UV/Vis, IR and 1H NMR spectrophotometric studies of some bisazo-dianil compounds based on bis-(hydroxy, formyl) phenylazo phenylene and anthranilic acid

The electronic absorption spectra of some bisazo-dianils are studied in organic solvents of different polarity and in buffer solutions of varied pH. The different absorption bands are assigned to the corresponding electronic transitions, the solvent effect on the CT band energy is also discussed. The spectral study in buffer solutions is utilized for the determination of the pKa of the phenolic OH-groups. The important bands in the IR spectra as well as the signals of the 1H NMR spectra are assigned and discussed in relation to molecular structure. The fluorescence spectra of the compounds are recorded. The fluorescence quantum yield and pK in the ground and excited states are determined.     

Synthesis of fluorescent and coloured pyrylium and pyridinium salts

The synthesis is described of fluorescent and coloured pyrylium and pyridinium salts, including water-soluble derivatives, designed to serve as marker reagents for primary amines.     

Dielectric relaxation and ac conduction of AgTlTe2 amorphous semiconductor

Measurements of the dielectric properties of AgTlTe₂ in the solid and liquid states were carried out in a wide range of frequencies and temperatures. The material shows dielectric dispersion. Cole-Cole diagrams have been used to determine the distribution parameter and the molecular relaxation time. The ac conduction mechanism and dielectric loss are attributed to correlated barrier hopping in the amorphous solid.     

Synthesis and Diels-Alder reactivity of ortho-carbazolequinones

Oxidation of 2- and 3-hydroxycarbazoles with Frémy's salt gave the corresponding ortho-carbazolequinones. These molecules react as carbodienophiles in Diels-Alder reaction with 1-acetoxy-1,3-butadiene and 1,3-cyclopentadiene to provide the novel benzocarbazolequinone structures 15, 16, 18 and 19.     

Long-range electron transfer across Peptide bridges: the transition from electron superexchange to hopping

Long-range electron transfer rate constants for complexes of the type [(bpy)2RuIIL-Pron-apyRuIII)(NH3)5]5++ proline residues (n) varying from 0 to 9 were determined by complementary electron pulse radiolysis and flash photolysis techniques from the picosecond to the millisecond time scales. The activationless kmax values from both techniques coalesce into one data set. The distance dependence of the reactions is consistent with a smooth transition from a superexchange mechanism with attenuation constant beta = 1.4 A-1 to a hopping mechanism with attenuation constant beta = 0.17 A-1. The transition occurs between n = 3 and 4 prolines, and the virtual hopping rate constant at the shortest distance is about 1 x 106 times slower than that observed for the superexchange value.     

Estimation of the offspring mean of a supercritical or near-critical size-dependent branching process

We consider a single-type supercritical or near-critical size-dependent branching process ${\left\{N_n\right\}}_n$ such that the offspring mean converges to a limit $m?1$ with a rate of convergence of order $N_n^{\alpha }$ as the population size $N_n$ grows to ∞ and the variance may change at the rate $N_n^{\beta }$, where $\alpha >0$ and $?1?\beta <1$. The offspring mean depends on an unknown parameter ${\theta }_0$ that we estimate on the non-extinction set by using the conditional least squares method. We prove the strong consistency of the estimator of ${\theta }_0$ as $n\to \infty$ under some general conditions on the asymptotic behavior of the process. We also give its asymptotic distribution for a certain class of size-dependent branching processes. To cite this article: N. Lalam, C. Jacob, C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Hecke algebras of semidirect products

We consider group-subgroup pairs in which the group is a semidirect product and the subgroup is contained in the normal part. We give conditions for the pair to be a Hecke pair and we show that the enveloping Hecke algebra and Hecke -algebra are canonically isomorphic to semigroup crossed products, generalizing earlier results of Arledge, Laca and Raeburn and of Brenken.

     

NF-kappaB activation is associated with homocysteine-induced injury in Neuro2a cells

Background  

Perinatal exposure to hyperhomocysteinemia might disturb neurogenesis during brain development and growth. Also, high levels of homocysteine trigger neurodegeneration in several experimental models. However, the putative mechanisms of homocysteine-induced toxicity in the developing nervous system have poorly been elucidated. This study was aimed to investigate homocysteine effects in undifferentiated neuroblastoma cells, Neuro2a.