Wink D A, Nims R W, Saavedra J E, Utermahlen W E, Ford P C
Chemistry Section, National Cancer Institute, Frederick Cancer Research and Development Center, MD 21702.
Proc Natl Acad Sci U S A. 1994 Jul 5;91(14):6604-8. doi: 10.1073/pnas.91.14.6604.
The application of kinetic probes that allow one to determine relative reactivities of biologically relevant substrates with oxidizing intermediates in the Fenton reagent (H2O2 plus Fe2+ in acidic aqueous solution) is described. These results lead to the conclusion that there are two key intermediates with very different reactivity patterns. One (X) is proposed to be an iron complex formed via direct reaction of H2O2 with Fe2+, which reacts with N-nitrosodimethylamine to generate a strong transient absorption at 450 nm. This provides a sensitive spectrophotometric probe of the competitive reactivities toward X of biologically relevant substrates such as nucleic acid components and amino acids. The second intermediate (Y) is probed by its oxidation of the Ru(bpy)2+3 ion (bpy = 2,2'-bipyridine) to a product with an absorption band centered at 500 nm. In the absence of other substrates, Ru(bpy)2+3 is oxidized at rates independent of the Ru concentration, but the product yield is diminished by competing reactions with substrates that can intercept X. Competition studies demonstrate reactivity patterns for X and Y that are clearly distinct from the pattern predicted for the hydroxyl radical, the intermediate commonly invoked in discussions of Fenton oxidations. These data require reevaluation of the mechanisms by which the Fenton reagent oxidizes biological substrates.
本文描述了动力学探针的应用，该探针可用于确定生物相关底物与芬顿试剂（酸性水溶液中的H2O2加Fe2+）中的氧化中间体的相对反应活性。这些结果得出结论，存在两种具有非常不同反应模式的关键中间体。一种（X）被认为是通过H2O2与Fe2+直接反应形成的铁络合物，它与N-亚硝基二甲胺反应，在450nm处产生强烈的瞬态吸收。这为生物相关底物（如核酸成分和氨基酸）对X的竞争反应活性提供了一种灵敏的分光光度探针。第二种中间体（Y）通过其将Ru(bpy)2+3离子（bpy = 2,2'-联吡啶）氧化为吸收带中心位于500nm的产物来探测。在没有其他底物的情况下，Ru(bpy)2+3以与Ru浓度无关的速率被氧化，但产物产率会因与能够拦截X的底物的竞争反应而降低。竞争研究表明，X和Y的反应模式与在芬顿氧化讨论中通常提到的中间体羟基自由基所预测的模式明显不同。这些数据需要重新评估芬顿试剂氧化生物底物的机制。
