An EPR and DFT study on the primary radical formed in hydroxylation reactions of 2,6-dimethoxy-1,4-benzoquinone

摘要

The cluillone corilPound 2,6-dimethoxY-1,4-berizoquirione is hydroxylat d in alkaline aqueous so u Lion with pH above 11 Electron paramagnetic resonance experiments showed that twotransient rad cals are formed in this reaction. The radical appearing first is assigned to a one electron reduced 2,6-dimethoxy-1,4-benzoquinone, receiving the electron from an intermediate anionic hydroxylated species. For this primary radical, all proton couplings were determined (quinoid ring protons:1.453 G, methyl protoris: 0.795 G). The density functional theory method was applied to obtain electronic and structural information of the primary radical and a solution structure is suggested. For approaching he experimental hyperfine couplings in theoretical models, it was necessary to consider effects of external polarisation arising from water molecules near one carbonyl group, and the orientation o methoxy groups towards the guinone ring, With this approach, the secondary radical formed in the hydroxylatiori reaction, and the transient radicals found for other biologically importarit quinones including coenzymes Q) and their hydroxylated species may become accessible.