Catalytic N-sulfonyliminium ion-mediated cyclizations to alpha-vinyl-substituted isoquinolines and beta-carbolines and applications in metathesis

[reaction: see text] Catalytic Sn(OTf)2-induced cyclization of linear, aryl-containing allylic N,O-acetals produced vinyl-substituted tetrahydroisoquinolines and tetrahydro-1H-beta-carbolines. The usefulness of the vinyl moiety in the resulting products was demonstrated via the synthesis of various key building blocks for alkaloid structures. The alpha-vinyl moiety was utilized in a [2,3] sigmatropic rearrangement, in ring-closing metathesis and a cross-metathesis-based synthesis of vincantril, an antianoxia agent, and a synthetic member of the vincamine type natural products.     

Asymptotics for the Low-Lying Eigenstates of the Schrödinger Operator with Magnetic Field near Corners

The Neumann realization for the Schr?dinger operator with magnetic field is considered in a bounded two-dimensional domain with corners. This operator is associated with a small semi-classical parameter h or, equivalently, with a large magnetic field.We investigate the behavior of its eigenpairs as h tends to zero, like in a semi-classical limit. We prove, in the situation where the domain is a polygon and the magnetic field is constant, that the lowest eigenvalues are exponentially close to those of model problems associated with the corners. We approximate the corresponding eigenvectors by linear combinations of functions concentrated in corners at the scale If the domain has curved sides and the magnetic field is smoothly varying, we exhibit a full asymptotics for eigenpairs in powers of Communicated by Christian Gérard Submitted: October 13, 2005 Accepted: December 19, 2005     

Functionally relevant electric-field induced perturbations of the prosthetic group of yeast ferrocytochrome c mutants obtained from a vibronic analysis of low-temperature absorption spectra

We have measured the low temperature (T = 20 K) absorption spectra of the N52A, N52V, N52I, Y67F, and N52AY67F mutants of ferrous Saccharomyces cerevisiae (baker's yeast) cytochrome c. All the bands in the Q0- and Q(v)-band region are split, and the intensity distributions among the split bands are highly asymmetric. The spectra were analyzed by a decomposition into Voigtian profiles. The spectral parameters thus obtained were further analyzed in terms of the vibronic coupling model of Schweitzer-Stenner and Bigman (Schweitzer-Stenner, R.; Bigman, D. J. Phys. Chem. B 2001, 7064-7073) to identify parameters related to electronic and vibronic perturbations of the heme macrocycle. We report that the electronic perturbation is of B(1g) symmetry and reflects the heterogeneity of the electric field at the heme, that is, the difference between the gradients along the perpendicular N-Fe-N axis of the heme core. We found that all the investigated mutations substantially increase this electronic perturbation, so that the spectral properties become similar to those of horse heart cytochrome c. Moreover, the electronic perturbation was found to correlate nonlinearly with the enthalpy changes associated with the reduction of the heme iron. Group theoretical arguments are invoked to propose a simple model which explains how a perturbation of the obtained symmetry can stabilize the reduced state of the heme iron. Finally, vibronic coupling parameters obtained from the analysis of the Q(v)-band region suggest that the investigated mutations decrease the nonplanar deformations of the heme group. This finding was reproduced by a normal mode structural decomposition (NSD) analysis of the N52V and N52VY67F heme conformations obtained from a 1 ns molecular dynamics simulation. We argue that the reduced nonplanarity contributes to the stabilization of the reduced state.     

A doubly folded spacer in a self-assembled hybrid material

The hydrolysis of a bridged alpha,omega-bis(trialkynylstannylated) compound leads to a hybrid material ordered by self-assembly where the spacer forms two six-membered [1,2]oxastanninane rings by intramolecular coordination.     

On‐site analysis of Limoges enamels from sixteenth to nineteenth centuries: an attempt to differentiate between genuine artefacts and copies

A selection of 15 painted enamels, most of which belong to Limoges productions, from 1500 to 1900 A.D. , has been studied on‐site in the storage rooms of musée des Arts décoratifs in Paris. The Raman signatures of the transparent and/or opacified glass matrix are discussed and compared with those which were previously recorded on glazed pottery, enamelled and stained glasses as well as Chinese cloisonné enamels. Analysed enamels mostly belong to soda‐lime‐based glass. Three types of compositions such as soda‐lime (fifteenth to sixteenth century), soda‐rich (fifteenth, sixteenth/nineteenth centuries) and lead‐potash‐lime (sixteenth and nineteenth centuries) are identified on the basis of the Raman signature of the glaze according to the wavenumber maxima of the Si O stretching and bending multiplets. The pigment signatures are similar to those recorded on ceramic glazes and glass enamels, which proves the similarity of the technologies. Cassiterite as an opacifier and hematite red and Naples yellow pigment variations give characteristic Raman signatures. The presence of lead arsenate as a pigment opacifier in nineteenth‐century samples is confirmed. Attempts are made to establish tools for the differentiation between genuine artefacts and nineteenth‐century restoration or fakes. Copyright © 2010 John Wiley & Sons, Ltd.     

Comportement asymptotique à haute conductivité de l'épaisseur de peau en électromagnétisme

We study a three-dimensional model for the skin effect in electromagnetism. We first give a multiscale asymptotic expansion for the solution of the harmonic Maxwell equations set on a domain made of two materials, dielectric and highly conducting, with a regular interface between them. To measure the skin effect, we introduce a suitable skin depth function defined on the interface and generalizing the classical scalar quantity. We then prove an asymptotic expansion at high conductivity for this function, which exhibits the influence of the geometry of the interface on the skin depth.     

Accuracy Improvement in the Measurement of the Non-Linear Coefficient of Optical Fibers Based on Self-Phase Modulation

Abstract

A novel and simple procedure to improve the accuracy of the measurement of the third-order Kerr non-linear coefficient of optical fibers based on self-phase modulation is described. It includes an efficient method to identify the chirp of the input pulse. A standard single-mode fiber and a highly non-linear microstructure chalcogenide fiber have been measured. The accuracy of the measurement is increased to ±5% instead of ±19% with the classical self-phase modulation method in this case.     

Sur la thermogravimétrie des précipités analytiques : Dosage du zinc

With the help of the CHEVENARD thermobalance, the authors have traced the pyrolysis curves of the precipitates which serve for the gravimetric determination of zinc. In the table, the temperature limits and the forms in which the precipitates are weighed, are listed. Eight new reagents for the automatic determination of zinc are included in the table.