EXAFS STUDIES OF AN AQUEOUS FE(IV) INTERMEDIATE

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。Fenton反应机理的复杂性和在催化化学、大气和环境过程、老化和疾病方面的广泛参与，使其成为有史以来研究最多、争论最多的反应之一。严格地说，Fenton反应是在酸性水溶液中用过氧化氢氧化水中的铁(II)离子。这种转变也被认为发生在生物环境中，那里的pH更接近7-8，铁(II)中心可能与细胞内可用的配体配位。这种化学已经被用来使一些活性氧物种的产生合理化，并解释了铁络合物、过氧化氢和一种还原剂对DNA切割的影响。关于反应中间体(S)的性质，已经提出了羟基自由基[(H2O)nFeIVO]2+和金属配位过氧化氢[(H2O)5Fe(H2O2)]2+的实验证据和论点。原则上，这个机械问题的答案在于对每个被提议的中间体的反应性研究，这些中间体可以独立产生。直到最近，只有羟基自由基才能独立于其他化学来源获得。最近，我们已经证实，在水溶液中，[Fe(H2O)6]2+与O_3在pH为1的条件下反应生成FeIV中间体。这种短暂的物种被冷冻捕获，并通过M？Auer光谱研究证实了存在一个具有S=2基态的高自旋FeIV物种。我们对两个样品进行了初步的XAS研究，M？Auer光谱确定其纯度分别为50%和58%。我们注意到XANES光谱中有一个明显的1S 3D跃迁。目前的项目将继续这些研究。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The mechanistic complexity and wide-spread involvement of the Fenton reaction in catalytic chemistry, atmospheric and environmental processes, aging and disease have made it one of the most studied and debated reactions of all time. Strictly speaking, the Fenton reaction is the oxidation of aqueous iron(II) ions with hydrogen peroxide in acidic aqueous solutions. This transformation is also proposed to occur in biological milieu where the pH is closer to 7-8 and the iron(II) center is presumably coordinated to ligands available within the cell. Such chemistry has been used to rationalize the production of some reactive oxygen species and to explain the effects of the combination of iron complexes, H2O2 and a reductant on DNA cleavage. Regarding the nature of the reactive intermediate(s), experimental evidence and arguments have been advanced for hydroxyl radicals, [(H2O)nFeIVO]2+, and metal-coordinated peroxide, [(H2O)5Fe(H2O2)]2+. In principle, the answer to this mechanistic question lies in reactivity studies of each proposed intermediate that can be generated independently. Until recently, only hydroxyl radicals can be obtained independently from other chemical sources. Recently, we have established that an FeIV intermediate is generated at pH 1 in aqueous solution from the reaction of [Fe(H2O)6]2+ and O3. This short-lived species was freeze-trapped and characterized by M¿¿¿auer spectroscopic studies that confirm the existence of a high-spin FeIV species with an S = 2 ground state. We carried out initial XAS studies on two samples for which M¿¿¿auer spectroscopy established the purity of 50% and 58%. We noted a pronounced 1s 3d transition in the XANES spectrum. The current project will continue these studies.