Biocatalysis reactions

However, the reactions were not enantioselective ones, though the most important aspect of the biocatalysis reaction should be in the enantioselective reaction. We and KragF independently reported the first enantioselective lipase-catalyzed reaction in February-March 2001. Since lipase was anchored by the IL solvent and remained in it after the extraction work-up of the product, we succeeded in demonstrating that recyclable use of the lipase in the [bmim][PFg] solvent system was possible (Fig. 2). ... 

Bioreactions. The use of supercritical fluids, and in particular C02, as a reaction media for enzymatic catalysis is growing. High diffusivities, low surface tensions, solubility control, low toxicity, and minimal problems with solvent residues all make SCFs attractive. In addition, other advantages for using enzymes in SCFs instead of water include reactions where water is a product, which can be driven to completion increased solubilities of hydrophobic materials increased biomolecular thermostability and the potential to integrate both the reaction and separation bioprocesses into one step (98). There have been a number of biocatalysis reactions in SCFs reported (99—101). The use of lipases shows perhaps the most commercial promise, but there are a number of issues remaining unresolved, such as solvent—enzyme interactions and the influence of the reaction environment. A potential area for increased research is the synthesis of monodisperse biopolymers in supercritical fluids (102). 

Figure 11.1 Paradigm shift in design of biocatalysis reactions (Burton, 2002).

Interestingly, this is also a good description of many (but not all) homogeneous catalysis and biocatalysis reactions. Here the reactant or the substrate first coordinates to the metal complex or to the enzyme, then a reaction occurs. Finally, the product dissociates from the catalyst and diffuses back into the solution. 

Of the various enzymes available for enzyme catalyzed organic reactions the Novozym 435 preparation of CALB has extensively been used in biocatalysis reactions, using a broad range of substrates, often combined with outstanding chemo-, regio-, and/or enantioselectivity (see also Chapters 3-5, 11 and 12) [lOd,... 

Consider the following Uni Uni biocatalysis kinetic scheme that involves two biocatalyst-substrate species intermediates that are generated prior to product formation and release (Scheme 8.15). Most of the steps involve the inter-conversions of biocatalyst-substrate or biocatalyst-product species and hence microscopic inter-conversion rates will depend only upon single-species concentrations. In other words, these inter-conversions must obey first order kinetics. Similarly, if S and E are combined under conditions where [S] [E], such that [S] is effectively unchanged during reaction, then the microscopic inter-conversion rate from E to ES will once again depend effectively only upon [E] such that this inter-conversion obeys pseudo-first-order kinetics. Accordingly, every step/inter-conversion shown in the biocatalysis reaction scheme above obeys and could be analysed by appropriate variations of Equation (8.80). 

Electrochemical genosensors for the detection of bacteria were introduced about a decade ago. Miniaturization and advanced microfabrication technology have made it compatible with bacteria DNA diagnostic. This technology is cost effective, fast, and accurate. The bioaffinity and biocatalysis reactions generate either amper-ometric, voltametric, impedimetric, or conductimetric signals on screen-printed transducer chips (SPC), which is proportional to the number of immobilized DNA copies on the SPC surface. 

Recent achievements of Baeyer-Villiger reaction in homogeneous, heterogeneous and biocatalysis reactions have been reviewed the relation between catalyst substrate and mechanism is clarified for different systems and future development of the... 

FIGURE 42 Semipreparative SFC stacked chromatogram of biocatalysis reaction sample source. Target impurity A is labeled with topmost arrow and lactol product with lower arrow. 

Biocatalysis Chemical reactions mediated by biological systems (microbial communities, whole organisms or cells, cell-free extracts, or purified enzymes aka catalytic proteins). 

The aspects of medium engineering summarized so far were a hot topic in biocatalysis research during the 1980s and 1990s [5]. Nowadays, all of them constitute a well-established methodology that is successfully employed by chemists in synthetic applications, both in academia and industry. In turn, the main research interests of medium engineering have moved toward the use of ionic liquids as reaction media and the employment of additives. 

In recent years ionic liquids have also been employed as media for reactions catalyzed both by isolated enzymes and by whole cells, and excellent reviews on this topic are already available [47]. Biocatalysis has been mainly conducted in those room-temperature ionic liquids that are composed of a 1,3-dialkylimidazolium or N-alkylpyridinium cation and a noncoordinating anion [47aj. 

Nowadays biocatalysis is a well-assessed methodology that has moved from the original status of academic curiosity to become a widely exploited technique for preparative-scale reactions, up to the point that the so-called industrial biotechnology (to which biocatalysis contributes to the most extent) is one of the three pillars of the modern sustainable chemistry. 

In the enzyme design approach, as discussed in the first part of this chapter, one attempts to utilize the mechanistic understanding of chemical reactions and enzyme structure to create a new catalyst. This approach represents a largely academic research field aiming at fundamental understanding of biocatalysis. Indeed, the invention of functional artificial enzymes can be considered to be the ultimate test for any theory on enzyme mechanisms. Most artificial enzymes, to date, do not fulfill the conditions of catalytic efficiency and price per unit necessary for industrial applications. 

To carry out the enzymatic amidation of carboxylic acids, normally two strategies are considered the use of ionic liquids or the removal of water from the reaction media at high temperature or reduced pressure. For instance, one of the first examples of the use of ionic liquids in biocatalysis has been the preparation of octanamide from octanoic acid as starting material and ammonia in the presence of CALB (Scheme 7.3) [11]. 

Since stereoselectivities of biocatalytic reductions are not always satisfactory, modification of biocatalysis are necessary for practical use. This section explains how to find, prepare, and modify the suitable biocatalysts, how to recycle the coenzyme, and how to improve productivity and enantioselectivity of the reactions. 

Biocatalysis refers to catalysis by enzymes. The enzyme may be introduced into the reaction in a purified isolated form or as a whole-cell micro-organism. Enzymes are highly complex proteins, typically made up of 100 to 400 amino acid units. The catalytic properties of an enzyme depend on the actual sequence of amino acids, which also determines its three-dimensional structure. In this respect the location of cysteine groups is particularly important since these form stable disulfide linkages, which hold the structure in place. This three-dimensional structure, whilst not directly involved in the catalysis, plays an important role by holding the active site or sites on the enzyme in the correct orientation to act as a catalyst. Some important aspects of enzyme catalysis, relevant to green chemistry, are summarized in Table 4.3. 

Previously, we have shown that functional secretion of OPH molecules into the periplasmic space induced about 2.8-fold higher specific whole cell OPH activity [10]. From the detail reaction kinetic studies in this work, we showed that this periplasmic space-secretion strategy provided much improved bioconversion capability and efficiency ( 1.8-fold) for Paraoxon as a model organophosphate compound. From these results, we confirmed that Tat-driven periplasmic secretion of OPH can be successfully employed to develop a whole cell biocatalysis system with notable enhanced bioconversion efficiency and capability for environmental toxic organophosphates. 

The use of ionic liquids (ILs) to replace organic or aqueous solvents in biocatalysis processes has recently gained much attention and great progress has been accomplished in this area lipase-catalyzed reactions in an IL solvent system have now been established and several examples of biotransformation in this novel reaction medium have also been reported. Recent developments in the application of ILs as solvents in enzymatic reactions are reviewed. 

Important topics in biocatalysis for organic synthesis are described in this book, for experts and non-experts. Especially, the book focuses on those reactions that are under development now and will be more significant in the future. Therefore, each chapter describing a specific theme summarizes not only the present state but also the direction of the research. The prospects and dreams that will become possible, using biocatalysis, in the future to construct a sustainable society are also included. 

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