Cytochrome c nitrite reductase (CcNiR) is a multi-heme enzyme that catalyzes the six-electron, eight-proton reduction of nitrite to ammonium as part of the global nitrogen cycle. In this talk, the activity of iron and cobalt electrocatalysts that mimic the activity of CcNiR will be described. One is a small cobalt-peptide complex (CoGGH) that catalyzes the complete reduction of nitrite to ammonium with an onset potential of -0.65 V vsv Ag/AgCl (1 M KCl) at pH 7.2. CoGGH also catalyzes the reduction of proposed intermediates nitric oxide and hydroxylamine to ammonium. The second catalyst is an iron complex featuring a macrocyclic redox-active ligand (FeN5H2) that catalyzes nitrite reduction with an onset potential of -0.90 V to form hydroxylamine; FeN5H2 forms ammonium by catalyzing disproportionation of hydroxylamine. FeN5H2 is notable for being an iron catalyst active toward nitrite reduction near neutral pH. Progress toward understanding mechanism and the effects of catalyst modifications on activity will be described.

Electrocataytic nitrite reduction to hydroxylamine and ammonium in neutral water

ACS Spring Meeting 2021

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