Spontaneous Emulsification of Organometallic Complexes Applied to the Synthesis of Nanocapsules Active for H2 Release from Ammonia-Borane.

Herein, we achieved spontaneous emulsification of organometallic precursors to elaborate subµm metal nanocapsules after interfacial reduction. Depending on the proportion of the three components, water, solvent, and the metal precursor, either thermodynamically stable "surfactant-free microemulsions" (SFME) or metastable Ouzo emulsions are formed. We investigated the catalytic transition metals Au, Pd, and Pt, individually or combined, and stabilized by various ligands. Upon reduction of the precursors, either shells of discrete nanoparticles (NPs) or continuous shells were obtained, for the SFME and Ouzo emulsions, respectively. The Au/Pd mixed emulsions lead to a unique structural morphology, in which the Au-Pd nanoparticles are embedded in a continuous submicronic metal shell. The AuNPs are available to grow larger particles within the NP shell using a seeded growth approach. The water-stable and surfactant-free nanocapsules are appealing as catalysts, and, as such, were evaluated for the hydrolysis of ammonia-borane as a promising catalytic strategy for H2 release from an H-high-content storage material. This work establishes for the first time a genuine activity of water-compatible gold colloids for this reaction.

Simple elaboration of drug-SPION nanocapsules (hybridosomes®) by solvent shifting: Effect of the drug molecular structure and concentration.

Drug nanocapsules coated with iron oxide nanoparticles (SPION) were elaborated by the simultaneous nanoprecipitation of the drug and the nanoparticles, through solvent shifting. We examined four drugs: sorafenib, sorafenib tosylate, α-tocopherol and paclitaxel, to cover the cases of molecular solids, ionic solids, and molecular liquids. We first investigated the formation of the drug core in the final mixture of solvents at different concentrations. A Surfactant-Free Micro-Emulsion domain (SFME, thermodynamically stable) was observed at low drug concentration and an Ouzo domain (metastable) at high drug concentration, except for the case of paclitaxel which crystallizes at high concentration without forming an Ouzo domain. When co-nanoprecipitated with the molecular drugs in the Ouzo domain (sorafenib or α-tocopherol), the SPION limited the coalescence of the drug particles to less than 100 nm, forming capsules with a drug encapsulation efficiency of ca 80 %. In contrast, larger capsules were formed from the SFME or when using the ionic form (sorafenib tosylate). Finally, the sorafenib-SPION capsules exhibit a similar chemotherapeutic effect as the free drug on the hepatocellular carcinoma in vitro.

Shedding light on the formation and stability of mesostructures in ternary "Ouzo" mixtures.

HYPOTHESIS: Ternary systems made of water, a water-miscible solvent, and hydrophobic solutes spontaneously produce metastable particles by the "Ouzo effect" and thermodynamically stable "Surfactant-Free Micro Emulsions" (SFME). However, the use of different analyses has led to a variability in the criteria to determine the boundaries of the Ouzo domain. We hypothesized that this could be clarified by investigating the stability and the physical state of the particles. EXPERIMENTS: We investigate four systems using both solid and liquid solutes and two different solvents, and achieved a careful investigation of their phase diagrams, using DLS, Nanoparticle Tracking Analysis, NMR, Multiple Light Scattering, electrophoretic mobility, and fluorescence analysis. FINDINGS: Our results evidence that the transition from the monophasic to the Ouzo domains does not coincide with the cloudiness curve, and that compositions in the Ouzo domain can look fully transparent, in contrast to what is often considered. This transition is best determined by stability analysis. The cloudiness curve corresponds to the formation of particles with a large size dispersity. In the Ouzo domain, we observed an exchange of solute between the continuous phase and solute particles swollen with solvent. In addition, the particles are stabilized against coalescence by their high negative charge.

Effect of nanoparticles on spontaneous Ouzo emulsification.

Particles stabilize fluid interfaces. In particular, oil/water Pickering emulsions undergo limited coalescence, yielding droplets of smaller size as the amount of particles is increased. Herein, we studied the effect of hydrophobic nanoparticles (<10 nm, alkyl-coated) on submicronic droplets (ca 100 nm) formed in an Ouzo system. We investigated thoroughly the water/tetrahydrofuran (THF)/butylated hydroxytoluene (BHT) reference diagram, in the absence and in the presence of nanoparticles, using the Nanoparticle Tracking Analysis (NTA) technique. This allowed us to characterize the size distributions in a much finer way than what is usually obtained using conventional Dynamic Light Scattering (DLS). Both a Surfactant-Free Microemulsion (SFME, thermodynamically stable) and an Ouzo (metastable spontaneous emulsion) domains were identified and the transition from one to the other could be characterized by specific features of the droplet size distributions. We found that the presence of the nanoparticles limits coalescence in the metastable domain. We also show that the alkyl-coated nanoparticles are irreversibly attached to the liquid-liquid interface.