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Title: Bioinspired, heterogeneous amino acid complexes for benign oxidation catalysis
Author: Dzierzak, Joanna
ISNI:       0000 0004 2715 881X
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2011
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Metalloenzymes catalyse the most fundamental reactions in organic chemistry from oxidation of hydrocarbons to complex C-C bond forming reactions with exceptional selectivity. Mimicking the active site of a metalloenzyme by immobilising well-defined amino acids containing catalytically active transition metal centres based on transitionmetals on a robust inorganic framework, affords powerful catalysts that can be utilised in oxidation reactions. Porous aluminosilicates, mesoporous silicas and polymers offer suitable supports for single-site bio-derived catalysts. Dispersion of catalytically active centers within porous solids with high surface area improves site-isolation which is essential in catalytic processes. These materials can be created from a range of methodologies and the different strategies used for immobilisation can greatly affect the nature of the active catalyst. The routes by which these catalysts are immobilised have given the potential to derivatize inorganic porous hosts and organic polymer structures with amino acids for complexation to metal centres. These bio-derivatized frameworks offer advantages over the homogeneous counterparts in terms of easy separation, recover and recyclability and can carry out selective oxidation reactions with great effectiveness. Herein, heterogenous bioinspired complexes of two amino acids; proline and valine with a series of transition metals (Fe, Cu) were synthesised and immobilised within zeolite cages, mesoporous silica MCM-41 and polystyrene. The preparation methods allowed the synthesis of materials with varying loadings of immobilized active sites. The structural information obtained by spectral and elemental analysis suggested tetrahedral geometry for iron complexes and distorted square planar geometry for copper complexes. Both amino acids coordinated to metal ions through the nitrogen atom of amino group and oxygen atom of carboxylate group via dissociation of the acidic proton as bidentate N,O-donors. The resulting biomimetic complexes were employed as catalysts for oxidation of cyclohexane, cyclohexene, benzyl alcohol and dimethyl sulfide, using molecular dioxygen (O2), tert-butyl hydroperoxide (TBHP) and acetylperoxyborate (APB) as oxidants. The observed trends in catalytic activity showed that the metal loading and separation of the active sites played key role in the selective oxidation reactions. By decreasing the loading of metal active centres, their spatial separation increased which strongly enhanced the activity of catalysts. The decrease in metal active site content resulted in significant increase in TON and TOF. The product selectivity was dependent on the nature of oxidant, hydrophobicity/hydrophilicity of the support, loading of metal active centres and the metal/substrate ratio.
Supervisor: Raja, Robert ; Stulz, Eugen Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry