Gilles Guerrero

Hybrid materials from organophosphorus coupling molecules

Organophosphorus acids and their derivatives (salts, esters) are quite complementary of organosilicon coupling molecules for the preparation of hybrid organic–inorganic materials, by sol–gel processing or surface modification. Organosilicon compounds are best suited for the anchoring of organic groups to silicon-containing inorganic matrices or supports, such as silica, silicates, silicon carbide, etc., whereas organophosphorus coupling molecules appear well adapted to matrices or supports based on metals or transition metals: oxides, hydroxides, as well as carbonates and phosphates. The different reactivity of organophosphorus coupling molecules leads to different structures and stabilities of the final hybrid materials and may provide decisive advantages in the sol–gel synthesis of homogeneous hybrids, the preparation of surface monolayers or the selective surface modification of nanopatterned supports.

Phosphonate monolayers functionalized by silver thiolate species as antibacterial nanocoatings on titanium and stainless steel

Titanium and stainless steel substrates were modified by grafting with mercaptododecylphosphonic acid (MDPA) followed by reaction with silver nitrate (AgNO3), in order to investigate the potential of phosphonate self-assembled monolayers functionalized by silver thiolate species as antibacterial nanocoatings for inorganic biomaterials. The samples were characterized by Fourier transform infrared (FTIR) spectroscopy in grazing-incidence mode, water contact angle measurements, and X-ray photoelectron spectroscopy (XPS). The influence of the surface modification on bacterial adhesion and biofilm growth was investigated in vitro using Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus strains. The stability of the monolayer in blood-mimicking medium was examined. Despite their very low silver content, MDPA + AgNO3 monolayers strongly decreased bacterial adhesion (>99.9% reduction in the number of viable adherent bacteria) and biofilm formation in comparison to the bare substrates.

In vitro and in vivo characterization of antibacterial activity and biocompatibility: A study on silver-containing phosphonate monolayers on titanium

Infections associated with implanted medical devices are a major cause of nosocomial infections, with serious medical and economic repercussions. A variety of silver-containing coatings have been proposed to decrease the risk of infection by hindering bacterial adhesion and biofilm formation. However, the therapeutic range of silver is relatively narrow and it is important to minimize the amount of silver in the coatings, in order to keep sufficient antibacterial activity without inducing cytotoxicity. In this study, the antibacterial efficiency and biocompatibility of nanocoatings with minimal silver loading (∼0.65 nmol cm(-2)) was evaluated in vitro and in vivo. Titanium substrates were coated by grafting mercaptododecylphosphonic acid (MDPA) monolayers followed by post-reaction with AgNO3. The MDPA/AgNO3 nanocoatings significantly inhibited Escherichia coli and Staphylococcus epidermidis adhesion and biofilm formation in vitro, while allowing attachment and proliferation of MC3T3-E1 preosteoblasts. Moreover, osteogenic differentiation of MC3T3 cells and murine mesenchymal stem cells was not affected by the nanocoatings. Sterilization by ethylene oxide did not alter the antibacterial activity and biocompatibility of the nanocoatings. After subcutaneous implantation of the materials in mice, we demonstrated that MDPA/AgNO3 nanocoatings exhibit significant antibacterial activity and excellent biocompatibility, both in vitro and in vivo, after postoperative seeding with S. epidermidis. These results confirm the interest of coating strategies involving subnanomolar amounts of silver exposed at the extreme surface for preventing bacterial adhesion and biofilm formation on metallic or ceramic medical devices without compromising their biocompatibility.

X-ray crystal structures of novel platinum(II) and palladium(II) complexes of dialkyl phosphonated phosphines

Abstract Two diethyl phosphonated phosphine ligands of formula Ph2P(CH2)3PO3Et2 (ligand L) and Ph2P(4-C6H4PO3Et2) (ligand L′) were used to prepare different complexes of platinum(II) (1, cis-PtCl2L2; 2, trans-PtCl2L2·H2O; 3A and 3B, cis- and trans-PtCl2L′2) and palladium(II) (4, [PdCl2L]2; 5, trans-PdCl2L2·H2O; 6, trans-PdCl2L′2·CH2Cl2). The single-crystal X-ray structure analyses of complexes 1, 2, 4–6 indicate that complexation involved only the phosphine end, whereas the strong polarization of the PO bond was highlighted by the formation of hydrogen bonds with a water molecule in 2 and 5, and with a dichloromethane molecule in 6, with an exceptionally short CH⋯O hydrogen bond length (C⋯O separation 3.094(3) A).

