Ionic Liquid-based Biphasic Systems Research Articles

A general method for the separation of amphiphilic surface-active poly(ethylene glycol) mono- and di-esters with long-chain ionic liquid-based biphasic systems

A new method for the effective separation of amphiphilic poly(ethylene glycol) mono- and di-esters with long-chain ionic liquid-based biphasic systems has been developed. These biphasic systems exhibited high selectivity, a large distribution coefficient and a good ability to eliminate the emulsification resulting from the surface active character of those amphiphilic molecules.

Efficient anti-Prelog enantioselective reduction of acetyltrimethylsilane to (R)-1-trimethylsilylethanol by immobilized Candida parapsilosis CCTCC M203011 cells in ionic liquid-based biphasic systems.

BackgroundBiocatalytic asymmetric reductions with whole cells can offer high enantioselectivity, environmentally benign processes and energy-effective operations and thus are of great interest. The application of whole cell-mediated bioreduction is often restricted if substrate and product have low water solubility and/or high toxicity to the biocatalyst. Many studies have shown that a biphasic system is often useful in this instance. Hence, we developed efficient biphasic reaction systems with biocompatible water-immiscible ionic liquids (ILs), to improve the biocatalytic anti-Prelog enantioselective reduction of acetyltrimethylsilane (ATMS) to (R)-1-trimethylsilylethanol {(R)-1-TMSE}, which is key synthon for a large number of silicon-containing drugs, using immobilized Candida parapsilosis CCTCC M203011 cells as the biocatalyst.ResultsIt was found that the substrate ATMS and the product 1-TMSE exerted pronounced toxicity to immobilized Candida parapsilosis CCTCC M203011 cells. The biocompatible water-immiscible ILs can be applied as a substrate reservoir and in situ extractant for the product, thus greatly enhancing the efficiency of the biocatalytic process and the operational stability of the cells as compared to the IL-free aqueous system. Various ILs exerted significant but different effects on the bioreduction and the performances of biocatalysts were closely related to the kinds and combination of cation and anion of ILs. Among all the water-immiscible ILs investigated, the best results were observed in 1-butyl-3-methylimidazolium hexafluorophosphate (C4mim·PF6)/buffer biphasic system. Furthermore, it was shown that the optimum substrate concentration, volume ratio of buffer to IL, buffer pH, reaction temperature and shaking rate for the bioreduction were 120 mM, 8/1 (v/v), 6.0, 30°C and 180 r/min, respectively. Under these optimized conditions, the initial reaction rate, the maximum yield and the product e.e. were 8.1 μmol/min gcwm, 98.6% and >99%, respectively. The efficient whole-cell biocatalytic process was shown to be feasible on a 450-mL scale. Moreover, the immobilized cells remained around 87% of their initial activity even after being used repeatedly for 8 batches in the C4mim·PF6/buffer biphasic system, exhibiting excellent operational stability.ConclusionsFor the first time, we have successfully utilized immobilized Candida parapsilosis CCTCC M203011 cells, for efficiently catalyzing anti-Prelog enantioselective reduction of ATMS to enantiopure (R)-1-TMSE in the C4mim·PF6/buffer biphasic system. The substantially improved biocatalytic process appears to be effective and competitive on a preparative scale.

Separation of poly- and disaccharides by biphasic systems based on ionic liquids

In this work, separation of poly- and disaccharides is achieved by means of novel biphasic systems based on ionic liquids as alternative to the volatile organic compounds used in large amounts for precipitation of the polysaccharides produced from disaccharides in microbial culture broths. Xanthan and maltose are employed to represent a charged (anionic) polysaccharide and a neutral disaccharide. For the separation, two kinds of systems are applied, a specially designed biphasic system of water/1-hexyl-3-methylimidazolium tetrafluoroborate ([C6mim][BF4]), and an aqueous biphasic system of 3-methyl-1-octylimidazolium chloride/K2HPO4. In the system of [C6mim][BF4] the effects of the alcohol (isopropyl), added as modifier, and of the temperature on the system volume partitioning and separation are investigated. Recycling and reuse of the [C6mim][BF4] are shown. In both ionic liquid-based systems, complete isolation with simultaneous concentration of the polysaccharide in the upper phase of the system is obtained, and 80% of the initial disaccharide is retained in the lower phase. The mechanism of the polysaccharide transfer is revealed in terms of the possible interactions of the xanthan polyanion with the imidazolium cations assisted by the polymer dehydration caused under the addition of isopropyl alcohol or kosmotropic K2HPO4. Drawbacks of the ionic liquid-based biphasic systems are also discussed.

High performance separation of sparingly aqua-/lipo-soluble bioactive compounds with an ionic liquid-based biphasic system

Separation of high value bioactive compounds is a viable route to make full use of the biomass resources and improve the profitability. However, the sparing aqua- and lipo-solubility of the bioactive compounds makes their separation really challenging. Considering that ionic liquids show good solubility of biomass and could easily form biphasic systems with organic solvents, an ionic liquid (IL)-based biphasic system consisting of ionic liquid, water and ethyl acetate is proposed in this study. Ginkgolide homologues were selected as model compounds to evaluate its practicality. Adequate distribution coefficients, relatively high extraction capacity and selectivity were obtained with the novel biphasic system. The improved distribution coefficients of the ginkgolides are mainly attributed to the multiple interactions between ginkgolide and IL, which were confirmed by means of quantum chemistry calculations. Moreover, the effect of the interactions between ginkgolides and the extraction solvent on the selectivity coefficient was studied by measuring the Kamlet–Taft parameters of the extraction solvent. Based on the results of fractional extraction, which was simulated by calculation and validated by experiments, as well as the comparison of organic solvent consumption, the employed IL-based extraction would be a valid and clean method as an alternative to chromatographic methods for separating bioactive compounds in large-scale operations. It is noteworthy that the amount of organic solvents consumed with this method was supposed to be less than 1/11 of the most widely used chromatographic method.

Efficient asymmetric hydrolysis of styrene oxide catalyzed by Mung bean epoxide hydrolases in ionic liquid-based biphasic systems

The asymmetric hydrolysis of styrene oxide to (R)-1-phenyl-1,2-ethanediol using Mung bean epoxide hydrolases was, for the first time, successfully conducted in an ionic liquid (IL)-containing biphasic system. Compared to aqueous monophasic system, IL-based biphasic systems could not only dissolve the substrate, but also effectively inhibit the non-enzymatic hydrolysis, and therefore markedly improve the reaction efficiency. Of all the tested ILs, the best results were observed in the biphasic system containing C4MIM·PF6, which exhibited good biocompatibility with the enzyme and was an excellent solvent for the substrate. In the C4MIM·PF6/buffer biphasic system, it was found that the optimal volume ratio of IL to buffer, reaction temperature, buffer pH and substrate concentration were 1/6, 35°C, 6.5 and 100mM, respectively, under which the initial reaction rate, the yield and the product e.e. were 18.4mM/h, 49.4% and 97.0%. The biocatalytic process was shown to be feasible on a 500-mL preparative scale.