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In this study, we explored the extent to which hydrotropes can be used to increase the aqueous solubilities of redox-active compounds previously used in flow batteries. We measured how five hydrotropes influenced the solubilities of five redox-active compounds already soluble in aqueous electrolytes (≥0.5 M). The solubilities of the compounds varied as a function of hydrotrope type and concentration, with larger solubility changes observed at higher hydrotrope concentrations. 4-OH-TEMPO underwent the largest solubility increase (1.18 ± 0.04 to 1.99 ± 0.12 M) in 20 weight percent sodium xylene sulfonate. The presence of a hydrotrope in solution decreased the diffusion coefficients of 4-OH-TEMPO and 4,5-dihydroxy-1,3-benzenedisulfonate, which was likely due to the increased solution viscosity as opposed to a specific hydrotrope-solute interaction because the hydrotropes did not alter their molecules' hydraulic radii. The standard rate constants and formal potentials of both 4-OH-TEMPO and 4,5-dihydroxy-1,3-benzenedisulfonate remained largely unchanged in the presence of a hydrotrope. The results suggest that using hydrotropes may be a feasible strategy for increasing the solubilities of redox-active compounds in aqueous flow batteries without substantially altering their electrochemical properties.

The present work describes the applications of Bronsted acid hydrotrope combined catalyst (BAHC) as a mild, efficient and reusable catalyst for synthesis of indoloquinoxalines and bis-tetronic acids in water. Using BAHC, we synthesized many indoloquinoxaline derivatives from isatins and o-phenylene diamine using 10 mol% PTSA in 40% aqueous hydrotropic (NaPTS) solution at room temperature with 83–90% yields. On the other hand, the reaction of tetronic acid with the aldehydes/isatins forms bis-tetronic acids with 83–88% yields through Knoevengel condensation-Michael addition pathway in same BHAC. Moreover, the BAHC can be recycled upto 5th cycles with slight decrease in product yields. The extremely simple operational methodology, green solvent, ambient reaction conditions and high yields render this approach extremely appealing for the synthesis of different heterocyclic compounds.

The biogenic synthesis of copper oxide nanoparticles (CuO NPs) from the leaf extract of Alpinia zerumbet was investigated in this protocol. The basic nature of A. zerumbet leaf extract helps in CuO NPs synthesis. The catalytic activity of A. zerumbet-fabricated CuO NPs is explored in water at room temperature only in the presence of NaPTS hydrotrope. The green catalytic protocol is investigated via synthesis of 1,8-dioxooctahydroxanthene. The biogenic leaf extract fabricated CuO NPs are efficiently reactive, stable and recyclable in aqueous solution of sodium p-toluenesulfonate (NaPTS) hydrotrope. CuO/NaPTS proved to be the best catalytic system as synergistic nanotrope in terms of yield and time of reaction in water at room temperature. The green synthetic approach of CuO NPs, greener medium, easy workup and proficient recyclability are advantages in the said protocol. This is first time report of catalytic activity of biogenic CuO NPs in water at room temperature in the presence of NaPTS.

Carbon dots (CDs) have drawn considerable attention in recent decades due to their outstanding biocompatibility and environmental friendliness. In this study, we synthesized ionic liquid (1-aminopropyl-3-methyl-imidazolium bromide)-modified carbon dots (IL-CDs) showing good peroxidase-like activity. Furthermore, we investigated their enzymic behavior in the presence of two different amphiphilic molecules, namely tert-butanol (TBA, a typical hydrotrope) and sodium bis (2-ethylhexyl) sulfosuccinate (AOT, a typical anionic surfactant). In an aqueous solution of TBA, a microscopic heterogeneous structure was formed in a certain concentration range of TBA, which resulted in an anomaly in the reaction process. However, in the AOT aqueous solution, the situation became more complicated. IL-CDs formed vesicles or precipitation at different concentrations of AOT, which led to different enzymic activities of IL-CDs due to the variance in the structure and the surface electronic density.

Hypothesis The self-assembly of ionic surfactants in deep eutectic solvents has recently been demonstrated, opening up new possibilities in terms of the development of formulated products and templating of nanostructured materials. As it occurs in an aqueous environment, the solvophobic effect drives the formation of micelles in these solvents and specific-ion interactions alter the resulting structures. We hypothesized that the presence of hydrotropic salts would greatly affect the micellar structure in deep eutectic solvents, ultimately leading to the formation of worm-like aggregates. Experiments A systematic investigation performed on hydrotrope-surfactant assemblies in neat and hydrated 1:2 choline chloride:glycerol is presented. The effect of choline salicylate on the micellization of hexadecyltrimethylammonium chloride at different hydrotrope-to-surfactant ratios was probed by contrast variation small-angle neutron scattering. Findings Here the first investigation on salt-induced micellar growth in deep eutectic solvents is presented. The microscopic characterization of the system shows that the micelle-hydrotrope interaction in pure and hydrated deep eutectic solvents results in a significant increase in micelle elongation. The condensation of the hydrotrope on the micelle, which alters the effective monomer packing, leads to the formation of worm-like micelles with tunable morphology and flexibility. The results presented here present new possibilities in terms of self-assembly and co-assembly in neoteric solvents, where micelle morphology can be controlled through surfactant-salt interactions.

Hydrotropes are the small amphiphilic molecules which help in solubilizing hydrophobic entities in an aqueous medium. Recent experimental investigation has provided convincing evidence that adenosine triphosphate (ATP), besides being the energy currency of cell, also can act as a hydrotrope to inhibit the formation of protein condensates. In this work, we have designed computer simulations of prototypical macromolecules in aqueous ATP solution to dissect the molecular mechanism underlying ATP's newly discovered role as a hydrotrope. The simulation demonstrates that ATP can unfold a single chain of hydrophobic macromolecule as well as can disrupt the aggregation process of a hydrophobic assembly. Moreover, the introduction of charges in the macromolecule is found to reinforce ATP's disaggregation effects in a synergistic fashion, a behavior reminiscent of recent experimental observation of pronounced hydrotropic action of ATP in intrinsically disordered proteins. Molecular analysis indicates that this newfound ability of ATP is ingrained in its propensity of preferential binding to the polymer surface, which gets fortified in the presence of charges. The investigation also renders evidence that the key to the ATP's superior hydrotropic role over chemical hydrotropes (sodium xylene sulfonate, NaXS) may lie in its inherent self-aggregation propensity. Overall, via employing a bottom-up approach, the current investigation provides fresh mechanistic insights into the dual solubilizing and denaturing abilities of ATP.

Hydrotropes are small amphiphilic molecules which help in solubilizing hydrophobic entities in aqueous medium. Recent experimental investigation has provided convincing evidences that, adenosine triphosphate (ATP), besides being an energy currency of cell, also can act as hydrotrope to inhibit the formation of protein condensates. In this work, we have designed computer simulations of prototypical macromolecules in aqueous ATP solution to dissect the molecular mechanism underlying ATP’s newly discovered role as a hydrotrope. The simulation demonstrates that ATP can unfold a single-chain of hydrophobic macromolecule as well as can disrupt the aggregation process of a hydrophobic assembly. Moreover, the introduction of charges in the macromolecule is found to reinforce ATP’s disaggregation effects in a synergistic fashion, a behaviour reminiscent of recent experimental observation of pronounced hydrotropic action of ATP in intrinsically disordered proteins. A molecular analysis indicates that this new-found ability of ATP are ingrained in its propensity of preferential binding to the polymer surface, which gets fortified in presence of charges. The investigation also renders evidence that the key to the ATP’s superior hydrotropic role over chemical hydrotrope (Sodium xylene sulfonate, NaXS) may lie in its inherent self-aggregation propensity. Overall, via employing a bottom-up approach the current investigation provides fresh mechanistic insights into the dual solubilizing and denaturing abilities of ATP.

