Oxidizing biocatalysis

Nevertheless, for the production of the flavour-active aromatic alcohol derivatives, such as the corresponding aldehydes and acids, metabolic engineering approaches have to compete with conventional oxidative biocatalysis starting from the natural alcohol as a substrate. For instance, the whole-cell oxidation system based on Pichia pastor is AOX already described in Sect. 23.4.1.2 can also be used to convert benzyl alcohol to benzaldehyde in aqueous media although product inhibition restricted the final product concentration to about 5 g L h indicating the need for aqueous-organic two-phase reaction media [51]. Phenylacetalde-... 

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. 

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]. 

S. H. Stanley, H. Dalton (1992) The biotransformation of propylene to propylene oxide by Methylococcus capsulatus (Bath) 1. Optimization of rates. Biocatalysis, 6 163-175... 

In each of these areas the relative merits of biocatalysis versus other catalytic methodologies will be assessed. Note that the text is given an asterisk ( ) when mention is made of a catalyst for a reduction or oxidation reaction that is featured in the later experimental section of this book. 

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],... 

Figure 15.13 Biocatalysis for the oxidation of n-octane to 1-octanol at 10,000 tons/year.

Given the wide utility of biocatalysis in the fine chemical industry, why is there such an in-house reliance on classical methods of enantioseparation In fact, why is biocatalysis not applied more generally as a replacement for atom-inefficient or hazardous reactions that are intensively used in the pharmaceutical industry, such as amidation, reduction and oxidation ... 

Biological fuel cells have a long history in the literature,but in recent years, they have come to prominence as more conventional fuel cell technologies have approached mass-market acceptance. Driving the recent ascendance of biofuel cells are the aspects of biocatalysis that are unmatched by conventional low-temperature oxidation—reduction catalysts, namely, activity at near-room temperatures and neutral pH and, more importantly, selective catalytic activity. 

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

Oxidoreductases, which catalyze oxidation-reduction reactions and are acting, for example, on aldehyde or keto groups. An important application is the synthesis of chiral molecules, especially chiral PFCs (22 out of 38 chiral products produced on large industrial scale are already made using biocatalysis). 

Catalysis in reaction systems with undissolved substrates and products is not restricted to biocatalysis. High yields in sobd-state synthesis, sohd-to-sohd reactions, and solvent-free systems have also been reported for aldol condensation, Baeyer-Villiger oxidation, oxidative coupling of naphthols, and condensation of amines and aldehydes [1, 2]. 

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). 

Ryu. K.. D.R. Stafford, and J.S. Dordick Peroxidase-Catalyzed Polymerization of Phenols Kinetics of p-Cresol Oxidation in Organic Media, in Biocatalysis in Agncultural Biotechnology, J.R. Whitake, ed. ACS Symp. Ser. No. 389. 

Franssen MCR (1994) Halogenation and Oxidation Reactions with Haloperoxidases. Biocatalysis 10 87... 

Matsuda T, Yamanaka R et al (2009) Recent progress in biocatalysis for asymmetric oxidation and reduction. Tetrahedron Asymmetry 20 513-557... 

Combining whole-cell biocatalysis and radical polymerization, researchers at Imperial Chemical Industries (ICI) published a chemoenzymatic route to high-molecular-weight poly(phenylene) [86], This polymer is used in the fibers and coatings industry. However, since it is practically insoluble, the challenge was to make a soluble polymer precursor that could first be coated or spun, and only then converted to poly(phenylene). The ICI process starts from benzene, which is oxidized by Pseudomonas putida cells to cyclohexa-3,5-diene-l,2-diol (see Figure 5.17). The... 

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