Delocalization of the Unpaired Electron in the Quercetin Radical: Comparison of Experimental ESR Data with DFT Calculations.

ABSTRACT: In the antioxidant activity of quercetin (Q), stabilization of the energy in the quercetin radical (Q^•) by delocalization of the unpaired electron (UE) in Q^• is pivotal. The aim of this study is to further examine the delocalization of the UE in Q^•, and to elucidate the importance of the functional groups of Q for the stabilization of the UE by combining experimentally obtained spin resonance spectroscopy (ESR) measurements with theoretical density functional theory (DFT) calculations. The ESR spectrum and DFT calculation of Q^• and structurally related radicals both suggest that the UE of Q^• is mostly delocalized in the B ring and partly on the AC ring. The negatively charged oxygen groups in the B ring (3' and 4') of Q^• have an electron-donating effect that attract and stabilize the UE in the B ring. Radicals structurally related to Q^• indicate that the negatively charged oxygen at 4' has more of an effect on concentrating the UE in ring B than the negatively charged oxygen at 3'. The DFT calculation showed that an OH group at the 3-position of the AC ring is essential for concentrating the radical on the C2-C3 double bond. All these effects help to explain how the high energy of the UE is captured and a stable Q^• is generated, which is pivotal in the antioxidant activity of Q.

SUBMITTER: Li Z 

PROVIDER: S-EPMC7139295 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature