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Published byJoanna Martin Modified over 8 years ago
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The Molybdenum Cofactor: Moco What early experiments indicated: … but it wasn’t entirely correct.
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Now we know that there is not just one Moco, but a family of related Moco structures in molybdenum enzymes:
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Questions asked of molybdoenzymes and their model compounds: -What is the redox potential ( energy of) Mo redox reactions? - What are the structural details? What is bond order? (angles, bond distances) -How well do models mimic reactions of Mo in enzymes? in structure? in reactivity?
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A “second generation” Moco model: the Holm-Berg model
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Mimicking the Catalytic Reactions of Moco Berg-Holm Model Sulfite Oxidase
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What would the Berg-Holm model system suggest? a 2 e- process between Mo(6+) and Mo(4+), and only the Mo(6+) and Mo(4+) ox. states are required. BUT, it was known that Mo(5+) plays a role (by EPR)
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A proposed mechanism for Moco Catalysis of Sulfite Oxidation: OAT and CEPT
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Why such a BIG Ligand on Mo?
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Mo(5+)- Mo(5+) dimer CN = 6 Terminal vs bridging Mo-O Step 1: Step 2:
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BIG Ligand is intended to prevent dimerization Except… it didn’t!!! Later researchers showed formation of
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Technique: Infrared Spectroscopy Application to Berg-Holm model and Mo-dimer: detection of Mo=O groups number of absorption related to number Mo=O frequency related to Mo oxidation state frequency also reveals Mo-O-Mo
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Technique: Column Chromatography Review: chromatographic separations are based on: dipolar interaction of molecules with solid support (SiO 2 ) partitioning of molecule between support and solvent In practice: Silica gel column chromatography elutes most non-polar first, most polar last. Different species may be selectively eluted with increasing the polarity of solvents, e.g., CH 2 Cl 2, then acetone, then methanol
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This week’s reactions: 1.MoO 2 (detc) 2 + excess PPh 3 --> RED 2.RED + propylene sulfide --> BLUE 3.Chromatography to separate:
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What is the sulfur donor ligand for the family of related Moco structures in molybdenum enzymes?
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Mo The Ligand is called Molybdopterin pterin dithiolene nucleotide
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