Asymptotic aspects of Schreier graphs and Hanoi Towers groups

We present relations between growth, growth of diameters and the rate of vanishing of the spectral gap in Schreier graphs of automaton groups. In particular, we introduce a series of examples, called Hanoi Towers groups since they model the well known Hanoi Towers Problem, that illustrate some of the possible types of behavior. To cite this article: R. Grigorchuk, Z. ?unik´, C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Di-μ-hydroxo complexes of palladium(II) with α-diimines

The binuclear hydroxo α-diiminate palladium complexes [Pd2(R′N=CR-CR=NR′)2(μ-OH)2][ClO4]2 (R=H, R′= C6H4Me-o or C6H4Me-p; R=Me, R′=Ph, C6H4Me-o or C6H4Me-p) have been prepared by reacting the corresponding chloro complexes with AgClO4 in Me2CO–H2O. The hydroxo complexes react with the protic electrophiles ethanoic acid, acetylacetone and8-hydroxoquinoline to give the corresponding acetylacetonate, acetate and 8-hydroxiquinolinate complexes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Lefschetz pencil structures for 2-calibrated manifolds

We prove that for closed 2-calibrated manifolds there always exist Lefschetz pencil structures. This generalizes similar results for symplectic and contact manifolds. To cite this article: A. Ibort, D. Marti´nez Torres, C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Theoretical study of the reaction H + ClCH3 → HCl + CH3

The reaction H + ClCH₃ has theoretically studied in a LEPS potential energy surface with a single-particle approximation for the methyl group. The LEPS adjustable parameters were selected to reach a good agreement with experimental values of activation energy and exothermicity. A wide set of quasi-classical trajectories for that system has been calculated within a energy range covering the significative values of relative velocities at temperatures between 300 and 1000 K. Calculated reactive cross sections increase with translational energy and with the initial vibrational level, but they are not influenced by rotational excitation of the reactants. Microscopic and total reaction rate constants have been obtained within the temperature range and agree quite well with available experimental results. Final energy distribution shows that most of the exoergicity is consumed in increasing the relative velocity of the products, while HCl molecules remain in their vibrational ground state.     

Synthesis of telehelic oligodimethylsiloxanes with 4-carboxypyrrolidone fragments: rheological and thermal properties

Telehelic oligodimethylsiloxanes containing 4-carboxypyrrolidone fragments were synthesized by the reactions of oligodimethylsiloxanes bearing terminal 3-aminopropyl groups with itaconic acid. The thermal and rheological properties of the obtained polymers were studied. The activation energies of viscous flow of the oligomers obtained and the previously synthesized oligodimethylsiloxanes containing terminal fragments of undecenoic or benzoic acid are compared.

     

High-performance liquid chromatographic assay of fleroxacin in human serum using fluorescence detection

A HPLC method has been developed for the direct assay of fleroxacin in serum, without previous extraction. Serum samples, after the addition of sodium dodecylsulfate (0.5%), were injected directly into an LC Hisep column. The mobile phase consisted of acetonitrile, water and triethylamine in a per cent volume ratio 18:80:2. The pH of the mobile phase was adjusted to 6.50 with the addition of phosphoric acid. The drug was detected fluorometrically at lambda (ex )=280 nm and lambda (em )=450 nm . The linear concentration range of fleroxacin was between 0.01 and 2.0mg/l with a detection limit of 1ng/ml.     

Pre´paration chimique et structure cristalline de l'iodate d'argent AgIO3

A new chemical preparation of silver iodate AgIO₃ is given. The crystal structure has been determined by single-crystal X-ray diffraction methods and refined to a finalR value of 0.051 for 1280 independent reflections. The unit cell is orthorhombic witha = 7.265(2), b = 15.17(4), c = 5.786(2)A?,Z = 8. The space group isPbc2₁. IO₃ groups and AgO₆ octaedra form a compact bidimensional framework perpendicular to theb axis.     

