Imprinting isolated single iron atoms onto mesoporous silica by templating with metallosurfactants.

HYPOTHESIS: One of the main drawbacks of metal-supported materials, traditionally prepared by the impregnation of metal salts onto pre-synthesized porous supports, is the formation of large and unevenly dispersed particles. Generally, the larger are the particles, the lower is the number of catalytic sites. Maximum atom exposure can be reached within single-atom materials, which appear therefore as the next generation of porous catalysts. EXPERIMENTS: Herein, we designed single iron atom-supported silica materials through sol-gel hydrothermal treatment using mixtures of a non-ionic surfactant (Pluronic P123) and a metallosurfactant (cetyltrimethylammoniumtrichloromonobromoferrate, CTAF) as porogens. The ratio between the Pluronic P123 and the CTAF enables to control the silica structural and textural properties. More importantly, CTAF acts as an iron source, which amount could be simply tuned by varying the non-ionic/metallo surfactants molar ratio. FINDINGS: The fine distribution of iron atoms onto the silica mesopores results from the iron distribution within the mixed micelles, which serve as templates for the polymerization of the silica matrix. Several characterization methods were used to determine the structural and textural properties of the silica material (XRD, N2 sorption isotherms and TEM) and the homogeneous distribution and lack of clustering of iron atoms in the resulting materials (elemental analysis, magnetic measurements, pair distribution function (PDF), MAS-NMR and TEM mapping). The oxidation and spin state of single-iron atoms determined from their magnetic properties were confirmed by DFT calculations. This strategy might find straightforward applications in preparing versatile single atom catalysts, with improved efficiency compared to nanosized ones.

Improved tribological properties, thermal and colloidal stability of poly-α-olefins based lubricants with hydrophobic MoS2 submicron additives.

HYPOTHESIS: Newtonian liquids, usually used as base oil lubricants, exhibit low viscosity under extreme thermal conditions, needed for the functioning of wind turbines. This is directly affecting the colloidal stability and the tribological properties of the formulations containing additives, such as MoS2. Here, it was hypothesized that the surface hydrophobization of MoS2 particles will allow for an increased colloidal stability of the resulting formulations, for temperatures as high as 80 °C. EXPERIMENTS: The antifriction properties and the thermal stability of the designed formulations were determined on submicron MoS2 particles dispersed in poly-α-olefins (PAO) base oils of different dynamic viscosities (from 32 to 1650 mPa·s at 25 °C). The submicron particles of MoS2 (300-500 nm in diameter) were synthesised by a simple one-pot solvothermal method under mild conditions. The resulting particles were hydrophobized in situ in PAO base oils using alkyltrichlorosilane grafting agents with two chain lengths (C8 and C18). FINDINGS: The covalent grafting of alkylsilanes through Mo-O-Si bonds was confirmed by DFT calculations and FT-IR measurements. Turbiscan optical analysis revealed that thermal and colloidal stabilities can be significantly improved depending on oil viscosity and chain length of the grafting agent. The formulations in the PAO65 oil remained highly stable (TSI < 1), even at 80 °C. Herein, we demonstrate the impact of hydrophobization degree on the tribological properties of the lubricants, which, importantly, could reach ultra-low friction coefficients, less than 0.02.

In situ follow-up of hybrid alginate-silicate microbeads formation by linear rheology.

Hybrid alginate-silicate microbeads of about 10-20 µm were synthesized by combining alginate crosslinking, silica condensation in a one pot approach using a food grade emulsion as template. A fine tuning of the formulation composition (alginate, silica and calcium sources) is necessary in order to obtain core-shell microbeads instead of unshaped and irregular fragments or even perforated spherical beads. Importantly, in situ linear rheology provides insights into the reaction mechanism as a result of the rheological fingerprint profile obtained during beads formation.

Core-shell alginate@silica microparticles encapsulating probiotics.

Lactobacillus rhamnosus GG (LGG) was encapsulated in core-shell alginate-silica microcapsules by coating the electrosprayed ionogel with a silica shell via hydrolysis/condensation of alkoxysilane precursors. The viability of encapsulated LGG highly depends on the mineralisation conditions (in aqueous or organic phases), identified as a critical step. More importantly, due to the unswelling of silica and to its mesoporosity that allows nutriment-metabolite diffusion, it was possible to avoid cell leakage and additionally insure bacterial growth inside the microcapsules. The results of this work gave a proof-of-concept for controlled bacterial proliferation in microcompartments, which have straightforward applications in oral delivery of probiotics.

