Biocatalysis in organic solvents

Vazquez-Duhalt, R. Fedorak, P. M., and Westlake, D. W. S., Role of Enzyme Hydrophobicity in Biocatalysis in Organic-Solvents. Enzyme and Microbial Technology, 1992. 14(10) pp. 837-841. 

Over the last twenty years, biocatalysis in organic solvents has emerged as an important area of research and has led to the widespread industrial use of enzymes. In an aqueous medium, with which enzymes are naturally associated, most substrates are poorly soluble, and this leads to low reaction rates and high reaction volumes. In addition, in water, undesired side reactions and degradation of organic compounds often occur. Also, the thermodynamic equilibrium is unfavorable and product recovery can be difficult. Working in organic solvent avoids these problems, and enzymes often show beneficial behavior in such systems [12-14]. 

The solid-to-solid approach clearly combines the good rates observed in aqueous solution, with the high yields typical of biocatalysis in organic solvents. Many successful examples of precipitation-driven reactions for the synthesis of peptides have been published in recent years (Table 12.3). 

C. S. Chen and C. J. Sih, Enantioselective biocatalysis in organic solvents. Lipase catalyzed reactions, Angew. Chem. 1989,... 

C. Laane, S. Boeren, K. Vos, and C. Veeger, Rules for optimization of biocatalysis in organic solvents, Biotechnol. Bioeng. 1987, 30, 81-87. 

Castro, G.R. and Knubovets, T. (2003) Homogeneous biocatalysis in organic solvents and water-organic mixtures. Crit. Rev. Biotechnol., 23, 195. 

Many enzymatic processes can be of practical value, if they are carried out in anhydrous media instead of water. While biocatalysis in organic solvents is well established, the use of supercritical fluids, in particular supercritical carbon dioxide (SC-CO2), is still restricted to research on laboratory scale. 

Chen, C.-S., Sih, C. J. Enantioselective biocatalysis in organic solvents with lipases. Angew. Ch. 101 711-724... 

It is generally stated that biocatalysis in organic solvents refers to those systems in which the enzymes are suspended (or, sometimes, dissolved) in neat organic solvents in the presence of enough aqueous buffer (less than 5%) to ensure enzymatic activity. However, in the case of hydrolases water is also a substrate and it might be critical to find the water activity (a ) value to which the synthetic reaction (e.g. ester formation) can be optimized. Vahvety et al. [5] found that, in some cases, the activity of Candida rugosa lipase immobihzed on different supports showed the same activity profile versus o but a different absolute rate. With hpase from Burkholderia cepacia (lipase BC), previously known as lipase from Pseudomonas cepacia, and Candida antarctica lipase B (CALB) it was found that the enzyme activity profile versus o and even more the specific activity were dependent on the way the enzyme was freeze dried or immobihzed [6, 7]. A comparison of the transesterification activity of different forms of hpase BC or CALB can be observed in Tables 5.1 and 5.2, respectively. 

Laane C, Boeren S, Vos K, and Veeger C. Rules for Optimized Biocatalysis in Organic Solvents. Biotechnol Bioeng 1987 30 81—87. 

Lee JK, Kim M-J (2002) Ionic liquid-coated enzyme for biocatalysis in organic solvent. J Org Chem 67 6845-6847... 

Wong, C. H., Enzymatic catalysts in organic synthesis. Science, 244, 1145-1152. Faber, K. and Franssen, M. C. R., Prospects for the increased application of biocatalysts in organic transformations. Trends Biotechnol., 11, 461-470, 1989. Kvittingen, L., Some aspects of biocatalysis in organic solvents. Tetrahedron, 50, 8253-8274, 1994. 

Kvittingen, L. (1994) Some Aspects of Biocatalysis in Organic-Solvents. Tetrahedron, 50 (28), 8253-8274. 

Enzymes have been used for biocatalysis in organic solvents since the early 1980s, and in ILs since 2000 [17]. As biological catalysts, enzymes accelerate reactions but do not affect the equilibrium distribution. Hence, hydrolytic enzymes that, as an example, under normal circumstances in aqueous solutions hydrolyze esters and amides, will, when placed in water-free conditions, also catalyze the reverse reaction, the condensation of an acid with an alcohol or an amine, to give esters and amides, respectively. Further, under water-free conditions hydrolytic enzymes can accept alternative nucleophiles to catalyze reactions such as transesterifications. An important industrial example of this is the lipase-catalyzed transesterification of triglycerides to obtain fats with a desired melting point [18]. 

Biocatalysis in organic solvents has unique advantages compared to traditional aqueous enzymology/fermentation. Often times in nonaqueous media enzymes exhibit properties drastically different from those displayed in aqueous buffers. These novel properties are given in Table 4.3. In addition to those mentioned in Table 4.3, the solubility of hydrophobic substrates and/or products increases in organic solvents, which diminishes diffusional barriers for bioconversions, and thus speeds up the reactions and improves the potential for direct applications in industrial chemical processes. Once organic solvent becomes a reaction medium, there cannot be contamination, which thus precludes release of proteolytic enzymes by microbes and favors the direct application of the process in an industrial setting. Most proteins (enzymes) inherently function in an aqueous environment, and hence their behavior in nonaqueous solvents is completely different due to the loss in the three-dimensional structure. Thus, only polar solvents... 

Chen, C.H. Sih, C.J. General Aspect and Optimization of Enantiose-lective Biocatalysis in Organic Solvents The Use of lipases. Ange- 20. wandte Chemie International Edition 28, 695-707 (1989). 

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