Quantum molecular modeling of quercetin—Simulation of the interaction with the free radical t ‐BuOO ⋅ *

Quercetin is one of the most potent antioxidants belonging to the flavonoids, which are a naturally occurring family of molecules. The optimized forms of the 3′‐, 4′‐, 3‐, 5‐, and 7‐quercetin radicals were computed using ab initio procedure at the 6‐31G* level. We have deduced that the 3′‐, 4′‐, and 3‐radicals are the most energetically favored. The simulation of the H abstraction at the 4′‐hydroxyl of quercetin by the free radical t ‐BuOO ⋅ ( tert ‐butyl peroxyl) was conducted using the supermolecular model composed of quercetin in interaction with t ‐BuOO ⋅ . The mechanism of the scavenging of the free radical by quercetin is discussed on the basis of various AM1 and ab initio (level 6‐31G*) quantum molecular computations and the obtained frontier orbitals and total spin density. The analysis of the spin density around the obtained free radical 4′‐quercetin indicates that the major density of spin α(↑) is concentrated in the B ring on the O4′ oxygen; we observe also a slight delocalization of spins α(↑) and β(↓) on the B ring and on a part of the C ring. In conclusion, the antioxidant power of quercetin may be associated mainly with the B ring and a half of the C ring. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002