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Solubility, extraction and stabilization of curcumin extracted from Curcuma longa are still a challenge. Either the solubility power of the extracting solvent mixture is not at its optimum or non-sustainable solvents are used or the curcumin instability against oxidation is a problem. In order to tackle these problems, we consider here a promising alternative solvent medium, which is a ternary system composed of water/sodium salicylate (an anionic, preservative hydrotrope)/ethyl acetate. The effects of the structuring of the system are also studied. The position of the new critical point and the orientation of tie-lines in the liquid/liquid area were determined and further examined via interfacial tension and diffusion ordered spectroscopy (DOSY NMR) measurements. The critical point between the mono-phasic region and the liquid/liquid area is a classical one, around which no special nano-structuring is found, in contrast to some other ternary mixtures with hydrotropes. The system was investigated in terms of its curcumin solubility and its extraction power thereof. Good extraction yields (~90% of the Soxhlet reference) could be achieved in the area of best solubility. Surprisingly, the hydrophobic curcumin shows a significant solubility in systems that contain a significant amount of water in presence of sodium salicylate. These mixtures are far from the critical point but show significant structuring. The solubility is even higher than in pure ethyl acetate. At the point of highest solubility (water/sodium salicylate/ethyl acetate 7/13/80 w/w/w) 15.48 mg of curcuminoids per g Curcuma longa are successfully extracted. The partition coefficient in the lower liquid/liquid two-phasic region was determined for a subsequent purification of curcumin by precipitation. Surprisingly, curcumin accumulates at the “oil-water” interface in the more polar phase. Sodium salicylate could be removed from the precipitated curcumin by washing it with water (no trace of sodium salicylate has been detected with NMR after the washing process). The preservative effect of salicylate against the oxidative effect of light on curcumin was found to be significant. A better stabilization of curcumin was observed far away from the critical point and was most efficient in the region, where aggregates could be detected. So, extraction, solubilization, and chemical stabilization of a light sensitive substance could be performed using an anti-oxidative hydrotrope.

Nanometric ions, such as polyoxometalates (POMs) or ionic boron clusters, with low charge density have previously shown a strong propensity to bind to macrocycles and to adsorb to neutral surfaces: micellar, surfactant covered water–air and polymer surfaces. These association phenomena were shown to arise from a solvent-mediated effect called the (super-)chaotropic effect. We show here by combining cloud point (CP) measurements, scattering (SAXS/SANS) and spectroscopic techniques (NMR) that Keggin POMs: H4SiW12O40 (SiW) and H3PW12O40 (PW), induce the self-assembly of an organic solvent: dipropylene glycol n-propylether (C3P2), in water. The strong interaction between SiW/PW with C3P2 leads to a drastic increase in the CP, and aqueous solubility, of C3P2, e.g. SiW enables reaching full water-C3P2 co-miscibility at room temperature. At high POM concentrations, SiW leads to a continuous increase of the CP, forming SiW-[C3P2]1-2 complexes, whereas PW produces a decrease in the CP attributed to the formation of nearly “dry” spherical [PW]n[C3P2]m colloids, with n ~ 4 and m ~ 30. At high C3P2/PW contents, the [PW]n[C3P2]m colloids turn into large interconnected structures, delimiting two pseudo-phases: a PW-C3P2-rich phase and a water-rich phase. It is proposed that the stronger electrostatic repulsions between SiW (4−), compared to PW (3−), prevents the formation of mesoscopic colloids.

Understanding and Prediction of the Clouding Phenomenon by Spontaneous and Effective Packing Concepts. N2 - In this work, we show by which mechanism branching of the hydrocarbon chains influences the cloud point of nonionic, ethoxylated surfactants. The temp.-induced sepn. into a dil. and a concd. liq. phase is of liq.-gas type and can be explained by the relative probability of endcaps and branching points of the cylindrical micelles in both phases. The influence of branches on the hydrocarbon chains can be easily understood by means of spontaneous and effective packing concepts, while quantification via hydrophilic/lipophilic balance (HLB), hydrophilic-lipophilic difference (HLD), and HLD-Net Av. Curvature requires parametrization. The phase equil. above the cloud point phenomenon is equiv. to the Winsor I type phase equil., one of the five known phase equil. in ternary systems.

