Marie Gressier

An efficient route to aqueous phase synthesis of nanocrystalline γ-Al2O3 with high porosity: from stable boehmite colloids to large pore mesoporous alumina.

In this paper we emphasise the important role of Pluronic F127 on the porosity of mesoporous alumina prepared from boehmite colloids. By focusing on the F127/boehmite interactions we show how the concepts of interface science may help to predict and improve the textural characteristics of mesoporous alumina. By varying the synthetic parameters, in particular the copolymer content, we show that the porosity of γ-Al(2)O(3) can be enhanced by 400% and the average pore diameter can be expanded from 5 to 14 nm. These results are discussed in terms of interactions between the Pluronic F127 and boehmite colloids, and are correlated to the critical micelle concentration (CMC) of the copolymer. The textural characteristics of the mesoporous alumina can be further improved either by introducing hydrocarbons in the preformed boehmite/copolymer sols or by concentrating the sols. In comparison with as-synthesised alumina, those prepared with F127 showed improved thermal stability. Furthermore, boehmite/copolymer sols were stable for all surfactant concentrations investigated and can give high quality coatings suitable for catalytic applications.

Functionalization of synthetic talc-like phyllosilicates by alkoxyorganosilane grafting

A range of talc-like phyllosilicates were prepared via a hydrothermal synthesis performed at five different temperatures from 160 to 350 °C. The organization of the lattice and the degree of crystallinity of the new materials were evaluated by different techniques such as XRD, FTIR, solid-state 29Si NMR, TEM, FEG-SEM and TG-DTA. When synthesized at low temperature the material presents high degree of hydration, low crystallinity and flawed structure. This was attributed to stevensite-talc interstratified product present in the samples. The stevensite/talc ratio and the hydration decrease in the talc-like phyllosilicate samples when the hydrothermal synthesis temperature increases and so the crystallinity becomes higher. A thermal treatment at 500 °C allowed a significant flaw reduction in talc-like phyllosilicate structure; the synthesized sample at 350 °C and heat treated presents a structure close to that of talc. The different talc-like phyllosilicates were grafted covalently by two organoalkoxysilane reagents, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (IM2H) and 2-hydroxy-4-(3-triethoxysilylpropoxy)-diphenylketone (HTDK). The grafted amounts of the hybrids, determined by elemental analysis and confirmed by thermogravimetric data, are dependent on the hydrothermal synthesis temperature and organoalkoxysilanes; they become smaller when the synthesis temperature increases and when HTDK is used. FTIR and solid-state 13C CP MAS NMR were applied to characterize the grafted organic groups. So, in this work it is shown that by choosing the hydrothermal synthesis temperature or by performing an additional annealing it is possible to adjust the amount of defects in the structure of talc-like phyllosilicates which seems to be strongly correlated to the grafting performance.

Organosilylated Complex [Eu(TTA)3(Bpy-Si)]: A Bifunctional Moiety for the Engeneering of Luminescent Silica-Based Nanoparticles for Bioimaging

A new highly luminescent europium complex with the formula [Eu(TTA)3(Bpy-Si)], where TTA stands for the thenoyltrifluoroacetone, (C4H3S)COCH2COCF3, chelating ligand and Bpy-Si, Bpy-CH2NH(CH2)3Si(OEt)3, is an organosilyldipyridine ligand displaying a triethoxysilyl group as a grafting function has been synthesized and fully characterized. This bifunctional complex has been grafted onto the surface of dense silica nanoparticles (NPs) and on mesoporous silica microparticles as well. The covalent bonding of [Eu(TTA)3(Bpy-Si)] inside uniform Stöber silica nanoparticles was also achieved. The general methodology proposed could be applied to any silica matrix, allowed high grafting ratios that overcome chelate release and the tendency to agglomerate. Luminescent silica-based nanoparticles SiO2-[Eu(TTA)3(Bpy-Si)], with a diameter of 28 ± 2 nm, were successfully tested as a luminescent labels for the imaging of Pseudomonas aeruginosa biofilms. They were also functionalized by a specific monoclonal antibody and subsequently employed for the selective imaging of Escherichia coli bacteria.

Europium(III) complexes containing organosilyldipyridine ligands grafted on silica nanoparticles.

