TiO2 nanoparticle dispersions in water and nonaqueous solvents studied by gravitational sedimentation analysis: Complementarity of Hansen Parameters and DLVO interpretations

Hansen Solubility Parameters (HSP) have been shown to be an effective approach for rationalizing and predicting the stability of titanium dioxide nanoparticles (TiO2 NPs) dispersions. However, interparticle electrostatic interactions, not considered in Hansen's approach but taken into account in the DLVO theory, are expected to play a significant role in organic solvents having a notable dielectric constant. Zeta potential zeta of TiO2 P25 NPs was measured in both aqueous and organic media to identify DLVO-stabilized dispersions from those stabilized by more specific NP-solvent interaction. Stability was quantified using a Turbiscan optical device which provides Stokes diameters and Relative Turbiscan Stability Index (RTSI). When the zeta potential of NPs and the dielectric constant of the solvent are both high, the dispersion benefits from additional stabilization while when the electrostatic repulsion is negligible, only the solvents within a Hansen dispersion sphere give stable dispersions. The two interpretations are therefore complementary to describe the behavior of TiO2 dispersions in organic solvents

Novel green production of natural-like vanilla extract from curcuminoids

The demand for natural vanilla extract, and vanillin in particular, by far exceeds the current production, as both the cultivation of vanilla beans and the extraction of vanillin are laborious. For this purpose, most vanillin used today is produced synthetically, contrary to the general trend toward bio-based products. The present study deals with the synthesis of nature-based vanillin, starting with the more accessible rhizomes of the plant Curcuma longa. Besides vanillin, vanillic acid and p-hydroxybenzaldehyde are synthesized that way, which are also found in the natural vanilla bean. The extraction of the curcuminoids and, finally, their conversion to the flavors are performed using visible light and food-grade chemicals only. A binary mixture of ethanol and triacetin, as well as a surfactant-free microemulsion consisting of water, ethanol, and triacetin, are investigated in this context. The results exceed the literature values for Soxhlet extraction of vanilla beans by a factor > 7

Solubilization and extraction of curcumin from Curcuma Longa using green, sustainable, and food-approved surfactant-free microemulsions

Curcumin is a powerful coloring agent widely used in the food industry. Its extraction from the plant Curcuma longa is commonly done with aqueous solvent solutions. In contrast to the conventional extraction methods, the present study aimed to compare two different green and bio-based surfactant-free microemulsion (SFME) extraction systems, which are approved for food and yield a higher extracting power of curcuminoids. Two SFMEs, water/ethanol/triacetin and water/diacetin/triacetin, were investigated via dynamic light scattering. Curcumin solubility in binary mixtures consisting of ethanol/triacetin or diacetin/triacetin was studied both experimentally and theoretically using UV-Vis measurements and COSMO-RS. The SFMEs were further examined and compared to a common ethanol/water (80/20) extraction mixture with respect to their extracting ability using high performance liquid chromatography. The SFMEs containing ethanol were found to extract similar to 18% more curcuminoids than the SFMEs containing diacetin and similar to 53% more than the ordinary ethanol/water mixture

Salting-in and salting-out effects of short amphiphilic molecules: a balance between specific ion effects and hydrophobicity

Amphiphilic molecules (e.g. hydrotropes) that enhance the solubility of hydrophobic compounds in water are often charged. As a result, such compounds also show specific ion effects. These effects can either strengthen or weaken the solubilisation power of amphiphilic molecules, depending on their degree of ion hydration. They can even prevail and transform an apparent solubilizer into an "anti-hydrotrope", i.e. a salting-out agent. In the present paper, we discuss this subtle balance between specific (Hofmeister) effects exerted by ionic headgroups and the hydrophobicity of the residual compound structure, including the size of the molecule and the presence of electron-withdrawing groups

Enforced Electronic-Donor-Acceptor Complex Formation in Water for Photochemical Cross-Coupling

The amino alcohol meglumine solubilizes organic compounds in water and enforces the formation of electron donor acceptor (EDA) complexes of haloarenes with indoles, anilines, anisoles or thiols, which are not observed in organic solvents. UV-A photoinduced electron transfer within the EDA complexes induces the mesolytic cleavage of the halide ion and radical recombination of the arenes leading, after rearomatization and proton loss to C–C or C–S coupling products. Depending on the substitution pattern selective and unique cross-couplings are observed. UV and NMR measurements reveal the importance of the assembly for the photoinduced reaction. Enforced EDA aggregate formation in water allows new activation modes for organic photochemical synthesis