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Nitrogenase Bioelectrocatalysis: ATP-Independent Ammonia Production Using a Redox Polymer/MoFe Protein System

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journal contribution
posted on 05.06.2020 by Yoo Seok Lee, Mengwei Yuan, Rong Cai, Koun Lim, Shelley D. Minteer
Nitrogenase is the only biological catalyst that is known to be able to convert nitrogen gas to ammonia. In microorganisms, the MoFe catalytic protein of nitrogenase is reduced by a transient Fe protein binding and separate hydrolysis of ATP. However, the requirement of 16 ATP molecules by the Fe protein for the 8 electron transfer is an energy-intense caveat to the enzymatic synthesis of NH3 and is challenging from an electrochemical perspective. Thus, we report the redox polymer-based ATP-free mediated electron-transfer system of MoFe nitrogenase using cobaltocene-functionalized poly­(allylamine) (Cc-PAA), which is able to reduce the MoFe nitrogenase directly with a low redox potential of −0.58 V vs SHE. An efficient immobilization of MoFe nitrogenase via Cc-PAA allowed for the bioelectrocatalytic reduction of N3, NO2, and N2 to NH3. Bulk bioelectrosynthetic experiments produced 7 ± 2 and 30 ± 5 nmol of NH3 from NO2 and N3 reduction for 30 min, respectively. In addition, biosynthetic N2 reduction to NH3 was confirmed by 15N2 labeling experiments with NMR analysis. This mediated electron-transfer approach of the immobilized nitrogenase using the Cc-PAA redox polymer provides a valuable technological basis for scale-up and industrial uses in the future of bioelectrosynthesis.