期刊
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 15, 期 19, 页码 7370-7378出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c3cp44605k
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资金
- Ministry of Science of the Republic of Serbia [172015, 172016]
- Ministry of Science, Education and Sports of the Republic of Croatia [079-0000000-3211]
- Serbia-Croatia Bilateral agreement [69-00-74/2010-02]
- Croatia-Serbia Bilateral agreement
- Center for Scientific Research of the Serbian Academy of Sciences and Arts
- University of Kragujevac
It has been generally accepted that, due to high ionization potential values, single electron transfer followed by proton transfer (SET-PT) is not a plausible mechanism of antioxidant action in flavonoids. In this paper the SET-PT mechanism of quercetin (Q) was examined by revealing possible reaction paths of the once formed quercetin radical cation (Q(+center dot)) at the M0-52X/6311+G(d,p) level of theory. The deprotonation of Q(+center dot) was simulated by examining its chemical behavior in the presence of three bases: methylamine (representative of neutral bases), the MeS anion (CH3S-) and the hydroxide anion (representative of anionic bases). It was found that Q(+center dot) will spontaneously be transformed into Q in the presence of bases whose HOMO energies are higher than the SOMO energy of Q(+center dot) in a given medium, implying that Q cannot undergo the SET-PT mechanism in such an environment. In the reaction with the MeS anion in both gaseous and aqueous phases and the hydroxide anion in the gaseous phase Q(+center dot) accepts an electron from the base, and so-formed Q undergoes the hydrogen atom transfer mechanism. On the other hand, SET-PT is a plausible mechanism of Q in the presence of bases whose HOMO energies are lower than the SOMO energy of Q(+center dot) in a given medium. In such cases Q(+center dot) spontaneously donates a proton to the base, with energetic stabilization of the system. Our investigation showed that Q conforms to the SET-PT mechanism in the presence of methylamine, in both gaseous and aqueous phases, and in the presence of the hydroxide anion, in the aqueous solution.
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