EXAFS STUDIES OF AN AQUEOUS FE(IV) INTERMEDIATE

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 芬顿反应在催化化学、大气和环境过程、老化和疾病中的机理复杂性和广泛参与使其成为有史以来研究和争论最多的反应之一。严格地说，芬顿反应是在酸性水溶液中用过氧化氢氧化含水铁（II）离子。这种转化也被认为发生在pH值接近7-8的生物环境中，并且铁（II）中心可能与细胞内可用的配体配位。这种化学已被用来合理化的生产一些活性氧物种，并解释的铁络合物，H2 O2和还原剂的组合对DNA切割的影响。关于反应性中间体的性质，实验证据和论点已经提出了羟基自由基，[（H2O）nFeIVO]2+和金属配位过氧化物，[（H2O）5 Fe（H2 O2）]2+。原则上，这个机制问题的答案在于对每个可以独立生成的拟议中间体的反应性研究。直到最近，只有羟基自由基可以独立于其他化学来源获得。最近，我们已经建立了一个FeIV的中间体是在pH值为1的水溶液中产生的反应[Fe（H2O）6]2+和O3。这种短寿命的物种被冷冻捕获，并通过穆斯堡尔谱学研究证实了S = 2基态的高自旋FeIV物种的存在。我们对两个样品进行了初步的XAS研究，穆斯堡尔谱确定了50%和58%的纯度。我们注意到一个明显的1 s-3d转换的XANES光谱。 本项目将继续进行这些研究。

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¿ssbauer 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¿ssbauer 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.