Metal oxide materials, such as ZnO, have attracted considerable interest in photocatal-ysis due to their ability to generate reactive species under UV irradiation, which are useful for the degradation of organic or inorganic pollutants. However, the efficiency of photocatalysis re-lies on the intrinsic properties of the photocatalyst, such as its specific surface area or stability, or even aggregation when it is in the form of nanoparticles. To address these issues, we synthesized and thoroughly characterized ZnO nanoparticles confined in a mesoporous silica matrix. Several synthesis parameters were investigated, including the method of silica synthesis, the nature of the zinc precursor and the calcination temperature. The resulting materials exhibited a large specific surface area, and nanoparticles of 2 nm were homogeneously dispersed within the silica matrix. The optical properties, UV-visible absorption and photoluminescence, were examined and photocatalytic properties were evaluated through the photoreduction of Cr(VI).

Due to their shape, thermal and mechanical stability, and high content of functional groups, ladder polysilsesquioxanes (LPSQs) are attractive structures for the design of hybrid materials. In this article, we describe the syntheses of two macroalkoxyamines-grafted LPSQs that differ in the nature of radicals released upon thermal initiation, which can be a nitroxide or a benzyl radical. Styrene nitroxide-mediated polymerization using these initiators is described. The impact of alkoxyamine structures on the polymerization process and on the properties of the hybrid materials formed is discussed. The kinetic studies reveal that, regardless of the specific LPSQ-macroalkoxyamine combination used, the styrene polymerization is not fully controlled, leading to high dispersity in the final hybrid materials. Nevertheless, the LPSQ-macroalkoxyamine which releases benzyl radical shows a better polymerization control in terms of molecular weight than the one releasing nitroxide radical. The resulting hybrid polystyrene grafted LPSQs exhibit enhanced thermal and viscoelastic properties in the form of increased glass transition temperature, storage, and loss moduli compared to their organic analogues and the simple PS/LPSQ blend, even at low silica loadings.

In this study we report on the efficiency of a furane-indole-chromenone-based organic derivative (FIC) as a photocatalyst in the α-arylation of enol acetate upon LED irradiation at 405 nm, and as a photoinitiator/photocatalyst in the free radical polymerization of an acrylate group in the presence of bis-(4-tert-butylphenyl)iodonium hexafluorophosphate (Iod) as an additive, or in the presence of both Iod and ethyl-4-(dimethyl amino) benzoate (EDB) under LED irradiation at 365 nm. The photochemical properties of this new light-sensitive compound are described, and the wide redox window (3.27 eV) and the high excited-state potentials FIC*/FIC●− (+2.64 V vs. SCE) and FIC●+/FIC* (−2.41 V vs. SCE) offered by this photocatalyst are revealed. The chemical mechanisms that govern the radical chemistry are discussed by means of different techniques, including fluorescence-quenching experiments, UV-visible absorption and fluorescence spectroscopy, and cyclic voltammetry analysis.

Alkoxyamine-functionalized polysilsesquioxane lamellar materials were used as fillers and radical polymerization initiator in the synthesis of nanocomposites. This work is divided into three parts: (i) the synthesis and the characterization of functionnalized-lamellae, (ii) the study of their delamination and (iii) the polymerization leading to the nanocomposites. The presence of covalently bonded siloxane filler reinforced the polystyrene. In addition, the EPR analysis showed that alkoxyamine groups were still present on the nanocomposite and could be homolyzed under thermal condition to enable further potential functionalisations.

