The selective oxidation of CH3OH to HCHO over supported vanadium oxide catalysts has emerged as the model system for gas phase oxidation reactions over oxide catalysts in recent years because the structure-activity relationship for this catalytic system is becoming fairly well understood due to recent extensive fundamental characterization and theoretical studies. Selective oxidation reactions with supported vanadium oxide catalysts in aqueous media, however, are problematic because hydrolysis of the bridging V-O-Support bonds. In order to circumvent this issue, inorganic-organic vanadium complexes are typically employed as oxidation catalysts in aqueous media. For example, the human enzyme vanadium haloperoxidase (VHPO), an insulin mimic that lowers glucose levels in blood, is an excellent aqueous oxidation biocatalyst. Thus, there is currently an excellent research opportunity to bridge the oxidation catalysis fields of gas-solids over inorganic supported vanadium oxide catalysts and V-complexes/V-enzymes in aqueous media by using CH3OH oxidation as a redox 2 electron chemical probe molecule.
Intellectual Merit. The objectives of this proposed research are to (1) establish effective characterization methods and approaches for the study vanadium oxide catalysts in the aqueous phase in the presence of HOOH and CH3OH environments with time-resolved in situ and operando spectroscopy studies in the millisecond to minutes time scale (Raman, UV-vis, 51V NMR, EPR, rapid scan ATR-IR and quick-XANES/EXAFS), (2) extend the in situ and operando spectroscopic characterization methodologies to aqueous vanadium haloperoxidase and its functional organic mimics in HOOH and CH3OH environments, (3) apply the advanced methodologies to study the VOx structures, oxidation states, reaction intermediates, mechanism, and kinetics of homogeneous vanadium haloperoxidase as a biocatalyst for the aqueous phase oxidation of methanol, (4) develop an effective method to "heterogenize" vanadium haloperoxidase by anchoring the enzyme onto a solid support, (5) examine the catalytic effect of a rich aqueous electron environment (to be imposed by an electric current) on catalytic activity of homogeneous as well as immobilized vanadium haloperoxidase, and (6) examine the effect of site directed mutagenesis (genetic engineering) on the VHPO catalytic activity.
Broader Impact. The proposed research program would extend the previous gas-solid CH3OH oxidation catalysis studies to liquid phase oxidation of CH3OH and also bridge inorganic catalysis with aqueous bioinorganic catalysis of enzymes. The development of time-resolved in situ and operando spectroscopic methodologies for investigating aqueous phase catalysis of inorganic and bioinorganic catalysts will be significantly advanced by this undertaking and will have wide reaching implications for numerous aqueous phase catalytic applications. Application of time-resolved in situ or operando spectroscopic approaches to enzyme catalysis and methanol oxidation by vanadium haloperoxidases is essentially nonexistent and, therefore, much is still not known about the fundamentals of these reactions (mechanism, kinetics, reaction intermediates, structural rearrangements, etc.). An outcome of the proposed research program will be the development of a faster, more efficient, selective biocatalyst for oxidation reactions and a thorough fundamental understanding of the mechanism and functionality of characteristic amino acid residues (ligands) necessary for enzyme biocatalytic activity. Vanadium haloperoxidase may provide a "green" alternative to traditional inorganic catalysts currently used in oxidation reactions and the new fundamental insights may assist in the development of improved pharmaceuticals, therapeutics, and management of diabetes. The versatile nature of vanadium haloperoxidase catalysis may also lead to biocatalytic improvements in multiple industrial applications.
Vanadium enzyme mimics are being medically investigated for treating humans with diabetes (type 2) and the objective of the research is to obtain a fundamental molecular level understanding of the reduction-oxidation (redox) mechanism of vanadium enzyme mimics. Cutting edge spectroscopic characterization techniques were applied to monitor the redox cycle of aqueous vanadium enzyme mimics in real time during oxidative dehydrogenation of an alcohol molecule (methanol chemical probe molecule). The research successfully determined the fundamental molecular level reaction steps involved in the redox mechanism of oxidative dehydrogenation of vanadium enzyme mimics. In addition, the research extended characterization techniques typically employed for gas-solid heteroegeneous catalysis to aqueous phase vanadium enzyme mimics. Dissemination of research findings were made via technical presentations, class lectures and journal publications. The informational resources generated about vanadium enzyme mimics for methanol oxidation can be used by others in their research and educational training. The participating graduate student was a female (Ms. Julie Molinari). Ms. Molinari participated in Lehigh's CHOICES program for local middle school girls, which exposed the middle school females to her research program on vanadium enzyme mimics and their medical applications for type 2 diabetes. Ms. Molinari also had a positive international experiences when she visited our collaborator in Turkey. The international experience allowed her to compare her experimental findings with the theoretcial calculations performed by our collaborator in Turkey. The research and educational skills of Ms. Molinari have positively developed during the course of this research project.
