Aqueous/organic two phase system

Multi-phase reactors are of interest in biocatalytic reactions if one or several components of the reaction are insoluble or insufficiently soluble in aqueous phases but if an aqueous phase has to be kept, if only for the biocatalyst. However, a two-phase system can be utilized advantageously for the shifting of an equilibrium this is demonstrated below. We analyze the simple reaction A <=> B in an organic-aqueous two-phase system with the assumption that reactant A and product B partition between the two phases. The partition coefficients Pw and Porg are de-... 

Fig. 32 Reduction of cyclohexanone catalyzed by HLADH with simultaneous hydrogenase-driven regeneration of NADH in an organic-aqueous two-phase system...

Tundo, P., and P. Venturello, Catalysis Mechanism of Phosponium Salts Supported on Silica Gel in Organic-Aqueous Two-Phase Systems, /. A/ner. Chem. Soc., 103, 856 (1981). 

A significant number of general reviews on ISPR techniques in whole cell bioprocessing have been published [1,3,14-21]. Furthermore,more specialized reviews exist that cover either a certain product category such as ethanol [4] or butanol [22,23] or the use of certain specialized ISPR techniques such as aqueous two-phase system [24,25], organic-aqueous two-phase systems [26-30],or solid adsorbents [31]. 

Once the problems of product toxicity were surmounted by sophisticated process engineering, microbial epoxidation of alkenes became also feasible on an industrial scale [1153, 1154]. The latter was achieved by using organic-aqueous two-phase systems or by evaporation for volatile epoxides. For instance, the epoxy-phosphonic acid derivative fosfomycin [1155], whose enantiospecific synthesis by classical methods would have been extremely difficult, was obtained by a microbial epoxidation of the corresponding olefinic substrate using Penicillium spinulosum. 

The addition of nucleophiles such as carbon nucleophiles to electrophiles such as unsaturated carbon-heteroatom bonds is an important reaction in organic chemistry, allowing carbon-carbon bond formation. Although these reactions are usually performed in organic or eventually in organic/aqueous two-phase system, it was recently shown that they could be performed in water alone or in a monophasic water/organic system. This development has also allowed reactions to proceed under less drastic conditions. 

Andersson, M., Hofrnberg, H., and Adlercreutz, P. (1998) Evaluation of Alcaligenes eutrophus cells as an NADH regenerating catalyst in organic-aqueous two-phase system. Biotechnol. Bioeng., 57, 79-86. 

The enantioselective reduction of alkyl 3-oxobutanoates by carbonyl reductase (SI) from C. magnoliae was also performed in organic-aqueous two-phase reaction system (Figure 8.15) [llc,d]. 

Ionic liquids are particularly applicable for use in microwave-mediated liquid-phase reactions as they efficiently couple with microwaves resulting in very rapid heating profiles (see Section 4.3.3.2). Furthermore, ionic liquids are immiscible with a wide range of organic solvents and provide an alternative non-aqueous two-phase system. An interesting approach involves the attachment of ionic liquid components to organic substrates. 

Although the general principles of separation processes are applicable widely across the process industries, more specialised techniques are now being developed. Reference is made in Chapter 13 to the use of supercritical fluids, such as carbon dioxide, for the extraction of components from naturally produced materials in the food industry, and to the applications of aqueous two-phase systems of low interfacial tensions for the separation of the products from bioreactors, many of which will be degraded by the action of harsh organic solvents. In many cases, biochemical separations may involve separation processes of up to ten stages, possibly with each utilising a different technique. Very often, differences in both physical and chemical properties are utilised. Frequently... 

Recently however, it has been recognized that liquid extraction is a potential method in the primary recovery of fermentation cell culture products, such as proteins and amino acids. The separation problem, however, is difficult because the product mixtures are often complex, including cell debris and enzymes. Proteins are not suitable for conventional solvent extraction because of incompatibility with organic solvents, but can be handled in aqueous two-phase systems or by extraction in reverse micellar systems (Chapter 15). 

Few industrially important bioprocesses are carried out exclusively in organic solvents. Two-phase systems are more common, however, consisting of a water-immiscible solvent that allows adequate dissolution of substrates and products, and an aqueous phase containing the biocatayst.20... 

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