Nanocomposite materials composed of an organic matrix and an inorganic nanofiller have been the subject of intense research in recent years. Indeed, the synergy between these two phases confers improved properties thanks to an increased surface–volume ratio, which reinforces the interactions between the particles and the polymer matrix. These interactions depend on many factors such as the shape, size and dispersion of the nanoobjects. Polysilsesquioxanes (PSQs) are a silicon polymer family that offers different sizes, shapes and structures and possesses ceramics properties (i.e., high thermal and/or oxidative resistance and high chain rigidity), thanks to the siloxane backbone. In this article, we propose to incorporate polymer-grafted ladder polysilsesquioxanes (LPSQs) as nanofillers in thermoplastic matrices. Chloride-functionalized LPSQs were synthesized from two different precursors and thoroughly characterized by 1H, 13C and 29Si NMR, as well as by SEC and WAXS. The well-defined LPSQ was then converted into an azide analog. The resulting hybrid material was functionalized with poly(ethylene glycol) (PEG) chains and incorporated into poly(ethylene oxide) or poly(methyl methacrylate) matrices. We found that the viscoelastic properties of the nanocomposite materials were impacted by plasticizing or the reinforcement effect depending on the grafted PEG chain length.

In this study, nuclear magnetic resonance (NMR) is used to investigate the crystallisation behaviour of aspirin within a mesoporous SBA-15 silica material. The potential of dynamic nuclear polarisation (DNP) experiments is also investigated using specifically designed porous materials that incorporate polarising agents within their walls. The formation of the metastable crystalline form II is observed when crystallisation occurs within the pores of the mesoporous structure. Conversely, bulk crystallisation yields the most stable form, namely form I, of aspirin. Remarkably, the metastable form II remains trapped within the pores of mesoporous SBA-15 silica material even 30 days after impregnation, underscoring its persistent stability within this confined environment. In this study, nuclear magnetic resonance (NMR) is used to investigate the crystallisation behaviour of aspirin within a mesoporous SBA-15 silica material.

Recent applications of bi-, oligo-, or polyradicals tospin scienceshave generated considerable interest in the design of new bi-/oligoradicalorganic molecules. Nevertheless, studies of physicochemical propertiesopen shell systems are generally based on stable homonuclear organicradicals, which represent only a small portion of the existing radicals.In this context, diazene precursors of heteroatomic radicals wereincorporated into the SBA-15 silica framework. Photolysis at 360 nmof the diazene moiety resulted in the formation of two face-to-faceoxygen- and sulfur-centered radicals. These systems were characterizedby X-, Q-, and W-band EPR spectroscopy by comparing them to silicasfunctionalized with either face-to-face sulfur-centered radicals orface-to-face oxygen-centered radicals. These EPR studies allowed measuringtheir half-life as well as their relaxation times (T (1) and T (2)). The propertiesof silicas functionalized with sulfur- and oxygen-centered radicalsfall between those measured for the two reference systems functionalizedwith only sulfur- or oxygen-centered radicals. These nanostructuredsilicas functionalized by two radicals of different nature are newpotential candidates as a polarizing agent for DNP NMR.

Dynamic nuclear polarisation (DNP) can significantly enhance the sensitivity of solid-state nuclear magnetic resonance (SSNMR) experiments by transferring the electron spin polarisation of paramagnetic species to nuclei through microwave irradiation of the sample at cryogenic temperatures. Paramagnetic species required for DNP can be provided in the form of mesoporous silica materials containing nitroxide radicals either located on the porous surface or embedded in the pore walls. The present study focuses specifically on porous materials with wall-embedded radicals that were synthesised using conventional molecular imprinting protocols. More remarkably, by changing the molecular structure of the TEMPO precursor, the theoretical distance between the oxygen atoms in a pair of wall-embedded face-to-face TEMPO radicals was increased stepwise (0.7, 0.9, 1.1, 1.3 and 1.5 nm). The thermal activation of these five series of materials led to 37 TEMPO-functionalised silica materials with different radical concentrations. Their efficiency as DNP polarising agents was subsequently investigated at 9.4 T and ∼110 K under magic-angle spinning conditions (10 kHz) after impregnating them at room temperature with an aqueous solution of isotopically enriched proline. Our results show that the highest DNP efficiency was obtained for the silica materials that exhibited the shortest theoretical oxygen-oxygen distance between the TEMPO rings, suggesting that the design rules accepted for soluble DNP polarising agents may not be transposed to these materials with wall-embedded pairs of nitroxides.

