Search

Bone is created by osteoblasts that secrete osteoid after which an ordered texture emerges, followed by mineralization. Plywood geometries are a hallmark of many trabecular and cortical bones, yet the origin of this texturing in vivo has never been shown. Nevertheless, extensive in vitro work revealed how plywood textures of fibrils can emerge from acidic molecular cholesteric collagen mesophases. This study demonstrates in sheep, which is the preferred model for skeletal orthopaedic research, that the deeper non‐fibrillar osteoid is organized in a liquid‐crystal cholesteric geometry. This basophilic domain, rich in acidic glycosaminoglycans, exhibits low pH which presumably fosters mesoscale collagen molecule ordering in vivo. The results suggest that the collagen fibril motif of twisted plywood matures slowly through self‐assembly thermodynamically driven processes as proposed by the Bouligand theory of biological analogues of liquid crystals. Understanding the steps of collagen patterning in osteoid‐maturation processes may shed new light on bone pathologies that emerge from collagen physico‐chemical maturation imbalances. [ABSTRACT FROM AUTHOR]

Magnesium silicates combining acidic and basic surface properties are known to be interesting as heterogeneous catalysts. Nevertheless, their catalytic performances are highly dependent on the synthesis method used. In this study, a series of magnesium silicates was synthesized for the first time using a coprecipitation method with a micromixer. It is first shown that changes in synthesis/precipitation pH led to magnesium silicates with different Mg/Si ratios: the higher the synthesis pH, the higher the Mg/Si ratio. Moreover, prepared silicates with a final Mg/Si ratio greater than 0.7, thus prepared at high pH, exhibit negligible specific surface area, whereas relatively high values (>180 m2/g) have been obtained for lower Mg/Si ratios. A set of experimental characterization data obtained by N2 physisorption, SEM, XRD, TGA-DTA as well as Raman and 29Si NMR spectroscopies are presented and discussed. They show the existence of two distinct families with a similar Magnesium Silicate Hydrate (MSH) phase, but they reveal different aggregation states and textural properties. Finally, the surface acid–base reactivity of the co-precipitated magnesium silicates was determined using the model reaction of 2-methylbut-3-yn-2-ol (MBOH) conversion. The results obtained suggest that it is possible to prepare silicates with a wide range of surface acid–base properties, from purely basic solids to those with both acidic and basic properties, by adjusting the final Mg/Si ratio via the control of the synthesis parameters. [ABSTRACT FROM AUTHOR]

Immobilization of gold nanoparticles on planar sur-faces is of great interest to many scientific communities; chemists, physicists, biologists, and the various communities working at the interfaces between these disciplines. Controlling the immobilization step, especially nanoparticles dispersion and coverage, is an important issue for all of these communities. We studied the parameters that can influence this interaction, starting with the nature of the terminal chemical function. Thus, we have carefully grafted silanes terminated by either amine or thiol groups starting from aminopropyltriethoxysilane (APTES) or mercaptopropyltriethoxysilane. We also changed the chain length for thiolterminated layers through covalent grafting of mercaptoundecanoic acid (MUA) on APTES-modified layers, and the protocol of nanoparticles deposition to evaluate whether other factors must be taken into consideration to rationalize this interaction. The formed layers were characterized by X-ray photoelectron spectroscopy and gold nanoparticles deposition was monitored by scanning electron microscopy and surface-enhanced Raman scattering. We observed significant differences in terms of nanoparticles dispersion and density depending on the nature of the chemical layer on silicon. The use of ultrasounds during the deposition process was very efficient to limit aggregates formation. The optimal deposition procedures were obtained through the use of APTES and APTES/MUA functionalization. They were compared in terms of coverage, dispersion, and densities of isolated nanoparticles. The APTES/MUA surfaces clearly showed better results that may arise from both the longer chain and the dilution of thiol end groups. Keywords Gold nanoparticles. Silicon surface. Silane grafting. Surface functionalization. XPS. Scanning electron microscopy, Introduction The fabrication of solid substrates with gold nanoparticles assemblies immobilized on their surface is currently the subject of growing interest because of the key role these substrates could play [...]

The catalysts with various gold loadings are prepared by the modified impregnation procedure and the nature of the supported gold phase is characterized. The Au/Ti[O.sub.2] catalysts prepared by this modified procedure of impregnation are almost as active as those prepared by deposition-precipitation with urea in the CO oxidation reaction performed at room temperature.

The photoluminescence measurements on siliceous and vanadium loaded mesoporous molecular sieves (MCM-41) are reported. This is done to receive information about the defects in the materials used.