Nonconventional media

Most nonconventional media used for bioreaction consist of more than one distinct phase. The organic phase can be used as nonpolar fluid, which acts as a reservoir for one or many reactants. It is generally a continuous phase. The other phase contains the biocatalyst and is generally the site for the reaction. This relatively polar phase is continuous or dispersed in the organic phase. 

One of the most interesting research fields in biocatalysis is the study of biocatalyst denaturation and stabilization in the reaction environment. In nonconventional media,... 

Another environmental issue is the use of organic solvents. The use of chlorinated hydrocarbons, for example, has been severely curtailed. In fact, so many of the solvents favored by organic chemists are now on the black list that the whole question of solvents requires rethinking. The best solvent is no solvent, and if a solvent (diluent) is needed, then water has a lot to recommend it. This provides a golden opportunity for biocatalysis, since the replacement of classic chemical methods in organic solvents by enzymatic procedures in water at ambient temperature and pressure can provide substantial environmental and economic benefits. Similarly, there is a marked trend toward the application of organometal-lic catalysis in aqueous biphasic systems and other nonconventional media, such as fluorous biphasic, supercritical carbon dioxide and ionic liquids. ... 

Enzyme catalysis in nonconventional media can be divided into a number of different categories depending on whether the aqueous and organic phases are miscible or immiscible and whether the biocatalyst is dissolved or not. In this section, only free enzymes will be considered. Thus, the field can be simplified to just two categories, depending on whether the solvent is water miscible or immiscible (systems employing water-immiscible solvents, where water is present in quantities that are below its solubility limit, have been considered as monophasic) ... 

For some recent reviews on the use of enzymes in nonconventional media, see (a) Dreyer, S., Lembrecht, J., Schumacher, J. and Kragl, U., Enzyme catalysis in nonaqueous media past, present, and future in biocatalysis in the pharmaceutical and biotechnology industries, 2007, CRC Press, pp. 791-827 . (b) Torres, S. and Castro, G.R., Non-aqueous biocatalysis in homogeneous solvent systems. Food Technol. BiotechnoL, 2004, 42, 271-277 (c) Carrea, G. and Riva, S., Properties and synthetic applications of enzymes in organic solvent. Angew. Chem. Int. Ed., 2000, 39, 2226-2254. 

Hailing, P.J., Thermodynamic predictions for biocatalysis in nonconventional media theory, tests, and recommendations for experimental design and analysis. Enzyme Microb. TechnoL, 1994,16, 178-206. 

P. Nikolova and O. P. Ward, Whole cell biocatalysis in nonconventional media,... 

Chiral Catalyst Immobilization Using Nonconventional Media... 

However, the use of nonaqueous solvents as reaction media for enzyme-catalyzed reactions is not always an easy task. Enzymes, as catalysts of living systems, may easily disrupt their folded three-dimensional (3-D) structure outside the natural aqueous environment, resulting in full deactivation. Water is the key component in all nonconventional media because of the importance that enzyme-water interactions have in maintaining the active conformation of enzymes [5]. 

Yanlong Gu et al. [109] summarized recent results of a multicomponent reaction obtained in nonconventional media including water, ILs, polyethylene glycol, and bio-based solvents. Wang et al. [110] have recently reported a three-component reaction in IL (Scheme 7.8). 

Krishna SH (2002) Developments and trends in enzyme catalysis in nonconventional media. Biotechnol Adv 20 239-267... 

Hailing, P. J. 1994. Thermodynamic Predictions for Biocatalysis in Nonconventional Media Theory, Tests, and Recommendations for Experimental Design and Analysis. Enzyme and Microbial Technology 16 (3) 178-206. 

In this chapter, latest advancements in solvent engineering in bioreductions and greener needs for bioreaction media have been discussed in depth with recent examples. Solvents for bioreductions may be categorized as (i) aqueous (ii) water/water-miscible (monophasic aqueous-organic system) (iii) water/ water-immiscible (biphasic aqueous-organic system) (iv) nonaqueous (mono-phasic organic system, including solvent-free system) and (v) nonconventional media (e.g., ionic liquids, supercritical fluids, gas-phase media, and reverse micelles). 

Imidazohum-based ILs were used as nonconventional media in alcohol dehydrogenase (ADH)-catalyzed reactions in enzymatic catalysis. When containing up to 50% of the IL, the overall conversion could be improved in some cases, while the stereoselectivity of the enzyme remained unaltered. 

SchOin 1 Enzyme-catalyzed reactions in nonconventional media. 

Operation Compatible with a range of media Operable in aqueous, mixed, low-water, and anhydrous liquid media, and with gaseous substrates. Few applications in nonconventional media... 

A Marty, JS Gondoret, D Combes. Fatty acid esterification in supercritical carbon dioxide. In Tramper et al., eds. Biocatalysis in Nonconventional Media, Vol. 8. New York, Elsevier, 1992, pp 425-432. 

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