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 (NH2) 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

Design of Stable Nanoporous Hybrid Chitosan/Titania as Cooperative Bifunctional Catalysts

A new method describing the synthesis of hybrid porous materials based on chitosan/titania featuring high surface area and shaped as microspheres is reported. The particular self-assembly properties of chitosan in addition to the mutual chemical interaction between the glucosamine units and the titania precursors control the titania condensation inside the beads of chitosan. The intimate mixing of organic and inorganic frameworks entails a notable improvement on the hydrolytic stability of resulting material when compared to the individual component ones. Moreover, highly active and selective catalytic properties for monoglyceride synthesis stems from the coexistence of the basic sites (NH2 from biopolymer) and acid sites (titanium center) through their cooperative effect

Orthogonal Synthesis of Covalent Polydendrimer Frameworks by Fusing Classical and Onion-Peel Phosphorus-Based Dendritic Units

We report novel and new giant three-dimensional polymers having dendrimers as repeating units. The approach is illustrated here for macromolecular synthesis by polymeric condensation of well-defined single phosphorus dendrimers units. Specifically, classical and onion-peel phosphorus dendrimers, constructed by a divergent method from a cyclotriphosphazene core, were fused within the same tectonic nanostructure by several polymeric condensation approaches including hydrazine-to-aldehyde Schiff-base formation and amine-to-carboxylic acid peptide-like coupling. These reticular, easy to run metal-free routes afford a new library of hyperbranched macromolecular materials, featuring various phosphorus layers (both alternated and dissymmetrical), well-defined textured nanospheres, and controllable nanometric ordered substructures. The scope of the concept is successfully expanded to the integration of electro-redox viologen units resulting in the synthesis of new photoactive macromolecular materials

Amphiphilic Polyesters Derived from Silylated and Germylated Fatty Compounds

New classes of amphiphilic polyesters were prepared from metallated (Si, Ge) fatty methyl ester (FAME) precursors and poly(tetramethylene oxide) glycol. Hydrosilylation of 10-undecenoic methyl ester by tetramethyldisiloxane occurred at 80 °C in the presence of Karstedt’s catalyst, and hydrogermylation of the same FAME derivative was obtained at the same temperature under radical AIBN initiation. These diester precursors, obtained in high yields (≈90%), reacted with poly(tetramethylene oxide) glycol under free solvent to give silicon polymers or germanium oligomers. These condensed materials display both the characteristic of organic−inorganic hybrid materials and those of amphiphilic polymers. The nature of organometallic fragment (hydrophobicity of tetramethyldisiloxy and sterical hindrance of diphenylgermyl) was shown to influence the chemical reactivity of the polymerizable monomers and the physical properties of the resulting copolymers. The amphiphilicity of these materials provides a driving force for the formation of small objects (∼1 nm), making them very attractive as hybrid nanocontainers

Hybrid Materials and Periodic Mesoporous Organosilicas Containing Covalently Bonded Organic Anion and Cation Featuring MCM-41 and SBA-15 Structure

We report the synthesis of a new trialkoxysilylated ionic liquid based on disilylated guanidinium and monosilylated sulfonimide species. This compound allowed the successful preparation of new periodic mesoporous organosilicas containing covalently anchored ion-pair through both organo-cationic and organo-anionic moieties which have never been reported up to now. Two classes of hybrid materials containing guanidinium−sulfonimide ion-pairs (IPs) have been synthesized. The first type of material was prepared by grafting the silylated IP onto both MCM-41-type and SBA-15-type silicas according to a surface sol−gel polymerization. The second class was synthesized following a one-pot sol−gel procedure using silylated IP and tetraethoxysilane as framework precursors. These latter materials correspond to so-called periodic mesoporous organosilicas (PMOs) and gave “organo-ionically” modified MCM-41 and SBA-15 related solids. The materials were characterized by a series of techniques including XRD, nitrogen sorption, solid-state NMR, FTIR, transmission electronic microscopy, and elemental analysis. The highest structural regularity in terms of pore size distribution and channel size homogeneity was observed for IP-PMOs possessing SBA-15-type architecture due to an enhanced trialkoxysilylated IP precursor/surfactant interaction. Solvatochromic experiments with Reichardt’s dye showed good accessibility of the silica-supported ion-pair and suggested the formation of monophasic materials

Solvent-Free Production of Singlet Oxygen at the Gas−Solid Interface: Visible Light Activated Organic−Inorganic Hybrid Microreactors Including New Cyanoaromatic Photosensitizers

We synthesized new cyanoaromatics, benzo[b]triphenylene-9,14-dicarbonitrile (DBTP) 1a and a graftable derivative, 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid (DBTP-COOH) 1b, easily prepared from commercial reagents. Their photosensitizing properties were investigated. Hybrid porous silica monoliths loaded with encapsulated 1a or grafted 1b were prepared, and their adsorption, spectroscopic and photosensitizing properties, as well as stability, were compared. Solvent-free, efficient oxidation of dimethylsulfide (DMS) was observed at the gas−solid interface under visible light irradiation. Quantum yields of formation of 1O2 inside the porous monoliths are comparable to those of phenalenone. Singlet oxygen lifetimes (∼25 μs) were found to be longer in silica monoliths than in usual polar solvents such as methanol or ethanol. This new class of hybrid materials work as porous, transparent, and highly efficient microreactors for oxidation reactions under visible light

Biological Activity of Mesoporous Dendrimer-Coated Titanium Dioxide: Insight on the Role of the Surface–Interface Composition and the Framework Crystallinity

Hitherto, the field of nanomedicine has been overwhelmingly dominated by the use of mesoporous organosilicas compared to their metal oxide congeners. Despite their remarkable reactivity, titanium oxide-based materials have been seldom evaluated and little knowledge has been gained with respect to their “structure–biological activity” relationship. Herein, a fruitful association of phosphorus dendrimers (both “ammonium-terminated” and “phosphonate-terminated”) and titanium dioxide has been performed by means of the sol–gel process, resulting in mesoporous dendrimer-coated nanosized crystalline titanium dioxide. A similar organo-coating has been reproduced using single branch-mimicking dendrimers that allow isolation of an amorphous titanium dioxide. The impact of these materials on red blood cells was evaluated by studying cell hemolysis. Next, their cytotoxicity toward B14 Chinese fibroblasts and their antimicrobial activity were also investigated. Based on their variants (cationic versus anionic terminal groups and amorphous versus crystalline titanium dioxide phase), better understanding of the role of the surface–interface composition and the nature of the framework has been gained. No noticeable discrimination was observed for amorphous and crystalline material. In contrast, hemolysis and cytotoxicity were found to be sensitive to the nature of the interface composition, with the ammonium-terminated dendrimer-coated titanium dioxide being the most hemolytic and cytotoxic material. This surface-functionalization opens the door for creating a new synergistic machineries mechanism at the cellular level and seems promising for tailoring the biological activity of nanosized organic–inorganic hybrid materials

Biological Properties of New Viologen-Phosphorus Dendrimers

Some biological properties of eight dendrimers incorporating both phosphorus linkages and viologen units within their cascade structure or at the periphery were investigated for the first time. In particular cytotoxicity, hemotoxicity, and antimicrobial and antifungal activity of these new macromolecules were examined. Even if for example all these species exhibited good antimicrobial properties, it was demonstrated that their behavior strongly depends on several parameters as their size and molecular weight, the number of viologen units and the nature of the terminal groups