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.

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.

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.

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.

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.

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.

Risk factors for typhoid fever in the Mekong delta, southern Viet Nam: a case-control study

In order to identify risk factors for typhoid fever in a highly endemic area, we undertook a case-control study in the Mekong delta, Viet Nam. Cases were 144 consecutive patients admitted to hospital with blood culture-confirmed typhoid fever. Two controls (1 in the hospital and 1 in the community) were chosen for each case. Standardized interviews were conducted with questions regarding recent contact with a typhoid fever patient, eating habits, hygiene and socio-economic level. Cases were more likely to have been in contact with a patient with typhoid fever than hospital controls (adjusted odds ratio (OR) = 5.2, 95% confidence interval (95% CI) 1.7-15.9) or community controls (adjusted OR = 11.9, 95% CI 2.3-60.7); 11% and 14% of typhoid fever cases (compared to hospital or community controls, respectively) were attributable to recent contact with a patient with this disease. These findings suggest that strategies directed towards the persons in contact with a patient might reduce the incidence of secondary cases of typhoid fever.