Molybdenum-containing enzymes are present in all forms of life and are involved in the redox-based metabolism of oxygen, sulfur, and nitrogen. In molybdoenzymes except for nitrogenases, the catalytic center is a metal-binding pyranopterin ene-1,2-dithiolate cofactor referred to as the molybdenum cofactor (Moco). The Burgmayer group has synthesized a model complex Tp*Mo(X)S2BMOPP [Tp* = tris(pyrazolyl)hydroborate; X = O, S; BMOPP = 2-pivaloyl-6-(3-hydroxy-3-methylbutyne)pterin). In order to more accurately reproduce the cofactor, further research has been performed into the hydolysis of the molybdenum center from sulfido to oxo. Reductions have been performed on the pterin ring proximal to the molybdenum using a variety of borohydride salts. Spectroscopic data (UV-Vis, IR, and ESI-MS) indicate that attempts using potassium borohydride have successfully converted the dihydro form to the reduced tetrahydro form.Preliminary reactivity studies of the reduced tetrahydro form in various solvents have demonstrated differences in reactivity. While the tetrahydro Moco model exists in the Mo(IV) state, UV/Vis analysis of the oxidation in air over time in MeOH has shown transition to the dihydro Mo(V) state, whereas oxidation in air over time in ACN has shown transition to the dihydro Mo(IV) state.Past studies by the Burgmayer group has shown that there may be reversible ring-cleavage of the pyran ring of the dihydro Tp*Mo(O)S2BMOPP structure. The percentage of �ring-closed� versus �ring-open� is dependent on solvent, with nonpolar solvents such as chloroform showing almost 100% �ring-open,� and most solvents showing some �ring-open,� and some �ring-closed.� The differences in reactivity of the tetrahydro model further demonstrates possible structural and electronic differences depending on solvents, which has many implications for biological regulation of Moco.This undergraduate research was funded by Bryn Mawr College.

Molybdenum pyranopterin dithiolene complexes: Synthesis, reduction, and reactivity of molybdenum cofactor models??????????

247th National Meeting (2014)

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