Biocatalysis solvent engineering

S Kamat. Biocatalysis in supercritical fluids control of enzyme activity and selectivity by solvent engineering. Diss Abstr Int B 58(3) 1405, 1996. 

Efficient biocatalysis in neat organic solvent depends on the careful choice of the method of dehydrated enzyme preparation and solvent used. Optimization of these factors towards a given transformation is often known as catalyst formulation and solvent, or medium, engineering respectively, both of which will be briefly discussed below. Catalyst engineering which also provides a powerful method of improving activity and stability, is discussed in Chapter 2. 

Further advantages of biocatalysis over chemical catalysis include shorter synthesis routes and milder reaction conditions. Enzymatic reactions are not confined to in vivo systems - many enzymes are also available as isolated compounds which catalyze reactions in water and even in organic solvents [28]. Despite these advantages, the activity and stability of most wild-type enzymes do not meet the demands of industrial processes. Fortunately, modern protein engineering methods can be used to change enzyme properties and optimize desired characteristics. In Chapter 5 we will outline these optimization methods, including site-directed mutagenesis and directed evolution. 

Whether processes include biocatalysis followed by chemistry or vice versa, it would be advantageous to match the solvent composition, pH, and process intensities of both steps. In many cases the solution of choice may be to modify the enzyme to operate most effectively under conditions that favor the chemical transformation (i.e., in an organic solvent or an aqueous-organic solvent biphasic mixture). The engineering principles governing the design of such processes are... 

Tjalsma H, Koetje EJ, Kiewiet R et al. (2004) Engineering of quotum-sensing systems for improved production of alkaline protease by Bacillus subtilis. J Appl Microbiol 96(3) 569-578 Torres S, Castro G (2004) Non-aqueous biocatalysis in homogeneous solvent systems. Food Tech-nol Biotechnol 42(4) 271-277... 

The last two decades have seen an explosion of interest in ionic liquids [1]. Their use as solvents has been the subject of widespread academic study [2] and they have been applied in a number of commercial processes [3]. Much of the interest in ionic liquids has centered on their possible use as green solvents [4]. However, this has been the subject of much controversy [5], and the concept of a green solvent itself is now somewhat dated. There have been many reviews of ionic liquids. Some of these have focused on particular applications, for example, analysis [6], biocatalysis [7], catalysis [8], electrochemical devices [9], or engineering fluids [10]. Others have concentrated on particular subgroups of ionic liquids, for example, task-specific ionic liquids [11]. This chapter summarizes what is known about the physicochemical properties that are of particular interest for supported ionic hquid phases (SILPs). 

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