Synthesizing a biomimetic model of the Mo-Cu catalytic site of carbon monoxide dehydrogenase

The carbon monoxide dehydrogenase in Oligotropha carboxidovorans is a molybdenum containing metalloenzyme that catalyzes the formation of carbon dioxide, two protons, and two electrons from carbon monoxide and water. This enzyme in soil bacteria remediates about 10-25 % of atmospheric carbon monoxide annually. However, our understanding of the CO oxidation of this enzyme is still incomplete. Previous efforts have been made to synthesize biomimetic models based on the active site of this enzyme. These efforts have yielded models that mimic portions of the catalytic site but lack both a mimicry of the entire site and catalytic activity. The reaction catalyzed by this enzyme is particularly interesting as the same reaction is used in the industrial production of hydrogen gas through the water-gas shift reaction.

Here we report on our attempt to synthesize a functional model complex based on the active site of carbon monoxide dehydrogenase from O. carboxidovorans, closely following a published procedure by Gourlay et al (Gourlay et al. 2018). Prior computational modeling by our group was used to select a ligand with appropriate steric bulk and electron density donation for the complex that could be easily modified, tris-(2-pyridylmethyl)amine (TPA or a 4 N-coordinated ligand, N₄). A prior synthesis attempt with this ligand yielded a different di-metal complex than the desired one, thus we have modified the design of the ligand in our current trials.

Two modifications of the TPA ligand were N,N-bis(mercaptoethyl)(aminomethyl)-2-pyridine (referred to as N₂S₂) and N,N-bis(2-pyridylmethyl)aminoethanethiol (referred to as N₃S). We will report our progress of the synthesis of these ligands and their complexation with molybdenum centers as well as our attempts, and thoughts on the final complexation reaction.