Biochemical and Biophysical Research Communications, Vol.346, No.1, 321-329, 2006
ABTS radical-driven oxidation of polyphenols: Isolation and structural elucidation of covalent adducts
The formation of covalent adducts obtained from the reaction of the polyphenols, trans-3,3',4',5,7-pentahydroxyflavan (catechin) and 1,3,5-trihydroxybenzene (phloroglucinol), with ABTS radicals is reported. Two adducts derived from (+)-catechin and three adducts from phloroglucinol were isolated and identified using reversed-phase high performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS). The molecular masses of the (+)-catechin-derived adducts (I-c and IIc) were found to be 802 and 559 Da, respectively, whereas the masses of phloroglucinol-derived adducts (I-p, IIp, and IIIp) were 638, 395, and 381 Da, respectively. The initially formed adducts (I-c, I-p) were unstable and degraded to secondary adducts (IIc, IIp, and IIIp) releasing part of the ABTS molecule. The structures of these adducts were elucidated by interpreting the results of MS/MS analysis of prominent ions generated by both positive and negative ion ESI-MS. The adducts were found to scavenge ABTS radicals, an observation that could explain the complex kinetic behaviour manifested by the reactions of ABTS radicals with polyphenols. A mechanism, which accounts for both the formation of the adducts and the degradation products of ABTS radicals, is proposed. (c) 2006 Elsevier Inc. All rights reserved.