Details

Autor(en) / Beteiligte

• MARKOVIC, Zoran
• AMIC, Dragan
• MILENKOVIC, Dejan
• DIMITRIC-MARKOVIC, Jasmina M
• MARKOVIC, Svetlana

Titel

Examination of the chemical behavior of the quercetin radical cation towards some bases

Ist Teil von

• Physical chemistry chemical physics : PCCP, 2013-01, Vol.15 (19), p.7370-7378

Ort / Verlag

Cambridge: Royal Society of Chemistry

Erscheinungsjahr

2013

Quelle

MEDLINE

Beschreibungen/Notizen

• 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(+)˙) at the M0-52X/6311+G(d,p) level of theory. The deprotonation of Q(+)˙ 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(+)˙ will spontaneously be transformed into Q in the presence of bases whose HOMO energies are higher than the SOMO energy of Q(+)˙ 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(+)˙ 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(+)˙ in a given medium. In such cases Q(+)˙ 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.