Our latest work on pyranopterin molybdenum enzymes focuses on understanding electronic structure contributions to substrate oxidation and reduction, as well as how the Mo center is coupled into long-range superexchange pathways for electron transfer regeneration of the active site.  First, we present our studies on the unique pyranopterin dithiolene ligand, which is comprised of a dithiolene, a pyran ring, and a heterocyclic pterin ring system fused to the pyran ring.  Roles suggested for the pyranopterin dithiolene in catalysis include acting as an electronic conduit to couple the Mo ion with other electron transfer centers in the protein, and modulating the Mo reduction potential.  We will show our latest spectroscopic and bonding studies that detail how the pyranopterin is involved in electron transfer.  This includes a remarkable study that shows the redox state of the pyranopterin affects its ability to display either �wire-like� or �diode� behavior, supporting a complex and flexible electronic structure of the pyranopterin dithiolene that underscores its critical role in enzyme function.  Second, we will present our most recent work on the mechanism of CO oxidation to CO2 by the Mo-Cu carbon monoxide dehydrogenase (CODH).  Analysis of both the frontier molecular orbitals and natural bond orbitals provides new insight into the CODH mechanism and reveals electronic structure contributions to reactivity that are remarkably similar to the structurally related molybdenum hydroxylases, which catalyse the oxidation of N-heterocyclic and aldehyde substrates. A calculated reaction barrier is in agreement with the experimental activation energy determined from kinetic studies on CODH.

Spectroscopic and electronic structure studies of reactivity in pyranopterin molybdenum enzymes

248th National Meeting (2014)

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