Patrick Seta

Cellular localisation of a water-soluble fullerene derivative

Fullerenes are a new class of compounds with potential uses in biology and medicine and many insights were made in the knowledge of their interaction with various biological systems. However, their interaction with organised living systems as well as the site of their potential action remains unclear. In this work, we have demonstrated that a fullerene derivative could cross the external cellular membrane and it localises preferentially to the mitochondria. We propose that our finding supports the potential use of fullerenes as drug delivery agents as their structure mimics that of clathrin known to mediate endocytosis.

The double layer and ion adsorption at the interface between two non miscible solutions: Part I. Interfacial tension measurements for the water-nitrobenzene tetraalkylammonium bromide systems

Abstract The classical treatment of the double layer has been extended to the interface between two immiscible solutions. The model presented is composed of an inner compact layer, characterized by a dipolar potential drop, between two diffuse type layers. The systems studied are composed of C 2 to C 5 quaternary ammonium bromides at partition equilibrium between water and nitrobenzene for which the inner potential difference, for a given electrolyte, is independent, at least in the lower concentration range, of the concentration. Drop weight interfacial measurements and the use of the Gouy-Chapman approach show that the tetraethyl-, tetrapropyl- and tetrabutylammonium ions are not adsorbed within the inner compact layer, and the dipolar potential drop of this layer can then be determined. Tetrapentylammonium ions on the contrary are specifically adsorbed but the amount of adsorbed ions within the compact inner layer cannot be evaluated because of the impossibility, in this case, of determining the dipolar potential drop.

Efficient facilitated transport of lead, cadmium, zinc, and silver across a flat-sheet-supported liquid membrane mediated by lasalocid A

Flat-sheet-supported liquid membranes incorporating lasalocid A (a natural ionophore) were shown in previous works to achieve the transport of divalent transition metal cations such as Cd2+ and Zn2+ against a proton gradient, which is the driving force behind the process. This transport process has been extended to other metal species such as Pb2+ and Ag+ and also to the case where the two metal species compete for transport. A higher transport flux for Pb2+ as compared to Cd2+ and Zn2+ is observed, which is partly explained by a higher rate of interfacial complexation due to a smaller hydration shell of this species. This effect is confirmed by the data obtained with Ag(I).

PHOTOPHYSICAL PROPERTIES OF THREE METHANOFULLERENE DERIVATIVES

The three [6,6]-ring bridged methanofullerenes 1, 2, and 3 were synthesized; their ground-state absorption spectra in toluene and cyclohexane solutions are presented and possible assignments discussed. Although these three molecules are very different, they have very similar triplet–triplet spectra and near-unity values for the quantum yield for O2(1Δg) production by energy transfer from the triplet states, implying that the quantum yield of triplet production is approximately 1.

The transfer mechanism of tetraalkylammonium ions across a water-nitrobenzene interface and the structure of the double layer

Abstract The transfer of tetraalkyl (from tetraethyl to tetrapentyl) ammonium ions (R+) from water to nitrobenzene is investigated by means of chronopotentiometric measurements. The systems studied are formed by an aqueous solution of R+Br− with an excess of NaBr as supporting electrolyte. These aqueous phases are in contact with a nitrobenzene solution of 10−2 M or 10−3 M tetraphenyl borate of the same R+ ion. Electrocapillary results obtained previously, with the same systems, suggest that the interfacial charge distributions are only spread within the diffuse layers, showing a continuity of the electrical potential across the central layer. Starting from this point a treatment has been proposed to deduce from the chronopotentiometric results the values of the ion transfer rate constants and how the central layer is affected by the overvoltage. In some regions of overvoltage, discrepancies are observed between these values and those calculated from electrocapillary curves.

The antioxidant role of bile pigments evaluated by chemical tests

Bilirubin, biliverdin and their serum albumin complexes were tested as oxyradical scavengers (superoxide generated by the xanthine/xanthine oxidase system and peroxyl radical-trapping antioxidant ability). As superoxide scavengers the free bile pigments showed activities near to that of serum albumin, higher than the water soluble vitamin E analog Trolox and lower than ascorbic acid. The peroxyl radical-trapping antioxidant abilities of the tested bile pigments were much higher than those of the serum albumin and of the same order as their serum albumin complexes. This interaction with peroxyl radicals showed different stoichiometric factors for bilirubin (approximately 2) and biliverdin (approximately 4).

Optical limiting and nonlinear optical absorption properties of C60–polystyrene star polymer films: C60 concentration dependence

The optical limiting behavior and the nonlinear optical properties of pure C60–(polystyrenex)y (C60–(PSx)y) star polymer, and C60–(PSx)y incorporated in a polystyrene matrix, are reported. Two, four and six polystyrene arms of controllable length were grafted directly on the C60 cage, preventing aggregation of the fullerene molecule, and consequently permitting achievement of high C60 concentrations. The optical limiting behavior of these films was measured below the damage threshold, and the nonlinear absorption coefficient β was determined by the Z-scan technique, using nanosecond 532 nm and sub-picosecond 497 nm laser radiation. In some of the samples, the high concentration of C60 gives rise to intermolecular interactions, which diminish the average molecular nonlinear optical properties of the film. However, the observed dependence of the nonlinear optical properties as a function of laser pulse duration and C60 concentration may be relevant to applications of these compounds in solid state devices.

Surface modification of microporous polypropylene membranes by the grafting of poly(γ-stearyl-l-glutamate)

Abstract A polypeptide, poly(γ-stearyl- l -glutamate) (PSLG), was grafted on the surface of hydrophobic polypropylene hollow fiber membranes through the ring opening polymerization of N-carboxyanhydride (NCA) of γ-stearyl- l -glutamate initiated by amino groups which was generated by ammonia plasma. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), together with water contact angle and bovium serum albumin adsorption measurements were used to characterize the modified membrane surface. The XPS and FT-IR spectra demonstrated that polypeptide was actually grafted on the membrane surface despite of the low degree of graft polymerization due to the hydroxyl groups on the membrane surface. To subject the ammonia plasma-treated membrane with γ-(aminopropyl)triethanoxysilane (γ-APS) which can react with hydroxyl groups and leave amino groups, the degree of graft polymerization could be improved. The bovium serum albumin adsorption measurement was conducted to further examine the surface properties of modified and original membranes. Potential applications of the PSLG grafted membranes are expected for enantiomer separation and/or enzyme immobilization.

Photophysical properties of three hydrofullerenes

Abstract The ground state and lowest triplet state properties of three hydrofullerenes, C60H2, C60H4 and [1-methylsuccinate-4-methyl-cyclohexadiene-2,3]buckminsterfullerene, have been investigated in toluene at room temperature. Their visible ground state absorption spectra are compared to those of methanofullerenes and methanolfulleroids. The triplet properties, including the absorption spectrum between 300 and 800 nm, molar absorption coefficient, quantum yield of formation and quantum yield for the photosensitized production of O 2 ( 1 Δ g ) , are compared to those of other C60 derivatives.

A new Multi-charged C60 Derivative: Synthesis and Biological Properties

A new water-soluble multi-charged monoadduct fullero[60]pyrrolidine derivative with three ethylene glycol chains and three ammonium groups has been synthesized by means of two alternative synthetic pathways. Increasing the concentration of this C60 derivative did not show a significant modification of concentration of superoxide anion radical O2·−, generated by the xanthine/xanthine oxidase system. Moreover, this C60 derivative was ineffective for neuroprotection in quantitative assessment of a neuronal injury considered to occur via radicals. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)