Nonionic hydrotropes (low-molecular-weight amphiphiles) demonstrate striking dual actions in bulk solutions and interfaces, exhibiting both surfactant-like and co-solvent properties. We report on peculiar, strongly affected by this duality, liquid-liquid and air-liquid-liquid interfacial behavior in aqueous ternary systems, containing hydrotropes and hydrocarbons, in a broad range of compositions and at various temperatures. Phase diagrams of the studied systems, containing tertiary butanol (TBA), as a hydrotrope, are of Type 1: the hydrotrope, at the experimental conditions, is completely miscible with water and with all investigated hydrocarbons [cyclohexane (CHX), toluene (TOL), and n-decane (DEC)], whereas the ternary mixtures exhibit liquid-liquid phase separation terminated at corresponding critical points. The shape and location of the phase separation boundary are only weakly dependent on temperature and the hydrocarbon's nature; however, the critical point in the water-TBA-DEC system is significantly shifted toward a higher TBA concentration. For the experimentally studied systems and for available data reported in the literature, we confirmed an apparently generic (for nonionic hydrotropes) phenomenon of a dual action at water-oil interfaces (earlier found in water-TBA-CHX [J. Phys. Chem. C 2017, 121, 16423]): at low concentrations, hydrotropes saturate the water-oil interface like a surfactant, whereas at higher concentrations they act as co-solvents, resulting in vanishing interfacial tension at the liquid-liquid critical point. We suggest a universal crossover function that accurately interpolates the two theoretically based limits of interfacial behavior. This crossover function also accounts for earlier deviations from Langmuir-von Szyszkowski limiting behavior in the water-TBA-DEC system, caused by lower solubility (relative to other studied hydrocarbons) of DEC in water. An intriguing correlation between the dual action of hydrotropes at the water-oil interface and the behavior of the liquid-air interfaces is also discussed.

Self-organization of nanoparticles into one-dimensional (1D) nanochains leads to new unpredicted physiochemical properties, which are further exploited to develop photonic or electronic devices. Thus, the controlled fabrication of 1D nanochains requires nanotemplate, which acts as building blocks for the self-assembly of nanoparticles. To address this issue, we designed a hydrotrope (sodium salicylate)-based CTAB/ n-hexanol/water/heptane reverse micellar system. Hydrotrope, herein, modulates electrostatic interactions between reverse micellar droplets and paves the way for the formation of self-assembled structures. Small-angle X-ray scattering studies were performed on the CTAB/heptane reverse micellar system by varying hydrotrope concentrations and water-to-surfactant ratios (W x). The aqueous content of the reverse micellar pool is determined from the W x value, where W x = [H2O]/[CTAB] and [CTAB] = 0.05 M. SAXS studies were performed for CTAB/heptane reverse micellar systems at three different W x values, that is, 6, 12, and 16 and represented by W6, W12, and W16, respectively. All SAXS profiles were modeled with a spherical form factor and a Baxter sticky hard sphere structure factor. The interaction between droplets was predicted in terms of stickiness parameter. The effect of W x on the formation of self-assembled structures and forces governing the assembly has been discussed in detail. For the W6 system, the electrostatic repulsion between reverse micellar droplets decreases, resulting in the formation of the 1D chain-like assembly of nanodroplets. In the case of the W12 system, the dual feature of the hydrotrope has been observed, it increases the size of the reverse micellar system and reduces electrostatic repulsion between droplets because of which the formation of chain-like assemblies cannot be determined with accuracy. For the W16 system, the decrease in micellar size with the increase in the hydrotrope concentration has been observed. Thus, our reverse micellar templates may provide a comprehensive method for the fabrication of high aspect ratio 1D nanochains of a variety of materials and harnessing their collective properties for magnetic, catalytic, and opto-electronic applications.

In this work, the aggregation behavior of 1-butyl-3-methylimidazolium p-toluenesulfonate (BmimTOS), a new type of cationic hydrotrope, was investigated, where two distinct inflection points C1 and C2 were reflected by the change of conductivity, micro-polarity, surface tension. Therefore, it is speculated that small aggregate was formed in BmimTOS aqueous solution after C1 and structure change of these aggregates may be presented to form larger aggregates after C2. The formation of aggregate and the change of the aggregate size were further confirmed by dynamic light scattering (DLS) measurements. However, as suggested by micro-polarity measurements, these aggregates are not typical micelle-like ones. Furthermore, such two-step aggregation behavior was shown to be presented at a wide temperature region from 288.15 K to 318.15 K; however, the phenomenon cannot be observed when the alkyl chain length on imidazolium cation was changed into ethyl-, hexyl-, or octyl-.

Solubilizing agents are widely used to extract poorly soluble compounds from biological matrices. Aqueous solutions of surfactants and hydrotropes are commonly used as solubilizers, however, the underlying mechanism that determines their action is still roughly understood. Among these, ionic liquids (IL) are often used not only for solubilization of a target compound but in liquid–liquid extraction processes. Molecular dynamics simulations can shed light into this issue by providing a microscopic insight of the interactions between solute and solubilising agents. In this work, a new coarse-grained (CG) model was developed under the MARTINI framework for gallic acid (GA) while the CG models of three quaternary ammonium ionic liquids and salts (QAILS) were obtained from literature. Three QAILS were selected bearing in mind their potential solubilising mechanisms: trimethyl-tetradecylammonium chloride ([N1,1,1,14]Cl) as a surfactant, tetrabutylammonium chloride ([N4,4,4,4]Cl) as a hydrotrope, and tributyl-tetradecylammonium chloride ([N4,4,4,14]Cl) as a system combining the characteristics of the other compounds. Throughout this hydrotrope-to-surfactant spectrum and considering the most prevalent GA species across the pH range, the solvation of GA at two concentration levels in aqueous QAILS solutions were studied and discussed. The results of this study indicate that dispersive interactions between the QAILS and GA are generally the driving force in the GA solubilization. However, electrostatic interactions play an increasingly significant role as the GA becomes deprotonated, affecting their placement within the micelle and ultimately the solvation mechanism. The hydrotropic mechanism seen in [N4,4,4,4]Cl corroborates recent models based on the formation of a hydrotrope-solute aggregates driven by dispersive forces. This work contributes to the application of a transferable approach to partition and solubilization studies using molecular dynamics, which could complement experimental assays and quickly screen molecular candidates for these processes. published

