Abstract
The effects of catechins and tannins on the uranyl ion (UO22+)-hydrogen peroxide (H2O2) system were examined using the spin-trapping method. Epigallocatechin (EGC), having low •OH-scavenging ability, significantly enhanced and accelerated the hydroxyl radical (•OH) formation in the UO22+–H2O2 solution. Epigallocatechin gallate (EGCG), having high •OH-scavenging ability, fairly enhanced and accelerated hydroxyl radical (•OH) formation in the UO22+–H2O2 solution. These results indicate that the enhancement and acceleration of •OH formation are caused by the reduction of UO22+ to UO2+ by EGC and EGCG. The effects of tannins on •OH formation in the UO22+–H2O2 solution varied with tannins. Mimosa (MMT) and quebracho (QBT) tannins enhanced and accelerated •OH formation, while chestnut (CNT), mylobaran (MBT) and Chinese gallo- (CGT) tannins heavily depressed it. In the solution containing persimmon (PST) and gambir (GBT) tannins, the depression of •OH formation caused by the strong coupling with UO22+ ion should be added to the enhancement caused by the reduction of UO22+ to UO2+. MBT indicated the highest ability to scavenge •OH in the UV-irradiated H2O2 solution, and MMT, the lowest. In summary, MMT and QBT, classified as condensed tannins, have very high abilities to reduce UO22+ to UO2+, similarly to catechins such as EGC and EGCG, while MBT, a hydrolysable tannin, has higher abilities to scavenge •OH.
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