Aggregation Behavior of Sodium Dioctyl Sulfosuccinate in Deep Eutectic Solvents and Their Mixtures with Water: An Account of Solvent's Polarity, Cohesiveness, and Solvent Structure

Evidence for an L3 phase in ternary deep eutectics: composition-induced L3-to-Lα transition of AOT

Pure and hydrated deep eutectic solvents (DES) are proposed to form self-assembled nanostructures within the fluid bulk, similar to the bicontinuous L3 phase common for ionic liquids (ILs). Labelled choline chloride : urea : water DES were measured using small-angle neutron scattering (SANS), showing no long-range nanostructure. However, solutions of the surfactant AOT in this DES yielded scattering consistent with the L3 "sponge" phase, which was fitted using the Teubner-Strey model. A disclike model gave local structural information, namely, a linear increase in radius versus solvent water content (w = molar ratio of DES : water), eventually forming large, turbid lamellar phases at 10w; an L3-to-Lα transition was observed. Simultaneous multi-contrast SANS fits show the surfactant headgroup region is dominated by interactions with poorly-soluble Na+ at low water contents, and numerically-superior [cholinium]+ as water content increases. The modified interfacial Gaussian curvature from cation : anion volume matching stabilizes the lamellar morphology, allowing the bilayer aggregation number to increase.

Water Induced Alterations in Self-Assembly of a Bio-Surfactant in Deep Eutectic Solvent for Enhanced Enzyme Activity

Deep eutectic solvents (DESs) meet important requirements for green solvent technology, including non-toxicity, biodegradability, sustainability, and affordability. Despite possessing low cohesive energy density than water, DESs have been found to support the self-assembly of amphiphiles. It is very much pertinent to examine the effect of water on self-assembly of surfactants in DESs as the presence of water alters the inherent structure of DES, which is expected to affect the characteristic properties of self-assembly. Following this, we have investigated the self-assembly of amino-acid based surfactant, Sodium N-lauroyl sarcosinate (SLS), in DES-water mixtures (10, 30 and 50 w/w% of water) and explored the catalytic activity of Cytochrome-c (Cyt-c) in the formed colloidal systems. Investigations using surface tension, fluorescence, dynamic light scattering (DLS), and isothermal titration calorimetry (ITC) have shown that DES-water mixtures promote the aggregation of SLS, resulting in the lower critical aggregation concentration (cac ∼1.5-6-fold) of the surfactant as compared to water. The nanoclustering of DES at low water content and it's complete de-structuring at high water content affects the self-assembly in a contrasting manner governed by different set of interactions. Further, Cyt-c dispersed in DES-water colloidal solutions demonstrated 5-fold higher peroxidase activity than that observed in phosphate buffer.

Thermodynamic Insights of the Molecular Interactions of Dopamine (Neurotransmitter) with Anionic Surfactant in Non-Aqueous Media

This study was aimed at establishing the interactions prevailing in an anionic surfactant, sodium dodecyl sulfate, and dopamine hydrochloride in an alcoholic (ethanol) media by using volumetric, conductometric, and tensiometric techniques. Various methods were utilized to estimate the critical micelle concentration (cmc) values at different temperatures. The entire methods yielded the same cmc values. The corresponding thermodynamic parameters viz. the standard free energy of micellization (Gmico), enthalpy of micellization (Hmico), and entropy of micellization (Smico) were predicted by applying the pseudo-phase separation model. The experimental density data at different temperatures (298.15 K, 303.15 K, 308.15 K, and 313.15 K) were utilized to estimate the apparent molar volumes (Vϕo) at an infinite dilution, apparent molar volumes (Vφcmc) at the critical micelle concentration, and apparent molar volumes (ΔVφm) upon micellization. Various micellar and interfacial parameters, for example, the surface excess concentration (Γmax), standard Gibbs free energy of adsorption at the interface (ΔGoad), and the minimum surface area per molecule (Amin), were appraised using the surface tension data. The results were used to interpret the intermolecular interactions prevailing in the mixed systems under the specified experimental conditions.

Photophysics of thiazole orange in deep eutectic solvents

Photophysics and torsional dynamics of thiazole orange (TO) as a function of temperature have been studied in two deep eutectic solvents (DESs) using spectroscopic techniques. Two DESs are used as a solvent namely DES-I (choline chloride + urea, mole ratio 1: 2) and DES-II (N,N diethyl ethanol ammonium chloride + urea, mole ratio 1: 2). We explore the influence of DESs on the photophysical properties of TO. The fluorescence quantum yield and fluorescence lifetime of TO decreases with increasing temperature due to thermal deactivation. At higher temperature, fluorescence quantum yield of TO decreases in DESs may be due to the molecular rotor nature of TO, with the benzothiazole and quinoline ring of this dye being able to be rotated relative to each other in the excited state. In these solvents, the free volume idea was found to provide a truthful report of the solvent viscosity-temperature behavior, and the probe torsional dynamics. Fluorescence lifetime imaging microscopy (FLIM) was used to insight and observed the distribution of lifetime of TO in the surface of both DESs. The contact angle was determined to show the hygroscopic nature of the DESs.