The present study scrutinized in depth the ability of alkanolammonium-based Protic Ionic Liquids (PILs) with carboxylate anions to dissolve Kraft lignin at 323.15 K. A focus was put on understanding the role of both PIL ions and water on the dissolution process. The results demonstrated that the anion plays a more important role in lignin dissolution than the cation. Furthermore, lignin dissolution was favored by increasing the alkyl chain of the carboxylate anion, while a smaller cation with lower number of hydroxyalkyl groups performed better. Among the studied solvents, the 2-hydroxyethylammonium hexanoate (HEAH) displayed the highest lignin solubility (37 wt%). In general, the addition of water had a negative influence on lignin solubility with the tested PILs. A sharp decrease in lignin solubility curves of 2-hydroxyethylammonium formate (HEAF) and acetate (HEAA) was observed, while a more softly effect was observed for 2-hydroxyethylammonium propionate (HEAP) and HEAH with the addition of water. However, a distinct behavior was observed for 2-hydroxyethylammonium octanoate (HEAO) that acted as hydrotrope enhancing lignin solubility in aqueous solutions to a maximum value at 40 wt% water content. Furthermore, by increasing the temperature, the lignin solubility was favored due to endothermic behavior of lignin dissolution process. The dissolution of Kraft lignin was also performed at 393.15 K to unravel any lignin modification unleashed by PILs. GPC, FTIR-ATR and 2D NMR were employed for lignin characterization and the changes observed between native lignin and recovered lignin samples were negligible demonstrating the non-derivatizing char- acter of the PILs. Moreover, the recycle of 2-hydroxyethylammonium propionate (HEAP) was successfully de- monstrated for at least 3 cycles. In this way, PILs are herein revealed as promising solvents to apply in lignin valorization towards more efficient and eco-friendly processes. Suzano Papel & Celulose published

Benzothiazole has potent and significant biological activity, which makes it an important compound in many areas. Synthesis of benzothiazole is also of interest for organic synthetic chemists. The synthesis mainly takes place by condensation of 2-aminothiophenol with a carbonyl functional group of an aldehyde or, a carboxylic acid or other derivatives followed by cyclization. Different methodologies, such as use of transition metal catalysts, different solvents, temperature variation, enzymatic catalysis, etc., have been applied for improving the synthesis of benzothiazoles. Synthesis of organic compounds in water is of interest in current research because of the benign nature of water. But poor solubility of many organic reactants in water however restricts the reaction progress. Hydrotrope as an additive, however, increases the solubility of sparingly soluble or insoluble organic solutes in water, which helps to enhance the rate of reaction and conversion of reactants and to improve the yield of the product. The use of hydrotrope and reaction set up are not tedious, while recovery of product and reuse of hydrotrope are easy. Here, we report benzothiazole synthesis in the aqueous medium of sodium cumene sulphonate as a function of hydrotrope concentration and temperature. This scheme gives an average 97% yield of benzothiazole by conventional heating. The hydrotrope recycle by three times, without any treatment, gave 95% product yield. The method is easy to handle with reduced reaction time, and generates no waste. It increases productivity as the recovery of the product happens by mere precipitation of the product. Process intensification in an indigenously developed ultrasonic batch reactor gave 98% yield of the product in 30-45 min as against 1-2h without ultrasound.

Resveratrol, extracted from plants has both anti-bacterial and anti-fungal activity. A hydrotrope is a compound that solubilizes hydrophobic compounds in aqueous solutions by means other than micellar solubilization. Hydrotropes are compounds that improve the solubility of surfactants in water, particularly those structured to contain high levels of builders or alkalinity. Sodium xylene sulphonate, Toluene sulfonic acid, Na salt and sodium cumene sulphonate are used as hydrotrope since it has the ability to solubilize resveratrol in water. An efficient ultrasound-assisted extraction is used to process for resveratrol along with hydrotrope of known concentration. Since the resveratrol is highly sensitive to light the research is done in a dark environment. The solubility of the resveratrol in the solution was determined by the UV-visible spectrometer. The study was made with various concentration of resveratrol in defined (50 ml) of a hydrotrope. The analysis was done by varying concentration and temperature of the water bath. The sample is projected to HPLC to infer the purity or the concentration of the resveratrol in the solution. From the results, it is clear that the solubility increases with increase in the temperature. Particularly, sodium xylene sulphonate and sodium cumene sulphonate are identified as best hydrotropes for the extraction of resveratrol.

To exploit a green way to produce polymer nanoparticles using biodegradable and renewable macromolecules instead of petroleum-based ones, we initiated a novel and facile method to synthesize lignin nanoparticles (LNPs). The LNPs, having a hydrodynamic diameter ranging from ca. 80 to 230 nm, were formed by self-assembly in a recyclable and non-toxic aqueous sodium p-toluenesulfonate (pTsONa) solution at room temperature, with a lowest concentration of up to 48 g/L. We eliminated the unfavorable factors of restricted processing pH and lignin species by taking advantage of the hydrotropic chemistry and the synergistic dissociation of the entrapped pTsONa and intrinsic phenolic hydroxyl and carboxylic acid moieties of the LNPs. Because of the hydrotropic system, various water-soluble or water-insoluble drugs can be dissolved and encapsulated in the LNPs with an encapsulation efficiency of up to 90%. The drug-encapsulated LNPs also showed great properties, with sustained drug-releasing capability and biocompatibility. Furthermore, the unloaded drugs and free pTsONa could be easily recycled for multiple use, thereby achieving environmental sustainability. This synthesis approach with broad processing window could realize the industrial scale-up production of LNPs and have wide potential applications, including but not limited to versatile drug/bioactive macromolecule loading in the biomedical field.

Hypothesis: The structural details, viscosity trends and dynamic phenomena in t-butanol/water solutions are closely related on the molecular scales across the entire composition range. Utilizing the experimental small- and wide-angle x-ray scattering (SWAXS) method, molecular dynamics (MD) simulations and the complemented-system approach method developed in our group it is possible to comprehensively describe the structure-viscosity-dynamics relationship in such structurally versatile hydrogen-bonded molecular liquids, as well as in similar, self-assembling systems with pronounced molecular and supramolecular structures at the intra-, inter-, and supra-molecular scales. Experiments: The SWAXS and x-ray diffraction experiments and MD simulations were performed for aqueous t-butanol solutions at 25 {\deg}C. Literature viscosity and self-diffusion data were also used. Findings: The interpretive power of the proposed scheme was demonstrated by the extensive and diverse results obtained for aqueous t-butanol solutions across the whole concentration range. Four composition ranges with qualitatively different structures and viscosity trends were revealed. The experimental and calculated zero-shear viscosities and molecular self-diffusion coefficients were successfully related to the corresponding structural details. The hydrogen bonds, that were, along with hydrophobic effects, recognized as the most important driving force for the formation of t-butanol aggregates, show intriguing lifetime trends and thermodynamic properties of their formation., Comment: Main manuscript file AND Supplemental Information, united in one file

Lignin nanoparticles (LNPs) from renewable lignocelluloses can be a valuable building block for a variety of applications and could contribute to the economic development in rural agricultural communities. Current technologies for producing LNPs are not cost effective and use toxic solvents. In this study, LNPs were produced by fractionating poplar wood at ≤80°C with a recyclable hydrotrope p-toluenesulfonic acid (p-TsOH) in an aqueous system. The dissolved lignin was separated as LNPs simply by diluting the spent liquor (SL) to the minimal hydrotrope concentration (HCmin) of 11.5%. The p-TsOH, a solid acid, can be easily recycled by re-concentrating the diluted SL after lignin separation. The LNP size, morphology, and surface charge were controlled by the dilution ratio, speed, pH, and ionic strength of the LNP sol. The LNPs were analyzed by dynamic light scattering (DLS) and found to be fairly stable in terms of mean particle size and surface charge over a period of 2 weeks. Fractionation conditions also affected LNP properties.

