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Nitrogenase Bioelectrochemistry for Synthesis Applications.
Accounts of Chemical Research ( IF 16.4 ) Pub Date : 2019-12-04 , DOI: 10.1021/acs.accounts.9b00494
Ross D Milton 1 , Shelley D Minteer 2
Affiliation  

The fixation of atmospheric dinitrogen to ammonia by industrial technologies (such as the Haber Bosch process) has revolutionized humankind. In contrast to industrial technologies, a single enzyme is known for its ability to reduce or "fix" dinitrogen: nitrogenase. Nitrogenase is a complex oxidoreductase enzymatic system that includes a catalytic protein (where dinitrogen is reduced) and an electron-transferring reductase protein (termed the Fe protein) that delivers the electrons necessary for dinitrogen fixation. The catalytic protein most commonly contains a FeMo cofactor (called the MoFe protein), but it can also contain a VFe or FeFe cofactor. Besides their ability to fix dinitrogen to ammonia, these nitrogenases can also reduce substrates such as carbon dioxide to formate. Interestingly, the VFE nitrogenase can also form carbon-carbon bonds. The vast majority of research surrounding nitrogenase employs the Fe protein to transfer electrons, which is also associated with the rate-limiting step of nitrogenase catalysis and also requires the hydrolysis of adenosine triphosphate. Thus, there is significant interest in artificially transferring electrons to the catalytic nitrogenase proteins. In this Account, we review nitrogenase electrocatalysis whereby electrons are delivered to nitrogenase from electrodes. We first describe the use of an electron mediator (cobaltocene) to transfer electrons from electrodes to the MoFe protein. The reduction of protons to molecular hydrogen was realized, in addition to azide and nitrite reduction to ammonia. Bypassing the rate-limiting step within the Fe protein, we also describe how this approach was used to interrogate the rate-limiting step of the MoFe protein: metal-hydride protonolysis at the FeMo-co. This Account next reviews the use of cobaltocene to mediate electron transfer to the VFe protein, where the reduction of carbon dioxide and the formation of carbon-carbon bonds (yielding the formation of ethene and propene) was realized. This approach also found success in mediating electron transfer to the FeFe catalytic protein, which exhibited improved carbon dioxide reduction in comparison to the MoFe protein. In the final example of mediated electron transfer to the catalytic protein, this Account also reviews recent work where the coupling of infrared spectroscopy with electrochemistry enabled the potential-dependent binding of carbon monoxide to the FeMo-co to be studied. As an alternative to mediated electron transfer, recent work that has sought to transfer electrons to the catalytic proteins in the absence of electron mediators (by direct electron transfer) is also reviewed. This approach has subsequently enabled a thermodynamic landscape to be proposed for the cofactors of the catalytic proteins. Finally, this Account also describes nitrogenase electrocatalysis whereby electrons are first transferred from an electrode to the Fe protein, before being transferred to the MoFe protein alongside the hydrolysis of adenosine triphosphate. In this way, increased quantities of ammonia can be electrocatalytically produced from dinitrogen fixation. We discuss how this has led to the further upgrade of electrocatalytically produced ammonia, in combination with additional enzymes (diaphorase, alanine dehydrogenase, and transaminase), to selective production of chiral amine intermediates for pharmaceuticals. This Account concludes by discussing current and future research challenges in the field of electrocatalytic nitrogen fixation by nitrogenase.

中文翻译:

用于合成应用的固氮酶生物电化学。

通过工业技术(例如Haber Bosch工艺)将大气中的二氧化氮固定为氨,已经彻底改变了人类。与工业技术相反,已知一种酶具有还原或“固定”二氮:固氮酶的能力。氮酶是一种复杂的氧化还原酶系统,包括催化蛋白(其中的二氮被还原)和电子传递还原酶蛋白(称为Fe蛋白),该蛋白传递固氮所需的电子。催化蛋白最通常包含FeMo辅助因子(称为MoFe蛋白),但也可以包含VFe或FeFe辅助因子。除了将二氮固定为氨的能力外,这些固氮酶还可以将底物(例如二氧化碳)还原为甲酸盐。有趣的是,VFE固氮酶也可以形成碳-碳键。围绕固氮酶的绝大多数研究都使用铁蛋白来转移电子,这也与固氮酶催化的限速步骤有关,还需要三磷酸腺苷的水解。因此,人们对将电子人工转移到催化固氮酶蛋白有很大的兴趣。在此帐户中,我们回顾了固氮酶的电催化作用,其中电子从电极传递至固氮酶。我们首先描述使用电子介体(钴茂)将电子从电极转移到MoFe蛋白。除了将叠氮化物和亚硝酸盐还原为氨以外,还实现了将质子还原为分子氢。绕开铁蛋白内的限速步骤,我们还描述了该方法如何用于讯问MoFe蛋白质的限速步骤:FeMo-co处的金属氢化物质子水解。该帐户接下来回顾了使用钴茂介导电子转移到VFe蛋白的过程,在那里实现了二氧化碳的还原和碳-碳键的形成(促进了乙烯和丙烯的形成)。这种方法还成功地介导了向FeFe催化蛋白的电子转移,与MoFe蛋白相比,FeFe催化蛋白表现出了更好的二氧化碳减少。在介导的电子转移到催化蛋白的最后一个例子中,该帐户还回顾了最近的工作,其中红外光谱与电化学的结合使一氧化碳与FeMo-co的电势依赖性结合得以研究。作为介导的电子转移的替代方法,还综述了最近的研究,该研究试图在不存在电子介体的情况下(通过直接电子转移)将电子转移至催化蛋白。该方法随后使得能够为催化蛋白的辅因子提出热力学领域。最后,该文献还描述了固氮酶的电催化作用,其中电子首先从电极转移到Fe蛋白,然后再与三磷酸腺苷水解一起转移到MoFe蛋白。以这种方式,可以通过二氮固定来电催化地产生增加量的氨。我们将讨论这如何导致电催化产生的氨与其他酶(黄递酶,丙氨酸脱氢酶,和转氨酶),以选择性生产用于药物的手性胺中间体。本文通过讨论目前和将来通过固氮酶固定电催化固氮领域中的研究挑战作为总结。
更新日期:2019-12-05
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