Mosto Bousmina

Clean chemical synthesis of 2-amino-chromenes in water catalyzed by nanostructured diphosphate Na2CaP2O7

A versatile, alternative and environmentally benign three-component strategy to the synthesis of a series of 2-amino-chromenes has been successfully performed in water, using nanostructured diphosphate Na2CaP2O7 (DIPH) as a basic catalyst. The products are obtained in high recoveries from the one-pot multi-component reaction procedure involving carbonyl compounds, malononitrile and 1-naphtol, resulting in a green synthetic protocol with high atom economy. The catalyst is waste-free, easily prepared, and efficiently re-used. The prepared 2-amino-chromenes, in presence of acetic anhydride, have been easily converted to benzo(a)anthracene derivatives.

Pd embedded in chitosan microspheres as tunable soft-materials for Sonogashira cross-coupling in water–ethanol mixture

Easy shaping of chitosan (CS) as porous self-standing nanofibrillar microspheres allows their use as a palladium carrier. Amino-groups on CS enable the modulation of Pd coordination, giving rise to three different support-catalyst interactions: weakly-coordinated Pd-CS in native CS, incarcerated Pd-CS-Glu in cross-linked CS and strongly-ligated Pd-CS-SH, obtained by the introduction of thiol arms in CS. These catalysts efficiently promote Sonogashira cross-coupling of a large library of functional substrates under mild and sustainable conditions (water–ethanol as solvent at 65 °C) and stand as recyclable, metal-scavenging catalytic systems.

Improving Catalytic Activity by Synergic Effect between Base and Acid Pairs in Hierarchically Porous Chitosan@Titania Nanoreactors

The beneficial effect of the bifunctional character of the chitosan@titania hybrid in heterogeneous catalysis was elucidated: considering a prototypical Henry condensation, Michael addition, and Jasminaldehyde synthesis, the cohabitation of a basic site (NH(2)) and an acidic site (Ti) in the same reactor provided clear activity and selectivity enhancements, with respect to the monofunctional acidic titania and basic chitosan counterparts.

Low temperature synthesis of ordered mesoporous stable anatase nanocrystals: the phosphorus dendrimer approach

The scarcity of low temperature syntheses of anatase nanocrystals prompted us to explore the use of surface-reactive fourth generation phosphorus-dendrimers as molds to control the nucleation and growth of titanium-oxo-species during the sol-gel mineralization process. Unexpectedly, the dendritic medium provides at low temperature, discrete anatase nanocrystals (4.8 to 5.2 nm in size), in marked contrast to the routinely obtained amorphous titanium dioxide phase under standard conditions. Upon thermal treatment, heteroatom migration from the branches to the nanoparticle surface and the ring opening polymerization of the cyclophosphazene core provide stable, interpenetrating mesoporous polyphosphazene-anatase hybrid materials (-P[double bond, length as m-dash]N-)n-TiO2. The steric hindrance of the dendritic skeleton, the passivation of the anatase surface by heteroatoms and the ring opening of the core limit the crystal growth of anatase to 7.4 nm and prevent, up to 800 °C, the commonly observed anatase-to-rutile phase transformation. Performing this mineralization in the presence of similar surface-reactive but non-dendritic skeletons (referred to as branch-mimicking dendrimers) failed to generate crystalline anatase and to efficiently limit the crystal growth, bringing thus clear evidence of the virtues of phosphorus dendrimers in the design of novel nanostructured materials.

Insightful understanding of the role of clay topology on the stability of biomimetic hybrid chitosan-clay thin films and CO2-dried porous aerogel microspheres.

