Biphasic biocatalysis

In systems used in biphasic biocatalysis, maximum interfacial area is observed for a volume fraction of the organic phase close to that observed for phase inversion, which occurs within a 0.4 to 0.7 range. Extreme values of the volume fraction of the organic phase, under 0.1 or over 0.9 should also be avoided, since phase separation is poor and makes product recovery difficult. 

The combination of ILs and SCCO2 as a reaction medium has also attracted the attention of the biocatalysis community. In an interesting study the new concept of continuous biphasic biocatalysis was described. A homogeneous enzyme solution was immobilized in one liquid phase and the substrates and products resided largely... 

Biocatalysis in Liquid-Liquid Biphasic Media Coupled Mass Transfer and Chemical Reactions... 

In 1982, Lilly [21] reviewed the first two-liquid phase biocatalysis. In 1987 and 1992, Lilly s group [39,40] published reviews dealing with process engineering of biphasic bioreactors. In 1993, Van Sonsbeek et al. [41] gave an overview on biocatalysis in different biphasic... 

In a biphasic medium, two situations are distinguished for the reaction. Biocatalysis occurs at the liquid-liquid interface [42,43] or in the bulk of the aqueous phase [25,27]. Models have been developed for both types, and interaction between mass transfer and enzyme-catalyzed reactions has been also studied. 

Biocatalysis localization in the biphasic medium depends on physicochemical properties of the reactants. When all the chemical species involved in the reaction are hydro-phobic, catalysis occurs at the liquid-liquid interface. However, when the substrate is hydrophobic (initially dissolved in the apolar phase) and the product is hydrophilic (remains in the aqueous phase), the reaction occurs in the aqueous phase [25]. The majority of biphasic systems use sparingly water-soluble substrates and yield hydrophobic products therefore, the aqueous phase serves as a biocatalyst container [34,35] [Fig. 2(a)]. Nevertheless, in some systems, one of the reactants (substrate or product) can be soluble in the aqueous phase [23,36-38] (Fig. 2(b), (c)). 

The present section deals with the improvement in the performance of biocatalysis when carried out in organic-aqueous biphasic systems. Such systems are very useful in equilibrium reactions and conversion yield where substrates and products can be dissolved and drawn into different phases. Subsequently the synthesis in the reactive aqueous phase is allowed to continue. 

As proven in this review and other papers, organic-aqueous biphasic media have been useful in many areas of biocatalysis applications. We summarize the potential advantages in carrying out biocatalysis in biphasic systems ... 

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. ... 

Part Three Biocatalysis in Biphasic and New Reaction Media... 

Biocatalysis in Biphasic Systems General Table 8.1 Some recent examples of biphasic systems in biocatalysis. 

Most studies of biocatalysis in ionic liquids have been concerned with the use of isolated enzymes. It should not be overlooked, however, that the first report on biocatalysis and ionic liquids involved a whole-cell preparation Rhodococcus R312 in a biphasic [BMIm][PF(s]-water system [7]. It was shown, using a nitrile hydrolysis test reaction, that the microorganism maintained its activity better in ionic liquid than in a biphasic toluene-water system. 

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