Low-melting mixtures based on choline ionic liquids.

In this article a strategy is proposed for the design of low toxic, room temperature liquid low-melting mixtures (LMMs) which are entirely composed of natural materials. From literature it is well known that, in general, deep eutectic solvents based on choline chloride and dicarboxylic acids are LMMs, but not liquids at room temperature, with one exception: a 1 : 1 molar mixture of malonic acid and choline chloride. Therefore, the starting point of this study was the decrease of the melting point of one of the components, namely the dicarboxylic acid, which is succinic, glutaric or adipic acid. For this purpose, one of the two protons of the acidic group was exchanged by a bulky unsymmetrical choline cation. The resulting ionic liquids (ILs) were still solid at room temperature, but have a reduced melting temperature compared to the corresponding acids. In the second step, mixtures of these ILs with choline chloride were prepared. It turned out that choline glutarate-choline chloride mixtures are liquids at room temperature at compositions containing 95-98 wt% of choline glutarate. Finally, urea was added as another hydrogen bond donor. Density, conductivity and viscosity measurements were performed for all obtained mixtures. Moreover, a Walden plot was drawn which indicates that all mixtures are liquids with fully dissociated ions moving independently. Therefore, they are considered as "good" ionic liquids and, thus, for example they can be used to exchange more toxic or less biodegradable ILs in application processes. A brief outlook containing application possibilities is given. It is demonstrated that choline dodecylsulfate is readily soluble in these mixtures, forming aggregates in the LMM at temperatures exceeding 55 °C.

Influence of chain length and double bond on the aqueous behavior of choline carboxylate soaps.

In preceding studies, we demonstrated that choline carboxylates ChC(m) with alkyl chain lengths of m = 12 - 18 are highly water-soluble (for m = 12, soluble up to 93 wt % soap and 0 °C). In addition, choline soaps are featured by an extraordinary lyotropic phase behavior. With decreasing water concentration, the following phases were found: micellar phase (L(1)), discontinuous cubic phase (I(1)' and I(1)"), hexagonal phase (H(1)), bicontinuous cubic phase (V(1)), and lamellar phase (L(α)). The present work is also focused on the lyotropic phase behavior of choline soaps but with shorter alkyl chains or different alkyl chain properties. We have investigated the aqueous phase behavior of choline soaps with C(8) and C(10) chain-lengths (choline octanoate and choline decanoate) and with a C(18) chain-length with a cis-double bond (choline oleate). We found that choline decanoate follows the lyotropic phase behavior of the longer-chain homologues mentioned above. Choline octanoate in water shows no discontinuous cubic phases, but an extended, isotropic micellar solution phase. In addition, choline octanoate is at the limit between a surfactant and a hydrotrope. The double bond in choline oleate leads also to a better solubility in water and a decrease of the solubilization temperature. It also influences the Gaussian curvature of the aggregates which results in a loss of discontinuous cubic phases in the binary phase diagram. The different lyotropic mesophases were identified by the penetration scan technique with polarizing light microscope and visual observations. To clarify the structural behavior small (SAXS) and wide (WAXS) angle X-ray scattering were performed. To further characterize the extended, isotropic micellar solution phase in the binary phase diagram of choline octanoate viscosity and conductivity measurements were also carried out.

Effect of choline carboxylate ionic liquids on biological membranes.

Choline carboxylates, ChCm, with m=2-10 and choline oleate are known as biocompatible substances, yet their influence on biological membranes is not well-known, and the effect on human skin has not previously been investigated. The short chain choline carboxylates ChCm with m=2, 4, 6 act as hydrotropes, solubilizing hydrophobic compounds in aqueous solution, while the longer chain choline carboxylates ChCm with m=8, 10 and oleate are able to form micelles. In the present study, the cytotoxicity of choline carboxylates was tested using HeLa and SK-MEL-28 cells. The influence of these substances on liposomes prepared from dipalmitoylphosphatidylcholine (DPPC) was also evaluated to provide insights on membrane interactions. It was observed that the choline carboxylates with a chain length of m>8 distinctly influence the bilayer, while the shorter ones had minimal interaction with the liposomes.

Removal of acrylic coatings from works of art by means of nanofluids: understanding the mechanism at the nanoscale.

Conservation of works of art often involves the inappropriate application of synthetic polymers. We have proposed the use of alternative methodologies for conservation and formulated innovative cleaning nanostructured systems to remove previously applied polymer films and grime from painted surfaces. In particular, a novel "micellar system" composed of water, SDS, 1-pentanol, ethyl acetate and propylene carbonate was recently formulated and successfully used to remove acrylic and vinyl/acrylic copolymers from Mesoamerican wall paintings in the archeological site of Cholula, Mexico. This contribution reports on the mechanism of the interaction process that takes place between the nanostructured fluid and the polymer coating at the nanoscale. The structural properties of the "micellar solution" and of the polymer film are investigated before, during and after the interaction process using several surface and solution techniques. Rather than a classical detergency mechanism, we demonstrate that micelles act as solvent containers and interact with the polymer film leading to its swelling and detachment from the surface and to its segregation in a liquid droplet, which phase-separates from the aqueous bulk. After the removal process the micelles become smaller in size and undergo a structural re-arrangement due to the depletion of the organic solvents. These findings can be framed in an interaction mechanism which describes the removal process, opening up new perspectives in the design and formulation of new cleaning systems specifically tailored for intervention on particular conservation issues.