipyapong, Nuttawisit Yasarawan


Intramolecular proton transfer (IPT) reactions of four flavonols. i.e. kaempferol, morin, morin-5*-sulfonate and morin-7-O-sulfate in aqueous solution have been investigated using density functional methods with under polarizable continuum model (PCM). The levels of theory used were B3LYP/6-311++G(d,p) and CAM-B3LYP/6-311++G(d,p). Transition states of reactions were calculated using the QST2 method. For all flavonols tested, the normal form is much more stable than its respective zwitterionic form, due to the marked uniformity of electron density distribution in the molecular structure of the former. The potential for each flavonol to undergo IPT depends considerably on either the strength of intramolecular hydrogen bonding or electronic effect of substituents. The computed thermodynamic and kinetic data altogether manifest that the most and the least favorable IPT reactions belong to morin-7-O-sulfate and kaempferol, respectively.

Keywords :  Density Functional Theory, PCM, proton transfer, flavonols

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