Establishing mechanistic understanding of crystallization processes at the molecular level is challenging, as it requires both the detection of transient solid phases and monitoring the evolution of both liquid and solid phases as a function of time. Here, we demonstrate the application of dynamic nuclear polarization (DNP) enhanced NMR spectroscopy to study crystallization under nanoscopic confinement, revealing a viable approach to interrogate different stages of crystallization processes. We focus on crystallization of glycine within the nanometric pores (7–8 nm) of a tailored mesoporous SBA-15 silica material with wall-embedded TEMPO radicals. The results show that the early stages of crystallization, characterized by the transition from the solution phase to the first crystalline phase, are straightforwardly observed using this experimental strategy. Importantly, the NMR sensitivity enhancement provided by DNP allows the detection of intermediate phases that would not be observable using standard solid-state NMR experiments. Our results also show that the metastable β polymorph of glycine, which has only transient existence under bulk crystallization conditions, remains trapped within the pores of the mesoporous SBA-15 silica material for more than 200 days.

Polymer functionalization of ordered mesoporous silicas (OMS) offer wide applications owing to their synergy properties. In this study, a new approach for polymer functionalization of OMS is demonstrated by the cocondensation of silica precursor and a functional polymer bearing triethoxysilane end-group in the presence of a tailored poly (ethylene oxide)-b-polystyrene (PEO-b-PS) amphiphilic copolymer used as pore template. The novelty of this strategy resides in the co-micellization of PEO-b-PS and functional polymer that enables the incorporation of the latter into the mesoporous silica. By changing the nature of the functional polymer, as well as their loading concentration and process conditions, different ordered polymer-mesoporous silicas containing aryl, nitro or amide groups and high polymer content, up to 38 wt% were synthesized. These materials exhibit high specific surface area (488 m2 g-1) and large pores (8 nm) with acceptable CO2 adsorption capacity and selectivity towards CH4 and N2.

The formation of radical species in solution can be triggered through thermal or photochemical activation of a suitable precursor. This EPR study aimed to establish if these two activation modes were as effective in mesoporous silicas as in solution. First, a calibration system was devised and validated to reliably quantify the radical formation. Alkoxyamines were selected to generate stable nitroxyl radicals upon heating or irradiation. Thanks to direct synthesis by the sol-gel process, these precursors were selectively located on the pore surface or in the framework of mesoporous silicas. The thermal or photo-chemical activation of the functionalized materials showed that nitroxides were formed in yields comparable to those observed in solution. No significant differences were observed with the implementation of these activation modes between the solution and the mesoporous silicas. Moreover, the thermal experiments enabled to measure the C–O bond dissociation constants of alkoxyamines covalently anchored to a nanostructured silica, their values were in the same order of magnitude than those determined in solution.

Plant dirigent proteins (DIRs) control the stereoselectivity of the monolignol coniferyl alcohol radical coupling. The main mechanistic hypothesis on this chemo- and stereoselective reaction invokes a binding of coniferyl alcohol radical substrates in the dirigent protein active site so that only one enantiomeric form can be produced. We have studied the influence of the Arabidopsis thaliana AtDIR6 protein on the transient coniferyl alcohol radical by EPR. Herein, we show that AtDIR6 stabilizes coniferyl alcohol radicals prior to directing their coupling towards the formation of (-)-pinoresinol.

The generation of superoxide radical anion in biological systems is one of the major initiating events in the redox biology of NADPH oxidases and mitochondrial redox signalling. However, the pallette of chemical tools for superoxide detection is very limited, hampering progress in understanding the chemical biology of superoxide. Although EPR spin trapping is regarded as the most rigorous technique for superoxide detection, rapid reduction of the EPR-active superoxide spin adducts to EPR-silent hydroxylamines, or to hydroxyl radical adducts by bioreductants, significantly limits the applicability of this technique in biological systems. To overcome these limitations, in this work, we report the synthesis and characterization of a new mesoporous silica functionalized with a phosphorylated cyclic spin trap (DIPPMPO nitrone). The DIPPMPO-grafted silica is a versatile spin-trap agent enabling the identification of a wide range of carbon or oxygen-centered transient radicals in organic and in aqueous media. Moreover, superoxide was efficiently trapped under in vitro conditions in both cell-free and cellular systems. The generated superoxide adduct exhibited an exceptional half-life of 3.5 h and a resistance toward bioreductant agents such as glutathione for several hours.

