Studies and development of deep eutectic solvents for the extraction of seaweed metabolites for cosmetic purposes

Dans ce travail, nous développerons l’utilisation de solvants eutectiques profonds (DES) pour l’hydrolyse des polysaccharides et l’extraction de métabolites de macroalgues. Nos cibles privilégiées seront les polyphénols, les caroténoïdes ou encore les chlorophylles présentant un pouvoir antioxydant intéressant en cosmétique. L’objectif de ces travaux est de caractériser les DES et d’extraire des métabolites d’algues avec ces solvants pour qu’ils soient formulés en cosmétique. Les DES sont composés de deux ou trois constituants pouvant s’associer via des liaisons hydrogènes. Ils ont la particularité de former un eutectique leur donnant un point de fusion plus bas que leurs composants seuls. De nombreux constituants peuvent jouer le rôle d’accepteur et de donneur de liaison hydrogène dans les DES comme les alcools, les sucres, les acides organiques, les acides aminés ou encore les ammoniums quaternaires. Dans ce manuscrit, nous aborderons la caractérisation physico-chimique de ces solvants (teneur en eau, miscibilité, pH, viscosité, conductivité, polarité…). Une étude de l’impact de la dilution dans l’eau sera également effectuée. Une partie de ces travaux sera consacrée aux interactions et liaisons hydrogènes établies par spectroscopie RMN, spectrométrie de masse et RAMAN. Après l’étude de ces paramètres physico-chimiques et structuraux, les différents facteurs d’extraction des composés d’intérêt seront évalués. Nous aborderons ainsi l’influence de l’espèce d’algue utilisée, le pourcentage de matière sèche introduit, le solvant utilisé, la température ou encore le temps d’extraction. L’ensemble de ces facteurs sera étudié au travers de plans d’expériences de criblage.In this work, we will develop the use of deep eutectic solvents (DES) for the hydrolysis of polysaccharides and the extraction of seaweed metabolites. Our selected target will be polyphenols, carotenoids or chlorophylls which show antioxidant capacity interesting for cosmetics. The aim of this work is to charaterize DES and extract seaweed metabolites with these solvents for formulation in cosmetics. DES are formed by association of two or three constituents via hydrogen bonds. The eutectic giving them a lower melting point than their separated components. Many constituents can be hydrogen bond acceptors or donnors in DES such as alcohols, sugars, organic acids, amino acids or quaternary ammoniums. In this manuscript, we will discuss the physicochemical characterization of these solvents (water content, miscibility, pH, viscosity, conductivity, polarity…). Impact of the water dilution will also be performed. Part of this work will be devoted to the interactions and hydrogen bonds established by NMR spectroscopy, mass spectrometry and RAMAN. After the study of this physicochemical and structural parameters, different extraction factors of the compounds of interest will be assessed. We will broach in this way the influence of the species of seaweed, the percentage of dry matter, the solvent used and the extraction temperature and time. All of this factors will be studied through design of experiments

Electrochemical Determination and Antioxidant Capacity Modulation of Polyphenols in Deep Eutectic Solvents

International audienceDeep eutectic solvents (DES) are currently developed as ecofriendly and efficient solvents for polyphenol extraction. However, a challenge remains in these processes concerning polyphenol determination that is routinely performed through colorimetric Folin-Ciocalteu assays. Besides the fact that these assays use toxic reagents, they may have serious limitations in some DES media due to possible side reactions or interferences with the DES components as found herein with ethaline (choline chloride/ethylene glycol (1:2)) or betaine/citric acid (2:3). An alternative method based on simple electrochemical analyses directly performed in DES-based media is proposed. Since the direct electrochemistry of polyphenols in DES has been hardly explored, nine polyphenolic standards including seven flavonoids are examined and their electrochemical behaviors are found closely related to those classically obtained in traditional solvents, notably in aqueous solutions. A linear relationship is obtained between concentration and peak current intensity for quercetin in the range 10-5-10-4 mol·L-1, demonstrating the potential of the method for polyphenol content quantitation. More importantly, their antioxidant capacity is evaluated by differential pulse voltammetry through the measurements of the redox potentials. An interesting variation is observed according to the nature of the DES components, suggesting that the antioxidant activity of polyphenols can be modulated through the choice of the DES. Moreover, a good stability of the polyphenol samples in the DES-water mixture under study is obtained after storage for 10 months at 30 ° C. These results open appealing perspectives in polyphenol extraction processes using eutectic solvents as extracting media that can be part of formulation for cosmetic or pharmaceutical applications, resulting in high-added-value extracts.

