Organic aqueous two-phase

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]. 

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...

Fig. 4 Countercurrent separation of various samples by the coil planet centrifuge, (a) Separation of basic dyes with an organic/aqueous two-phase solvent system. M.G. methyl green M.B. methylene blue N.R. neutral red F.B. basic fuchsin. (From Ref. [3].) Solvent system consisted of isoamyl alcohol/ethanol/acetic acid/water (4 2 1 5, v/v).

The enantioselective hydrolysis is carried out in an organic-aqueous two-phase reactor (toluene/water), where the phase contact is established by a hydrophilic hollow-fiber membrane (polyacrylonitrile). The lipase is immobilized onto a spongy layer by pressurized adsorption. The productivity is about 40 kg trans-(2R,3S)-(4-methoxyphenyl) glycidic acid methyl ester m-2 a-1. This process has been operated since 1993. 

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). 

It is important to make the distinction between the multiphasic catalysis concept and transfer-assisted organometaUic reactions or phase tranfer catalysis (PTC). In this latter approach, a catalytic amount of quaternary ammonium salt (Q] (X] is present in an aqueous phase. The catalyst lipophUic cation [Q] transports the reactant s anion Y to the organic phase, as an ion-pair, and the chemical reaction occurs in the organic phase of the organic/aqueous two-phase mixture [2]. 

Fig. 41 Polymer membrane formation under organic/aqueous two-phase flow in an X-shaped microchannel...

The organic phase may also be used as a substrate reservoir, besides their use for product stripping from the aqueous phase. The effectiveness of membrane-assisted organic-aqueous two-phase bioconversions relative to direct-contact two-phase emulsion reactors was demonstrated by Westgate et al. [150]. These authors observed a fivefold increase in the maximum specific activity of hydrolysis of menthyl acetate catalyzed by B. subtilis cells when a 0.2 pm nylon flat membrane reactor was used, as compared to an emulsion reactor. This result was attributed to a continuous interfacial contact, which could only be achieved in an emulsion bioreactor at the cost of high power inputs. Doig and co-workers operated a dense membrane bioreactor for the production of citronellol from geraniol with a product accumulation rate similar to the one obtained in an emulsion reactor [124]. Some examples of membrane-assisted two-liquid phase bio-conversions/fermentations are presented in Table 9. 

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]. 

Reddy V, Zahn ID (2005) Interfacial stabilization of organic aqueous two phase miraoflows for a miniaturized DNA extractirm module. J Colloid Interface Sci 286(1) 158-165... 

This type J high-speed CCC system equipped with the multilayer coil separation column can separate a variety of natural and synthetic products with high partition efficiency using organic-aqueous two-phase solvent systems. The system, however, fails to retain a satisfactory amount of stationary phase in low interfacial aqueous-aqueous polymer phase systems due to intensive emulsification. 

More recently, the effect of Coriolis force was demonstrated in the separation of organic acids with organic/aqueous two-phase solvent systems in a centrifugal partition chromatograph equipped with a separation column consisting of rectangular partition compartments connected in series.As shown in Fig. 4, clockwise column rotation (CW) shows substantially better peak resolution than... 

V. Reddy, J.D. Zahn, Interfadal stabilization of organic-aqueous two-phase microflows for a miniaturized DNA extraction module,/. Colloid Interface Sci.,... 

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. 

InoknchiT,MatsumotoT,NishiyamaT, Torii S (1990) Indirect electrooxidatirai of alcohols by a double medi-atray systems with two redox couples of [R2bF = O]/ R2NO and [Br ot Br /Br in an organic-aqueous two-phase solution. J Org Chem 56 2416—2421... 

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. 

Organic aqueous two-phase solvent systems are also widely applied for other biotransformations, for example, in hydrolase-catalyzed processes [37,49]. A typical example is the enantioselective hydrolysis of a racemic, water-immisdble ester as a substrate. The reaction yields a water-soluble carboxylic acid (in depro-tonated form as a salt). Ionic liquids have also been used in biphasic systems, a topic that is discussed in detail in Chapter 3 in this book [50]. 

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