This work focuses on the grafting of transition metal complexes on silica surface nanoparticles. Nanoscale silica particles in aqueous sols are used as starting silicated materials. We have undertaken the synthesis of europium(III) complexes containing organosilyldipyridine ligands, (EtO)3Si(CH2)3NHCH2-bipy (1) and (EtO)(CH3)2Si(CH2) 3NHCH 2-bipy (2), in view of a direct grafting reaction on silica nanoparticles. Reaction of one molar equivalent of 1 and 2 with Eu(tmhd)3 (tmhd= 2,2,6,6-tetramethyl-3,5-heptanedionato), as precursor, leads to octacoordinated silylated europium(III) complexes [Eu(tmhd)3(1)] (3) and [Eu(tmhd)3(2)] (4) as white solids in 34-54% yields. Europium complexes were characterized by elemental analysis, mass spectrometry, FT-IR, UV, and luminescence spectroscopies. These new complexes are reacting in a 1:10 (v/v) water and ethanol mixture with silica nanoparticles colloidal sol. Elemental analysis and thermogravimetric data indicated grafting ratios of 0.41 and 0.26 mmol of europium(III) complexes per gram of silica. Functionalized silica nanoparticles were characterized by DRIFT spectroscopy and TEM microscopy. The first analysis shows that the chemical integrity of the complexes is retained on the silica surface together with the size and the monodispersity of the nanoscale particles. As expected for europium(III) complexes, luminescence is observed under UV irradiation. Emission and excitation spectra indicate that the metal coordination environment is not modified on the silica surface. Moreover, the sharpness of the luminescence bands and the strong antenna effect are maintained when complexes are covalently bonded to silica. New luminescent europium(III) complexes grafted on silica nanoparticles are therefore obtained from our approach.

Bidentate phosphinophenol R2POH ligands. Oxo and imido Re(V) complexes of 2-diphenylphosphinomethyl-4-methylphenol (POH). Crystal structure of ReOCl(PO)2

Abstract The PPh 3 ligands were displaced and ReOCl 3 (POH) 2 ( 1 ) was formed when ReOCl 3 (PPh 3 ) 2 and 2 equiv. of the title ligand (POH) were refluxed in acetonitrile. In the presence of the proton quencher NEt 3 , ligand deprotonation took place and the bis-chelate complex ReOCl(PO) 2 ( 2 ) was isolated. Under similar conditions, ReO(OEt)(PO) 2 ( 3 ) was obtained from ReO(OEt)Cl 2 (PPh 3 ) 2 . NMR data are consistent with the trans -O–ReO- cis -P,P ‘twisted’ octahedral geometry for these species. The corresponding phenylimido complex Re(NPh)Cl(PO) 2 ( 4 ), similarly prepared from Re(NPh)Cl 3 (PPh 3 ) 2 , adopts the trans -O–Re–NPh- trans -P,P arrangement. The structure of 2 was confirmed by X-ray diffraction. The methylene group in the side-arm imparts flexibility to the chelate ring and allows the bond angles to be closer to the ideal octahedral values than in the corresponding diphenylphosphinophenolato compound. The six-membered rings adopt a flattened boat conformation bringing the phenolate unit out of the coordination plane and making the overall van der Waals envelope substantially different from that of the diphenylphosphinophenol-based complex.

Rheological behaviour and spectroscopic investigations of cerium-modified AlO(OH)colloidal suspensions

The rheological behaviour of aqueous suspensions of boehmite (AlO(OH)) modified with different Ce-salts (Ce(NO(3))(3), CeCl(3), Ce(CH(3)COO)(3) and Ce(2)(SO(4))(3)) was investigated at a fixed Ce/Al molar ratio (0.05). Freshly prepared boehmite suspensions were near-Newtonian and time-independent. A shear-sensitive thixotropic network developed when Ce-salts with monovalent anions were introduced in the nanoparticle sols. The extent of particle aggregation dramatically increased with ageing for Ce(NO(3))(3) and CeCl(3) whereas an equilibrium value was reached with Ce(CH(3)COO)(3). The addition of Ce(2)(SO(4))(3) with divalent anions involved no thixotropy but rather a sudden phase separation. The combined data set of IRTF and DRIFT spectra indicated that free NO(3)(-) anions of peptized boehmite adsorb on the nanoparticle surface by H-bond. The introduction of Ce-salts in the boehmite sol led to the coordination between Ce(3+) ions and NO(3)(-) anions adsorbed on boehmite i.e. to [Ce(NO(3))(4)(H(2)O)(x)](-) complex. Such coordination led to a thixotropic behaviour which was lower with Ce(NO(3))(3) compared to CeCl(3) and Ce(CH(3)COO)(3). In contrast, Ce(2)(SO(4))(3) formed insoluble complexes with dissolved aluminium species. The formation of H-bonded surface nitrate complexes was found to play a decisive role on the particle-particle interactions and consequently on the rheological behaviour of the sols.

