Philippe Gaveau

Nanoconfined phosphorus in mesoporous carbon as an electrode for Li-ion batteries: performance and mechanism

Phosphorus–mesoporous carbon composites have been prepared by direct vaporization–condensation of phosphorus onto mesoporous carbon. The as-prepared P1–C1 composite showed improved performance in batteries vs. Li compared with classical P mainly due to the electronic modification of the nanoconfined P. By combining the electrochemical analysis with 31P and 7Li NMR, in situ X-ray diffraction and Raman spectroscopy we have characterized the electrochemical mechanism of the P1–C1 composite vs. Li in the battery. Such activated P is able to react reversibly with Li to form Li3P and this reaction takes place at higher potential than that of classical P. This study demonstrates that the effects of nano-confinement of an active material (AM) (here P) on mesoporous carbons paves a way (i) to stabilize different polymorphs of an active element (vs. Li) that present a modified reactivity vs. Li and (ii) to enhance the electrochemical performance of AM vs. Li. Last but not least it is demonstrated that the nature of carbon is determinant for the electrochemical performance.

Periodic mesoporous organosilica containing ionic bis-aryl-imidazolium entities: Heterogeneous precursors for silica-hybrid-supported NHC complexes

The synthesis of periodic mesoporous organosilica incorporating ionic diarylimidazolium species was achieved by hydrolysis–polycondensation of a bis-silylated diarylimidazolium (Si-IMes-) precursor in the presence of non-ionic triblock copolymer as structure directing agents. Although hydrolysis polycondensation of the pure precursor gave materials with moderate porosity, highly porous solids were obtained by the addition of tetraethoxysilane (TEOS) to the sol solution. The architecture of the materials on a mesoscopic scale strongly depends on the TEOS/Si-IMes ratio in the sol. Materials with highly regular hexagonal symmetry were obtained using high molar excess of TEOS. The obtained PMO type materials incorporating diarylimidazolium substructures are promising heterogeneous precursors for the formation of silica hybrid supported N-heterocyclic carbene complexes and therefore have great potential in heterogeneous catalysis.

Self-assembly of layered organosilicas based on weak intermolecular interactions

New layered hybrid organic-inorganic materials were obtained directly by hydrolysis and polycondensation of monosilylated precursors of type (EtO)(3)Si(CH(2))(3)NH(C=O)NHC(n)H(2n+1) (n = 3, 8, 12 and 16). These precursors were easily prepared by reaction between commercially available triethoxysilylpropylisocyanate and primary aminoalkanes. The obtained materials were characterized by combining elemental analysis, X-ray powder diffraction, (13)C, (29)Si NMR and FT-IR spectroscopies. They were found to be well condensed, and stable in water. We showed that their formation results from a cooperative effect between hydrogen bonding interactions originating from ureido groups and hydrophobic interactions between the long alkyl chains. There is no formation of material when n = 2, or from (EtO)(3)SiC(n)H(2n+1) when n = 18, thus proving that both types of weak intermolecular interactions are required. The chelating property of these materials towards europium(III) ions was tested.

14N and 81Br quadrupolar nuclei as sensitive NMR Probes of n-alkyltrimethylammonium bromide crystal structures. An experimental and theoretical study.

This is the first time a comprehensive study has been carried out on n-alkyltrimethylammonium bromide salts using (14)N and (81)Br solid state NMR, X-ray diffraction, and theoretical calculations. The investigation represents a necessary step toward further (14)N and (81)Br NMR characterization of the environment of cationic and anionic groups in materials, accounting for the amphiphilic properties of cationic surfactants. The NMR spectra of five C(x)H(2x+1)(CH(3))(3)N(+)Br(-) polycrystalline samples with different n-alkyl chain lengths (x = 1, 12, 14, 16, 18) were recorded and modeled. The (14)N and (81)Br quadrupolar coupling interaction parameters (C(Q), eta(Q)) were also estimated from spectrum modeling and from computer simulation. The obtained results were discussed in depth making use of the experimental and reoptimized crystal structures. In the study, both (14)N and (81)Br nuclei were found to be sensitive probes for small structural variations. The parameters which influence the NMR properties the most are mobility, deviation of C-N-C bond angles from T(d) angles, and variations in r(N-Br) distances.

Structural study of calcium phosphonates: a combined synchrotron powder diffraction, solid-state NMR and first-principle calculations approach

The structures of four Ca-phosphonate phases are reported here: Ca(C6H5–PO3H)2 (1), Ca(C6H5–PO3)·2H2O (2), Ca(C4H9–PO3H)2 (3) and Ca(C4H9–PO3)·H2O (4). Structural models were obtained ab initio by using a combined synchrotron powder diffraction, solid-state nuclear magnetic resonance, and gauge including projector augmented wave (GIPAW) calculation approach. The 1H, 13C, 31P and 43Ca NMR parameters calculated from these structural models were found to be in good agreement with the experimental values, thereby indicating the high accuracy of the DFT-optimized structures. Correlations between the NMR parameters and structural features around the phosphonate were then analyzed, showing in particular the high sensitivity of the 31P asymmetry parameter ηCS and the 43Ca isotropic chemical shift to changes in local structure around the phosphonate groups and the Ca2+, respectively. Finally, the NMR data of a new mixed Na–Ca phosphonate phase, Ca1.5Na(C4H9–PO3)2, are reported.