Hypericin (Hyp) is a hydrophobic pigment found in plants of the genus Hypericum which exhibits low levels of solubility in water. This work shows that the solubility of Hyp can be significantly increased through the addition of cromolyn disodium salt (DSCG). Performed studies using UV-VIS absorption and fluorescence spectroscopies demonstrate that Hyp remains in a predominantly biologically photodynamic active monomeric form in the presence of DSCG at concentrations ranging from 4.6×10-3 to 1.2×10-1mol·L-1. The low association constant between Hyp and DSCG (Ka=71.7±2M-1), and the polarity value of 0.3 determined for Hyp in a DSCG-water solution, lead to a suggestion that the monomerization of Hyp in aqueous solution can be explained as a result of the hydrotropic effect of DSCG. This hydrotropic effect is most likely a result of interactions between two relative rigid aromatic rings of DSCG and a delocalized charge on the surface of the Hyp molecule. The triplet-triplet (T-T) electronic transition observed in is Hyp in the presence of DSCG suggests a possible production of reactive oxygen species once Hyp is irradiated with visible light in a DSCG aqueous solution.

We investigated a novel catalytic application of nickel-doped zinc oxide (Ni-ZnO) nanoparticles and zinc oxide (ZnO) nanoflakes at room temperature in an aqueous hydrotropic solution for the synthesis of biologically active dihydropyrimidones (DHPMs). Ni-ZnO is a stable, recyclable, green, efficient heterogeneous catalyst which shows maximum yield in a shorter reaction time than ZnO nanoflakes in very mild conditions of hydrotropic aqueous medium for DHPMs syntheses.

Batch crystallization studies of curcumin from hydrotropic solutions of sodium cumenesulphonate (NaCS) and of cinnamic acid from a photosensitive hydrotropic medium of sodium cinnamate (Na-CIN) were carried out, in an agitated reactor for the effect of alternate heating and cooling cycles on crystal morphology. The crystal characterization by Scanning electron microscopy (SEM) and crystal size distribution (CSD) showed formation of spheroidal curcumin crystals while cinnamic acid formed porous aggregates when subjected to thermal cycles. The UV irradiation of cinnamic acid however showed no formation of the aggregates. The type of hydrotrope used and the initial crystal morphologies of curcumin and cinnamic acid are shown to be important factors to result in a different behaviour of the crystal morphology upon thermal cycles. The CSD data were effectively used for estimation of nucleation and growth rate parameters.

Hydrotropes, the substances consisting of small amphiphilic molecules, demonstrate striking duality in aqueous solutions and at the oil–water interface. The question arises, how do specific properties of different hydrotropes affect their generic dual actions? A higher hydrophobicity of 2-butoxyethanol (BEG), with respect to the reference hydrotrope, tert-butanol (TBA), is responsible for the difference in their behavior. The higher hydrophobicity increases the adsorption of hydrotropes at the oil–water interface in the dilute regime and the oil–water co-solvency at higher concentrations of hydrotropes. We investigated phase equilibrium and interfacial phenomena of the system water – BEG – toluene. For the equilibrium phases, we determined the density, compositions, viscosity, and interfacial tension. The critical point in the ternary system water – BEG – toluene is shifted towards the water vertex due to the higher hydrophobicity of BEG when compared with a “perfect amphiphile”, TBA. However, this shift alone does not explain the differences between the properties of the ternary systems containing either BEG or TBA. The higher adsorption of BEG results in the earlier decrease of interfacial tension and phase density difference. The dramatic decrease of the interfacial tension upon the approach to the consolute critical point, observed in both systems, demonstrates a high degree of universality after proper rescaling of the hydrotrope concentration. The viscosity in the oil phase increases due to the higher solubilization ability of BEG; the effect is attributed to the formation of hydrogen bonds with water.

Hemiesters and Hemiamides of maleic and succinic acid viz. sodium lauryl succinate (C12SE), sodium lauryl maleate (C12ME), sodium lauryl succinamide (C12SA), sodium lauryl maleamide (C12MA), sodium hexadecyl succinate (C16SE) and sodium hexadecyl maleate (C16ME) were synthesized and investigated as surfactants in the pure water and aqueous hydrotrope [sodium p-toluene sulfonate (NaPTs)] solution. The chemical structures of the prepared surfactants were established by FTIR and 1H NMR spectroscopy. The surface tension measurements depicted low CMC and a high adsorption efficiency (pC20) which is highly beneficial for creating personal care formulations. The dynamic light scattering (DLS) technique indicated the formation of larger micelles which was important for skin care as larger micelles cannot penetrate the skin layer. Moreover, these surfactants depicted good foamability and stability attributed to faster monomer adsorption and small bubble size which was preferred for cleansing application. Additionally, low protein/lipid solubilization by these surfactants indicated its mild behaviour on skin as compared to other commonly used conventional anionic [sodium lauryl sulfate (SLS)], zwitterionic [cocamidopropyl betaine (CAPB)] and nonionic [decyl glucoside (DG)] surfactants. Viscosity measurements suggested decent thickening ability of surfactants in the presence of co-surfactant like lauramine oxide. Basis of all the properties discussed, these novel hemiesters and hemiamides seem promising as surfactants for improving various characteristics in potential personal care formulations.

We performed molecular dynamics simulations to study the pH-induced structural transitions for aqueous mixtures of a cationic surfactant (cetyltrimethylammonium bromide, CTAB) and a hydrotrope (sodium salicylate, NaSal). We obtained rigid cylindrical, spherical, and flexible cylindrical micelles at pH 7, 2, and 0, respectively, which agrees well with the experimental results of Umeasiegbu et al. (Langmuir 2016, 32, 655). By analyzing the different micellar structural properties, including distribution and molecular orientation of CTA+ and Sal- inside the micelle, we found that the binding form of the protonated salicylate molecules with CTA+ is different from that of Sal- ions. Because of the protonation of salicylate molecules with reduction in pH, their hydrogen bonding interactions with water molecules strengthened and the electrostatic interactions with CTA+ headgroups weakened. Thus, the repulsion of the CTA+ headgroups led to the breakage of the cylindrical micelle into spherical ones. At pH 0, the H-bond-strengthened cation-π interactions between salicylate and CTA+ were verified. We concluded that the penetration of salicylate molecules inside the micelle and the strong association of Cl- ions on the micellar surface play a key role in the formation of a flexible cylindrical micelle. This work provides an atomic-level insight into the mechanism of pH-induced shape transitions in the CTAB/NaSal systems, which is expected to be helpful to understand the aggregate behavior of cationic surfactant-hydrotrope solution.

In this work, we reported for the first time, an easy and cheap route of the synthesis of three polymerizable surfactants with a hydrotrope counterion the anilinium: dodecylsulfate (DSA), tetradecylsulfate (TSA), and hexadecylsulfate (HSA). This approach was based on a hydrolysis reaction of the sodium: dodecylsulfate (SDS), tetradecylsulfate (STS) and hexadecylsulfate (SHS) with aniline hydrochloride (AHC). Besides, we have completed the characterization, morphological and thermodynamically of the aggregates spontaneously formed in the bulk aqueous solutions for both the sodium and anilinium surfactant series. For this purpose, a combination of different experimental techniques involving density, sound velocity, electrical conductivities and surface tension of these compounds at several concentrations and temperatures were performed. The thermodynamic and morphological properties of the aqueous solutions for both surfactant series were compared and discussed on the basis of the hydrotrope effect.

