Etude théorique de la durée de vie radiative du triplet métastable de quelques composés carbonylés

Les paramètres de phosphorescence (force d'oscillateur et durée de vie), sont déterminés théoriquement pour quelques composés carbonylés (formaldéhyde, benzaldéhyde, acétophénone, propiophénone, 2,4,5-triméthylbenzaldéhyde, et 3,4-diméthylacétophénone). La fonction d'onde de l'état singulet fondamental est obtenue à l'aide d'un calcul SCF utilisant la méthode CNDO/S de Del Bene et Jaffé. Les fonctions d'onde, les énergies et les moments de transition dipolaire électrique S_I ←S ₀ et T_J ←T ₁ sont déterminés à l'aide d'une interaction portant sur des configurations mono et diexcitées par rapport à l'état singulet fondamental.

Les paramètres de phosphorescence sont calculés en utilisant une approximation monocentrique et monoélectronique de l'opérateur hamiltonien de couplage spin-orbite. Cette approximation est justifiée par la comparaison des résultats obtenus avec les valeurs expérimentales, compte tenu de la concordance entre les conditions d'expérience et les hypothèses de calcul.     

On the calculation of inner shell ionization energies and E.S.C.A. shifts

In the calculation of inner-shell ionization potentials, the Koopmans theorem is unsatisfactory owing to a large ‘relaxation’ of the valence electron distribution, following the creation of an inner-shell ‘hole’. The effects of this relaxation are studied, using a group-function formulation to analyse the energy into core and valence contributions. Applications to the lithium atom and the methane molecule indicate that relaxation effects can be large. The importance of these results in the interpretation of E.S.C.A. data is discussed.     

Spin squeezing in Bose—Einstein condensates: Limits imposed by decoherence and non-zero temperature

We consider dynamically generated spin squeezing in interacting bimodal condensates. We show that particle losses and non-zero temperature effects in a multimode theory completely change the scaling of the best squeezing for large atom numbers. We present the new scalings and we give approximate analytical expressions for the squeezing in the thermodynamic limit. Besides reviewing our recent theoretical results, we give here a simple physical picture of how decoherence acts to limit the squeezing. We show in particular that under certain conditions the decoherence due to losses and non-zero temperature acts as a simple dephasing.     

Kulinkovich-type reactions of thioamides: similar to those of carboxylic amides?

The behaviour of thioamides under Kulinkovich-type conditions is compared with the known reactivity of carboxylic amides. Dramatic differences are disclosed.     

Smoothing factor,order of prolongation and actual multigrid convergence

We consider the Fourier analysis of multigrid methods (of Galerkin type) for symmetric positive definite and semi-positive definite linear systems arising from the discretization of scalar partial differential equations (PDEs). We relate the so-called smoothing factor to the actual two-grid convergence rate and also to the convergence rate of the V-cycle multigrid. We derive a two-sided bound that defines an interval containing both the two-grid and V-cycle convergence rate. This interval is narrow and away from 1 when both the smoothing factor and an additional parameter are small enough. Besides the smoothing factor, the convergence mainly depends on the angle between the range of the prolongation and the eigenvectors of the system matrix associated with small eigenvalues. Nice V-cycle convergence is guaranteed if the tangent of this angle has an upper bound proportional to the eigenvalue, whereas nice two-grid convergence requires a bound proportional to the square root of the eigenvalue. We also discuss the well-known rule which relates the order of the prolongation to that of the differential operator associated to the problem. We first define a frequency based order which in most cases amounts to the so-called high frequency order as defined in Hemker (J Comput Appl Math 32:423–429, 1990). We give a firmer basis to the related order rule by showing that, together with the requirement of having the smoothing factor away from one, it provides necessary and sufficient conditions for having the two-grid convergence rate away from 1. A stronger condition is further shown to be sufficient for optimal convergence with the V-cycle. The presented results apply to rigorous Fourier analysis for regular discrete PDEs, and also to local Fourier analysis via the discussion of semi-positive systems as may arise from the discretization of PDEs with periodic boundary conditions.     

A simple cladding process to apply monolithic silica rods in high performance liquid chromatography

A simple cladding procedure was developed to apply monolithic silica rods in chromatography. This was used to evaluate the performances of new monolithic silica phases synthesised using a triblock copolymer as a phase separation inducer. The cladding procedure is found efficient after several tests, including scanning electron microscopy and mercury porosimetry, and the obtained columns present a relatively good efficiency in adsorption chromatography (H min is about 50 μm) as compared to other lab-scale developed columns.     

Development and Validation of a Normal-Phase HPTLC-Densitometric Method for the Quantitative Analysis of Fluconazole in Tablets

JPC – Journal of Planar Chromatography – Modern TLC - This paper presents the development and validation of an improved method for the analysis of fluconazole using high-performance...     

A new series of rod-like conjugated molecules with a pyrazine or a bipyrazine core. Synthesis and light emitting properties

In this paper, we describe the synthesis of a wide range of new rod-like conjugated molecules with a pyrazine or a bipyrazine core connected to electron acceptor (A) or donor (D) groups through π-conjugated bridges as transmitters for the internal charge transfer (ICT). The key steps of the synthesis involve metallation and subsequent transmetallation of 2-chloropyrazine derivatives followed by Sonogashira or Negishi cross-coupling reactions. The bipyrazine core was obtained with a Stille cross-coupling reaction between the 2-chloro-6-tributylstannylpyrazine and the 2-chloro-6-iodopyrazine. Functionalization of the 6,6′-dichloro-2,2′-bipyrazine was performed by metallation, transmetallation and cross-coupling reactions. The light emitting properties of the so obtained molecules are then investigated in terms of absorption and emission spectra.     

Capillary methods for drug analysis

This review gives an overview of the applicability of capillary electrophoresis, capillary liquid chromatography, capillary electrochromatography, and their derived techniques to analyze drug impurity mixtures, formulations, biological samples, and chiral compounds. For each application type, a few examples are given to illustrate the potential of the capillary technique. Details are provided about the capillaries used, chiral selectors, and stationary and mobile phases.