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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Redox and complexation chemistry of the Cr~(VI)/Cr~v/Cr~(IV)-D-glucuronicacid system
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Redox and complexation chemistry of the Cr~(VI)/Cr~v/Cr~(IV)-D-glucuronicacid system

机译：Cr〜（VI）/ Cr〜v / Cr〜（IV）-D-葡萄糖醛酸体系的氧化还原和络合化学

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摘要

When excess uronic acid over Cr~(VI) is used, the oxidation of D-glucuronic acid (Glucur) by Cr' yieldsD-glucaric acid (Glucar) and Cr"' as final products. The redox reaction involves the formation ofintermediate Cr~(VI) and Cr~V species, with Cr~(VI) and Cr~Vreacting with Glucur at comparable rates. The rateof disappearance of Cr~(VI), and Cr~V increases with[H~+]and [substrate]. The experimental resultsindicated that Cr~(VI) is a very reactive intermediate since its disappearance rate is much faster thanCr /Cry and decreases when [H~+]rises. Even at high[H*]Cr~(VI) intermediate was involved in fast stepsand does not accumulate in the reaction. Kinetic studies show that the redox reaction between Glucurand Cr"' proceeds through a mechanism combining one- and two-electron pathways for the reductionof intermediate Cr(iv) by the organic substrate: Cr~(VI) →Cr~(IV)→Cr~(II) and Cr~(VI) → Cr~(IV) Cr~(III). Themechanism is supported by the observation of free radicals, CrO_2~(2+)(superoxoCrion) and Cr~V asreaction intermediates. The EPR spectra show that five-co-ordinate oxo-Cr~Vbischelates are formed atpH < 4 with the uronic acid bound to Cr~V through the carboxylate and the a-OH group of the furanoseform. Five-co-ordinated oxo-Cr~Vmonochelates are observed as minor species in addition to the majorfive-co-ordinated oxo-Cry bischelates. At pH 7.5 the EPR spectra show the formation of a Crcomplexwhere the cis-diol groups of Glucur participate in the bonding to Cr. In vitro, our studies on the chemistry of Cr~V complexes can provide information on the nature of thespecies that are likely to be stabilized in vivo. In particular, the EPR pattern of Glucur-Cr~V species canbe used as a finger print to identify Cr~Vcomplexes formed in biological systems.
机译：当使用过量的糖醛酸超过Cr〜（VI）时，D'-葡萄糖醛酸（Glucur）被Cr'氧化，生成D-葡萄糖酸（Glucar），最终的产物为Cr“'。氧化还原反应涉及中间体Cr〜的形成。 （VI）和Cr〜V物种，其中Cr〜（VI）和Cr〜V与葡萄糖反应的速率相当; Cr〜（VI）和Cr〜V的消失速率随[H〜+]和[底物]的增加而增加。实验结果表明，Cr〜（VI）是一种非常活泼的中间体，因为它的消失速率比Cr / Cry快得多，当[H〜+]升高时其消失速率降低，甚至在高[H *] Cr〜（VI）中间体参与下也是如此。动力学研究表明，葡萄糖和Cr”之间的氧化还原反应是通过结合一电子路径和两电子路径的机理进行的，从而通过有机底物Cr〜（）还原中间Cr（iv）。 VI）→Cr〜（IV）→Cr〜（II）和Cr〜（VI）→Cr〜（IV）Cr〜（III）。自由基，CrO_2〜（2 +）（superoxoCrion）和Cr〜V作为反应中间体的观察支持了分子机理。 EPR谱表明，在pH <4时形成了五配位的氧代Cr-V-双螯合物，其中的糖醛酸通过呋喃糖形式的羧酸酯和a-OH基与Cr-V键合。除了主要的五个配位的氧代-Cry双螯合物外，还观察到五配位的氧-Cr-V-单螯合物。在pH 7.5时，EPR谱图显示出Cr络合物的形成，其中Glucur的顺式-二醇基团参与与Cr的键合。在体外，我们对Cr〜V配合物的化学研究可以提供有关可能在体内稳定的物种的性质的信息。尤其是，Glucur-Cr〜V物种的EPR模式可以用作指纹识别生物系统中形成的Cr〜V复合物。

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