The objective of this study was to evaluate the effect of hydrotropic delignification of cotton stalk on sugar release performance for bioethanol production. In this study, different alkyl benzene sulfonates were screened to select the best pretreatment agent, and the effectiveness of pretreatment was evaluated by enzymatic saccharification. Sodium cumene sulfonate was found to be the best hydrotropic agent in terms of reducing sugar yield. Parameters such as hydrotrope concentration, biomass loading and incubation time were optimized by adopting a central composite design. Under optimized pretreatment conditions, 0.211 g reducing sugar/g of dry biomass was obtained. Reusability of aqueous hydrotrope solution was also demonstrated.

Hydrotropes are substances containing small amphiphilic molecules, which increase solubility of nonpolar (hydrophobic) substances in water. Hydrotropes may form dynamic clusters (less or about 1 ns lifetime) with water molecules; such clusters can be viewed as “pre-micelles” or as “micellar-like” structural fluctuations. We present the results of experimental and molecular dynamics (MD) simulation studies of interfacial phenomena and liquid–liquid equilibrium in the mixtures of water and cyclohexane with the addition of a typical nonionic hydrotrope, tertiary butanol. The interfacial tension between the aqueous and oil phases was measured by Wilhelmy plate and spinning drop methods with overlapping conditions in excellent agreement between techniques. The correlation length of the concentration fluctuations, which is proportional to the thickness of the interface near the liquid–liquid critical point, was measured by dynamic light scattering. In addition, we studied the interfacial tension and water–oil i...

In this work, the linear viscoelastic properties of the sodium dodecylsulfate/aniline hydrochloride/water system were examined in detail as a function of aniline hydrochloride (AHC) to sodium dodecyl sulfate (SDS) molar ratio (R = [AHC]/[SDS]), SDS concentration and temperature. SDS aqueous solutions undergo a structural transition from sphere to rodlike micelles and subsequently to a viscoelastic network of wormlike micelles induced by the hydrotrope AHC at low and intermediate R molar ratios (i.e., R = 0.1–0.6 for 5 wt.% SDS), which screens the repulsions between the neighboring charged head groups. The rheological response indicates that at low R molar ratios and constant surfactant concentration, the rheological behavior of the system is predominantly viscous (G′ G″) and a maximum of the absolute value of the zero frequency complex viscosity ( | η 0 * | ) is observed, which suggest that the micellar length also goes through a maximum. The region of the elastic behavior diminishes at even greater R molar ratios and a predominantly viscous behavior appears again. This drop in | η 0 * | can be attributed to the transition from linear to branched wormlike micelles that conform the tridimensional viscoelastic network. The dynamic behavior of the system was analyzed in terms of the Granek-Cates theory, which indicates that the viscoelastic network is in the slow-breaking limit. Under these conditions, reptation is found to be the controlling relaxation mechanism for this system.

In this work we established three from altogether six proton dissociation constants (p K a ) of hydroxyl groups of hypericin in its monomeric form. The monomeric state of hypericin (5.0 × 10 −6 mol·L −1 ) in aqueous solution was stabilised by the presence of hydrotropic drug Cromolyn disodium salt (6.0 × 10 −2 mol·L −1 ). Data show that one acid-base transition occurs with the p K a of 7.8 and the other two are characterised by the apparent single p K a of 11.5. The spectral changes of hypericin above pH 13 indicate that the last two hydroxyls are deporotonized at this high pH values.

The aim of this work was to determine the detailed phase behavior of the sodium dodecyl sulfate/aniline hydrochloride/water system as a function of concentration of sodium dodecyl sulfate (SDS), aniline hydrochloride (AHC) to sodium dodecyl sulfate molar ratio (R = [AHC]/[SDS]) and temperature. Phase behavior information was obtained via polarizing microscopy, differential scanning calorimetry (DSC), cryo-scanning electron microscopy (Cryo-SEM) and oscillatory linear rheological measurements with good agreement among these techniques. It is well known that SDS in water forms spherical micelles at concentrations lower than 40 wt% and temperatures above its Krafft temperature (T k = 16–21 °C). In this region, the SDS/water system exhibits Newtonian rheological behavior, which is characteristic of spherical micellar solutions. The addition of the hydrotrope, aniline hydrochloride, to SDS aqueous solutions produces a viscosity increase in this system as R augments, and a maximum of about five orders of magnitude was found at R = 0.47 for 5 wt% SDS at 20 °C. Moreover, the system shows a transition from viscous to strong viscoelastic behavior. These changes in the rheological behavior are produced by the transitions from sphere to rodlike micelles, which are induced by the hydrophobicity of AHC causing it to be absorbed into the core and the hydrophilic interface of the micelles, which screens the repulsions between the charged head groups.

The initial definition of hydrotropy by Neuberg in 1916 describes a hydrotrope as a molecule which enhances the solubilization of hydrophobic substances in water. Sodium dodecyl sulfate (SDS) and sodium xylene sulfonate (SXS) are typical representatives fulfilling this old definition. They are either surfactants with a critical micellar concentration (CMC) or hydrotropes in the current sense of the term, showing a minimum hydrotrope concentration (MHC), respectively. In the present contribution, we consider the antagonistic salt PPh4Cl as a hydrotrope. Surface tension measurements and solubilization experiments on a hydrophobic dye confirm the solubilization behavior of PPh4Cl, which is in-between the one of SDS and SXS. With the help of scattering techniques (DLS, SLS, SAXS), NMR and conductivity measurements, we show that in contrast to SDS as a hydrotrope with an inherent CMC, PPh4Cl does not exhibit mesoscale aggregation. Therefore, PPh4Cl can be classified rather as a hydrotrope in the modern sense, with an inherent MHC just as SXS.

Aim: This work spotlights on fabrication of CD44-tropic, layer-by-layer (LbL) coated, liquid crystalline nanoparticles of rapamycin (Rap-LbL-LCNPs) to enhance its water solubility and enable its anticancer use. Methods: Rap-LCNPs were fabricated using hydrotrope method and then coated using LbL self-assembly technique. Results: LbL coating strategy successfully reduced monoolein-induced hemolysis and increased LCNPs serum stability. Lyophilized Rap-LbL-LCNPs were successfully sterilized using γ-radiations. In CD44-overexpressed MDA-MB-231 cells, Rap-LbL-LCNPs demonstrated superior cytotoxicity compared with the nontargeted formulation. Rap-LbL-LCNPs showed 3.35-fold increase in bioavailability compared with free drug. Rap-LbL-LCNPs significantly inhibited tumor growth, enhanced animal survival and reduced nephrotoxic and hyperglycemic effects of Rap. Conclusion: LbL coating strategy of Rap-LCNPs could serve as a promising approach that facilitates Rap use in cancer therapy.

