Bertrand Lefeuvre

Multiple single-molecule magnet behaviors in dysprosium dinuclear complexes involving a multiple functionalized tetrathiafulvalene-based ligand.

The reaction between the 2-(1-(2,6-di(pyrazol-1-yl)-4-methylpyridyl)-4,5-(4,5-bis(propylthio)-tetrathiafulvalenyl)-1H-benzimidazol-2-yl)-pyridine ligand (L) and 2 equiv of Dy(hfac)3·2H2O (hfac(-) = 1,1,1,5,5,5-hexafluoroacetylacetonate) and 1 equiv each of Dy(hfac)3·2H2O and Dy(tta)3·2H2O (tta(-) = 2-thenoyltrifluoroacetonate) metallic precursors leads to two dinuclear complexes, [Dy2(hfac)6(L)]·(CH2Cl2)2·C6H14 (1) and [Dy2(hfac)3(tta)3(L)] (2), respectively. Their X-ray structures reveal that the two coordination sites are occupied by one Dy(III) ion. The Dy(III) ion coordinated to the benzoimidazolylpyridine (bzip) moiety adopts a D4d coordination sphere, while the Dy(III) ion coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety is in a D3h surrounding. In a zero dc field, the dynamic magnetic measurements show a slow relaxation for the D4d eight-coordination Dy(III) magnetization for 1 and 2. Application of an external dc field induces multirelaxation signals of the magnetic susceptibility for both compounds. The low frequency and high frequency of the out-of-phase magnetic signals are attributed to the Dy(III) ion in D4d and D3h surroundings, respectively. The two complexes can be described as double induced-field mononuclear single-molecule magnets.

Magnetic and photo-physical investigations into DyIII and YbIII complexes involving tetrathiafulvalene ligand

Three lanthanide-based complexes involving a tetrathiafulvalene derivative (L) in which the lanthanide ion has a pseudo-D4d symmetry have been reported. One is a dinuclear compound of formula [Dy(hfac)3(L)]2 (1) while the two others are isostructural and described as mononuclear complexes of formulae [Ln(tta)3(L)]·xCH2Cl2 (LnIII = Dy and x = 1.41 (2); Yb and x = 2 (3)). The nuclearity of the species is driven by the nature of the ancillary ligands. Magnetic properties revealed that 1 and 3 behave as single molecule magnets, while 2 does not. The crystal field splitting of the ground multiplet state has been theoretically determined as well as the orientation of the easy axis of the ground MJ state. The results of ab initio calculations are in agreement with the experimental determinations of the anisotropy axis. Irradiation of the lowest-energy charge transfer bands of 3 led to an intense and resolved Yb-centred emission which can be correlated to the magnetic data. Thus 3 can be described as a redox-active luminescent field-induced single-molecule magnet.

Rational Design of a Lanthanide-Based Complex Featuring Different Single-Molecule Magnets

The rational synthesis of the 2-{1-methylpyridine-N-oxide-4,5-[4,5-bis(propylthio)tetrathiafulvalenyl]-1H-benzimidazol-2-yl}pyridine ligand (L) is described. It led to the tetranuclear complex [Dy4(tta)12(L)2] (Dy-Dy2-Dy) after coordination reaction with the precursor Dy(tta)3⋅2 H2O (tta(-) = 2-thenoyltrifluoroacetonate). The X-ray structure of Dy-Dy2-Dy can be described as two terminal mononuclear units bridged by a central antiferromagnetically coupled dinuclear complex. The terminal N2O6 and central O8 environments are described as distorted square antiprisms. The ac magnetism measurements revealed a strong out-of-phase signal of the magnetic susceptibility with two distinct sets of data. The high- and low-frequency components were attributed to the two terminal mononuclear single-molecule magnets (SMMs) and the central dinuclear SMM, respectively. A magnetic hysteresis loop was detected at very low temperature. From both structural and magnetic points of view, the tetranuclear SMM Dy-Dy2-Dy is a self-assembly of two known mononuclear SMMs bridged by a known dinuclear SMM.

