Products of intermediate oxidation of flavonoids in aqueous solutions and determination of their composition by high-performance liquid chromatography in combination with mass spectrometry
T14N3
V.V. Khasanov, K.A. Dychko, A. V. Labutin, S.S. Kravtsova, T.T. Kuryaeva
Using high-performance liquid chromatography in combination with electrospray ionization mass spectrometry [HPLC-MS-ESI(NEG)], quercetin [Q] and luteolin [L] oxidation intermediate products were investigated. It was established that in aqueous solutions at pH=8.0 under aerobic conditions, quercetin forms double and triple donor- acceptor type complexes of the {[Q][Q–H2]} and {[Q][Q–H2]2} composition, which can be separated by HPLC, but rapidly converted to deeper oxidation products. In the presence of another flavonoid, luteolin (L), the oxidized form of quercetin also forms mixed complexes of {[L][Q–H2]} and {[L][Q–H2]2} types. Luteolin during oxidation does not generate donor-acceptor {[L][L–H2]} complexes. Quercetin in complexes with luteolin is always present in an oxidized form. It can be assumed that these complexes are formed as a result of recombination of two radicals of flavonoids, which formed initially as a result of manifestation of the antioxidants properties (one-electron transfer). These transformations of flavonoids are possible if strict anaerobic conditions in their quantitative determination are not implemented.
