Elucidating the Role of Tetraethylammonium in the Silicate Condensation Reaction from Ab Initio Molecular Dynamics Simulations.

The understanding of the formation of silicate oligomers in the initial stage of zeolite synthesis is important. The use of organic structure-directing agents (OSDAs) is known to be a key factor in the formation of different silicate species and the final zeolite structure. For example, tetraethylammonium ion (TEA+) is a commonly used organic template for zeolite synthesis. In this study, ab initio molecular dynamics (AIMD) simulation is used to provide an understanding of the role of TEA+ in the formation of various silicate oligomers, ranging from dimer to 4-ring. Calculated free-energy profiles of the reaction pathways show that the formation of a 4-ring structure has the highest energy barrier (97 kJ/mol). The formation of smaller oligomers such as dimer, trimer, and 3-ring has lower activation barriers. The TEA+ ion plays an important role in regulating the predominant species in solution via its coordination with silicate structures during the condensation process. The kinetics and thermodynamics of the oligomerization reaction indicate a more favorable formation of the 3-ring over the 4-ring structure. The results from AIMD simulations are in line with the experimental observation that TEA+ favors the 3-ring and double 3-ring in solution. The results of this study imply that the role of OSDAs is not only important for the host-guest interaction but also crucial for controlling the reactivity of different silicate oligomers during the initial stage of zeolite formation.

Whole-Cell Biocatalysis in Ionic Liquids.

The use of whole-cell biocatalysis in ionic liquid (IL)-containing systems has attracted increasing attention in recent years. Compared to bioreactions catalyzed by isolated enzymes, the major advantage of using whole cells in biocatalytic processes is that the cells provide a natural intracellular environment for the enzymes to function with in situ cofactor regeneration. To date, the applications of whole-cell biocatalysis in IL-containing systems have focused on the production of valuable compounds, mainly through reduction, oxidation, hydrolysis, and transesterification reactions. The interaction mechanisms between the ILs and biocatalysts in whole-cell biocatalysis offer the possibility to effectively integrate ILs with biotransformation. This chapter discusses these interaction mechanisms between ILs and whole-cell catalysts. In addition, examples of whole-cell catalyzed reactions with ILs will also be discussed. Graphical Abstract.

Separation characteristics of hydrophilic ionic liquids from ionic liquids-water solution by ultrasonic atomization.

Ionic liquids (ILs) have attracted much attention as promising alternatives for volatile organic solvents. Although the applications of ILs have been found in a diverse range of fields, there are a limited number of methods for the recovery of ILs so far. As an efficient separation method, therefore, ultrasonic atomization has been attempted to recover hydrophilic ILs, [Bmim][BF4], from ILs-water solution. In order to examine the separation characteristics of hydrophilic ILs-water solution, ultrasonic atomization of hydrophilic ILs-water solution was performed under various operating conditions such as initial ILs concentration, ultrasonic electric power, carrier gas flow rate, and operating temperature. The result showed that hydrophilic ILs recovery yield increased with a decrease in ultrasonic electric power, gas velocity, and temperature. As an increase in initial ILs concentration, however, higher ILs recovery yield was obtained. After 6 h of ultrasonic atomization of 50% (v/v) [Bmim][BF4]-water solution, 93.4% of initial ILs amount was recovered without any changes in their structure at ultrasonic power of 10 W, carrier gas flow of 5 L/min and temperature of 20 °C. It demonstrated that ultrasonic atomization could be used for the recovery of ILs from ILs-aqueous solution.

Enhanced lipase-catalyzed synthesis of sugar fatty acid esters using supersaturated sugar solution in ionic liquids.