Unprecedented Sensitization of Visible and Near-Infrared Lanthanide Luminescence by Using a Tetrathiafulvalene-Based Chromophore

Ligand L was synthesized and then coordinated to [Ln(hfac)3]⋅2 H2O (Ln(III)=Tb, Dy, Er; hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion) and [Ln(tta)3]⋅2 H2O (Ln(III)=Eu, Gd, Tb, Dy, Er, Yb; tta(-)=2-thenoyltrifluoroacetonate) to give two families of dinuclear complexes [Ln2(hfac)6(L)]⋅C6H14 and [Ln2(tta)6(L)]⋅2 CH2Cl2. Irradiation of the ligand at 37,040 cm(-1) and 29,410 cm(-1) leads to tetrathiafulvalene-centered and 2,6-di(pyrazol-1-yl)-4-pyridine-centered fluorescence, respectively. The ligand acts as an organic chromophore for the sensitization of the infrared Er(III) (6535 cm(-1)) and Yb(III) (10,200 cm(-1)) luminescence. The energies of the singlet and triplet states of L are high enough to guarantee an efficient sensitization of the visible Eu(III) luminescence (17,300-14,100 cm(-1)). The Eu(III) luminescence decay can be nicely fitted by a monoexponential function that allows a lifetime estimation of (0.49±0.01) ms. Finally, the magnetic and luminescence properties of [Yb2(hfac)6(L)]⋅C6H14 were correlated, which allowed the determination of the crystal field splitting of the (2)F(7/2) multiplet state with M(J)=±1/2 as ground states.

Excess entropy and thermal behavior of Cu- and Ti-doped bioactive glasses

Bioactive glasses belong to the ceramic family. They are good materials for implantation due to their excellent capacities to create an intimate bond with bones. Copper is known for its anti-inflammatory, antibacterial, and antifungal properties. Titanium is biocompatible and resistant to corrosion. These chemical elements can be introduced in bioactive glasses to provide a wide variety of uses and to enhance the physiological properties of implanted biomaterials. In this work, bioactive glasses doped with different contents of copper and titanium were synthesized by the melting method. The purpose is to study the effect of doping metal element on the thermal characteristics (Tg, Tc, and Tf). The results revealed that the increase of the content of copper and titanium in the glass matrix decreases the melting temperature and induces an increase of the thermal stability. The excess entropies of pure and doped glasses were calculated. Obtained results highlighted the decrease of the excess entropy with the increase of metal elements contents.

New method of synthesis and in vitro studies of a porous biomaterial.

Biomaterials for bone reconstruction represent a widely studied area. In this paper, a new method of synthesis of a porous glass-ceramic obtained by thermal treatment is presented. The prepared biomaterial was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and induced couple plasma-optical emission spectroscopy (ICP-OES), mercury porosimetry and by the Archimedes method. In vitro evaluations in a simulated body fluid (SBF) and in contact with SaOS2 human osteoblasts were also carried out. The porous glass-ceramic is composed of a total porous network of 60% suitable for body fluid and cell infiltration, with pore sizes varying from 60 nm to 143 μm. The presence of two crystalline phases decreases the kinetic of bioactivity compared to an amorphous biomaterial (bioactive glass). A hydroxyapatite layer appears from 15 days of immersion on the surface and inside the pores, showing a biodegradation and a bioactivity in four steps. Cytotoxicity assessments present an increase of the cellular viability after 72 h proving the non-cytotoxic effect of the glass-ceramic. Thus, the results of these different studies indicate that the porous biomaterial may have a potential application for the bone regeneration. This paper also presents the novelty of this method. It is a rapid synthesis which combines simplicity and low cost. This represents an advantage for an eventual industrialization.

Antibacterial and in vivo reactivity of bioactive glass and poly(vinyl alcohol) composites prepared by melting and sol-gel techniques

