Biphasic solvent

Lin and coworkers disclosed that, at room temperature, nonenzymatic chemical addition was still observed in a water-organic solvent biphasic reaction system, though the volume of aqueous phases was relative small. Lin developed a method of preparing an active enzyme meal that contained essential water to retain its power for catalysis and found a new catalytic reaction system by application of the prepared meal in a nonaqueous monophasic organic medium (Figure 5.7). There was no problem over a wide range of temperature (from 0-30 °C) when the reactions were carried out under micro-aqueous conditions [50]. 

Figure 5.7 Comparison of a water-organic solvent biphasic system with a micro-aqueous organic phase system...

Li, Y.-N., Shi, X.-A., Zong, M.-H. et al. (2007) Asymmetric reduction of 2-octanone in water/organic solvent biphasic system with baker s yeast FD-12. Enzyme and Microbial Technology, 40, 1305-1311. 

Renewed interest in this method came recently from its adaptation to the immobilization of water/ organic solvent biphasic catalysts, resulting in the so-called supported aqueous phase catalysts (SAPCs).117 The molecular catalyst is immobilized via water, which is hydrogen bonded to the surface silanol groups reactants and products are in the organic phase (Figure 11)... 

The team of Crooks is involved in the synthesis and the use of dendrimers and, more particularly, poly(amidoamine) dendrimers (PAMAM), for the preparation of dendrimer-encapsulated mono- or bimetallic nanoparticles of various metals (Pt, Pd, Cu, Au, Ag, Ni, etc.) [55, 56]. The dendrimers were used as nanocatalysts for the hydrogenation of allyl alcohol and N-isopropylacrylamide or other alkenes under different reaction conditions (water, organic solvents, biphasic fluorous/or-ganic solvents or supercritical COz). The hydrogenation reaction rate is dependent on dendrimer generation, as higher-generation dendrimers are more sterically... 

Figure 18 Ligands for hydroformylation in ionic liquid/organic solvent biphasic system.

Water and water-miscible solvent biphasic systems Enhanced enzyme activity and stability at low concentration Inhibitory effect on the biocatalyst at high concentration... 

Organic solvent systems include mixtures of water and water-miscible solvents, biphasic systems of water and water-immiscible solvents, pure organic solvents, and reverse micellar systems. 

One method is to run the reaction in an aqueous buffer/organic solvent biphasic system. This makes it possible to work at high substrate and product concentrations and at the pH-optimum of the enzyme. In addition, in water-immiscible solvents the non-enzymahc addition of HCN to the carbonyl group is non-existent or extremely slow. Possible disadvantages are enzyme deactivation at the interface and the presence of organic solvent dissolved in the aqueous phase [15, 17, 18]. 

Chen C-S, Wu S-H et al (1987) Quantitative analyses of biochemical kinetic resolution of enantiomers. 2. Enzyme-catalyzed esterifications in water-organic solvent biphasic systems. J Am Chem Soc 109 2812-2817... 

Catalysts immobilized on resins are quite often used for catalytic reactions. Phase-transfer conditions, guaranteeing separation and recovery of the catalysts by use of water/organic solvent biphasic systems, are another possibility. Unlike homogeneous processes, these kind of catalytic processes take account of product loss and substrate selectivity. Furthermore,... 

Whether processes include biocatalysis followed by chemistry or vice versa, it would be advantageous to match the solvent composition, pH, and process intensities of both steps. In many cases the solution of choice may be to modify the enzyme to operate most effectively under conditions that favor the chemical transformation (i.e., in an organic solvent or an aqueous-organic solvent biphasic mixture). The engineering principles governing the design of such processes are... 

Silylation of MTS surface Firstly, the wall of preformed MTS is functionalized by the covalent linkage of organic moieties carried out by silylation of the surface with alkyl trialkoxysilane in anhydrous conditions in apolar solvent (biphasic conditions). 

Biphasic systems proved to be advantageous as well in the biocatalytic synthesis of (-)-l-trimethylsilylethanol which was performed by asymmetric reduction of acetyltrimethylsilane with an isolate from Rhodotorula sp. AS2.2241 [144]. Immobilized cells were employed due to the easy separation of the product as well as the improved tolerance against unfavorable factors. In an aqueous/organic solvent biphasic system higher product yield and enantiomeric excess were achieved as compared to an aqueous monophasic system. Several organic solvents were examined, and isooctane was found to be the most suitable organic phase for the reaction. 

It would appear that some more fundamental improvements are required to make metathesis in ionic liquids sufficiently attractive rather than extracting the product, which commonly requires a large amount of conventional solvent, biphasic systems that allow decantation of the product ought to be envisaged. As metathesis reactions are often performed at elevated temperatures, ionic liquids with higher melting points could also be considered to optimise and facilitate product separation. 

Partitioning of Solutes in Water-Organic Solvent Biphasic Systems.. . 180... 

Numerous efforts 38,40,42 46 51) were undertaken to find out in what manner the aqueous solubility and the partition coefficients of different solutes in water-organic solvent biphasic systems are related to the size of the solute molecules. Since the solute packing into the solvent clearly depends on the solute surface, a relationship between surface area and solution thermodynamics seems to be reasonable. 

Since the first of the above limitations can be bypassed with an approach based on the study of partitioning of solutes in water-organic solvent biphasic systems, most of the hydrophobicity estimates for chemical compounds have been obtained by this method. 

It is known I0.43.53 ° -62> that the partition coefficients of the same solutes in various solvent biphasic systems are interrelated according to the so-called solvent regression equation ... 

The kinetics of the water-organic-solvent biphasic reaction of PhCH2Br, Na [Co(CO)4]-, [Bu4N] C1", and CO to give [PhCH2COCo(CO)4] have been analyzed in terms of reactions (49) and (50), which occur in the organic phase. 

He, J., Sim, Z Ruan, W., and Xu, Y. (2006) Biocatalytic synthesis of ethyl (S)-4-chloro-3-hydroxy-butanoate in an aqueous-organic solvent biphasic system using Aureobasidium pullulans CGMCC 1244. Process Biochem., 41 (1), 244-249. 

Fragnelli, M.C., Hoyos, P., Romano, D., Gandolfi, R., Alcantara, A.R., and Molinari, F. (2012) Enantioselective reduction and deracemisation using the non-conventional yeast Pichia ucozyma in water/organic solvent biphasic systems preparation of (S)-l,2-diaryl-2-hydroxyethanones (benzoins). Tetrahedron, 68, 523-528. 

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