Computational investigation of [FeFe]-hydrogenase models: characterization of singly and doubly protonated intermediates and mechanistic insights.
Computational investigation of [FeFe]-hydrogenase models: characterization of singly and doubly protonated intermediates and mechanistic insights.
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DOI：
10.1021/ic5013523
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发表时间：
2014-10-06
影响因子：
4.6
通讯作者：
Hammes-Schiffer S
中科院分区：
文献类型：
--
作者：
Huynh MT;Wang W;Rauchfuss TB;Hammes-Schiffer S
[FeFe]-氢化酶以双核铁金属中心催化氢的氧化和生产。最近合成了仿生h2生成模型体系Fe2(adt)(CO)2(dppv)2 （adt=偶氮二硫酯，dppv=二膦）并进行了实验研究。在该体系中，偶氮硫酸桥通过质子继电器促进双质子化铵氢化物的形成。本文利用计算方法来研究该系统在各种氧化态和质子化态下的H2生成机制。计算结果与实验数据在几何形状、CO振动拉伸频率和还原势等方面吻合较好。计算结果表明，双质子化物质中的nh4···HFe二氢键距离对晶体结构中存在的铵离子与BF4 -反离子之间离子配对的影响高度敏感，其中BF4 -反离子的加入使二氢键的长度明显延长。非氢化物铁中心是末端氢化物和非对称桥接氢化物的还原位点，而被还原的对称桥接氢化物在铁中心之间表现出自旋离域。根据相对pKa值的实验测量和理论计算，中性氢化物的Fed中心比胺更具碱性，桥接氢化物比末端氢化物更具热力学稳定性。计算结果暗示了H2演化的可能途径，包括H2与一个Fe弱键的中间产物，与分子键长度相似的短H2距离，两个Fe中心的自旋密度离域，以及几乎对称桥接的CO配体。总的来说，本研究阐明了氨-氢化物相互作用、桥接CO配体的柔性化以及Fe中心之间的分子内电子转移在催化循环中的机制作用。这些见解将有助于设计更有效的生物启发氢气生产催化剂。结合理论计算和实验数据，分析了Fe2(adt)(CO)2(dppv)2催化析氢的机理途径。本研究阐明了还原位点和与单质子化和双质子化物质形成相关的pKa值，以及氨-氢化物相互作用、桥接CO配体的柔性化和Fe中心之间的分子内电子转移在催化制氢循环中的作用。
The [FeFe]-hydrogenase enzymes catalyze hydrogen oxidation and production efficiently with binuclear Fe metal centers. Recently the bioinspired H2-producing model system Fe2(adt)(CO)2(dppv)2 (adt=azadithiolate and dppv=diphosphine) was synthesized and studied experimentally. In this system, the azadithiolate bridge facilitates the formation of a doubly protonated ammonium-hydride species through a proton relay. Herein computational methods are utilized to examine this system in the various oxidation states and protonation states along proposed mechanistic pathways for H2 production. The calculated results agree well with the experimental data for the geometries, CO vibrational stretching frequencies, and reduction potentials. The calculations illustrate that the NH···HFe dihydrogen bonding distance in the doubly protonated species is highly sensitive to the effects of ion-pairing between the ammonium and BF4– counterions, which are present in the crystal structure, in that the inclusion of BF4– counterions leads to a significantly longer dihydrogen bond. The non-hydride Fe center was found to be the site of reduction for terminal hydride species and unsymmetric bridging hydride species, whereas the reduced symmetric bridging hydride species exhibited spin delocalization between the Fe centers. According to both experimental measurements and theoretical calculations of the relative pKa values, the Fed center of the neutral species is more basic than the amine, and the bridging hydride species is more thermodynamically stable than the terminal hydride species. The calculations implicate a possible pathway for H2 evolution that involves an intermediate with H2 weakly bonded to one Fe, a short H2 distance similar to the molecular bond length, the spin density delocalized over the two Fe centers, and a nearly symmetrically bridged CO ligand. Overall, this study illustrates the mechanistic roles of the ammonium-hydride interaction, flexibility of the bridging CO ligand, and intramolecular electron transfer between the Fe centers in the catalytic cycle. Such insights will assist in the design of more effective bioinspired catalysts for H2 production. Theoretical calculations in conjunction with supporting experimental data are used to analyze the mechanistic pathway for hydrogen evolution catalyzed by the bioinspired model Fe2(adt)(CO)2(dppv)2. This study elucidates the site of reduction and the pKa values associated with formation of the singly and doubly protonated species, as well as the roles of the ammonium-hydride interaction, flexibility of the bridging CO ligand, and intramolecular electron transfer between the Fe centers in the catalytic cycle for H2 production.
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DOI：
10.1039/b910147k
发表时间：
2010-03-28
期刊：
Dalton transactions (Cambridge, England : 2003)
影响因子：
--
作者：
Barton BE;Zampella G;Justice AK;De Gioia L;Rauchfuss TB;Wilson SR
通讯作者：
Wilson SR
影响因子：
3
作者：
FLORIS, F;TOMASI, J
通讯作者：
TOMASI, J
影响因子：
5.7
作者：
Fernandez, Laura E.;Horvath, Samantha;Hammes-Schiffer, Sharon
通讯作者：
Hammes-Schiffer, Sharon
影响因子：
3
作者：
FLORIS, FM;TOMASI, J;AHUIR, JLP
通讯作者：
AHUIR, JLP
影响因子：
15
作者：
Carroll, Maria E.;Barton, Bryan E.;Rauchfuss, Thomas B.;Carroll, Patrick J.
通讯作者：
Carroll, Patrick J.