Enemark Group HomePage Publications Curriculum Vitae Send eMail Telephone: (520) 621-2245 FAX: (520) 621-8407 jenemark@u.arizona.edu

This research program involves comparative studies of synthetic molybdenum compounds and molybdenum-containing enzymes, such as sulfite oxidase, in an effort to understand the structure and function of the oxo-molybdenum centers in these enzymes. The research includes synthesis of new compounds and the characterization of compounds and enzymes by X-ray structure determination and a wide variety of spectroscopies including: CW- and pulsed EPR, UV/vis, magnetic circular dichroism (MCD), resonance Raman, heteronuclear NMR, K- and L-edge X-ray absorption spectroscopy, and photoelectron (PES) spectroscopy.

I. Models for Pterin-Containing Molybdenum Enzymes.

Particular emphasis is being given to compounds that contain both an oxo-molybdenum center and an iron porphyrin center as models for the essential enzyme sulfite oxidase. The weak coupling between the Mo(V) and low-spin Fe(III) centers is being probed by both NMR and EPR spectroscopy.

II. Chemical and Spectroscopic Studies of Sulfite Oxidase.

Sulfite oxidase is an essential pterin-containing molybdenum enzyme that possesses an oxo-molybdenum center and a b-type cytochrome in a single polypeptide chain. The structure of the enzyme has recently been determined by X-ray crystallography. Intramolecular electron transfer between the two prosthetic groups is being studied by laser flash photolysis. The structure of the molybdenum center and its interaction with the b-type heme center are being probed by multiple frequency pulsed EPR spectroscopy.

III. Metal-Sulfur Covalency.

Metal-sulfur bonds play an important role in many biological and industrial catalysts. We are investigating the covalency of Mo-S bonds by EPR spectroscopy, gas phase photoelectron spectroscopy, and X-ray absorption spectroscopy. These studies suggest that under appropriate conditions, Mo-S bonds function as an "electronic buffer" to oxidation state changes at the metal center.

Selected Publications

"Electronic Spectral Studies of Molybdenyl Complexes: Implications for Oxo-Molybdenum Enzymes," Carducci, M.D.; Brown, C.; Solomon, E.I.; Enemark, J.H. J. Am. Chem. Soc. 1994, 116, 11856-11868.

"NMR Studies of Hindered Ligand Rotation, Magnetic Anisotropy, Curie Behavior, Proton Spin Relaxation, and Ligand Exchange in Some Novel Oxomolybdenum(V)/Iron(III) Porphyrinate Complexes," Basu, P.; Shokhirev, N.V.; Enemark, J.H.; Walker, F.A. J. Am. Chem. Soc. 1995, 117, 9042-9055.

"EPR Studies of Oxo-Mo(V) Complexes with Sulfur Donor Ligands: Implications for the Molybdenum Center of Sulfite Oxidase," Dhwan, I.K.; Enemark, J.H. Inorg. Chem. 1996, 35, 4873-4882.

"Multifrequency ESEEM Spectroscopy of Sulfite Oxidase in Phosphate Buffer: Direct Evidence for Coordinated Phosphate," Pacheco, A.; Basu, P.; Borbat, P.; Raitsimring, A.M.; Enemark, J.H. Inorg. Chem. 1996, 35, 7001-7008.

"Oxomolybdenum(V)/-Iron(III) Porphyrinate Complexes: The Effect of Axial Ligand Plane Orientation on Complex Stability, Reduction Potential, NMR and EPR Spectra," Basu, P.; Raitsimring, A.M.; Enemark, J.H.; Walker, F.A. Inorg. Chem. 1997, 36, 1088-1094.

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