Book chapter on sulfur oxygenation and functional models of NHase

Chapter 12 in the book “Bioinspired Catalysis”

Authors: Davinder Kumar and Craig A. Grapperhaus

This chapter highlights selected complexes with tetra- and penta-dentate chelates that provide key insights into the oxidized sulfur environment at the enzyme active site. Small-molecule mimics with variable S-oxidation levels provide an attractive method to address these interactions. It discusses a brief history of metal-thiolate sulfur-oxygenation is provided, followed by selected S-oxygenation studies relevant to nitrile hydratase (NHase). The NHase are divided by metal type and organized according to the donor atoms of the chelates. Several ruthenium catalysts have been reported as nitrile hydration catalysts. Ruthenium is also a logical choice for oxidation studies as the second-row transition metal maintains a consistent low spin, which was found to promote S-oxygenation.

Sequential Oxidations of Thiolates and the Cobalt Metallocenter in a Synthetic Metallopeptide: Implications for the Biosynthesis of Nitrile Hydratase

This is a paper in Inorganic Chemistry from the group of Anne K Jones looking at the use of a heptapeptide they call SODA (ACDLPCG) to model the oxidation process for the thiols and metal in the active site of cobalt centre NHases (DOI: 10.1021/ic400171z). First to oxidize is one of the thiolates to sulfinate, then the cobalt is oxidized to triply charged cobalt. Further sulphur oxidation is not observed and the complex is catalytically inactive. This complex does not have an axial thiolate ligand which may explain these last two obervations.