Extraction of Plant and Algal Polyphenols Using Eutectic Solvents

International audienc

Electron Transfer Kinetics in a Deep Eutectic Solvent

International audienceElectron transfer (ET) kinetic rate constants k in Ethaline (12 choline chloride + ethylene glycol) have been measured for two common redox couples (ferrocene/ferrocenium and ferrocyanide/ferricyanide) on a glassy carbon electrode and compared with ET kinetics in ionic liquids and classical organic solvents in the same conditions (acetonitrile and water). Particular care has been taken to treat ohmic drop in DES. For both couples, we found that ET rate constants are just a little lower than those measured in classical solvents (around 50% or less). These results contrast with ET rates in ionic liquids where electron transfers are considerably slower (100 times lower). Data are discussed as a function of the solvent relaxation time using Marcus Theory for an adiabatic electron transfer

Cold-spray ionization mass spectrometry of the choline chloride-urea deep eutectic solvent (reline)

International audienceCold-Spray Ionization mass spectrometry (CSI-MS) that can be compared to an electrospray ionization (ESI) source acting with a nebulizing gas cooled by liquid nitrogen is used for analyzing reline as Deep Eutectic Solvent (DES). The association of cholinium chloride salts with urea molecules is evidenced in negative CSI-MS through the chloride adduct formation. The structure of the supramolecular assemblies forming the reline ions that are observed on CSI mass spectra is rationalized by chemical quantum calculations. The theoretical studies indicate that the ionic network organization is only supported by a maximization of hydrogen bonds of the chlorides with the hydroxyl and methyl moieties of the cholinium cations and the amino groups of urea. The studies of gas-phase fragmentation of the supra-molecular ionic assemblies detected in CSI-MS are performed using the in-source collision-induced dissociation experiments. The experimental measurements in CSI-MS, interpreted at the light of the molecular modelization results, suggest that the insertion of urea in adducts of chlorides with cholinium cations does not lead to the most stable ions

Do Deep Eutectic Solvents Form Uniform Mixtures Beyond Molecular Microheterogeneities?

International audienceWe have performed small-angle neutron scattering in a momentum transfer range (0.05 < < 0.5 Å) to study long-range order and concentration fluctuations in deep eutectic solvents (DESs) and their aqueous solutions. Ethaline (choline chloride/ethylene glycol), glycerol/lactic acid, and menthol/decanoic acid mixtures were selected to illustrate individually the case of ionic, nonionic, and hydrophobic mixtures. Carefully designed isotopic labeling was used to emphasize selectively the spatial correlations between the different solvent components. For ethaline DESs and their aqueous solutions, a weak low- peak observed only for certain compositions and some partial structure factors revealed the mesoscopic segregation of ethylene glycol molecules that do not participate in the solvation of ionic units, either because they are in excess with respect to the eutectic stoichiometry (1:4 neat ethaline) or substituted by water (4-ethaline and higher aqueous dilutions). For the nonionic hydrophilic solutions, such a mesoscopic segregation was not observed. This indicates that the better balanced interactions between the three nonionic H-bonded components (water, lactic acid, and glycerol) favor homogeneous mixing. For the hydrophobic DESs, we observed an excess of coherent scattering intensity centered at = 0, which could be reproduced by a model of noninteracting spherical domains. Local concentration fluctuations are not excluded either. However, unlike liquid mixtures with a tendency to demix, we have found no evidence of expansion of domains with different compositions to a large scale

Di- and heptavalent nicotinic analogues to interfere with alpha 7 nicotinic acetylcholine receptors

International audienceIn the field of nicotinic acetylcholine receptors (nAChRs), recognized as important therapeutic targets, much effort has been dedicated to the development of nicotinic analogues to agonize or antagonize distinct homo-and heteropentamers nAChR subtypes, selectively. In this work we developed di- and heptavalent nicotinic derivatives based on ethylene glycol (EG) and cyclodextrin cores, respectively. The compounds showed a concentration dependent inhibition of acetylcholine-induced currents on alpha 7 nAChR expressed by Xenopus oocytes. Interesting features were observed with the divalent nicotinic derivatives, acting as antagonists with varied inhibitory concentrations (IC50) in function of the spacer arm length. The best divalent compounds showed a 16-fold lowered IC50 compared to the monovalent reference (12 vs 195 mu M). Docking investigations provide guidelines to rationalize these experimental findings