The current study investigated the mixed micellization of a phenothiazine drug, promethazine hydrochloride (PMT), with the anionic hydrotrope sodium benzoate (NaB) using a conductometric method in three different solvent media: water, 50 mmol.kg−1 sodium chloride (NaCl), and 300 mmol.kg−1 urea (U). Five different temperatures, ranging from 293.15 to 313.15 K, were chosen for the current study of both pure and mixed systems. PMT belongs to a class of drugs known as antihistamines, which are used to treat allergy symptoms. Various physicochemical parameters of both pure and mixed systems (PMT+NaB) were evaluated at different compositions and temperatures, using numerous theoretical models associated with mixed micellization. The attained critical micelle concentration (cmc) and ideal cmc (cmcid) values indicated the formation of mixed micelles due to interactions between the components. The evaluated cmc value for PMT, the minimum hydrotropic concentration (mhc) of NaB, and the cmc value for the PMT+NaB mixture decreased in the NaCl system and increased in the U system compared with these values in the aqueous solution. The cmc values of the studied mixed systems decrease due to an upsurge in the mole fraction (α1) of NaB, indicating the non-ideality of the evaluated solution mixtures. The interaction parameter (β) was negative, revealing that the interaction between the constituents increased with the increasing α1 of NaB in aqueous solution. In the NaCl solution, the β value increased, whereas, in the U solution, the value decreased. The degree of dissociation (g) values decreased by increasing the α1 of NaB in the solution mixture. Various thermodynamic parameters were also evaluated in detail. The activity coefficient values in all cases were below unity, which further indicated the non-ideality of the system. The assessed excess free energy (∆GexRb) of the system was found to be negative in all cases, displaying the stability of the formed mixed micelles. Across the different solvents, their magnitudes were observed in the following order: ∆GexRb in NaCl > ∆GexRb in water >∆GexRb in U. An ultraviolet (UV)-visible study showed a clear interaction between NaB and PMT in the aqueous system. A Fourier-transform-infrared (FT-IR) spectroscopy investigation revealed a shift in the frequency bands of the components due to the interactions between them.

The interaction between an amphiphilic phenothiazine drug—promethazine hydrochloride (PMT)—and anionic hydrotrope sodium p-toluenesulfonate (NaTS) mixtures was analyzed and the effect of different mole fractions (α1) of NaTS along with the variation of temperature was also investigated in three different media, water/NaCl (50 mmol.kg−1)/urea (U) (300 mmol.kg−1), using a conductometric method. Drug PMT is mainly utilized to cure allergic symptoms. From the study of pure components along with solution mixtures of components, various physicochemical parameters were evaluated and discussed thoroughly. The obtained results show that the experimental critical micelle concentrations (cmcs) are less than their corresponding ideal cmc (cmcid) values, showing the interaction amongst the constituents (PMT and NaTS). Mixing of dissimilar kinds of amphiphiles has an opportunity to bring about additional valuable acts owing to their attractive interaction. As hydrophobicity of the PMT + NaTS mixtures increased, therefore the cmc values remarkably decreased. The degree of dissociation (g) of the studied system was also evaluated and found to increase with a rise in temperature and decrease via an increase in α1 of NaTS. In salt (NaCl) solution, cmc and g-value of PMT and PMT+ NaTS at all compositions were decreased compared with an aqueous system while in U solution their value was found to be greater than in aqueous solution. Various theoretical models were also considered to estimate the fraction of hydrotrope in mixed micelles PMT + NaTS, the parameter is named the micellar mole fraction (X1Rb (Rubingh model), X1Rd (Rodenas model) and their ideal value is X1id), and the obtained value shows the higher composition of NaTS in mixed micelles along with their value increasing through an increase of α1 of NaTS in the solution mixture. One other parameter, called the interaction parameter (β), was observed as negative throughout the study, also proving the attractive interaction/synergism amongst the components of the solution mixture (PMT + NaTS). Assessed activity coefficients were all below one, showing the nonideality of the studied system. Several thermodynamic parameters of micellization, such as Gibbs free energy (ΔGm0), enthalpy (ΔHm0), and entropy (ΔSm0) have been determined in all studied media and compositions. UV–visible spectroscopy also confirmed the interaction amongst PMT and NaTS. Scanning electron microscope (SEM) images depicted a clear-cut interaction of PMT and NaTS interaction. The outcomes from the current study are significant in the expansion of the operative model drug delivery process.

The knowledge about the solubility behavior of different biomolecules can be of interest to the pharmaceutical, chemical, and food industries. In this work, the designer solvents were evaluated as additives to aqueous media to enhance the solubility of hydrophobic biomolecules, namely: quercetin, curcumin, and gallic acid. The solubilities of these biomolecules were explored in terms of experimental data and COSMO-based models' prediction (COSMO-RS and COSMO-SAC). The following designer solvents were evaluated as additives: DES (composed of cholinium chloride and xylitol, 2:1 M fraction), cholinium chloride (HBA), xylitol (HBD) and the simple mixture of cholinium chloride and xylitol in the same molar ratio of the DES. For the more hydrophobic biomolecules, i.e., curcumin, and quercetin, these solvents promoted an increase of solubility. The quercetin solubility increased more than 1000-fold in the solution containing 70 wt% of cholinium chloride compared to the pure water. In the same conditions, the curcumin solubility increased around 700-fold. For the less hydrophobic biomolecule, gallic acid, a hydrotrope effect was observed when DES and the simple mixture of cholinium chloride and xylitol were used as an additive. Moreover, comparing the aqueous solutions containing DES with that one composed of the cholinium chloride and xylitol mixture is possible to observe the effect of the hydrogen bonds from DES at low water content solutions. Also, the COSMO models were able to predict the affinity behavior of biomolecules in different solvents, and the COSMO-SAC predicted the hydrotrope behavior of the aqueous solution of cholinium chloride when solubilizing gallic acid.

Potassium perfluorooctane sulfonate (KPFOS) and sodium perfluorooctane sulfonate (NaPFOS) exhibit poor surface activities in aqueous solution at room temperature because of their high Krafft points. In this work, we attempted to increase the solubility of KPFOS and NaPFOS and consequently improve their surface activities at room temperature with sodium p-methylbenzene sulfonate (BS) and urea, which are typical hydrotropes in industrial applications. The effects of BS and urea on the surface tension of the aqueous solutions of KPFOS and NaPFOS were investigated at 25 °C. When the hydrotropes were added, the effectiveness of KPFOS and NaPFOS in surface tension reduction was greatly enhanced and KPFOS showed higher efficiency in surface tension reduction than NaPFOS. On the other hand, BS had much stronger ability than urea to reduce the surface tension of KPFOS and NaPFOS in water. In particular, with the assistance of BS the minimum surface tension of KPFOS approached 19 mN/m at 25 °C. It was worth noting that in the presence of BS, the surface tension of an apparently “saturated” solution (i.e., with coexisting surfactant solid) continuously decreased with increasing surfactant concentration. This behavior was ascribed to enrichment of branched PFOS isomers in aqueous phase with the assistance of BS, as evidenced by high-resolution 19F NMR. Hydrotropes were able to recover the inherent character of KPFOS and NaPFOS as highly surface-active fluorinated surfactants by increasing the solubility of branched isomers. This is an easy way to enhance the effectiveness in surface tension reduction at room temperature for fluorinated surfactants with high Krafft points.

