Switchable self-assembly of Prussian blue analogs nano-tiles triggered by salt stimulus.

Prussian blue analogs (PBAs) are materials well known for their bulk physical and (electro)-chemical properties, with an outstanding selectivity for caesium in ion exchange processes. Crystalline nano-tiles, made of copper based PBA, are produced and dispersed in water by tuning their electrostatic interactions. The shape and size of the nano-crystals are determined by combining scattering, microscopic and spectral techniques. We show here that Cu-PBA nano-tiles form planar superstructures by an edge to edge self-assembly process controlled by specific cation effect and ionic strength. Sedimentation and (re-)dispersion of the nano-tiles are found to be fully reversible. This switchable anisotropic self-assembly triggered by salt stimulus makes PBA nanocrystals potentially interesting for applications.

Covalent amphiphilic polyoxometalates for the design of biphasic microemulsion systems.

Covalent amphiphilic polyoxometalates generated from alkylphosphonic acids have been synthesized, characterized and monitored by multinuclear NMR spectroscopy. Among them, K3H[γ-SiW10O36(C12H25PO)2] has been successfully used as a surfactant for the stabilization of a Winsor I type microemulsion system.

Solubilization in alkanes by alcohols as reverse hydrotropes or "lipotropes".

Hydrotropes in aqueous systems do not aggregate in micelles, inhibit presence of mesophases and allow significant and progressive solubilization of "insoluble" molecules in water. It was shown that n-alcohols in alkanes develop the same properties, including the power-law for maximum solubilization of "hydrophilic" molecules. The aim of this paper is to highlight properties of reverse hydrotropes or "lipotropes" by taking n-alcohol/alkane mixtures as model systems. So as to establish a clear parallel between lipotropes and hydrotropes the same methodology used to characterize hydrotropes was applied to these systems. The solubilization of solutes insoluble in alkane, i.e. water and a hydrophilic dye in dodecane, enabled by the addition of n-alcohols ( n = 2, 3, 4 and 7) was studied. In parallel, the nonmicellar aggregation state of butan-1-ol and heptan-1-ol in dodecane was investigated by small-angle X-ray scattering. By applying the Porod's treatment the specific area of the H-bond network formed by heptan-1-ol and the area occupied by hydroxyl group in this network were determined as a function of concentration. A correlation between the aggregation of alcohols in dodecane and the solubilization was made. The disrupting of concentrated mesophases by a lipotrope was illustrated by studying the effect of adding n-alcohols to water/oil/extractant ternary systems used in liquid/liquid extraction. Under some conditions the organic phase splits up into two phases: an extractant mesophase and nearly pure oil. The amount of n-alcohols required to make the extractant mesophase disappear was determined for water/alkane/malonamide extractant systems. The influence of the chain length of the n-alcohol on the efficiency as lipotrope was also experimentally studied. The trend obtained was similar to the one observed with the solubilization experiments.

Relation between the hydrophile/hydrophobe ratio of malonamide extractants and the stability of the organic phase: investigation at high extractant concentrations.

In the present paper, it is shown that in malonamide extractant/dodecane mixtures, change in the shape of the extractant aggregate may promote phase demixion. This phenomenon is known as the 3rd phase formation in extractant systems. The shape of the aggregates is dictated by the length of the alkyl chains stabilizing the reverse microemulsion by steric repulsion. Small angle scattering experiments are used to investigate the aggregation states of diamide extractant molecules, namely N,N'dimethyl-N,N'dibutyl-tetradecyl malonamide (DMDBTDMA) and N,N'dimethyl-N,N'dibutyl-pentyl malonamide (DMDBPMA), in dodecane. The results are described in a consistent way by the packing parameter concept and by expressing steric repulsion versus Van der Waals inter-aggregate interactions, both curvature dependants. Non-monotonous change in the extractant Critical Micellar Concentration (CMC) as a function of the extractant alkyl chain length is rationalized by comparing Van der Waals attraction between the alkyl chains of both the extractant and the solvent.

Specific alkali cation effects in the transition from micelles to vesicles through salt addition.

The transition of ionic micelles to vesicles with added salts is explored in this paper. The catanionic surfactant solution was comprised of sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) with an excess of SDS. The micellar size increased with concentration for all salts. No anion specificity was found, probably because of the excess of SDS. However, when the cation of the added salt was varied, large differences were observed in the hydrodynamic radii of the aggregates. A classification of the cations according to their ability to increase the measured hydrodynamic radii follows a Hofmeister series. The change in aggregate size can be explained by modified counterion binding and dehydration of the surfactant headgroups.

Unified concept of solubilization in water by hydrotropes and cosolvents.

In the present work hydrophobic dyes, i.e. disperse red 13 (DR-13; (2-[4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino]ethanol) and Jaune au gras W1201 (1H-indene-1,3(2H)-dione,2-(2-quinolinyl)), are solubilized in water with the help of different additives: acetone and 1-propanol as typical cosolvents, sodium xylene sulfonate (SXS) as a representative of a classical hydrotrope, sodium dodecyl sulfate (SDS) as a typical surfactant, and finally some "solvosurfactants" [ propylene glycol monoalkyl ether derivatives (CiPOj: i = 1, j = 1 and 3; i = 3, j = 1 and 2; i = 4 and tertio-butyl, j = 1) and 1-propoxy-2-ethanol (C3EO1)]. These solvosurfactants are short amphiphiles that do not form well-defined structures in water such as micelles. For all additives an exponential increase in the solubilizations of the two studied hydrophobic dyes was observed when their concentrations in water were increased. Except for the SDS solution, no difference in the overall shapes of the solubilization curves (dye solubility against additive concentration) was found. All the studied molecules were classified according to their hydrotropic efficiencies, i.e., their abilities to solubilize a hydrophobic, sparingly soluble compound in water. The volume of the hydrophobic parts of the studied additives, roughly evaluated by simple calculations, was found to influence strongly the hydrotropic efficiency; i.e. the larger the hydrophobic part of the additive, the better the hydrotropic efficiency. By contrast, the hydrophilic part carrying a charge or not is of minor importance. Taking the hydrophobic part of the molecules as the key parameter, the water solubilization efficiency of cosolvents, hydrotropes, and solvosurfactants can be described in a coherent way.

Hofmeister effects in biology: effect of choline addition on the salt-induced super activity of horseradish peroxidase and its implication for salt resistance of plants.

The effect of choline addition on the salt-induced super activity of horseradish peroxidase (HRP) is investigated. HRP is presented in the literature as an efficient H(2)O(2) scavenger, and choline is the precursor of glycine betaine, a strong osmoprotectant molecule. Both the regulations of H(2)O(2) and of osmoprotectant concentrations are implicated in plants in order to counteract salt-induced cell damage. For the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), sulfate anions were found to play a crucial role in the increase of HRP activity. This induced super activity can be strongly reduced by adding choline chloride. The phenomena provide an example of physicochemical Hofmeister effects playing a central regulatory role in an important biological system.