Biocatalysis oxidizing enzymes

Enzymes from plants have been used since andent times, even though their nature remained obscure until the nineteenth century. Malting of cereals and the hydrolysis of complex polysaccharides are two of the oldest uses of enzymes in human history. Like their animal counterparts, most commerdally available plant-derived enzymes are hydrolases, particularly lipases and proteases. Papain, a cysteine protease from papaya, is the best-known plant-derived hydrolytic enzyme. Bromelain from pineapple and ficain from fig latex are similar cysteine proteases that have also found applications in biocatalysis. Horseradish peroxidase is a versatile oxidative enzyme obtained from its namesake that oxidizes many organic compounds, especially phenols. Hydroxynitrile lyase (often called oxynitrilase) from bitter almond is one of the most important plant-derived... 

The oxidation of heteroatoms and, in particular, the conversion of sulfides to asymmetric sulfoxides has continued to be a highly active field in biocatalysis. In particular, the diverse biotransformations at sulfur have received the majority of attention in the area of enzyme-mediated heteroatom oxidation. This is particularly due to the versatile applicability of sulfoxides as chiral auxiliaries in a variety of transformations coupled with facile protocols for the ultimate removal [187]. 

Membranes can be used as a matrix for immobilization of a catalyst. Four basic types of catalysts are relevant (a) enzymes and (b) whole cells for biocatalysis (c) oxides and (d) metals for nonbiological synthesis. Biocatalysts will be considered first since their immobilization in (or on) the membrane was explored much earlier. Five techniques have been studied in varying degrees. They are (1) enzyme contained in the spongy fiber matrix ... 

There is huge potential in the combination of biocatalysis and electrochemistry through reaction engineering as the linker. An example is a continuous electrochemical enzyme membrane reactor that showed a total turnover number of 260 000 for the enantioselective peroxidase catalyzed oxidation of a thioether into its sulfone by in situ cathodic generated hydrogen peroxide - much higher than achieved by conventional methods [52],... 

Mechanisms of Biological Oxidation and Implications for Multi-Enzyme Biocatalysis... 

The goal of this review is to highlight a progress in the transition-metal chemistry of some enzymes that catalyze oxidative and reductive reactions. These enzymes are referred to as oxidoreductases (1,2) and transition metals are usually found in their active sites. However, the discussion will not be devoted to these metals, which are absolutely essential for biocatalysis. Such information is brilliantly summarized in several recent fundamental reviews and monographs (3-9). 

In some cases, substrates and enzymes are not soluble in the same solvent. To achieve efficient substrate conversion, a large interface between the immiscible fluids has to be established, by the formation of microemulsions or multiple-phase flow that can be conveniently obtained in microfluidic devices. Until now only a couple of examples are published in which a two-phase flow is used for biocatalysis. Goto and coworkers [431] were first to study an enzymatic reaction in a two-phase flow in a microfluidic device, in which the oxidation ofp-chlorophenol by the enzyme laccase (lignin peroxidase) was analyzed (Scheme 4.106). The surface-active enzyme was solubilized in a succinic acid aqueous buffer and the substrate (p-chlorophenol) was dissolved in isooctane. The transformation ofp-chlorophenol occurred mainly at... 

When comparing chemical and biocatalytic methods, one could say that, especially for asymmetric oxidations, enzymatic methods enter the scene. This is most evident in the area of asymmetric Baeyer-Villiger oxidation, where biocatalysts take the lead and homogeneous chiral catalysts lag far behind in terms of ee values. Significant progress can be expected in the area of biocatalysis due to the advancement in enzyme production technologies and the possibility of tailor-made enzymes. 

Epoxide formation using biocatalysis is a useful process for the formation of chiral oxiranes (Scheme 29). The synthesis of enantioenriched epoxides using enzymes has been reviewed <1995BCSF769>. Chloroperoxidase has been examined for the oxidation of 2-methyl-l-alkenes, among other alkenes. The yields in some cases can be low, but the enantioselectivities can be high <1995JA6412, 1997JA443>. This enzyme has been used in a synthesis of... 

In MET, the thermodynamic redox potentials of the enzyme and the mediator should be accurately matched. The tuning of these potentials is of critical importance to EFC design as this will have a major bearing on cell voltage and catalytic current. When compared to the redox potential of the enzyme, the mediator should have a redox potential that is more positive for oxidative biocatalysis (at anode) and more negative for reductive biocatalysis (at cathode). For efficient electron transfer. 

Enzyme Catalysis Exploiting Biocatalysis and Aerobic Oxidations for High-Volume and High-Value Pharmaceutical Syntheses... 

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