Catanionic surfactant-hydrotrope mixtures have proven to be a striking alternative to tune microstructures over a wide range of compositions and also to minimize precipitation that is normally observed in catanionic mixtures at an equimolar ratio. These mixtures are supposed to be of great relevance in biological systems when a hydrotrope is a "drug". Keeping this in view, here we report composition- and dilution-induced structural changes in a catanionic mixture comprising ionic liquids (ILs), such as 1-dodecyl-3-methylimidazolium bromide (C12mimBr)/1-tetradecyl-3-methylimidazolium bromide (C14mimBr), and a drug, diclofenac sodium (DFNa), in aqueous solution. The structural changes are probed by small-angle neutron scattering (SANS), dynamic light scattering (DLS), and zeta-potential measurements. SANS data and size distribution curves clearly depict the formation of low curvature structures on going from the cation-rich to anion-rich composition up to a 0.7 mole fraction of DFNa (XDFNa). The amphiphilic nature of DFNa is supposed to alter the surface charge density, which is provoked by its incorporation into resulting aggregates, as confirmed by modified zeta-potential values. The modification of the average packing parameter resulting from the IL and DFNa complexation equilibrium seems to play a vital role in bringing out structural transitions of mixed aggregates. We also focused our attention to study the effect of dilution in concentrations ranging from 100 to 25 mM. At XDFNa = 0.0 and 0.1, the size of prolate ellipsoids decreases on dilution, mimicking classic behavior, but an opposite trend is observed at other XDFNa values. Dilution-induced transformation to larger aggregates is thought to be driven by the release of DFNa molecules from the mixed micelles on account of the critical micelle concentration (cmc) (solubility) mismatch between the two components. The role of other interactions such as cation-π and π-π in stabilizing the mixed aggregates in addition to hydrophobic interactions is probed by (1)H NMR.

The structural transitions occurring with change in pH for aqueous mixtures of a cationic surfactant (cetyltrimethylammonium bromide, CTAB) and a hydrotrope (sodium salicylate, NaSal) were investigated at various temperatures using dynamic light scattering and small-angle neutron scattering. Direct structural studies show a transition from rigid cylindrical micelles at neutral pH to spherical micelles at ∼ pH 2 upon protonation of salicylate molecules; however, an unanticipated reversion to flexible cylindrical micelles with further decrease in pH was observed. We also observed these microstructure transitions from cylinders at high pH to spherical micelles at intermediate pH to flexible cylindrical micelles at low pH were highly sensitive to temperature. Our results suggest that, in addition to the well-described electrostatic and hydrophobic interactions in cationic surfactant-hydrotrope mixtures, the pH-induced microstructural changes are potentially governed by complementary cation-π and hydrogen bonding interactions.

In this paper, we show how to tailor the structure and rheology of aqueous solutions of the cationic surfactant cetyltrimethylammonium tosylate, CTAT, by adding a hydrotrope (potassium phthalic acid, PPA) or changing pH. Aqueous solutions of neat CTAT and CTAT/PPA binary mixtures were evaluated under different hydrotrope concentrations and compared with solutions of an analogous surfactant, cetyltrimethylammonium chloride (CTAC). PPA content promotes substantial increases in micellar flexibility and inter-micellar entanglements, resulting in a higher degree of structure in the fluid. Increasing the pH in neat CTAT leads to significant increases in low shear rate viscosities in comparison with CTAT at its original pH, because the OH ions favor surfactant aggregation as well as the growth of worm-like micelles. Nevertheless, increasing the pH in CTAT/PPA mixtures produced a progressive decrease in the low shear rate viscosities. This result is due to the nature of the interactions between CTAT and PPA, as well as to the ionization degree of the functional groups present in PPA. Cryo-TEM and 1 H NMR measurements evidenced, respectively, the microstructural and chemical environmental changes of CTAT upon PPA addition and explain the rheological properties of the CTAT/PPA mixtures as a function of the fluid structure.

A simple, efficient and ligand-free protocol for the Suzuki–Miyaura reaction and base-free Heck–Matsuda reactions under mild reaction conditions have been developed over palladium supported on activated carbon (Pd/C) in an aqueous hydrotropic solution. The catalyst Pd/C was fully characterized by TG-DTA, SEM, EDS, XRD, XPS, BET and ICP-AES analyses. This green methodology represents a cost-effective and operationally convenient method for the synthesis of a variety of biaryls, prochiral ketones, and acrylates under the conditions that are tolerant for a broad range of functional groups with good to excellent yields. The developed Pd/C–aqueous hydrotrope combined catalytic system is well suited for the 3R approach (reducible, robust, and recyclable) for different cross-coupling reactions without an appreciable loss of its activity.

Phase behavior at water-oil and water-air interfaces has received much attention in the past sixty years. The study of detergents as surfactants and their applications to industry is widely known and under constant study. Other molecules, such as alcohols, can also act like surfactants between water and nonpolar molecules. Hydrotropes are amphiphilic molecules, with both a hydrophobic and a hydrophilic section, that also reduce the interfacial tension between two liquids or a vapor and a liquid. Tert-butyl alcohol (TBA) is a well-studied hydrotrope, but its behavior is not completely understood at low molar compositions in aqueous solution. In addition, few studies have examined the influence of different butanol isomers on the interfacial dynamics of mixtures. We used molecular dynamics to study the behavior of all four butanol isomers at the interface of water and cyclohexane. We observed a rapid decrease in surface tension at very low hydrotrope concentrations

Different microscopic and thermodynamic properties like the resonance light scattering intensity, microenvironment polarity, the density and heat capacity of {water + TBA} binary solution and the density of {water + TBA + IBA} ternary solution were precisely measured. Formation and structure transitions of alcohol-water aggregate in TBA aqueous solution and {water + TBA + IBA} ternary solutions at different compositions were investigated by analysis of both microscopic and thermodynamic properties. It is indicated from the results that the fine structure transitions in hydrotrope solutions can be well reflected by the variance of thermodynamic properties, which provides an efficient way to give deeper insight into the structure changes in aqueous hydrotrope solutions.

Association behavior between the cationic antidepressant drug imipramine hydrochloride (IPH) and anionic hydrotrope - sodium benzoate (NaBez) mixtures in aqueous solutions, along with the electrolytes NaCl (50 mmol·kg−1) and NaBr (50 mmol·kg−1) were studied using a conductometric technique at four different temperatures. The results showed a decrease in critical micelle concentration (cmc) of IPH (drug) in combination with NaBez, viewing a remarkable interaction amongst studied constituents along with cmc values of IPH drug further lessens through raised in mole fraction (α1) of NaBez. The electrolytes NaCl and NaBr reduced the cmc of IPH, NaBez together with their mixture (IPH-NaBez) in diverse ratio and NaBr was additionally effectual in reducing the cmc of the system in comparison to NaCl. Moreover, the cmc values of IPH and NaBez mixtures showed a lower than ideal cmc (cmcid) value characterizing the non-ideality in system. Additional parameters of the conductometric method such as the micellar mole fraction employing the Rubingh and Rodenas models, interaction parameter (β), activity coefficients of the mixed micelles, and excess Gibbs free energy using the Rubingh and Rodenas models and so on were evaluated. The activity coefficients values were lessened in electrolyte solvent in the entire systems showing the enhanced non-ideality of mixed system in electrolyte solution. At various temperatures, thermodynamic parameters were also evaluated in aqueous along with electrolyte solutions. The interactions amongst the studied constituents in the aqueous system were also evaluated by fluorescence and FT-IR studies and explored in detail.

