Nathalie Steunou

Synthesis through an in situ esterification process and characterization of oxo isopropoxo titanium clusters

Three titanium oxo-isopropoxo clusters Ti 6 O 4 (OOCCH 3 ) 4 (OPr 1 ) 12 ( 1 ), Ti 12 O 16 (OPr 1 ) 16 ( 2 ) and Ti 12 O 16 (OPr 1 ) 16 ·1.4CH 2 Cl 2 ( 3 ) are obtained by refluxing Ti(OPr 1 ) 4 with 1.2 equivalents of carboxylic acids over two days. The molecular structures of Ti 6 O 4 (OOCCH 3 ) 4 (OPr 1 ) 12 ( 1 ) and Ti 12 O 16 (OPr 1 ) 16 · 1.4CH 2 Cl 2 ( 3 ) have been resolved by single crystal X-ray diffraction. The titanium oxo organo cores of these clusters are also characterized in solution by 17 O NMR spectroscopy and in solid-state by 13 C CP MAS NMR spectroscopy.

Influence of pH and ionic strength on vanadium(V) oxides formation. From V2O5·nH2O gels to crystalline NaV3O8·1.5H2O

Na+ and TMA+ intercalated M0.3V2O5·1.5H2O (M = Na+ and TMA+) precipitates have been synthesized by adding chloride salts MCl or bases MOH to a metavanadate solution which was acidified using a proton exchange resin. As evidenced by X-ray diffraction, these vanadium oxides exhibit the layered structure of the V2O5·1.8H2O xerogels in which Na+ and TMA+ cations are intercalated between the layers. These precipitates result from the assembly of ribbon-like particles but in contrast to the V2O5·1.8H2O xerogels, the particles are no longer stacked on flat surfaces and their assembly is disorganized as evidenced by SEM and TEM. Depending on the final pH of the acidified metavanadate solution, the Na0.3V2O5·1.5H2O phase can be thermodynamically stable or can evolve with time. At a pH > 3, the Na0.3V2O5·1.5H2O phase disappears after a few days and is transformed to the crystalline NaV3O8·1.5H2O phase. The vanadium oxide phases were all characterized by X-ray diffraction, SEM, TEM, TGA, IR and 51V MAS NMR.

Ketones as an oxolation source for the synthesis of titanium-oxo-organoclusters

Two titanium-oxo clusters, [Ti3O(OPri)7(O3C9H15)] 1 and [Ti11O13(OPri)18] 2, have been obtained through the reactions of Ti(OPri)4 with ketones such as acetone, acetylacetone and diacetone alcohol. Complex 1 is composed of a trinuclear unit that is capped by a tridentate enolate ligand synthesized insitu. Complex 2 is a more condensed titanium cluster with a spherical oxo core. The titanium-oxo-organo cores of these clusters are preserved in solution as characterized by 17O, 13C, and 1H NMR spectroscopy. The possible different reactions involved in the formation of these clusters are discussed.

Metal–organic frameworks: a novel host platform for enzymatic catalysis and detection

The use of metal–organic frameworks (MOFs) as immobilization matrices for enzymes as a platform for emerging applications is reported. In addition to an overview of strategies developed to prepare enzyme–MOF biocomposites, the features that render MOFs interesting matrices for bio-immobilization are highlighted along with their potential benefits beyond a solid-state support in the design of innovative biocomposites.

Vanadium Oxide: From Gels to Nanotubes

Vanadium oxide nanotubes (VOx-NT) have been prepared by mixing hexadecylamine with V2O5·nH2O gels. This procedure was followed by an hydrothermal treatment (150–180°C, 2–7 days) which leads to a large quantity of VOx-NT. SEM and XRD analysis have been used to optimize the temperature and reaction time required for production of VOx-Nt and morphology of the nanotubes investigated by TEM.

