Molybdenum (Mo) enzymes are required by almost every form of life and can be traced back to the first organism, the ‘last universal common ancestor’, or LUCA. Mo enzymes have been linked to multiple human diseases, proper plant development, and is crucial to the global cycling of the elements nitrogen and sulfur. The molybdenum cofactor (Moco), composed of a molybdenum metal center and one or two pterin-dithiolene ligands, is the name of the active site in all molybdenum enzymes. Because Moco is unstable without its protein blanket, information about the role of the unusual pterin-dithiolene chelate is largely not available. To obtain some information regarding the chemical behavior of Mo bound to a pterin-dithiolene, the Burgmayer lab has synthesized a model system similar in structure to the biological Moco in order to explore the importance of the pterin, which is believed to play a role in the redox chemistry conducted by the cofactor. The work to be presented includes a description of the general synthesis of the pterin-dithiolene model system as well as two current investigations. The target model system is generally described as [TEA][Tp*Mo(X)(S2C2(pterin)(-C(CH3)2R)], where TEA is tetraethylammonium, Tp* is tris(3,5-dimethylpyrazolyl)hydroborate, X is either O or S, and R can be hydroxyl, methyl or methoxy. Current work is directed at developing the reaction chemistry of the model complex where R = OH which has previously been shown to undergo a reversible pyran cyclization. The first investigation studies the reactivity of the pyranopterin-dithiolene Mo complex upon protonation in the pyrazine ring. The protonated Mo-pterin-dithiolene model is redox reactive and readily participates in coupled proton-electron transfer with a variety of substrates. The second investigation explores the outcome of reacting the pyranopterin-dithiolene Mo complex with (PPh3I)+I- where initial spectroscopic results indicate a significant change in the electronic structure of the pterin-dithiolene.

Making a model for the molybdenum cofactor and investigating its reaction chemistry

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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