André Rassat

The heat capacity of solid C60

Abstract High resolution heat capacity measurements of the prototypic fullerene, C60, are presented between 13 and 300 K. The well-documented first-order phase transition is clearly observed at 257.6 K and is associated with enthalpy and entropy changes of 7.54 and 30.0 J K−1 mol−1, respectively. A more subtle transition is observed at 86.8 K. This transition is attributable to the onset of orientational glass behaviour related to the kinetics of molecular reorientation. The rate of the enthalpy relaxation at the glass transition is accurately reproduced by a simple exponential function. The Arrhenius parameters describing the temperature dependence of the relaxation time are Ea = 22.2 ± 1.0 kJ mol−1 and τ0 = 4×10−11±1s. At low temperatures, solid C60 is a glassy crystal in which molecular orientational disorder is frozen in as a consequence of the long relaxation time of the molecular reorientation.

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.

a one-pot procedure for the synthesis of alkynes and bromoalkynes from aldehydes.

Abstract Alkynes R-CCH were obtained in good yield through a one-pot procedure by a sequence of reactions starting from a Wittig-type condensation of the aldehydes RCHO with the ylide derived from dibromomethyltriphenylphosphonium bromide 5. The same reactions could also be used to prepare the intermediate dibromoalkenes RCHCBr2, and in certain cases, the bromoalkynes R-CCBr.

Quantitative analysis of C60 fullerene in blood and tissues by high-performance liquid chromatography with photodiode-array and mass spectrometric detection

A high-performance liquid chromatographic (HPLC) assay method for C60 fullerene, in blood, liver and spleen using photodiode-array detection or mass spectrometric detection (LC-MS) and C70 fullerene, as the internal standard, is described. The recovery from mouse blood and tissues spiked with micronized C60 exceeds 90%. The method is linear from 0.05 to 200 mg of C60 per liter of blood and from 0.05 to 5.00% of C60 per tissue weight. The limit of detection of the method is 0.1 ng of C60 per injection. This method was applied to mouse blood and tissue samples after intraperitoneal administration of a micronized C60 suspension.

Early effects of C60 Administration in Swiss Mice: A Preliminary Account for In Vivo C60 Toxicity.

Abstract High amounts of micronized C60 have been injected intraperitoneally into Swiss mice. Until the fourteenth day, they were still alive without any behaviour trouble. C60 was well absorbed, and found localized in spleen and liver. Inside the liver, C60 was

Thermodynamic Properties of a Single Crystal of Fullerene C60: A DSC Study

A 3.89 mg single crystal of fullerene C60 was grown by sublimation and its thermodynamic properties were determined through DSC measurements. The transition temperature and enthalpy are the highest ones that were ever measured (Ttr = (261.4 ± 0.5) K and ΔtrH = (9.0 ± 0.5) kJ mol-1, respectively) and are thought to be near-standard ones. However, it is shown that mechanical grinding smears out the DSC transition peak. Constraints which develop along free (111) surfaces are assumed to be responsible for this phenomenon.

Fullerene C60, 2CCl4 solvate. A solid-state study

By slowly evaporating solutions of fullerene C60 in CCl4 at room temperature, a stable solvate (C60, 2CCl4) crystallizes in a simple hexagonal system (Laue class 6/mmm) with a=10.10(5) A and c = 10.75(5) A. This solvate undergoes a phase transition at 210–220 K and decomposes at 397 K. Atomic force microscopy of the (001) face shows a C60 molecular packing analogous to that which exists in the {111} planes of face-centered cubic C60. It seems likely that C60 and CCl4 molecules are orientationally disordered at room temperature.

The geometric structure of deformed nanotubes and the topological coordinates

After summarizing the harmonic approach to topological coordinates and the null space embedding of graphs, three-coordinated tiling of the plane by hexagons, pentagons, and heptagons are presented and used for the construction of tubular, toroidal, and helical carbon structures. Physically realistic 3D geometries are formed from the corresponding adjacency matrices, and the final structure was obtained with the help of Brenner-potential based molecular mechanics methods.

Decagonal C60 crystals grown from n-hexane solutions: solid-state and aging studies

Abstract Decagonal C60 crystals grown from n-hexane solutions correspond to an orthorhombic 1:1 solvate (a=10.249 A, b=31.308 A, c=10.164 A). It forms with negative excess volume ( −55.5 A 3 per formula unit) and transforms on heating into fcc C60 (desolvation enthalpy of +50.6 kJ per solvate mole, close to the sublimation enthalpy for pure n-hexane) while n-hexane desorption from fcc C60 is accompanied by an enthalpy of +48.6 kJ per solvent mole. Thus solvate formation is preferred to solvent adsorption. Orthorhombic C 60 ·1 n -hexane undergoes no degradation when stored in air for 9 years at room temperature in the dark.

Synthesis of water‐soluble nitroxides and their use as mediators in aqueous‐phase controlled radical polymerization

Water-soluble nitroxides with different struc- tures were tested as mediators in the controlled free-radical polymerization of sodium 4-styrenesulfonate carried out in water at 130 °C. Nitroxides based on 1,1,3,3-tetramethyl- isoindolin-2-oxyl and 1,1,3,3-tetraethylisoindolin-2-oxyl with an ionic group on the aromatic ring (either a quaternary ammonium or a sulfonate substituent) exhibited better efficiency than water-soluble derivatives of 2,2,6,6-tetramethyl-1- piperidinyloxy radical (TEMPO). The steric hindrance at the nitroxide site (ethyl or methyl substituent) had a much larger influence on the activation-deactivation equilibrium than the type of ionic group. With nitroxides bearing four ethyl substituents, the equilibrium constant was one order of magnitude larger than that obtained for nitroxides with four methyl substituents. Final molar masses matched the predicted values, with narrow distribution. Livingness of the poly(sodium 4-styrenesulfonate)s was confirmed by successful reinitiation of sodium acrylate in water at 130 °C.