The Molybdenum Cofactor: Moco. What early experiments indicated:. … but it wasn’t entirely correct. Now we know that there is not just one Moco, but a family of related Moco structures in molybdenum enzymes:. Questions asked of molybdoenzymes and their model compounds:. - PowerPoint PPT Presentation
Text of The Molybdenum Cofactor: Moco
The Molybdenum Cofactor: MocoWhat early experiments indicated: but it wasnt entirely correct.
Now we know that there is not just one Moco, but a family of related Moco structures in molybdenum enzymes:
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?
A second generation Moco model:the Holm-Berg model
Mimicking the Catalytic Reactions of Moco
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)
A proposed mechanism for Moco Catalysis of Sulfite Oxidation: OAT and CEPT
Technique: Infrared SpectroscopyApplication 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
Technique: Column ChromatographyReview: chromatographic separations are based on: dipolar interaction of molecules with solid support (SiO2) partitioning of molecule between support and solventIn 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., CH2Cl2, then acetone, then methanol
This weeks reactions:MoO2(detc)2 + excess PPh3 --> RED
RED + propylene sulfide --> BLUE
Chromatography to separate:
What is the sulfur donor ligand for the family of related Moco structures in molybdenum enzymes?