A Simple Microextraction Method for Toxic Industrial Dyes Using a Fatty-Acid Solvent Mixture

A mixture of dodecanoic and hexanoic fatty acids was used to perform a simple and efficient microextraction method for industrial dyes such as methylene blue (MB), methyl violet (MV), and malachite green (MG) in aqueous solution. The fatty-acid microextractants were simply mixed and heated until the mixture became homogeneous before adding it to the dye solutions. The fatty-acid solvent and its components were characterized with Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR) measurements, while the dye concentrations were measured using UV-Vis spectroscopy. The performance of the extracting mixture was observed to vary across different dye contaminants, dosages of the extractant, concentrations of the dyes, and contact times. High extraction efficiencies of up to ~99% were obtained for MG as well as MV, and ~73% efficiency was achieved for MB. The study shows how a mixture of fatty acids can be used as a simple, efficient, green, and sustainable low-volume method for the removal of toxic industrial dyes in aqueous solutions.

Group contribution and atomic contribution models for the prediction of various physical properties of deep eutectic solvents

The urgency of advancing green chemistry from labs and computers into the industries is well-known. The Deep Eutectic Solvents (DESs) are a promising category of novel green solvents which simultaneously have the best advantages of liquids and solids. Furthermore, they can be designed or engineered to have the characteristics desired for a given application. However, since they are rather new, there are no general models available to predict the properties of DESs without requiring other properties as input. This is particularly a setback when screening is required for feasibility studies, since a vast number of DESs are envisioned. For the first time, this study presents five group contribution (GC) and five atomic contribution (AC) models for densities, refractive indices, heat capacities, speeds of sound, and surface tensions of DESs. The models, developed using the most up-to-date databank of various types of DESs, simply decompose the molecular structure into a number of predefined groups or atoms. The resulting AARD% of densities, refractive indices, heat capacities, speeds of sound and surface tensions were, respectively, 1.44, 0.37, 3.26, 1.62, and 7.59% for the GC models, and 2.49, 1.03, 9.93, 4.52 and 7.80% for the AC models. Perhaps, even more importantly for designer solvents, is the predictive capability of the models, which was also shown to be highly reliable. Accordingly, very simple, yet highly accurate models are provided that are global for DESs and needless of any physical property information, making them useful predictive tools for a category of green solvents, which is only starting to show its potentials in green technology.

Self-assembled luminescent cholate gels induced by a europium ion in deep eutectic solvents

Deep eutectic solvents (DESs) with excellent physicochemical properties similar to ionic liquids and biocompatibility are potential solvent candidates for designing novel lanthanide luminescent soft materials. In this paper, the fabrication and characterization of such luminescent gels in three choline chloride (ChCl)-based DESs through self-assembly of the sodium cholate and europium nitrate are presented. The microstructure and gel-like nature of the obtained eutectogels were explored and confirmed by scanning electron microscopy and rheology measurements. While Fourier transform infrared spectroscopy and small-angle X-ray scattering were used to analyze the gel formation mechanism, which was considered to be synergistically driven by metal coordination, hydrogen bonding and solvophobic interactions. All three eutectogels exhibited good photophysical properties. Among these, the one formed in ChCl/urea DES was found to possess the strongest mechanical strength. While the one formed in ChCl/glycerol DES exhibited the longest luminescence lifetime and quantum efficiency. The obtained results demonstrate the possibility of using DESs to construct lanthanide luminescent soft materials or control their properties through the choice of hydrogen-bond donor molecules.

Molecular packing of surface active ionic liquids in a deep eutectic solvent: a small angle X-ray scattering (SAXS) study

During the past decade, deep eutectic solvents (DESs) have shown promising application in the self-assembly of surfactants. Various aggregates such as micelles, vesicles, lyotropic liquid crystals, microemulsions and gels have been reported. In this research, the phase behaviours of imidazolium surface active ionic liquids (SAILs) CnmimBr (n = 12, 14, 16) were investigated in ChG. With the help of small angle X-ray scattering (SAXS), the types and structure parameters of aggregates were determined. The molecular packing of SAILs was influenced by the solvophobic chain length, surfactant concentration, temperature and solvent, accounting for their different aggregation behaviours. This study would give a good description of the molecular packing of surfactants in DESs.