Simultaneous Phase Transfer and Surface Modification of TiO2 Nanoparticles Using Alkylphosphonic Acids: Optimization and Structure of the Organosols

An original protocol of simultaneous surface modification and transfer from aqueous to organic phases of anatase TiO2 nanoparticles (NPs) using alkylphosphonic acids (PAs) is studied. The influence of the solvent, the nature and concentration of the PA, and the size, concentration, and aggregation state of the TiO2 NPs was investigated. Complete transfer was observed for linear alkyl chains (5, 8, 12, and 18 C atoms), even at very high sol concentrations. After transfer, the grafted NPs were characterized by (31)P solid-state MAS NMR. The dispersion state of NPs before and after phase transfer was monitored by dynamic light scattering (DLS). Small-angle neutron scattering (SANS) was used to characterize the structure of PA-grafted NPs in the organic solvent. Using a quantitative core-shell model cross-checked under different contrast conditions, it is found that the primary particles making up the NPs are homogeneously grafted with a solvated PA-layer. The nanometric thickness of the latter is shown to increase with the length of the linear carbon chain of the PA, independent of the size of the primary TiO2 NP. Interestingly, a reversible temperature-dependent aggregation was evidenced visually for C18PA, and confirmed by DLS and SANS: heating the sample induces the breakup of aggregates, which reassemble upon cooling. Finally, in the case of NPs agglomerated by playing with the pH or the salt concentration of the sols, the phase transfer with PA is capable of redispersing the agglomerates. This new and highly versatile method of NP surface modification with PAs and simultaneous transfer is thus well suited for obtaining well-dispersed grafted NPs.

Syntheses and single-crystal structures of novel soluble phosphonato- and phosphinato-bridged titanium oxo alkoxides

The reactions of PhP(O)(OH)2 or Ph2P(O)OH with Ti(OPri)4 in DMSO give the soluble tetranuclear complexes [Ti4(µ3-O)(OPri)5(µ-OPri)3(PhPO3)3]·DMSO 1 or [Ti(µ3-O)(OPri)(Ph2PO2)]4·0.5DMSO 2, the first examples of phosphonato- and phosphinato-bridged titanium oxo alkoxides, which have been characterised by single-crystal X-ray diffraction.

Design of Phosphonated Imidazolium-Based Ionic Liquids Grafted on γ-Alumina: Potential Model for Hybrid Membranes

Imidazolium bromide-based ionic liquids bearing phosphonyl groups on the cationic part were synthesized and grafted on γ-alumina (γ-Al2O3) powders. These powders were prepared as companion samples of conventional mesoporous γ-alumina membranes, in order to favor a possible transfer of the results to supported membrane materials, which could be used for CO2 separation applications. Effective grafting was demonstrated using energy dispersive X-ray spectrometry (EDX), N2 adsorption measurements, fourier transform infrared spectroscopy (FTIR), and special attention was paid to 31P and 13C solid state nuclear magnetic resonance spectroscopy (NMR).

Phosphonate Modified Titanium Alkoxides: Intermediates in the Sol-Gel Processing of Novel Titania / Phosphonate Inorganic-Organic Hybrids

We are currently developing a 2-step sol-gel route to metal oxide / phosphonate hybrid materials, based on the non-hydrolytic condensation of a metal alkoxide with a phosphonic acid, followed by hydrolysis / condensation of the remaining alkoxy groups. Several molecular intermediates in this process were obtained by reaction of Ti(O i Pr) 4 with phosphonic acids RPO 3 H 2 (R = Me, Ph, t Bu):[Ti 4 (O i Pr) 2 ( t BuPO 3 )] 4 (1),[Ti 4 (μ 3 -O)(O i Pr) 5 (μ-O i Pr) 3 (PhPO 3 ) 3 ]·DMSO (2), [Ti 4 (μ 3 -O)(O i Pr) 5 (μ-O i Pr) 3 (MePO 3 ) 3 ]·DMSO (3), [Ti 4 (μ 3 -O)(O i Pr) 5 (μ-O i Pr) 3 ( t BuPO 3 ) 3 ]·DMSO (4), which were characterized by single crystal X-ray structure analysis and/or NMR spectroscopy. These compounds give information on the sol-gel chemistry in our process and are structural models for the final hybrid materials. In all cases the non-hydrolytic condensation is complete, and the phosphoryl oxygen is coordinated to a titanium atom. In addition, these clusters are soluble in common organic solvents and contain hydrolyzable alkoxy groups, which make them potential building blocks in the sol gel process. Accordingly, the use of cluster 2 as a single source precursor was investigated.

Advanced Solid State NMR Techniques for the Investigation of the Organic-Mineral Interfaces in Biomaterials

High resolution solid state NMR experiments were carried out on several compounds, to see how this technique can now be used to investigate in detail the surface structure of different biomaterials. First, because the surface of titanium implants can be functionalized by phosphonic acids, for instance to prevent bacterial adhesion, 17 O NMR experiments were performed on model TiO 2 surfaces functionalized by 17 O enriched phosphonic acids, to look at the mode of grafting of these coupling agents. Results bring clear evidence of the formation of Ti-O-P bridges and of the presence of residual P=O and P-OH groups. Second, given that calcium phosphates are widely present in biological hard tissues and synthetic biomaterials, 43 Ca correlation experiments were performed on 43 Ca enriched materials (hydroxyapatite and calcium benzoate), to see how the proximities between this nucleus and neighbouring atoms can be analyzed. Results show that both Ca…C and Ca…H proximities can be evidenced, and could thus help elucidate interface structures. All in all, these studies should pave the way to future investigations of biomaterials, and in particular of the structure of organic-inorganic interfaces.