Defining Intermediates of Nitrogenase MoFe Protein during N2 Reduction under Photochemical Electron Delivery from CdS Quantum Dots
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Univ. of Colorado, Boulder, CO (United States)
- Utah State Univ., Logan, UT (United States)
- Washington State Univ., Pullman, WA (United States)
Coupling the nitrogenase MoFe protein to light-harvesting semiconductor nanomaterials replaces the natural electron transfer complex with Fe protein and ATP and provides low potential photoexcited electrons for photocatalytic N2 reduction. A central question is how direct photochemical electron delivery from nanocrystals to MoFe protein is able to support the multi-electron 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. 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 E0 resting state intensity that was accompanied by an increase in intensity of a new “geff = 4.5” EPR signal. The magnetic properties of the geff = 4.5 signal support assignment as a reduced S = 3/2 state, and reaction modeling was used to define it as a two-electron reduced “E2” intermediate. Use of a MoFe protein variant, ß-188Cys, which poises the P cluster in the oxidized P+ state, demonstrated 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 MoFe protein during reduction of N2 to ammonia, and the role of electron flux in the photochemical reaction cycle.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
- Grant/Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1660131
- Report Number(s):
- NREL/JA-2700-77378; MainId:26324; UUID:75dc299c-6924-47b8-aacf-819e0558adad; MainAdminID:15167
- Journal Information:
- Journal of the American Chemical Society, Vol. 142, Issue 33; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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