Synthesis and Characterization of Molybdenum Tetrasulfide Complexes and Pterinyl Alkyne

Posted July 26th, 2011 at 5:16 pm.

Abstract: Suyin Lee

Mentor: Dr. Sharon Burgmayer

The molybdenum co-factor (Moco) forms the active site of redox reactions in all eukaryotic molybdenum enzymes such as nitrogenase, nitrate reductases, sulfite oxidase and zanthin oxidoreductases. Two different systems, molybdopterin (Figure 1) and iron-molybdenum co-factor have been found to control redox and catalytic functions of molybdenum which serves as an efficient catalyst in electron-transfer reactions.

Figure 1. Molybdopterin

The pterin group in Moco positions the catalytic molybdenum atom within the active center to control redox behavior and electron transfer to or from the Mo atom. Over 50 different pterin-containing molybdenum enzymes are known and classified on the basis of the coordination chemistry of molybdenum in their active site. The core structure of a pterin-based molybdenum cofactor consists of a 6 carbon substituted pyrano ring, a terminal phosphate and a unique dithiolate group coordinating to a molybdenum atom.

The Burgmayer group developed a successful pathway to synthesize and characterize Mo complexes particularly containing the pterinyl-dithiolene ligand where molybdenum is in both Mo(4+) and Mo(5+) oxidation states. The synthesis of molybdopterin derives from two pathways, Pathway I producing molybdenum tetrasulfide reagents (Figure 1) and Pathway II producing pterin-substituted alkynes (Figure 2).

Pathway I

KTp* [TEA][Tp*Mo(CO)3] [TEA][Tp*Mo(S)S4]

Figure 2. The synthesis of tetrasulfide occurs in two steps

Pathway II

pterin-8-oxide 2-pivaloyl-6-chloropterin BMOPP

Figure 3. The synthesis of the pterinyl alkyne, BMOPP.

The objective of this research is to synthesize tetrasulfide reagents and a dimethylated pterinyl alkyne, TEA[Tp*MoIV(S)S4] and BMOPP respectively required for the synthesis of molybdopterin. With successful and efficient experimental methodologies previously conducted by the Burgmayer lab, this research focuses on the development of a more efficient larger-scaled production of pure molybdenum tetrasulfide and BMOPP reagents. Characterization methods commonly used in this research include electrospray ionization mass spectrometry, infrared spectroscopy and NMR.

Filed under: 2011,Burgmayer, Dr. Sharon,Lee, Suyin by Michelle Han

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