Bifunctional silica nanoparticles for the exploration of biofilms of Pseudomonas aeruginosa

Luminescent silica nanoparticles are frequently employed for biotechnology applications mainly because of their easy functionalization, photo-stability, and biocompatibility. Bifunctional silica nanoparticles (BSNPs) are described here as new efficient tools for investigating complex biological systems such as biofilms. Photoluminescence is brought about by the incorporation of a silylated ruthenium(II) complex. The surface properties of the silica particles were designed by reaction with amino-organosilanes, quaternary ammonium-organosilanes, carboxylate-organosilanes and hexamethyldisilazane. BSNPs were characterized extensively by DRIFT, 13C and 29Si solid state NMR, XPS, and photoluminescence. Zeta potential and contact angle measurements exhibited various surface properties (hydrophilic/hydrophobic balance and electric charge) according to the functional groups. Confocal laser scanning microscopy (CLSM) measurements showed that the spatial distribution of these nanoparticles inside a biofilm of Pseudomonas aeruginosa PAO1 depends more on their hydrophilic/hydrophobic characteristics than on their size. CLSM observations using two nanosized particles (25 and 68 nm) suggest that narrow diffusion paths exist through the extracellular polymeric substances matrix.

A simplified route to the synthesis of new 99mTc-specific tetradentate ligands

Abstract The synthesis of two new N 2 S 2 or N 2 SO tetradentate ligands and the preparation of their technetium-99m complexes are reported. Each ligand leads to a unique 99m Tc-complex with an excellent radiochemical yield. The in vivo stability of these complexes was determined by serum stability and cysteine challenge studies.

Bulk or surface grafted silylated Ru(II) complexes on silica as luminescent nanomaterials

A series of Ru(II) complexes with monosilylated-dipyridine ligand have been synthesized and fully characterized and were then covalently attached to silica nanoparticles. Two types of hybrids were obtained depending on the experimental procedure. In the first approach, metal complexes were incorporated inside the silica nanoparticles leaving a free hydroxylated silica surface for further functionalization. These silica based nanohybrids are similar to the well known nanoparticles encapsulating [Ru(bpy)3]2+ complexes preventing the release of the dye when used in aqueous or organic solutions. Size and luminescence properties vary throughout the series of metal complexes. The second approach leads to ruthenium(II) complexes covalently attached to the silica nanoparticle surface via hydrolysis and condensation of the ethoxysilyl group with silanol sites of Ludox type silica nanoparticles. This leads to the grafting of a monolayer for complexes with the monoethoxysilyl dipyridine ligand. In contrast, the complexes with triethoxysilyl ligands can lead to small amounts of oligomers, but their quantity is limited by the sterical constraints imposed by the molecular structure. The size of the hybrids depends on the starting particles. 29Si and 13C solid state NMR are used to characterize silica surface properties whereas TEM and SEM confirm nanosize and morphology of the hybrids. The complexes and the nanohybrids are luminescent, with variations for ruthenium(II) complexes that are covalently incorporated or grafted on the silica surface.

Synthesis and structural characterization of new oxorhenium and oxotechnetium complexes with XN2S-tetradentate semi-rigid ligands (X = O, S, N)

Twelve novel oxo-technetium and oxo-rhenium complexes based on N2S2-, N2SO- or N3S-tetradentate semi-rigid ligands have been synthesised and studied herein. By reacting the ligands with a slight excess of suitable [MO]3+ precursor (ReOCl3(PPh3)2 or [NBu4][99gTcOCl4]), the monoanionic complexes of general formula [MO(Ph-XN2S)]- could be easily produced in high yield. The complexes have been characterized by means of IR, electrospray mass spectrometry, elemental analysis, NMR and conductimetry. The crystal structures of [PPh4][ReO(Ph-ON2S)] 1b and [NBu4][99gTcO(Ph-ON2S)] 1c have been established. The [MO]3+ moiety was coordinated via the two deprotonated amide nitrogens, the oxygen and the terminal sulfur atoms in 1b and 1c. In both compounds, the ON2S coordination set is in the equatorial plane, and the complexes adopted a distorted square-pyramidal geometry with an axial oxo-group. The chemical and structural identity of the different prototypic complexes (rhenium, 99gTc complexes and their corresponding 99mTc radiocomplexes) have been also established by a comparative HPLC study.