Brausam Ariane, Eigler Siegfried, Jux Norbert, van Eldik Rudi
Department of Chemistry and Pharmacy, University of Erlangen-Nurnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
Inorg Chem. 2009 Aug 17;48(16):7667-78. doi: 10.1021/ic9005955.
A detailed study of the effect of pH, temperature, and pressure on the reaction of hydrogen peroxide with Fe(III)(P(8-)), where P(8-) represents the octa anionic porphyrin, was performed using stopped-flow techniques. Depending on the pH, different high valent iron-oxo species were formed. At pH < 9 formation of a two-electron oxidized species [(porphyrin(+))Fe(IV)=O] was observed. In contrast, at pH > 9 only the one electron oxidized species [(porphyrin)Fe(IV)=O] was found to be present in solution. Under selected conditions at pH 8 it was possible to determine rate constants for both the coordination of hydrogen peroxide and subsequent heterolytic cleavage of the O-O bond. At pH 11 a composite rate constant for coordination of H(2)O(2) and homolytic cleavage of the O-O bond could be measured. In addition, it was possible to determine the activation parameters for the overall reaction sequence leading to the formation of [(porphyrin)Fe(IV)=O]. Careful analysis of the obtained data supports an associatively activated mechanism for the coordination of hydrogen peroxide. The catalytic properties of Fe(III)(P(8-)) in the presence of H(2)O(2) were also investigated. Both high valent iron-oxo species turned out to be able to oxidize diammonium-2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) to the radical cation ABTS(+). At higher hydrogen peroxide concentrations a reduced yield of ABTS(+) was observed because of increased catalase activity of Fe(III)(P(8-)). At high pH disproportionation of ABTS(+) to ABTS and ABTS(2+) occurred, which could be suppressed by an excess of unreacted ABTS. In slightly basic to acidic solutions this reaction did not play a role.
采用停流技术对pH值、温度和压力对过氧化氢与Fe(III)(P(8-))反应的影响进行了详细研究，其中P(8-)代表八价阴离子卟啉。根据pH值的不同，会形成不同的高价铁氧物种。在pH < 9时，观察到形成了双电子氧化物种[(卟啉(+))Fe(IV)=O]。相反，在pH > 9时，溶液中仅存在单电子氧化物种[(卟啉)Fe(IV)=O]。在pH为8的特定条件下，可以确定过氧化氢配位以及随后O - O键异裂的速率常数。在pH为11时，可以测量H₂O₂配位和O - O键均裂的复合速率常数。此外，还可以确定导致[(卟啉)Fe(IV)=O]形成的整个反应序列的活化参数。对所得数据的仔细分析支持了过氧化氢配位的缔合活化机制。还研究了Fe(III)(P(8-))在H₂O₂存在下的催化性能。两种高价铁氧物种都能够将2,2'-偶氮双(3-乙基苯并噻唑啉-6-磺酸盐)二铵(ABTS)氧化为自由基阳离子ABTS(+)。在较高的过氧化氢浓度下，由于Fe(III)(P(8-))的过氧化氢酶活性增加，观察到ABTS(+)的产率降低。在高pH值下，ABTS(+)歧化为ABTS和ABTS(2+)，过量未反应的ABTS可以抑制这种现象。在弱碱性至酸性溶液中，该反应不起作用。
