de Groot Matheus T, Koper Marc T M
Laboratory of Inorganic Chemistry and Catalysis, Schuit Institute of Catalysis, Eindhoven University of Technology, P.O. Box 513, 5600, MB Eindhoven, The Netherlands.
Phys Chem Chem Phys. 2008 Feb 21;10(7):1023-31. doi: 10.1039/b714727a. Epub 2007 Dec 6.
The electrochemical redox behavior of immobilized chromium, manganese, iron, cobalt, and nickel protoporphyrins IX has been investigated over the pH 0-14 range. In the investigated potential domain the metalloporphyrins were observed in four different oxidation states (M(I), M(II), M(III) and M(IV)). The metalloporphyrins differ in the potentials at which the redox transitions occur, but the observed pH dependence of the redox transitions was similar for the different metalloporphyrins and revealed that the M(II)/M(III) and M(III)/M(IV) transitions were accompanied by a hydroxide transfer at high pH. The fact that the metalloporphyrins are immobilized on graphite does not seem to have a large influence on their redox behavior, as can be deduced from the comparable behavior of immobilized metalloporphyrins on gold and of watersoluble metalloporphyrins in solution. We also performed density functional theory (DFT) calculations on the metalloporphyrins in different oxidation states. The geometries and spin states predicted by these calculations agree well with experimentally determined values; the calculations were also able to predict the electrochemical potentials of the [M(II)]/[M(III)-OH] redox transition to within about 300 mV.
已在pH值0 - 14范围内研究了固定化铬、锰、铁、钴和镍原卟啉IX的电化学氧化还原行为。在所研究的电位范围内，观察到金属卟啉处于四种不同的氧化态（M(I)、M(II)、M(III)和M(IV)）。不同金属卟啉发生氧化还原转变的电位不同，但不同金属卟啉的氧化还原转变对pH的依赖性相似，表明在高pH值下，M(II)/M(III)和M(III)/M(IV)转变伴随着氢氧根转移。从固定在金上的金属卟啉和溶液中水溶性金属卟啉的可比行为可以推断，金属卟啉固定在石墨上这一事实似乎对其氧化还原行为影响不大。我们还对不同氧化态的金属卟啉进行了密度泛函理论（DFT）计算。这些计算预测的几何结构和自旋态与实验测定值吻合良好；计算还能够将[M(II)]/[M(III)-OH]氧化还原转变的电化学电位预测在约300 mV范围内。
