Analogues méso-hétérocycliques du dihydro-9,10 anthracène. XII — Sur quelques indoles dérivés de la dibenzo-p-dioxine

2-Aminodibenzo-p-dioxine undergoes facile condensation with different ω-bromoketones to give 2-aroylmethylaminodibenzo-p-dioxines, which undergo Möhlau-Bischler cyclisation under certain conditions. Some indolo[5,6-b] [1,4]benzodioxine were prepared by this method and their biochemical effect on the zoxazolamine hydroxylase in rats was studied.     

Preparation of both enantiomers of a synthon for novel nucleoside analogs by enzymatic desymmetrization of a meso-diol with a methylene cyclopropane skeleton

The enzymatic desymmetrization of methylenecyclopropane diol or its corresponding diacetate derivative, generated from a [2+1] cycloaddition between dioxepin and methylchlorocarbene, is described. After screening five commercial lipases, the two enantiomers of acetic acid 2-hydroxymethyl-3-methylene-cyclopropylmethyl ester are obtained in high yields and excellent enantioselectivities by using PFL or LPP in organic solvent. The stereostructure of the desymmetrization products was established by X-ray analysis. We also reported a new example with this non racemic chiral building block where the sign of optical rotation is dramatically solvent dependent and inverted. Using these enantiopure building blocks, a synthesis of novel nucleoside analogs is also presented.     

Electrical conductivity and crystallization in amorphous germanium

A simple model is presented which interprets conductivity variations due to crystallization in amorphous layers and allows the determination of the growth rate of crystallization. The validity of this model is demonstrated in the case of germanium.     

Acoustic microscopy applied to nonlinear characterization of biological media

The use of an acoustic microscope as a method for nonlinear characterization of biological media is evaluated. The method consists of measuring the second harmonic signal generated in a sample located at the focus of the acoustic lens. Two experimental configurations were compared: The first is the simple case where the sample is a liquid mixture filling the space between the lens cavity and the receiver; in the second case, the liquid mixture is confined to a thin layer at the focal plane, in order to simulate a real tissue layer. Aqueous solutions of ethylene glycol and methanol were used as liquid samples. Simple theoretical models are presented for each configuration and the predictions show good qualitative agreement with experimental measurements. These results confirm our belief that the acoustic microscope is potentially a good tool for nonlinear B/A imaging of biological systems.     

Global solutions for 2D quadratic Schrödinger equations

We prove global existence and scattering for a class of quadratic Schrödinger equations in dimension 2 with small and localized data. The proof relies on the idea of space–time resonance.     

Arsenic dopant mapping in state-of-the-art semiconductor devices using electron energy-loss spectroscopy

Knowledge of the dopant distribution in nanodevices is critical for optimising their electrical performances. We demonstrate with a scanning transmission electron microscope the direct detection and two-dimensional distribution maps of arsenic dopant in semiconductor silicon devices using electron energy-loss spectroscopy. The technique has been applied to 40–45 nm high density static random access memory and to n–p–n BiCMOS transistors. The quantitative maps have been compared with secondary ion mass spectrometry analysis and show a good agreement. The sensitivity using this approach is in the low 10¹⁹ cm^?3 range with a spatial resolution of about 2 nm.     

A versatile route to 3-(pyrimidin-4-yl)-imidazo[1,2-a]pyridines and 3-(pyrimidin-4-yl)-pyrazolo[1,5-a]pyridines

A two-step synthesis of 3-(2-chloropyrimidin-4-yl)imidazo[1,2-a]pyridines is presented. The late stage elaboration of the imidazopyridine through a cyclocondensation allows a rapid access to a variety of substitution patterns. The intermediate enol ethers were obtained from inexpensive reagents in a ligand-free Heck coupling. This methodology has been extended to the formation of pyrazolo[1,5-a]pyridines via a formal 1,3-dipolar cycloaddition.     

Physicochemical characterization of cholesterol-beta cyclodextrin inclusion complexes

Study and characterization of molecular complexes between cholesterol and beta cyclodextrin has been done using X-ray diffraction, thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (¹³C NMR). Whatever the value of the molar ratio cholesterol/βCD used during the preparation, the same compound is always obtained. Corresponding to a molar ratio 1/3 (cholesterol/βCD), this compound is a stable hydrate which, contrary toβCD, contains at room temperature a large amount of molecules of water. It can be dehydrated under low pressure but the thermal degradation occurs at 200°C (250°C forβCD). This implies that cholesterol is strongly bounded toβCD.