Methoxyphenols-antioxidant principles in food plants and spices: Pulse radiolysis, EPR spectroscopy, and density functional theory calculations

The phenoxyl radicals of several phenols and phenolic acids with o-methoxy groups were generated by pulse-radiolytic oxidation with azide radicals and their buildup and decay evaluated with kinetic spectroscopy. Structures of the phenoxyl radicals were obtained with EPR spectroscopy and the experimental isotropic coupling constants confirmed by hybrid density-functional calculations with Becke's three parameter hybrid functional using the Lee, Yang, and Parr functional theory and a variety of basis sets, and with consideration of the solvent. While the calculations resulted in reasonable correlations with the experimental data, the apparent distinction in the stability of the various radicals seems to be primarily due to kinetic rather than electronic effects. (C) 2002 Wiley Periodicals, Inc.