In the present contribution, we investigated the influence of the structuring of surfactant-free microemulsions (SFME) (water/1-propanol/limonene and water/tert-butanol/limonene) on the enzyme activity of horseradish peroxidase (HRP). To this purpose, the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) with hydrogen peroxide was chosen as a model reaction. Enzymatic activities in SFMEs of varying compositions were investigated by UV-Vis spectroscopy and compared to the enzyme activity in pure buffer solution. Dynamic light, small-angle-X-ray scattering and conductivity measurements were performed in order to obtain structural information on the used SFMEs. Findings presented in this study revealed that the ability of short-chain alcohols to form mesostructures (aqueous aggregates in oil) has a crucial effect on the enzyme activity in SFMEs. Mesoscale structuring with 1-propanol (NPA) was found to be more pronounced than for the more hydrophobic tert-butanol (TBA). It was concluded that the most pronounced mesoscale-structured SFMEs lead to the highest enzymatic activities.

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.

• The presence of nanostructures is demonstrated in a ternary melt of ethanol, 1-heptanol and rapeseed oil.

International audience; Ternary solutions containing one hydrotrope (such as ethanol) and two immiscible fluids, both being soluble in the hydrotrope at any proportion, show unexpected solubilization power and allow strange but yet unexplained membrane enzyme activity.We study the system-water-octanol as a simple model of such kinds of ternary solutions. The stability of “detergentless”micelles or microemulsions in such mixtures was proposed in the pioneering works of Barden and coworkers [Smith GD, Donelan CE, Barden RE (1977) J Colloid Interface Sci 60(3):488–496 and Keiser BA, Varie D, Barden RE, Holt SL (1979) J Phys Chem 83(10):1276–1281] in the 1970s and then, neglected, because no general explanation for the observations was available. Recent direct microstructural evidence by light, X-ray, and neutron scattering using contrast variation reopened the debate. We proposehere a general principle for solubilization without conventional surfactants: balance between hydration force and entropy. This balance explains the stability of microemulsions in homogeneous ternary mixtures based on cosolvents.

International audience

International audience

This paper gives an overview of weak aggregation due to long-range molecular forces beyond the first neighbor. Such subtle self-assemblies are an important part of modern colloidal chemistry and concern organic molecules as well as inorganic electrolytes and hybrid aggregates. Diverse aspects of such colloidal aggregations, as described in this special issue, can be characterized by the effective free energy per molecule involved. We discuss here expectations about emerging knowledge in this field and predictive modeling of inorganic as well as organic colloids and hybrid aggregates. Some still open questions are also given.

We show that three different morphologies exist near the two-phase boundary of ternary systems containing a hydrotropic cosolvent. Based on synchrotron small- and wide-angle X-ray scattering combined with molecular dynamics, we rationalize the specific scattering signature of direct, bicontinuous, and reverse mesoscale solubilization. Surprisingly, these mesostructures are resilient toward strong acids, which are required in industrial applications. However, on a macroscopic scale, the phase boundary shifts in salting-in and salting-out in the direct and respectively reverse regime, leading to a crossing of the binodals., Ultraflexible microemulsions that contain a hydrotropic cosolvent exist in three morphologies. Stability is reinforced by concentrated sulfuric acid in the water-rich corner and weakened in the octanol-rich corner.

International audience; In this work, we report that combination of levulinate as a renewably sourced anion with short chain alkyl ammonium as a cation yields room temperature ionic liquids that are capable of dissolving up to 10 wt% of microcrystalline cellulose. This dissolution results in a change of the cellulose crystalline structure from cellulose I to cellulose II, a pre-requisite step known to significantly improve the accessibility of cellulose to enzymes. As compared to previous methodologies, such ILs tolerate the presence of up to 18 wt% of water. Hence technical grade ILs can be used, thus avoiding the energy-consuming drying process generally required with traditional ILs before dissolution experiments. In addition, such ILs can be mixed with 20 wt% of.-valerolactone, a renewably-sourced co-solvent, resulting in an improvement of the cellulose dissolution up to 20 wt% while concomitantly increasing the sustainability of these media. Finally, prepared ILs were proved to be biodegradable according to the OCDE 301F directive, thus opening a promising route for the pre-treatment of cellulose with a higher eco-efficiency.