Bioactive glass particle is used in the repair of bone defects. This material undergoes a series of surface in vivo reactions, which leads to osteointegration. We evaluated the effect of the bioactive glass synthesis, sol-gel (BG(S)) versus melting (BG(M)), associated with polyvinyl-alcohol (PVA) on in vivo bioactivity with biochemical parameters, liver-kidney histological structure and antibacterial in vitro activity. These composites were testified in many bacteria and implanted in ovariectomized rat. The serum and organs (liver and kidney) of all groups, control and treated rats, were collected to investigate the side effects of our composites, BG(S)-PVA and BG(M)-PVA, in comparison with control and ovariectomized rats. Also, the implants, before and after implantation, were prepared for analysis using physicochemical techniques such as Fourier transform infrared spectroscopy and X-ray diffraction. Our results have shown the stability of natremia, kaliemia, calcemia and phosphoremia. The histological structures of liver and kidney in implanted rats are intact compared to control and ovariectomized rats. BG(S)-PVA is characterized by a higher antibacterial effect on negative and positive gram bacteria than BG(M)-PVA. The physicochemical results have confirmed a progressive degradation of BG(S)-PVA and BG(M)-PVA, while replacing the implant by an apatite layer. But this bioactivity of BG(S)-PVA is faster than BG(M)-PVA. We can therefore confirm, on the one hand, the biocompatibility of our two implants and, on the other hand, the beneficial effect of sol-gel synthesis technique versus melting, both on the antibacterial effect and on the rapid formation of layer hydroxyapatite, and consequently on osteogenesis.

The performance of a scaffold bioglass–chitosan in the treatment of bone defect

The present research work is an in vivo study that aimed to evaluate the potential role of bioglass–chitosan (BG–CS) and bioglass–chitosan–20%ciprofloxacin (BG–CS–20Cip) in antioxidant profile and osteointegration. These scaffolds were implanted in the defect bone of femoral condyles in ovariectomized rats. The treatment with BG–CS–20Cip has shown a significantly higher stress proteins concentration in comparison with that implanted with BG–CS group. The thiol and vitamin C in BG–CS–20Cip group were significantly enhanced when compared with those in BG–CS group. The histological and physicochemical analyses highlight the BG–CS implications in the bone construction. This property was found to decrease with the presence of ciprofloxacin that caused the delay of this phenomenon. ICP-OES has revealed that the introduction of this antibiotic to the composite led to decrease bone mineralization by evaluating Ca/P ratio. The SEM results have confirmed a progressive degradation of BG–CS and BG–CS–20Cip. However, such bioresorbability and bioactivity of BG–CS was proven to be faster than those of BG–CS–20Cip. Therefore, the incorporation of ciprofloxacin in BG–CS was characterized by a delaying effect of composite dissolution and the formation of apatitic phase. The development of BG–CS as a therapeutic biomaterial protector against oxidative stress is likely to make an effective choice for the application in tissue engineering.

In vivo study of hybrid biomaterial scaffold bioactive glass–chitosan after incorporation of Ciprofloxacin

The present study aimed to evaluate the effect of bioactive glass as well as the presence of Ciprofloxacin drug (%Cip) into bioactive glass–chitosan composite on the in vivo behavior of these scaffolds. These scaffolds were implanted in the femoral condyl of an ovariectomized rat. The serum and organs (liver and kidney) of the under investigated rats were analyzed. Also the physicochemical properties of the prepared implants were assessed using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) before and after implantation (at different periods of implantation). Biochemical and histological analyses of the under investigated rats proved the biocompatibility of the prepared scaffolds. The hydroxyapatite like layer was significantly precipitated on the surface of BG–CH scaffold than BG–CH–20Cip. In this same period, FT-IR of BG–CH shows complete disappearance of Si–O–Si. Their characteristics bands were replaced by P–O group arisen form bone apatite bands. Physicochemical results show progressive degradation of BG–CH and BG–CH–20Cip that occurred at the same time as replacement of the implant by an apatite layer. However, the bioresorbability and bioactivity of BG–CH are faster than those of BG–CH–20Cip. Therefore, the incorporation of the Ciprofloxacin in the BG–CH induces a retarding effect on the formation of the hydroxyapatite, and consequently on the ossification, without any side effects on the liver–kidney.

New hybrid agarose/Cu-Bioglass® biomaterials for antibacterial coatings

Agarose hydrogels, combined with 45S5 Bioglass®, were elaborated to serve as copper delivery systems. Our aim was to study the antibacterial properties of these hydrogels. The results show that the amount of glass does not influence the stiffness properties, but it improves the hydrophilicity and the swelling profile of agarose hydrogel. Two bacterial strains, Bacillus sp. 4J6 and Pseudomonas aeruginosa sp. PAO1, were chosen. Their retention on the substrates was analyzed by confocal laser scanning microscopy. The mechanical characteristics and the release of copper have an effect on the bacterial adhesion and the biofilm formation. All the obtained results indicate that these hydrogels could be adapted to a potential application to the antibacterial coatings