Isocyanate-mediated covalent immobilization of Mucor miehei lipase onto SBA-15 for transesterification reaction.

Mucor miehei lipase (Mm-L) covalently bind on a hexagonally ordered silica SBA-15 (Santa Barbara Amorphous), previously functionalized with isocyanate moieties, was examined as biocatalyst for transesterification of colza oil with methanol. The isocyanate-mesoporous silica (NCO-SBA-15) was obtained by condensation of silanol with triethoxysilane propyl isocyanate (TPI). The efficiency of the functionalization has been evidenced by infrared, (29)Si and (13)C NMR spectroscopies. The substrate provided a moderate hydrophobic microenvironment together with reactive sites for chemical immobilization of the enzyme. The biocatalyst containing 0.28 g of Mm-L per gram of support afforded a high level of transesterification activity (yield up to 80%) while using 1:1 molar ratio of methanol/colza oil and small amount of water. The biocatalyst showed higher operational stability than the corresponding physisorbed enzyme since it can be reused 6 times against 2 consecutive runs for the physisorbed enzyme.

Tailored jeffamine molecular tools for ordering mesoporous silica.

Herein, we report the formation of organized mesoporous silica materials prepared from a novel nonionic gemini surfactant, myristoyl-end-capped Jeffamine, synthesized from a polyoxyalkyleneamine (ED900). The behavior of the modified Jeffamine in water was first investigated. A direct micellar phase (L(1)) and a hexagonal (H(1)) liquid crystal were found. The structure of the micelles was investigated from the SAXS and the analysis by generalized indirect Fourier transformation, which show that the particles are globular of core-shell type. The myristoyl chains, located at the ends of the amphiphile molecule, are assembled to form the core of the micelles and, as a consequence, the molecules are folded over on themselves. Mesoporous materials were then synthesized from the self-assembly mechanism. The recovered materials were characterized by SAXS measurements, nitrogen adsorption-desorption analysis, and transmission and scanning electron microscopy. The results clearly evidence that by modifying the synthesis parameters, such as the surfactant/silica precursor molar ratio and the hydrothermal conditions, one can control the size and the nanostructuring of the resulting material. It was observed that, the lower the temperature of the hydrothermal treatment, the better the mesopore ordering.

Regulation of adhesion behavior of murine macrophage using supported lipid membranes displaying tunable mannose domains.

Highly uniform, strongly correlated domains of synthetically designed lipids can be incorporated into supported lipid membranes. The systematic characterization of membranes displaying a variety of domains revealed that the equilibrium size of domains significantly depends on the length of fluorocarbon chains, which can be quantitatively interpreted within the framework of an equivalent dipole model. A mono-dispersive, narrow size distribution of the domains enables us to treat the inter-domain correlations as two-dimensional colloidal crystallization and calculate the potentials of mean force. The obtained results demonstrated that both size and inter-domain correlation can precisely be controlled by the molecular structures. By coupling α-D-mannose to lipid head groups, we studied the adhesion behavior of the murine macrophage (J774A.1) on supported membranes. Specific adhesion and spreading of macrophages showed a clear dependence on the density of functional lipids. The obtained results suggest that such synthetic lipid domains can be used as a defined platform to study how cells sense the size and distribution of functional molecules during adhesion and spreading.

Ion-conduction pathways in self-organised ureidoarene-heteropolysiloxane hybrid membranes.

This paper reports on hybrid organic-inorganic dense membrane materials in which protons and ions are envisioned to diffuse along the hydrophilic pathways. The hierarchical generation of functional hybrid materials was realised in two steps. First, the self-assembling properties of 3-(ureidoarene)propyltriethoxysilane compounds 1-5 in aprotic solvents were determined, revealing the formation of supramolecular oligomers. Compounds 1-5 generate organogels in chloroform or in acetone, leading in a second sol-gel transcription step to hybrid membrane materials on a nanoscopic scale. The crystal structures of 1-5 indicate that the arrangement is mainly defined by periodic parallel sheets, resulting from the alignment of hydrophobic organic and inorganic silica layers. Hybrid materials MB 1-MB 4, with a similar lamellar structure, define particularly attractive functional transport devices; they are oriented along the organic layers and sandwiched between the two siloxane layers. These systems have been employed successfully to design solid dense membranes and illustrate how the self-organised hybrid materials perform interesting and potentially useful functions.