Boronate ligands in materials: Determining their local environment by using a combination of IR/solid-state NMR spectroscopies and DFT calculations

Boronic acids (R-B(OH)(2)) are a family of molecules that have found a large number of applications in materials science. In contrast, boronate anions (R-B(OH)(3)(-)) have hardly been used so far for the preparation of novel materials. Here, a new crystalline phase involving a boronate ligand is described, Ca[C(4)H(9)-B(OH)(3)](2), which is then used as a basis for the establishment of the spectroscopic signatures of boronates in the solid state. The phase was characterized by IR and multinuclear solid-state NMR spectroscopy ((1)H, (13)C, (11)B and (43)Ca), and then modeled by periodic DFT calculations. Anharmonic OH vibration frequencies were calculated as well as NMR parameters (by using the Gauge Including Projector Augmented Wave--GIPAW--method). These data allow relationships between the geometry around the OH groups in boronates and the IR and (1)H NMR spectroscopic data to be established, which will be key to the future interpretation of the spectra of more complex organic-inorganic materials containing boronate building blocks.

Drug nano-domains in spray-dried ibuprofen–silica microspheres

Silica microspheres encapsulating ibuprofen in separated domains at the nanometre scale are formed by spray-drying and sol-gel processes. A detailed (1)H and (13)C NMR study of these microspheres shows that ibuprofen molecules are mobile and are interacting through hydrogen bonds with other ibuprofen molecules. (1)H magnetisation exchange NMR experiments were employed to characterize the size of the ibuprofen domains at the nanometre scale. These domains are solely formed by ibuprofen, and their diameters are estimated to be ∼40 nm in agreement with TEM observations. The nature and formation of these particular texture and drug dispersion are discussed.

Drug delivery systems based on pharmaceutically active ionic liquids and biocompatible poly(lactic acid)

Poly(l-lactic acid) (PLLA) membranes containing pharmaceutically active ionic liquids (API-ILs) have been prepared by using a simple film casting from solvent evaporation method. Several sets of membranes were prepared from two different ionic liquids namely 1-methyl-3-butyl-imidazolium ibuprofenate (C4MImIbu) and lidocainium ibuprofenate (LidIbu) with different API-IL contents. Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Wide-Angle and Small-Angle X-ray Scattering (WAXS and SAXS) revealed the strong influence of both the IL nature and content on the morphology and the crystallinity of the resulting PLLA. At 20 weight%, LidIbu was shown to act as a plasticizer for PLLA and homogeneous membranes were obtained. In contrast, at the same IL content, phase separation occurred using C4MImIbu, resulting in the formation of porous PLLA. An increase of LidIbu content to 50 weight% results also in phase separation. 1H and 1H-13C CP-MAS NMR measurements evidenced the influence of different morphologies and crystallinities on IL mobility. C4MImIbu was found to be highly mobile whereas the mobility of LidIbu was content dependent. At low percent, low mobility was observed while at higher content, two populations with respectively high and low mobility were observed. These PLLA-IL membranes were further tested as drug delivery systems. In accordance with the morphology and mobility obtained, we demonstrated that release kinetics from PLLA membranes can be tuned by the nature and the content of API-ILs. Sustainable release kinetics were obtained with API-IL acting as a plasticizer while the fastest release was obtained with API-IL acting as a porogenic agent.

Synthesis of textured polysaccharide–silica nanocomposites: a comparison between cellulose and chitin nanorod precursors

The properties and formation mechanisms of silica-based nanocomposites textured by polysaccharide nanorods have been studied from a series of new materials obtained using cellulose nanocrystals (CNCs), and their comparison with those obtained using equivalent chitin nanorods. Stable ethanolic co-suspensions of CNCs and siloxane oligomers have been processed by spray-drying to form hybrid cellulose–silica nanocomposites. The materials’ surface and internal texture, before and after calcination, are highly informative about the distribution and templating role of the polysaccharide nanorods (cellulose or chitin). Both electron microscopy and nitrogen sorption analyses highlight the role of the particle dimensions in defining the porosity of calcined silica replicas. In addition, the structures of the polysaccharide crystals inside the nanocomposites were investigated by XRD and 13C solid-state NMR. From these results, it is concluded that both polysaccharide crystalline precursors form the same sort of silica-based nanocomposites, with no visible effect of their different surface chemistry towards templating. There are strong interactions between the polysaccharide surface and the siloxane oligomers that can be explained by the high density of hydroxyl groups on the sugar cycles. During the sol–gel processing, these interactions favour the formation of a silica shell around the nanocrystals accompanied by a slight contraction of the cellulose and chitin crystal structures, not observed until now. When the spray-dried nanocomposites are subjected to ammonia vapours, the siloxane condensation increases and, concomitantly, the role of the interactions at the siloxane–polysaccharide interface is decreased. This study leads therefore to new insights and opportunities for the design of nanocomposites or porous materials, the properties of which can be tuned by the choice of polysaccharide nanorods with specific dimensions and functionalities.