The development of new open shell systems is essential for advances in spin science. In this work, we report the synthesis and characterization of three nanostructured materials, namely SBA-15 silicas, periodic mesoporous organosilicas (PMOs) and lamellar polysilsesquioxanes, all functionalized with the same diazene-based phenoxyl radical precursor. The impact of the nature of the material, i.e. loading of radical precursor and structure, on half-lifetimes (t(1/2)) and relaxation times of phenoxyl radicals was investigated. Although phenoxyl radicals are transient in solution, their t(1/2) range from hours to years at room temperature (RT) when they are embedded in nanostructured materials. The above mentioned functionalized materials were used to generate the corresponding phenoxyl radicals and their relaxation times were measured (T-1e and T-m) from 50 K to RT. The results were rationalized in terms of limited mobility of the radical as a result of supramolecular interactions and structure rigidity. All these data show that it is possible to design functionalized nanostructured material with radicals possessing specific electronic relaxation properties which can be of interest in fields like DNP, organic magnetism or spin qubit.

Diazenes, precursors of sulfinyl radicals, were used to functionalize nanostructured SBA-15 silicas either in the framework or on the pore by formation of covalent links, or by simple adsorption on the surface. Depending on their design and on the experimental conditions, these materials proved to be effective tools to study the behavior and the reactivity of arylsulfinyl radicals made persistent because of confinement effects. When the covalently linked precursors were irradiated at room temperature, a spectacular increase of the lifetime of the expected sulfinyl radicals was registered (up to 17 h). At higher temperature, upon thermal initiation at 473 K, the decomposition of the adsorbed precursor enabled visualization of the rearrangement of the corresponding arylsulfinyl radicals into sulfonyl radicals via O-S coupling.

New polysilsesquioxane-based lamellar materials, functionalized with radical precursors, were synthesized. They play a double role in the preparation of composite materials: first, as filler homogeneously dispersed in the monomer after delamination, second as radical initiator in photopolymerization. These polysilsesquioxanes enable fast and efficient photopolymerization upon UV light for thick samples. High conversions in monomers as well as the formation of hybrid polymers covalently linked to the filler are observed. This strategy, based on a double bottom-up approach, avoids the solubility/dispersion problem encountered in the classical preparation of composite polymers from preformed organic polymers.

As the search for functionalized materials for CO2 capture continues, the role of theoretical chemistry is becoming more and more central. In this work, a strategy is proposed where ab initio calculations are compared and validated by adsorption microcalorimetry experiments for a series of, so far unexplored, functionalized SBA-15 silicas with different spacers (aryl, alkyl) and terminal functions (N3, NO2). This validation then permitted to propose the use of a nitro-indole surface functionality. After synthesis of such a material the predictions were confirmed by experiment. This confirms that it is possible to fine-tune CO2-functional interactions at energies much lower than those observed with amine species.

Nanostructured functionalized silicas were used as a platform to compare the behaviour of anchored arylsulfanyl radicals depending on the nature of the precursor (diazene/thiol). The radicals generated from thiols exhibit higher half-lifetimes than the radicals generated from diazenes. The ability of thiols to maintain the sulfanyl radical density via degenerate hydrogen atom transfer is likely to account for this sharp difference.

Upon irradiation at room temperature, symmetrical diazene precursors enabled the formation of phenoxyl radicals through β-fragmentation reaction in the solid state. This traceless generation of phenoxyl radicals was investigated by ESR. This study showed that although the fragmentation of β-phenoxy radicals is a slow process in solution, it could be useful in solid state thanks to the absence of faster competitive pathways.