A solvent-mediated method (SMM) was used to prepare supersaturated sugar solutions in hydrophobic and mixture of hydrophilic/hydrophobic ionic liquids (ILs), namely, [Bmim][Tf2N] and [Bmim][TfO]/[Bmim][Tf2N], respectively. In this method, sugars were first solubilized in a mixture of organic solvent and water (i.e. methanol:water, 1:1 v/v), and then added to [Bmim][Tf2N] and/or [Bmim][TfO]/[Bmim][Tf2N] mixture. Supersaturated sugar solution in ILs were obtained by removing organic solvents and water under vacuum evaporation. Sugar solubilities in ILs, especially in hydrophobic IL ([Bmim][Tf2N]) and in [Bmim][TfO]/[Bmim][Tf2N] mixture prepared by SMM were greater than in ILs prepared using water-mediated method (WMM), which suggested methanol aided sugar solvation in hydrophobic media. In addition, interactions between glucose molecules and between glucose and methanol, water, and IL were investigated by all-atom molecular dynamics (MD) simulation. The MD simulation results showed that initial water and water/methanol molecules around glucose were gradually replaced by IL anions. Notably, SMM resulted in stronger interaction between IL anions and glucose than WMM, which was attributed to greater solubility of sugar in ILs prepared by SMM. Resultantly, the productivity of lipase-catalyzed production of glucose laurate using supersaturated glucose solution in [Bmim][TfO]/[Bmim][Tf2N] mixture prepared by SMM was at least 1.76-fold greater than that obtained in IL mixture prepared by WMM.

Aspergillus niger whole-cell catalyzed synthesis of caffeic acid phenethyl ester in ionic liquids.

Synthesis of caffeic acid ester essentially requires an efficient esterification process to produce various kinds of medicinally important ester derivatives. In the present study, a comprehensive and comparative analysis of whole-cell catalyzed caffeic acid esters production in ionic liquids (ILs) media was performed. Olive oil induced mycelial mass of halotolerant Aspergillus niger (A.niger) EXF 4321 was freeze dried and used as a catalyst. To ensure maximum solubilization of caffeic acid for highest substrate loading several ILs were screened and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf2N]) was found to have the maximum solubility and favoured for enzymatic activity of freeze dried mycelia. The whole-cell catalyzed synthesis of caffeic acid phenethyl ester (CAPE) conditions were optimized and bioconversion up to 84% was achieved at a substrate molar ratio of 1:20 (caffeic acid:2-phenyl ethanol), 30°C for 12h. Results obtained during this study were encouraging and helpful to design a bioreactor system to produce caffeic acid derived esters.

Refolding of horseradish peroxidase is enhanced in presence of metal cofactors and ionic liquids.

The effects of various refolding additives, including metal cofactors, organic co-solvents, and ionic liquids, on the refolding of horseradish peroxidase (HRP), a well-known hemoprotein containing four disulfide bonds and two different types of metal centers, a ferrous ion-containing heme group and two calcium atoms, which provide a stabilizing effect on protein structure and function, were investigated. Both metal cofactors (Ca(2+) and hemin) and ionic liquids have positive impact on the refolding of HRP. For instance, the HRP refolding yield remarkably increased by over 3-fold upon addition of hemin and calcium chloride to the refolding buffer as compared to that in the conventional urea-containing refolding buffer. Moreover, the addition of ionic liquids [EMIM][Cl] to the hemin and calcium cofactor-containing refolding buffer further enhanced the HRP refolding yield up to 80% as compared to 12% in conventional refolding buffer at relatively high initial protein concentration (5 mg/ml). These results indicated that refolding method utilizing metal cofactors and ionic liquids could enhance the yield and efficiency for metalloprotein.

Enzymatic hydrolysis of penicillin and in situ product separation in thermally induced reversible phase-separation of ionic liquids/water mixture.

Enzymatic hydrolysis of penicillin G to produce 6-aminopenicillanic acid, key intermediate for the production of semisynthetic ß-lactam antibiotics, is one of the most relevant example of industrial implementation of biocatalysts. The hydrolysis reaction is traditionally carried out in aqueous buffer at pH 7.5-8. However, the aqueous rout exhibits several drawbacks in enzyme stability and product recovery. In this study, several ionic liquids (ILs) have been used as media for enzymatic hydrolysis of penicillin G. The results indicated that hydrophobic ILs/water two-phase system were good media for the reaction. In addition, a novel aqueous two-phase system based on the lower critical solution temperature type phase changes of amino acid based ILs/water mixture was developed for in situ penicillin G hydrolysis and product separation. For instance, hydrolysis yield of 87.13% was obtained in system containing 30 wt% [TBP][Tf-ILe] with pH control (pH 7.6). Since the phase-separation of this medium system can be reversible switched from single to two phases by slightly changing the solution temperature, enzymatic hydrolytic reaction and product recovery were more efficient than those of aqueous system. In addition, the ILs could be reused for at least 5 cycles without significant loss in hydrolysis efficiency.

Ionic liquids as novel solvents for the synthesis of sugar fatty acid ester.

