o-Quinone involvement in the prooxidant tendency of a mixture of quercetin and caffeic acid.

The oxidation products of a previously tested prooxidant mixture of quercetin (Q) and caffeic acid (CA) at 1:2 ratio were analysed by LC-MS. The UV-Vis and MS spectra of three chromatographic peaks eluting at t(R)=9.11min, t(R)=14.36min and t(R)=30.30min were studied further. The structures of the tentatively identified compounds indicate polymeric molecules. A pentamer formed by 3 units of quercetin and 2 units of caffeic acid was attributed in the case of peaks t(R)=9.11min and t(R)=14.36min. The quercetin quinone (QQ) - a polymerization intermediate - is a fragment of the compound identified in the MS spectrum with the m/z=323 coming from Q o-quinone m/z=300 plus 23 from Na(+). According to the UV-Vis spectrum, we suggest a different intermolecular arrangement which gives a more extended e-delocalisation. At t(R)=30.30min, the spectra helped us to tentatively identify this oxidation product as being a polymer of 4 CA units and 1 QQ.