Three natural clay-based microstructures, namely layered montmorillonite (MMT), nanotubular halloysite (HNT) and micro-fibrillar sepiolite (SP) were used for the synthesis of hybrid chitosan-clay thin films and porous aerogel microspheres. At a first glance, a decrease in the viscosity of the three gel-forming solutions was noticed as a result of breaking the mutual polymeric chains interaction by the clay microstructure. Upon casting, chitosan-clay films displayed enhanced hydrophilicity in the order CS<CS-MMT<CS-HNT<CS-SP. Irrespective to the clay microstructure, an improvement in the mechanical properties of the chitosan-clay films has been substantiated with CS-SP reaching the highest value at 5% clay loading. While clay addition provides a way to resist the shrinkage occurring for native chitosan, the enhanced hydrophilicity associated to the water content affects the efficacy of the CO2 super-critical drying as the most hydrophilic CS-SP microspheres face the highest shrinkage, resulting in a lowest specific surface area compared to CS-HNT and CS-MMT. Chitosan-clay exhibits enhanced thermal properties with the degradation delayed in the order CS<CS-MMT<CS-HNT<CS-SP. Under acidic environment, a longevity has been substantiated for chitosan-clay compared to native chitosan, evidencing the beneficial protective effect of the clay particulates for the biopolymer. However, under hydrothermal treatment, the presence of clay was found to be detrimental to the material stability as a significant shrinkage occurs in hybrid CS-clay microspheres, which is attributed again to their increased hydrophilicity compared to the native polymeric microspheres. In this framework, a peculiar behavior was observed for CS-MMT, with the microspheres standing both against contraction during CO2 gel drying and under hydrothermal conditions. The knowledge gained from this rational design will constitute a guideline toward the preparation of ultra-stable, practically-optimized food-packaging films and commercially scalable porous bio-based adsorbents.

Haemolytic activity and cellular toxicity of SBA-15-type silicas: elucidating the role of the mesostructure, surface functionality and linker length

In this contribution, amorphous silica (a-SiO2), native SBA-15 silica as well as four functional SBA-15-type silicates modified with aminopropyl (SBA-NH2), mercaptopropyl (SBA-SH), ethylcarboxylic (SBA-COOH) and undecenoic acid (SBA-FA-COOH) were prepared by the co-condensation route under similar self-assembly and sol-gel conditions. Next, the impact of these materials on red blood cells was evaluated by studying cell haemolysis and haemoglobin adsorption. Moreover, the influence of the presence of human serum albumin (HSA) on erythrocyte haemolysis and cytotoxicity toward B14 Chinese fibroblasts were investigated. Based on these variants, the role of the mesostructure, the nature of the functional group located on the silica surface and the influence of the linker length have been elucidated.

Organophosphonate bridged anatase mesocrystals: low temperature crystallization, thermal growth and hydrogen photo-evolution

The sol-gel co-condensation of organo-phosphonates to titanium alkoxides enables access to novel organic-inorganic hybrids based on phosphonate-bridged titanium dioxide. In this contribution, we bring new perspectives to the long established sol-gel mineralization of titanium alkoxide species, by harnessing the virtues of the well-designed phosphonate-terminated phosphorus dendrimers as reactive amphiphilic nanoreactor, confined medium and cross-linked template to generate discrete crystalline anatase nanoparticles at low temperature (T = 60 °C). An accurate investigation on several parameters (dendrimer generation, dendrimer-to-titanium alkoxide ratio, precursor reactivity, temperature, solvent nature, salt effect) allows a correlation between the network condensation, the opening porous framework and the crystalline phase formation. The evolution of the dendrimer skeleton upon heat treatment has been deeply monitored by means of (31)P NMR, XPS and Raman spectroscopy. Increasing the heteroatom content within a titania network provides the driving force for enhancing their photocatalytic water splitting ability for hydrogen production.

Nitroaldol condensation catalyzed by topologically modulable cooperative acid–base chitosan–TiO2 hybrid materials

Chitosan–TiO2 shaped as macroporous aerogels, lamellar cryogels or electrospun films act synergistically as acid–base bifunctional catalysts. Depending on the topology of the material, a marked difference in the selectivity for nitroaldol condensation is observed.

Periodic mesoporous organosilicas derived from amphiphilic bulky polymethylsiloxane

Novel organosilica materials have been prepared from the newly reported sol–gel processable polymethylorganosiloxane. Under acidic conditions, the intrinsic self-assembling properties of the starting siloxane constitute an impediment to tune the mesostructure. In contrast, the sol–gel polymerization undertaken under basic conditions ensures a monophasic polysiloxane–silica interpenetration, which results in the formation of MCM-41-type PMOs with well-defined ordered structures.