Several molecular dynamics (MD) simulations have been performed in order to obtain structural information on ionic liquids (ILs) based on amino-acid anions. Six hydrophilic ILs containing cholinium or imidazolium cations combined with alaninate, glycinate or lysinate anions were modelled using the all-atom CL&P and OPLS-AA force fields. Both pure ILs and their aqueous solutions have been studied. The MD data have allowed us to analyse structure factors, S(q), and pair radial distributions functions, g(r), as well as aggregation patterns and specific interactions. The results have shown us that in neat amino-acid-based ILs the anions interact mainly through their carboxylate moiety with the charged centres of the cations. Both the lack of heavy atoms and the small size of the interacting centre in the anion contribute to the absence of a charge ordering peak in the structure factor functions of the corresponding ILs. In turn, their aqueous solutions reveal the existence of small ionic aggregates. The size distribution of these aggregates is strongly dependent on the solution's concentration. This fact points to the possibility of using amino-acid-based ILs as agents to promote hydrotrope effects, significant for the solubilisation and stabilization of organic molecules and macromolecules in aqueous solution.

Hypothesis In contrast to anionic and nonionic amphiphilic substances, bio-based cationic ones are very rare. Cationic amphiphiles are mostly based on quaternary ammonium, pyridinium or imidazolium groups that are either badly biodegradable or have toxic residues even after degradation. In the search for green alternatives to cationic hydrotropes and amphiphiles, natural l -carnitine could be a promising candidate for a cationic headgroup. Experiments By esterification of carnitine in one step and with low cost, cationic molecules with alkyl chain length of n = 2–14 could be obtained. Their thermal properties, aggregation behaviour and cytotoxicity were determined. Hydrophobic compounds were solubilized in their aqueous solutions and the PIT-slope method was applied to determine a relative hydrophilicity. Findings It was found that some pure carnitine ester bromides were liquid at room temperature and thus can be classified as ionic liquids. They are highly water-soluble, and in aqueous solutions, they showed hydrotrope or surfactant behaviour depending on their alkyl chain length. Their high hydrotropic efficiency was demonstrated by solubilizing Disperse Red 13, while also biomolecules, like vanillin, could be dissolved in reasonable amounts. In all tests, they performed at least as good as the tested reference substances, while showing similar cytotoxicity towards human skin keratinocytes, thus demonstrating their potential as green functional amphiphilic molecules of positive charge.

Surfactant-free microemulsions (SFME) comprising a cleavable hydrotrope/hydrophobic component were investigated regarding potential applications for green, microemulsion-mediated extraction processes. To this purpose, dynamic light scattering (DLS) experiments were performed for ternary systems consisting of water/(2, 2-dimethy1-1, 3-dioxolan-4-yl)methanol (Solketal)/oleic acid and water/ethanol/triethyl citrate (TEC) in order to detect mesoscopic structured compositions. Further, kinetic measurements were performed for the add-catalyzed hydrolysis of Solketal (cleavable hydrotrope) and base-catalyzed hydrolysis of TEC (cleavable hydrophobic component) at different temperatures/different pH of the aqueous pseudo-phase. As proof of concept, a-tocopherol and vanillic acid were dissolved in the ternary mixtures as extractable surrogates in order to simulate an extraction and separation process. It was found that well-structured SFME can be obtained for both systems, which basically allows microemulsion-mediated extraction. Moderate changes of temperature and/or pH, lead to rapid hydrolysis of Solketal and TEC within a few hours. Finally, it could be shown that upon hydrolysis of Solketal/TEC, separation of the used surrogate solutes from the hydrolysed products is facilitated and quantitative separation could be achieved. (C) 2018 Elsevier B.V. All rights reserved.

A library of quinazolinones was prepared by the one-pot three-component reaction of isatoic anhydride, ammonium salts/amines, and various electrophiles using aqueous hydrotropic solution as an efficient, economical, reusable, and green medium giving good to excellent yields of products in very short time. The method offers a versatile way for the development of diversity-oriented synthesis of quinazolinones.

The ability to aggregate and the solubilizing activity were estimated for typical hydrotropic compounds and their structural analogues, i.e. salts of acetic and aromatic acids as well as non-electrolytes such as thymol and N-methylglucamine. The effect of these additives on aggregation characteristics, viscosity and solubilizing properties of typical surfactants was studied together with the self-aggregation in individual additive solutions. A decrease of the surface tension of aqueous surfactant solutions was observed in the presence of thymol, whereas conductivity has unchanged. Viscosity in the cetyltrimethylammonium bromide (CTAB)–thymol system increases by more than two orders of magnitude as compared to individual CTAB micelles. A maximum increase in the solubilizing ability of the CTAB solutions was observed in the presence of N-methylglucamine.

Hydrotropes are an important class of molecules that enhance the solubility of an otherwise insoluble or sparingly soluble solute in water. Besides this, hydrotropes are also known to self-assemble in aqueous solution and form aggregates. It is the hydrotrope aggregate that helps in solubilizing a solute molecule in water. In view of this, we try to understand the underlying mechanism of self-aggregation of hydrotrope sodium cumene sulfonate (SCS) in water. We have carried out classical molecular dynamics simulations of aqueous SCS solutions with a regime of concentrations. Moreover, to examine the effect of temperature change on SCS aggregation, if any, we consider four different temperatures ranging from 298 to 358 K. From the estimation of densities of different solutions we calculate apparent and partial molal volumes of the hydrotrope. The changes in these quantities increase sharply at a characteristic minimum hydrotrope concentration. The determination of molal expansibility at infinite dilution for different temperatures indicates the water structure breaking by SCS molecules, which is further confirmed by the calculations of water-water pair correlation functions. In comparison with typical surfactants in micelles, a slightly lower value of volumetric change upon aggregation per carbon atom suggests the formation of a more closely packed structure of hydrotrope aggregates. A close examination of different structural properties of hydrotrope solutions reveals that the hydrophobic interactions through their hydrophobic tails significantly contribute in hydrotrope aggregation,and the dehydration of hydrophobic tail at elevated temperatures is also visible. Remarkably, the aggregates have little or no impact on the average number of water-SCS hydrogen bonds.

The organic transformation carried out in suitable solvent as well as in presence of catalyst is more important due to its environmental impact. We try to optimize the organic transformation in aqueous hydrotropic solution because of it is a sustainable technique. Now days, the glycerine used as hydrotrope and it shows excellent hydrotropic properties. Glycerine has been show combine advantages of water like non-toxic, colourless, odourless liquid, large availability, renewability due to this important properties it recently proposed as a valuable green solvent.

The creation of smart self-assembling fluids that undergo a morphological transition in response to a specific pH value can allow for the enhanced accumulation of drug delivery agents. In this work, we developed a series of pH-responsive fluids composed of 1-alkyl-3-methylimidazolium bromide [Cnmim]Br (n = 12, 14) and one of the pH-responsive hydrotropes of potassium hydrogen phthalate ([C6H4COOKCOOH]), sodium sulfosalicylate ([C6H3OHCOOHSO3Na]), or m-carboxylbenzenesulfonate sodium ([C6H4COOHSO3Na]). The self-assembled structures of these ILs in aqueous hydrotrope solutions were investigated by surface tension, dynamic light scattering, cryogenic-transmission electron microscopy, small-angle X-ray scattering, polarized optical microscopy, and nuclear magnetic resonance spectroscopy. It was found that the ionic liquids, [Cnmim]Br (n = 12, 14), could self-assemble into vesicles with the addition of the hydrotrope, and a reversible transition between spherical micelles and vesicles was observed with the change of solution pH value. The transition in the self-assembled structures of the ILs is suggested to be driven by the change in the molecular structure and hydrophilicity/hydrophobicity of the hydrotrope.