Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States.
Department of Chemistry, University of Colorado-Boulder, Boulder, Colorado 80309, United States.
J Am Chem Soc. 2020 Aug 19;142(33):14324-14330. doi: 10.1021/jacs.0c06343. Epub 2020 Aug 5.
Coupling the nitrogenase MoFe protein to light-harvesting semiconductor nanomaterials replaces the natural electron transfer complex of Fe protein and ATP and provides low-potential photoexcited electrons for photocatalytic N reduction. A central question is how direct photochemical electron delivery from nanocrystals to MoFe protein is able to support the multielectron ammonia production reaction. In this study, low photon flux conditions were used to identify the initial reaction intermediates of CdS quantum dot (QD):MoFe protein nitrogenase complexes under photochemical activation using EPR. Illumination of CdS QD:MoFe protein complexes led to redox changes in the MoFe protein active site FeMo-co observed as the gradual decline in the E resting state intensity that was accompanied by an increase in the intensity of a new " = 4.5" EPR signal. The magnetic properties of the = 4.5 signal support assignment as a reduced = 3/2 state, and reaction modeling was used to define it as a two-electron-reduced "E" intermediate. Use of a MoFe protein variant, β-188, which poises the P cluster in the oxidized P state, demonstrated that the P cluster can function as a site of photoexcited electron delivery from CdS to MoFe protein. Overall, the results establish the initial steps for how photoexcited CdS delivers electrons into the MoFe protein during reduction of N to ammonia and the role of electron flux in the photochemical reaction cycle.
将固氮酶 MoFe 蛋白与光收集半导体纳米材料偶联取代了 Fe 蛋白和 ATP 的天然电子转移复合物，并为光催化 N 还原提供了低势能光激发电子。一个核心问题是，纳米晶体直接向 MoFe 蛋白的光化学电子传递如何能够支持多电子氨生产反应。在这项研究中，使用电子顺磁共振 (EPR) 在光化学激活下，使用低光通量条件来鉴定 CdS 量子点 (QD)：MoFe 蛋白氮酶复合物的初始反应中间体。CdS QD：MoFe 蛋白复合物的光照导致 MoFe 蛋白活性位点 FeMo-co 中的氧化还原变化，表现为 E 静止状态强度的逐渐下降，同时伴随着新的“= 4.5”EPR 信号强度的增加。“= 4.5”信号的磁性质支持其被分配为还原的“= 3/2”状态，并且反应建模用于将其定义为两个电子还原的“E”中间态。使用 MoFe 蛋白变体β-188 的实验证明，该变体使 P 簇处于氧化的 P 态，P 簇可以作为光激发电子从 CdS 向 MoFe 蛋白传递的位点。总体而言，这些结果确定了光激发 CdS 在将电子还原为氨的过程中如何进入 MoFe 蛋白的初始步骤，以及电子通量在光化学反应循环中的作用。