A transition from micelles to vesicles is reported when salts are added to a catanionic micellar solution composed of sodium dodecylcarboxylate (SL) and dodecyltrimethylammonium bromide (DTAB), with an excess of SL. The counterion binding and increase in aggregate size was monitored by mass spectrometry, rheology and dynamic light scattering measurements, whereas the vesicles were characterized by freeze-fracture and cryo-transmission microscopy experiments. The effect of counterions on the formation of vesicles was studied and compared to a previously studied catanionic system with a sulfate head group, SDS/DTAB. As in the latter case, no anion specificity was found, while large differences in the hydrodynamic radii of the formed objects were observed, when the cation of the added salt was varied. A classification of the cations could be made according to their ability to increase the measured hydrodynamic radii. It is observed that, if the sulfate headgroup of the anionic surfactant is replaced by a carboxylic group, the order of the ions is reversed, i.e. it follows the reversed Hofmeister series. Different morphologies are observed as the ionic strength of the system is increased. The aggregates are analogous to those found in the SDS/DTAB system.

The stepwise solvation-equilibrium model of Stokes and Robinson is used for a description of departures from ideality in ionic solutions. It is shown how to construct a thermodynamically consistent model including solvation effects. Simple expressions are derived for the mean ion solvation number. The model is applied to strong electrolyte solutions (pure water+salt and mixed aqueous solvent+salt) by taking the mean spherical approximation (MSA) for the long-range contribution to the Gibbs energy and a local composition model, the nonrandom two-liquid (NRTL) model, for the short-range contribution.

Osmotic coefficients of a series of 16 aqueous electrolyte solutions are described at concentrations up to about 1 M with the help of HNC calculations and solvent-averaged potentials of charged hard spheres with an additional necessary dispersion potential, omitted from all earlier treatments. The adjusted ionic radii and excess polarizabilities have values of the expected order of magnitude. Whereas the description of the bulk properties is satisfactory, the theory is not so successful in predicting the surface tensions of the corresponding solutions (Hofmeister series). The reasons for this are quite subtle and explored in the text. It is clear now how to make further progress and tackle hydration in a consistent way.

The kinetics of alcohol oxidation catalyzed by the enzyme horse liver alcohol dehydrogenase (HLADH) is studied in water/alcohol/C12E23 systems with a series of n-alcohols ranging from ethanol to 1-decanol or with ,-alkandiols, namely, 1,5-pentanediol and 1,7-heptanediol. Essentially, the water-rich part of the ternary systems is examined, either without C12E23 or at several constant C12E23 concentrations above the cmc (1, 8, and 22 mass %). The substrate inhibition of the enzyme allows one to infer alcohol partition coefficients between the outer aqueous pseudophase and the surfactant aggregation pseudophase. In the case of short-chain n-alcohol (ethanol, 1-propanol) and alkandiol (1,5-pentanediol) systems, the alcohol seems to remain in the aqueous pseudophase, whereas in the case of middle- and long-chain n-alcohol (1-butanol to 1-decanol) and alkandiol (1,7-heptandiol) systems, the alcohol participates in the structuration of the micelle.

Modelling of the thermodynamic properties of electrolyte solutions for industrial interestsThis work is aimed at providing a description of he thermodynamics properties of electrolyte solutions for industrial interests. The model used here is based on a previous study (N. Papaiconomou et al.) combining the Mean Spherical Approximation MSA (Mean Spherical Approximation) theory to describe long-range electrostatic interactions, with the popular model in chemical engineering, i.e. NRTL ( Nonrandom Two-Liquid), for the representation of short-range interactions. This previous description has been improved by adding the ionic solvation effect with the help of two distinct models : (a) Robinson and Stokes one which involves a constant solvation number vs. salt concentration, and (b) modellling of the thermodynamic of ionic solutions using a stepwise solvation equilibrium model. In addition to this work, we have attempted a description of VLE (Vapor-Liquid equilibria) for aqueous solutions in a wide range of temperature, 25°C to 100°C., Le présent travail se propose de décrire les propriétés thermodynamiques des solutions d'intérêt industriel. Notre modèle s'appuie sur un travail antérieur (N. Papaiconomou et al.), combinant la théorie Mean Spherical Approximation (MSA) pour décrire les interactions électrostatiques à longue portée et le modèle NRTL (très populaire en génie chimique), pour celles qui sont à courte portée. Par rapport à ce précédent travail, nous avons de plus pris en compte l'effet de solvatation ionique, à l'aide de deux modèles différents : (a) celui de Stokes et Robinson impliquant un nombre de solvatation constant (en fonction de la concentration du sel) ; (b) une solution procédant d'équilibre réactionnels avec les molécules d'eau, résultant en un degré de solvatation variant avec la concentration de sel. De plus, nous avons cherché à décrire les équilibres L-V pour des solutions aqueuses et de mélanges de solvants, pour des températures allant de 25°C à 100°C.