Aqueous Ionic Liquid Media Research Articles

Mixed micelle formation by sodium dodecylsulfate and dodecyltrimethylammonium bromide in aqueous ionic liquid media

Surfactant self-aggregation within ionic liquid (IL) - based media has been investigated to compare and contrast the role of such media with that of water. Behavior of a surfactant mixture constituting of two surfactants with oppositely charged head groups, namely anionic sodium dodecylsulfate (SDS) and cationic n-dodecyltrimethylammonium bromide (DTAB), is assessed in aqueous IL media. Contrary to what is observed in water, it is shown earlier that effective charge screening of the surfactant headgroups by IL ions in a typical IL 1-ethyl-3-methylimidazolium ethylsulfate ([C2C1im][EtSO4]) results in formation of (SDS + DTAB) mixed micelles with critical micelle concentrations (CMCs) ranging between those of SDS and DTAB, respectively. The miscibility of (SDS + DTAB) mixture in aqueous [C2C1im][EtSO4] reveals that as the content of IL [C2C1im][EtSO4] is increased, the miscibility of the surfactant mixture improves indicating increased charge screening involving ions of the IL and the surfactant headgroups. For water mole fraction (XW) ≤ 0.90, (SDS + DTAB) surfactant mixture is miscible in aqueous [C2C1im][EtSO4] system in all proportions. For 1.00 ≥ XW≥ 0.90, while synergism persists due to the presence of attractive electrostatic attraction between SDS and DTAB headgroups leading to mixture CMCs below the CMCs of SDS and DTAB, respectively, the extent of synergism diminishes with increase in IL [C2C1im][EtSO4] in the solution. For XW = 0.80, the (SDS + DTAB) mixture exhibits CMC values that are closest to the values estimated assuming ideal behavior. For 0.70 ≥ XW ≥ 0.30, the (SDS + DTAB) exhibits antagonistic trend with CMC values higher than those estimated for ideal solution; the antagonistic trend gradually decreases with increase in [C2C1im][EtSO4] and again attains close to ideal behavior in neat IL [C2C1im][EtSO4]. This trend is subsequently manifested in the composition of the mixed micelles as well as in the net interaction parameter, β. Addition of small proportion of IL to water helps in solubilization of surfactant mixture of oppositely charged surfactants due to effective charge screening of the surfactant headgroups and results in formation of mixed micelles in aqueous IL media over complete composition range.

Modulations in Self-Organization Properties of Surfactant in Aqueous Ionic Liquid Media

Abstract Ionic liquids (ILs) give a wide scope of favorable applications due to their much-upgraded properties. The strong electrostatic interactions between the cationic moiety of IL and the anionic surfactant play a very important role in the assembly of the large aggregates. We have investigated the aggregation behavior of anionic surfactants and IL in aqueous solution. Different temperatures and concentrations of IL have been taken to study the effect on critical micelles concentrations of surfactant. The critical micelle concentration values obtained by conductivity measurements are further confirmed by the fluorescence studies. The method is based on the fit of the experimental obtained raw data of fluorescence spectroscopy to a simple nonlinear category of a Boltzmann type sigmoidal function. Thermodynamical parameters of micellization Δ H m 0 $\Delta H_{m}^{0}$ , Δ G m 0 $\Delta G_{m}^{0}$ and Δ S m 0 $\Delta S_{m}^{0}$ have been considered to study the effect of aqueous IL 1-butyl-3-methylimidazolium bromide concentration and temperature on aggregation behavior of surfactant sodium dodecyl sulfate. FT-IR spectra have been studies to verify the structural changes arise in the aqueous IL and surfactant system.

A metal-free route towards 1,5-disubstituted 1,2,3-triazolylmethylene linked disaccharides: Synthesis in a biodegradable hydroxyl-ammonium-based aqueous ionic liquid media

Suitably protected carbohydrates were joined together using 1,5-disubstituted 1,2,3-triazolylmethylene (1,5-DTM) linkers. The DTM linker was built by the 1,3-dipolar cycloaddition reactions of a series of sugar azides with vinyl sulfonylmethylene-modified furanose or pyranose under metal free conditions. Three different biodegradable hydroxylammonium based ionic liquids were studied in water as the reaction media. The N,N-dimethyl ethanolammonium formate-water mixture was found to be the best reaction medium because the reaction time was shortened considerably to generate a dozen new 1,5-DTM-linked disaccharides.

