Chrystel Faure

A New Bio‐Inspired Route to Metal‐Nanoparticle‐Based Heterogeneous Catalysts

Onion-type multilamellar vesicles are made of concentric bilayers of organic surfactant and are mainly known for their potential applications in biotechnology. They can be used as microreactors for the spontaneous and controlled production of metal nanoparticles. This process does not require any thermal treatment and, hence, it is also attractive for material sciences such as heterogeneous catalysis. In this paper, silver-nanoparticle-based catalysts are prepared by transferring onion-grown silver nanoparticles onto inorganic supports. The resulting materials are active in the total oxidation of benzene, attesting that this novel bio-inspired concept is promising in inorganic catalysis.

Production of magnetic multilamellar liposomes as highly T2-efficient MRI contrast agents.

UNLABELLED Lipid-based multilamellar vesicles loaded with aminosilane-modified maghemite nanoparticles (a-MNPs), also called magnetonions (MO), were analyzed for their magnetic resonance imaging (MRI) contrast agent properties. They were shown to be better T(2)-MRI contrast agents than commercial contrast agents and other reported liposome-based contrast agents as shown by their higher value of relaxivity ratio (r(2)/r(1) = 17), although a lower magnetic field intensity was used (0.2 T). Their high efficiency was explained by the aggregation of a-MNPs in between multilamellar vesicles, bilayers induced by MO preparation, and evidenced by cryo-TEM imaging. Magnetonions are then a promising platform for diagnosis and therapy. FROM THE CLINICAL EDITOR In this study, magnetonions (MO) are presented as a very potent T2 relaxation enhancing MRI contrast agents. Such agents may be used in cell labeling and molecular imaging applications.

Effect of onion-type multilamellar liposomes on Trametes versicolor laccase activity and stability.

Trametes versicolor laccase was encapsulated into onion-type, lipid-based multilamellar vesicles (MLVs). When encapsulated, laccase was isolated from the assay medium but was still active once freed from its capsule. The encapsulation efficiency was larger than 65% at 25 °C and 37 °C and decreased to 55% by introducing 140 mM NaCl into the buffered medium (pH = 4.5). MLVs were shown to drastically improve both laccase stability and activity. At 25 °C, laccase activity was doubled in the presence of MLVs. At 37 °C in the salt-free medium, the half-life time of laccase was increased from 2 hr 30-65 h without and with MLVs, respectively. This effect was even more pronounced in the salted medium where laccase activity was unchanged for 6 days in the presence of MLVs. These beneficial effects were attributed to the immobilization of laccase onto MLV surface. Laccase activity as well as stability was notably shown to be directly correlated to MLV stability.

Multilamellar liposomes entrapping aminosilane-modified maghemite nanoparticles: “magnetonions”

4.6 nm-sized aminosilane-modified maghemite (γ-Fe(2)O(3)) nanoparticles (aMNPs) were synthesized and encapsulated into onion-type multilamellar vesicles of soybean phosphatidylcholine (90%mol) and monoolein (10%mol). The magnetic multilamellar vesicles were obtained by shearing lipids with an aqueous dispersion of the preformed aMNPs (ferrofluid). The influence of ferrofluid concentration on the stability of the constitutive lamellar phase and the resulting dispersed onions was analyzed by small-angle X-ray diffraction (SAXD) and cryo-TEM imaging, respectively. When [Fe(III)] <60 mM, stable, magnetic onions were produced with aMNPs inserted inside onion water compartments as isolated or aggregated particles. Encapsulation efficiencies were measured by EPR spectroscopy and magnetic measurements: much higher values (up to 75%) than unilamellar liposomes were found. The deduced aMNP-to-onion ratio increased with ferrofluid concentration before reaching a maximal value of ca. 45 as confirmed by cryo-TEM imaging. When [Fe(III)] >60 mM, uni- or oligolamellar vesicles in addition to onions formed, probably because of a two-phase separation between an aMNP-rich phase and an aMNP-containing lamellar phase as revealed by SAXD.

Ag-V2O5/TiO2 total oxidation catalyst: autocatalytic removal of the surfactant and synergy between silver and vanadia

Silver nanoparticles prepared at room temperature in multilayer organic vesicles are deposited onto a V2O5/TiO2 support to produce a bifunctional oxidation catalyst performing very well in the total oxidation of benzene. The synergy between Ag and V2O5 takes place only when the surfactant is eliminated by in situ calcination. This paper shows that vanadium oxide autocatalytically promotes the combustion of this organic matter. This effect allows treating the catalyst at lower temperature which leads to an enhanced doping effect of the small tailored Ag nanoparticles, presumably because sintering is avoided.