Metal Ion Interaction of Two New Tritopic N2O13 Macrobicycles with B15C5 Moieties in Acetonitrile Solution

The synthesis of two new tritopic crown ligands (L1 and L2) bearing two benzo-15-crown-5 lateral moieties linked through a dibenzo-trioxa chain together with their interaction with metal ions, in acetonitrile and acetonitrile–water (50%, v/v) solutions is reported. The influence of K⁺, Na⁺, Li⁺, Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and Al³⁺, on the spectroscopic properties of these diaza-polyoxa ligands was investigated by absorption spectrophotometry and in some cases by fluorescence emission spectroscopy. Coordination with alkaline (Na⁺, K⁺ and Li⁺) and alkaline earth (Ca²⁺and Ba²⁺) metal ions is assumed to be weak with both macrobicyclic ligands, while the interaction with both imine and amine derivatives causes a minor effect in the absorption spectra. Coordination with Cu²⁺, Zn²⁺ and Pb²⁺ in acetonitrile solution causes a major change in the absorption spectra of the chromophores. In the case of Cu²⁺, addition of the metal to L1 or L2 leads to a blue–violet complex in solution with an absorbance maximum centred at 590 nm. Interaction of the Schiff-base L1 with Pb²⁺ leads to a short wavelength shift in the absorption bands, comparable with the ZnL1 complex. Presence of transition metal ions such as Co²⁺, Ni²⁺and Cd²⁺ do not remarkably affect the absorption spectra of L1 and L2 in solution. Trivalent aluminium has a modest effect in the absorption bands of both N₂O₁₃ donor set bismacrocyclic ligands. The fluorescence study of L2 in the presence of Na⁺, K⁺, Ca²⁺, Ba²⁺, Co²⁺, Cu²⁺, Ni²⁺, Pb²⁺ and Al³⁺shows that Cu²⁺, Pb²⁺ and Al³⁺ complexes form non-fluorescent complexes.     

Recherche de matériauxa`conductivitéionique ame´liore´e de´rivant des hydrurofluorures de calcium CaF2−xHx: conductivite´ ionique des phases Ca1−yNay(F2−xHx)1−y/2

The doping of CaF_2?xH_x hydridefluorides by aliovalent ions is studied, the aim being the preparation of materials of improved ionic conductivity. It is shown that doping by monovalent Na⁺ ions is possible. Three hydrogen-rich phases, formulated Na_yCa_1?y(F_2?xH_x)_1?y/2 have been studied. Their conductivity is mainly ionic, but, compared with the same doping in CaF₂, the conductivity enhancement is low. This result is interpreted from energetic and structural considerations.     

Coordination geometries and cooperative ordering effects in copper(II) complexes with tridentate Schiff base dianions 5 E.p.r. spectra of [N-salicylidene-(R,S)-alaninato]copper(II) complexes with derivatives of imidazole and pyrazole and structure of 1-methylimidazole[N-salicylidene-(R,S)-valinato]copper(II)

1-Methylimidazole[N-salicylidene-(R,S)-valinato]copper(II) shows square-planar coordination around the Cu2+ ion, coordinated in the basal plane by O,N,O atoms from the tridentate Schiff base dianion and by N from the coordinated 1-methylimidazole. In the crystal structure, enantiomers related by an inversion centre are bound by H bonds to units with a CuCu distance of 8.039Å. Intermolecular H bonds stabilize stacking of such units, which are propagated along the [010] axis. Two such chain systems in the unit cell are related by a glide plane parallel to (010). The basal planes of two magnetically non-equivalent complexes are canted by an angle of 74.64. The shortest CuCu distance between non-parallel-aligned coordination polyhedra is 10.518Å. On the other hand, the closest CuCu spacing of parallel-orientated coordination polyhedra is 5.628Å. Hence, in the e.p.r. powder spectrum only the coupling between ferrodistortively ordered coordination polyhedra is manifested.E.p.r. and ligand field spectra of a series of [N-salicylidene-(R,S)-alaninato]copper(II) complexes with imidazole, pyrazole and some of their derivatives provide evidence for coordination geometries ranging from square-pyramidal, with various strengths of axial interaction, to square-planar. The cooperative ordering phenomena in the structure are discussed on the basis of the e.p.r. powder spectra. When the e.p.r. spectra yield crystal g values from two coupled molecular g tensors of orthorhombic symmetry, a simple model based on consistency of G parameters was developed for evaluation of the canting angle 2 between aligned coordination polyhedra and molecular g values, respectively. The data obtained from the e.p.r. powder measurements are in excellent agreement with the results of single X-ray structural studies.