Efficient multicomponent synthesis of 2-aminopyridines catalysed by basic mesoporous materials

Research on Chemical Intermediates - An efficient and green procedure for the synthesis of 2-aminopyridines derivatives via four-component reaction of acetophenone, malononitrile, triethoxymethane...     

Determination of doping effects on Si and GaAs bulk samples properties by photothermal investigations

The knowledge of doping effects on optical and thermal properties of semiconductors is crucial for the development of opto-electronic compounds. The purpose of this work is to investigate these effects by mirage effect technique and spectroscopic ellipsometry SE.

The near gap optical spectra are obtained from photothermal signal for differently doped Si and GaAs bulk samples. However, the above bandgap absorption is determined from SE. These spectra show that absorption in the near IR increases with dopant density and also the bandgap shifts toward low energies. This behavior is due to free carrier absorption which could be obtained by subtracting phonon-assisted absorption from the measured spectrum. This carrier absorption is related to the dopant density through a semi-empirical model.

We have also used the photothermal signal phase to measure the influence of doping on thermal diffusivity.     

Multiple resonances in the semi-classical limit

We construct for the Schrödinger operator in the semi-classical limit compact perturbations of a radial symmetric potential which give rise to resonances associated to arbitrarily high order poles for the meromorphic extension of the resolvent. Our results concern the hamiltonianP ₀=–h ²–x ² in the 2-dimensional case, as well as a fairly large class of radial-symmetric potentials in the 3-dimensional case. We show that the poles of the resolvent for such a potential are necessarily simple, and subsequently the degeneracy is due to a lack of symmetry.     

Intramolecular interactions in the triplet excited states of benzophenone-thymine dyads

Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Büchi cycloaddition to give oxetanes 3-6; however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 in its excited triplet state. The photobiological implications of the above results are discussed with respect to benzophenone-photosensitized damage of thymidine.     

The influence of antiferroelectric compounds on helical pitch of orthoconic W-1000 mixture

The influence of six antiferroelectric compounds on the helical pitch of mixture W-1000, which was reported as long pitch orthoconic antiferroelectric liquid crystalline mixture, was checked by spectrophotometry and polarimetry methods. The electro-optical properties for the mixture with the longest pitch were measured. An improvement in electro-optical response due to the long pitch is reported. The novelty in electro-optical properties is the good symmetry response.     

A characterization of be-critical trees

The b-chromatic number of a graph G is the largest integer k such that G admits a proper coloring with k colors for which each color class contains a vertex that has at least one neighbor in all the other $k?1$ color classes. A graph G is called $b_e$-critical if the contraction of any edge e of G decreases the b-chromatic number of G. The purpose of this paper is the characterization of all $b_e$-critical trees.     

Synthesis,characterization and optical properties of ZnO nanoparticles with controlled size and morphology

Zinc oxide monodispersed nanoparticles were synthesized using a modified polyol process without any requirement to use a catalyst or calcination step at high temperature. The morphology and the size of the resulting oxide particles were adjusted by using several synthesis parameters (temperature, alkaline ratio, hydrolysis ratio, etc.). The increasing of the alkaline ratio results in a great change of the elaborated particles morphology that evolved from irregular and anisotropic forms (conical, nanorod-like and elliptical) to spherical one. A growth mechanism of these particles was proposed on the basis of zincite crystal structure and the morphology evolution as a function of the synthesis parameters. The photoluminescence spectra show UV-excitonic and visible emission bands. The strongest intensity of the visible emission was observed in nanorod-like particles, which implies an increased fraction of oxygen vacancies in this sample. The rod-like particles with 1 μm length show the dominant UV-emission, which evidences their improved stoichiometry.     

Synthesis,characterization, crystal structure and electrochemical behavior of a nickel(II) complex of 5,6-dihydro-2H-pyran-3-aldehyde thiosemicarbazone

A new Ni^II complex of 5,6-dihydro-2H-pyran-3-aldehyde thiosemicarbazone (HDPTSC) has been synthesized and characterized by microanalyses, magnetic susceptibility, molar conductance measurements and by spectral methods (i.r., u.v.–vis., ¹H-n.m.r.). The structure of [Ni(DPTSC)₂] · B DMF has been solved using X-ray diffraction and found to be highly symmetrical with a trans -arrangement of the two bidentate ligands. The thiosemicarbazone coordinates as an anionic ligand via the thiosemicarbazone moietys azomethine nitrogen and thiolate sulfur [on loss of the N2 hydrogen]. The electrochemical behavior of the ligand and its Ni^II complex, determined by cyclic voltammetry, shows that the redox process of the ligand was highly irreversible, whereas the redox process of the Ni^II complex was observed as a one electron transfer process in a quasi-reversible and diffusion-controlled reaction.     

Stereo-differentiation in the excited state behaviour of naphthalene-thymine dyads

Using two diastereomeric dyads containing naphthalene and thymine units, significant chiral discrimination has been found in the photophysical processes involving the naphthalene excited states: singlet deactivation by hydrogen bonding molecules, singlet-singlet energy transfer from thymine and triplet decay.