Epoxidation hydrophobic molecules

Chloroperoxidase (CPO) is a very versatile enzyme capable of carrying out a number of reactions including epoxidation (1,2), sulfoxidation, alcohol oxidation, N-dealkylation, (3) and hydroxylation in the presence of a suitable reductant (4-7). Most of these hydrophobic molecules require the use of an organic solvent in the reaction medium to enhance solubility. However, the enzyme has very low activity in organic solvents (8), reducing its potential for industrial application. 

Peters et al. [143] used a valine-based chiral selector as the template molecule to prepare monolithic capillaries. These capillaries were used to successfully separate enantiomers of N-(3,5-dinitrobenzoyl)leucine. However, they found that the hydrophobicity of the monomers had a direct effect on the resolution and efficiency of the capillaries. The peaks tailed drastically due to reverse-phase interactions between the enantiomers and the monolith. They found that increasing the hydrophilicity of the monolith by the hydrolysis of the epoxide functionalities of the glycidyl methacrylate moieties resulted in a much more efficient separation. 

As an example. Table 6.2 compares the performance of Ti-MCM-41 [9] with a mesoporous silica-grafted Ti and a microporous Ti silicalite (TS-1) for propene epoxidation with EBHP. With TS-1, the pore diameter is 5.5 A, which imposes restrictions and limits the size of the molecules to be oxidized the diffusion of the oxidant is inhibited, and hence the conversion attained is less than with the mesoporous materials. The difference between the mesoporous catalyst and TS-1 is even greater when the epoxidation of propene is carried out with CHP. The affinity for propene is increased by conferring hydrophobic properties to the surface, by means of silylation. 

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