Artificial, Photoinduced Activation of Nitrogenase Using Directed and Mediated Electron Transfer Processes

Nitrogenase, a bacteria-based enzyme, is the sole enzyme able to generate ammonia by atmospheric nitrogen fixation. Thus, improved understanding of its mechanism and developing methods to artificially activate it may contribute greatly to basic research, as well as to the design of future artificial systems. Here, we present methods to artificially activate nitrogenase using photoinduced reactions. Two nitrogenase variants originating from Azotobecotor vinelinii were examined using photoactivated CdS nanoparticles (NPs) capped with thioglycolic acid (TGA) or 2-mercaptoethanol (ME) ligands. The effect of methyl viologen (MV) as a redox mediator of hydrogen and ammonia generation was tested and analyzed. We further determined the NPs conductive band edges and their effect on nitrogenase photo-activation. The nano-bio hybrid systems comprising CdS NPs and nitrogenase were further imaged by transmission electron microscopy, confirming their formation for the first time. Our results show that the ME-capped CdS NPs–nitrogenase enzyme biohybrid system with added MV as redox mediator, leads to a five-fold increase in the production of ammonia compared with the non-mediated biohybrid system.