Sugar fatty acid esters are bio-surfactants known for their non-toxic, non-ionic, and high biodegradability . With great emulsifying and conditioning effects, sugar fatty acids are widely used in the food, pharmaceutical, and cosmetic industries. Biosynthesis of sugar fatty acid esters has attracted growing attention in recent decades. In this study, the enzymatic synthesis of sugar fatty acid esters in ionic liquids was developed, optimized, and scaled up. Reaction parameters affecting the conversion yield of lipase-catalyzed synthesis of glucose laurate from glucose and vinyl laurate (i.e. temperature, vinyl laurate/glucose molar ratio, and enzyme loads) were optimized by response surface methodology (RSM). In addition, production was scaled up to 2.5 L, and recycling of enzyme and ionic liquids was investigated. The results showed that under optimal reaction conditions (66.86 °C, vinyl laurate/glucose molar ratio of 7.63, enzyme load of 73.33 g/L), an experimental conversion yield of 96.4% was obtained which is close to the optimal value predicted by RSM (97.16%). A similar conversion yield was maintained when the reaction was carried out at 2.5 L. Moreover, the enzymes and ionic liquids could be recycled and reused effectively for up to 10 cycles. The results indicate the feasibility of ionic liquids as novel solvents for the biosynthesis of sugar fatty acid esters.

Recovery of ionic liquid and sugars from hydrolyzed biomass using ion exclusion simulated moving bed chromatography.

Efficient recovery of ionic liquid (IL) from aqueous mixture of ILs and sugars (which derived from enzymatic or chemical catalyzed hydrolysis of ILs-pretreated biomass) is a major drawback for commercialization of biofuel and platform chemicals production from biomass utilized ILs as pretreatment solvent. In this study, simulated moving bed (SMB) chromatography equipped with ion exclusion column (containing [Emim]+ cation) was investigated to separate sugars (glucose and xylose) which are the main products from biomass hydrolysate and 1-ethyl-3-methylimidazolium acetate (EmimAc) which is the ILs used for biomass pretreatment. A four-zone SMB system with a configuration of 2-2-2-2 (2 ion exclusion columns in each zone) was used to recover glucose, xylose and EmimAc from their aqueous mixture with yield of 71.38, 99.37 and 98.92%, respectively. Moreover, the optimization of SMB zone configuration by simulation results in a complete recovery of ILs. This result indicates that for the first time, ion exclusion SMB chromatography could be used for complete recovery of ILs from aqueous sugar mixture.

Microwave-assisted pretreatment of cellulose in ionic liquid for accelerated enzymatic hydrolysis.

For increasing cellulose accessibility to the enzymatic attack, the pretreatment is a necessary step to alter some structural characteristics of cellulosic materials. As a new pretreatment method, microwave irradiation on cellulose dissolution pretreatment with ionic liquids (ILs) was investigated in this study. Microwave irradiation not only enhanced the solubility of cellulose in ILs but also significantly decreased the degree of polymerization of regenerated cellulose after IL dissolution pretreatment, resulting in significant improvement of cellulose hydrolysis. The rate of enzymatic hydrolysis of cotton cellulose was increased by at least 12-fold after IL dissolution pretreatment at 110 °C and by 50-fold after IL dissolution pretreatment with microwave irradiation. Our results demonstrate that cellulose pretreatment with ILs and microwave irradiation is a potential alternative method for the pretreatment of cellulosic materials.

Microwave-assisted separation of ionic liquids from aqueous solution of ionic liquids.

Microwave-assisted separation has been applied to recover ionic liquid (IL) from its aqueous solution as an efficient method with respect to time and energy compared to the conventional vacuum distillation. Hydrophilic ILs such as 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([Bmim][TfO]) and 1-ethyl-3-methylimidazolium methylsulfate ([Emim][MS]) could be recovered in 6 min from the mixture of ILs and water (1:1, w/w) under microwave irradiation at constant power of 10 W while it took at least 240 min to obtain ILs containing same water content (less than 0.5 wt%) by conventional vacuum oven at 363.15 K with 90 kPa of vacuum pressure. Energy consumptions per gram of evaporated water from the homogeneous mixture of hydrophilic ILs and water (1:1, w/w) by microwave-assisted separation were at least 52 times more efficient than those in conventional vacuum oven. It demonstrated that microwave-assisted separation could be used for complete recovery of ILs in sense of time and energy as well as relevant purity.