Design of metal organic framework–enzyme based bioelectrodes as a novel and highly sensitive biosensing platform

Nanocomposites combining the mesoporous iron(iii) trimesate MIL-100(Fe) (MIL: Matériaux Institut Lavoisier) and platinum nanoparticles (Pt-NPs) have been used as immobilization matrices of glucose oxidase (GOx). Due to the physico-chemical properties of Pt-NPs (electroactivity) and MIL-100(Fe) (high specific surface area and pore volume, biocompatibility), the resulting GOx-MIL-100(Fe)-PtNP bioelectrode exhibits excellent electrocatalytic performances for glucose detection. This novel glucose biosensor presents a high sensitivity of 71 mA M-1 cm-2 under optimum conditions and a low limit of detection of 5 μM with low response time (<5 s). In contrast, substitution of iron by chromium or aluminum in MIL-100 leads to a much lower sensitivity and higher response time values, suggesting that the iron centres of MIL-100(Fe) may be involved in a synergistic effect which indeed enhances the catalytic oxidation of glucose and biosensor activity. Thus, this work extends the scope of MOF nanoparticles with engineered cores and surface to the field of highly sensitive, durable glucose biosensors.

First example of biopolymer–polyoxometalate complex coacervation in gelatin–decavanadate mixtures

The first example of complex coacervation between a biopolymer and polyoxometalate clusters is identified in the gelatin-decavanadate system.

In situ growth of gold colloids within alginate films

Gold-alginate bionanocomposite films were prepared by impregnation of alginate films with HAuCl(4) followed by reduction with glucose. The mannuronate over guluronate ratio (M/G) of the polymer as well as the initial polymer concentration were shown to influence the film thickness, the amount of trapped Au(3 + ) ions, and the volume fraction of Au(0) nanoparticles but not the size of these colloids (about 4 nm). The homogeneity of the gold colloid dispersion within the alginate gels was studied by transmission electron microscopy (TEM) and confirmed by simulation of the surface plasmon resonance (SPR) spectra using the Maxwell-Garnett model. The calculated spectra also provided fruitful information about the gold colloid/alginate interface. Overall, the whole process is controlled by the balance between the M/G ratio, defining the polymer affinity for Au(III) species, and the solution viscosity, controlling the diffusion phenomena.

Single‐Molecule Magnet Behavior of Individual Polyoxometalate Molecules Incorporated within Biopolymer or Metal–Organic Framework Matrices

The chemically and structurally highly stable polyoxometalate (POM) single-molecule magnet (SMM) [(FeW9 O34 )2 Fe4 (H2 O)2 ](10-) (Fe6 W18 ) has been incorporated by direct or post-synthetic approaches into a biopolymer gelatin (Gel) matrix and two crystalline metal-organic frameworks (MOFs), including one diamagnetic (UiO-67) and one magnetic (MIL-101(Cr)). Integrity of the POM in the Fe6 W18 @Gel, Fe6 W18 @UiO-67 and Fe6 W18 @MIL-101(Cr) composites was confirmed by a set of complementary techniques. Magnetic studies indicate that the POMs are magnetically well isolated. Remarkably, in Fe6 W18 @Gel, the SMM properties of the embedded molecules are close to those of the crystals, with clear quantum tunneling steps in the hysteresis loops. For the Fe6 W18 @UiO-67 composite, the molecules retain their SMM properties, the energy barrier being slightly reduced in comparison to the crystalline material and the molecules exhibiting a tunneling rate of magnetization significantly faster than for Fe6 W18 @Gel. When Fe6 W18 is introduced into MIL-101(Cr), the width of the hysteresis loops is drastically reduced and the quantum tunneling steps are smeared out because of the magnetic interactions between the antiferromagnetic matrix and the SMM guest molecules.

A biocompatible calcium bisphosphonate coordination polymer: towards a metal-linker synergistic therapeutic effect?

A novel, biocompatible, calcium-based coordination polymer was hydrothermally synthesized using as linker the bone antiresorptive bisphosphonate alendronate. Its structure was determined using single-crystal X-ray diffraction and characterized by chemical analysis, infrared spectroscopy (IR), X-ray powder diffraction (XRPD), solid state nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). Its bioactivity was finally evaluated in vitro, revealing a very high stability towards simulated body fluid.