Simultaneous pretreatment and enzymatic saccharification of (ligno) celluloses in aqueous-ionic liquid media: A compromise

In view of decreasing the amount of IL to achieve efficient simultaneous pretreatment and saccharification, a comprehensive study was undertaken. Different types of lignocellulosic biomasses were investigated in various enzymatic aqueous-IL systems including 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) or 1-ethyl-3-methylimidazolium methylphosphonate ([C2mim][MeO(H)PO2]). To better understand how 10% (v/v) of IL in the reaction medium led to the highest yields of glucose without fractionation from sawdust, distinct cellulosic models were then used as substrates. Kinetic studies demonstrated that both ILs affect synergistic action of cellulolytic enzymes depending on both constitutive anion and cellulosic substrate. Concentrations above 10% v/v of ILs deactivated cellulase even on highly digestible model substrates. β and α Kamlet-Taft parameters constituted more physicochemical pertinent indicators than apparent pH value to investigate effects of IL on cellulase performances. Fine description of these effects was proposed onto individual EG, CBH and BG. [C2mim][MeO(H)PO2] was demonstrated a better compatible IL for enzymes up to a concentration of 30% (v/v). The efficiency of simultaneous pretreatment and saccharification was governed by a compromise between better substrate accessibility and enzyme deactivation.

Vinyl sulfone modified-azidofuranoside building-blocks: 1,4-/1,5-disubstituted-1,2,3-triazole linked trisaccharides via an aqueous/ionic-liquid route and “Click” chemistry

1,5-Disubstituted 1,2,3-triazole (1,5-DT) linked disaccharides have been synthesized from stable building blocks having both vinyl sulfone and azido groups using aqueous ionic-liquid media.

Efficient enzymatic in situ saccharification of cellulose in aqueous-ionic liquid media by microwave pretreatment

Several representative ionic liquids (ILs) were synthesized, and [Emim]OAc was chosen as environment-friendly solvent for enzymatic in situ saccharification in view of its biocompatibility with both natural and microcrystalline cellulose, as well as its enzymatic activity. With the microwave pretreatment of natural and microcrystalline cellulose, directly enhancing the in situ enzymatic saccharification, the rate was compared versus an untreated control by the detection of dinitrosalicylic acid (DNS). It is suggested that the molecular structure of cellulose in the process of pretreatment was changed, e.g. intramolecular hydrogen bonds were broken (detected by FT-IR), and the crystallinity (monitored by SEM and XRD) changed significantly from a crystalline to an amorphous pattern. These changes of cellulose led to an increase of reducing sugar conversion during cellulose enzymatic hydrolysis.

Enzymatic hydrolysis of Asclepias syriaca fibers in the presence of ionic liquids

Attempts have been made to enhance Asclepias syriaca (As) fiber saccharification by cellulase in the presence of ionic liquids. Three ionic liquids (1-butyl-3-methylimida- zolium chloride, (BMIM)Cl; 1-ethyl-3-methylimidazolium chloride, (EMIM)Cl; and 1-butyl-4-methylpyridinium chlo- ride, (BMP)Cl) were used. In comparison with conventional cellulose pretreatment processes, the ionic liquids were used under milder conditions corresponding to the optimum activity of cellulase. The structural modification and thermal properties of As fibers were analyzed by DSC, TG, DTG, and FT-IR. As fibers were hydrolyzed by cellulase more easily in aqueous ionic liquid media. For As fibers hydrolyzed in the presence of ionic liquids, saccharification rate during the first 3 h of the hydrolysis reaction was significantly improved, especially when the fibers were hydrolyzed in the presence of (BMP)Cl. FT-IR spectra revealed that As fibers undergo modification during enzymatic hydrolysis in the presence of ionic liquid. The increased rate of hydrolysis was accompa- nied by an increase in the degree of crystallinity of the As fibers. It was apparent from thermal analysis that the well ordered crystalline phase and the intermolecular regularity of carbohydrates obtained from the As fibers considered in this study were affected by the ionic liquid through changing of the fiber structure.

Enhancement of enzymatic in situ saccharification of cellulose in aqueous-ionic liquid media by ultrasonic intensification

A new approach for in situ enzymatic saccharification of cellulose in ionic liquids (ILs)-aqueous media is presented in which ultrasonic pretreatment was used to enhance the conversion of cellulose. For this purpose, the solubility of cellulose and the activity of cellulase were investigated in six alkylphosphate ILs. 1-Methyl-3-methylimidazolium dimethylphosphate ([Mmim][DMP]) giving favorable solubility and biocompatibility was selected to establish aqueous-ILs system for enzymatic in situ saccharification of cellulose. After further optimization of reaction parameters concerning cellulase concentration, temperature and IL concentration, higher conversion (95.48%) of cellulose was obtained in the media of aqueous-[Mmim][DMP] by conducting the pretreatment of cellulose with ultrasonic heating, whereas the conversion of cellulose untreated was 42.77%. Scanning electronic microscopy (SEM) and viscosity analysis indicated that IL-treated cellulose under ultrasonic condition was subjected to depolymerization, which led to more efficient saccharification. The findings of this study would have great implications for developing a continuous process for transformation of biomass such as straw cellulose to ethanol or other hydrocarbons.