4‐Benzoyl‐3,4‐dihydro‐2H‐1,4‐benzoxazine‐2‐carbonitrile: refinement using a multipolar atom model

The structural model for the title compound, C₁₆H₁₂N₂O₂, was refined using a multipolar atom model transferred from an experimental electron‐density database. The refinement showed some improvements of crystallographic statistical indices when compared with a conventional spherical neutral‐atom refinement. The title compound adopts a half‐chair conformation. The amide N atom lies almost in the plane defined by the three neighbouring C atoms. In the crystal structure, molecules are linked by weak intermolecular C—H...O and C—H...π hydrogen bonds.     

A Copper(I)-Catalyzed Sulfonylative Hiyama Cross-Coupling

An air-tolerant Cu-catalyzed sulfonylative Hiyama cross-coupling reaction enabling the formation of diaryl sulfones is described. Starting from aryl silanes, DABSO and aryliodides, the reaction tolerates a large variety of polar functional groups (amines, ketones, esters, aldehydes). Control experiments coupled with DFT calculations shed light on the mechanism, characterized by the formation of a Cu(I)-sulfinate intermediate via fast insertion of a SO₂ molecule.     

Tetrapterosides A and B,two new oleanane‐type saponins from Tetrapleura tetraptera

From the stem bark of Tetrapleura tetraptera, two new oleanane‐type saponins, tetrapteroside A 3‐O‐{6‐O‐[(2E,6S)‐2,6‐dimethyl‐6‐hydroxyocta‐2,7‐dienoyl]‐β‐D ‐glucopyranosyl‐(1 → 2)‐β‐D ‐glucopyranosyl‐(1 → 3)‐β‐D ‐glucopyranosyl‐(1 → 4)‐[β‐D ‐glucopyranosyl‐(1 → 2)]‐β‐D ‐glucopyranosyl}‐3,27‐dihydroxyoleanolic acid (1), and tetrapteroside B 3‐O‐{ β‐D ‐glucopyranosyl‐(1 → 2)‐6‐O‐[(E)‐feruloyl]‐β‐D ‐glucopyranosyl‐(1 → 3)‐β‐D ‐glucopyranosyl‐(1 → 4)‐[β‐D ‐glucopyranosyl‐(1 → 2)]‐β‐D ‐glucopyranosyl}‐3,27‐dihydroxyoleanolic acid (2), were isolated. Further extractions from the roots led to the isolation of four known oleanane‐type saponins. Their structures were elucidated by the combination of mass spectrometry (MS), one and two‐dimensional NMR experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

Measures on double or resonant eigenvalues for linear Schrödinger operator

In this paper we consider linear Schrödinger operator with double or resonant eigenvalues. The main result is the bound of the measure (in a suitable space of functions) of the potentials leading to such double or resonant eigenvalues. Namely we present measure type estimates evaluating neighborhoods of the so-called double or resonant set.     

Measurement Bias on Nanoparticle Size Characterization by Asymmetric Flow Field-Flow Fractionation Using Dynamic Light-Scattering Detection

In this work, we highlight the influence of the particle–particle interaction on the retention behavior in asymmetric flow field-flow fractionation (A4F) and the misunderstanding considering the size determination by a light-scattering detector (static and dynamic light scattering) by comparing fullerene nanoparticles to similar sized polystyrene nanoparticle standards. The phenomena described here suggest that there are biases in the hydrodynamic size and diffusion determination induced by particle–particle interactions, as characterized by their virial coefficient. The dual objectives of this paper are to (1) demonstrate the uncertainties resulting from the current practice of size determination by detectors coupled to an A4F system and (2) initiate a discussion of the effects of particle–particle interactions using fullerene nanoparticles on their characterization as well as their origins. The results presented here clearly illustrate that the simple diffusion coefficient equation that is generally used to calculate the hydrodynamic size of nanoparticles (NPs) cannot be considered for whole fractograms according to their size distribution. We tried to identify particle interactions that appear during fractionation and demonstrated using the fully developed diffusion coefficient equation. We postulate that the observed interaction-dependent retention behavior may be attributed to differences in the virial coefficient between NPs and between NPs and the accumulation wall (membrane surface) without quantifying it. We hope that our results will stimulate discussion and a reassessment of the size determination procedure by A4F-LS to more fully account for all the influential material parameters that are relevant to the fractionation of nanoscale particles by A4F.     

Isomeric effects on the self‐assembly of a plausible prebiotic nucleoside analogue: A theoretical study

The self‐assembly properties of N(9)‐(2,3‐dihydroxypropyl adenine) (DHPA), a plausible prebiotic nucleoside analogue of adenosine, were investigated using density functional theory. Two different isomers were considered, and it is found that while both isomers can form a variety of structures, including chains, one of them is also able to form cages and helixes. When these results were put in the context of substrate supported molecular self‐assembly, it is concluded that gas‐phase self‐assembly studies that consider isomer identity and composition not only can aid interpreting the experimental results, but also reveal structures that might be overlooked otherwise. In particular, this study suggest that a double‐helical structure made of DHPA molecules which could have implications in prebiotic chemistry and nanotechnology, is stable even at room temperature. For example electrical properties (energy gap of 4.52eV) and a giant permanent electrical dipole moment (49.22 Debye) were found in our larger double‐helical structure (3.7 nm) formed by 14 DHPA molecules. The former properties could be convenient for construction of organic dielectric‐based devices.     

Mixing is an aggregation processLe mélange est un processus d'agrégation

With the aid of several demonstration experiments, it is shown how a stirred scalar mixture relaxes towards uniformity through an aggregation process. The elementary bricks are stretched sheets whose rates of diffusive smoothing and coalescence build up the overall mixture concentration distribution. The cases studied, in particular, include mixtures in two and three dimensions, with different stirring protocols, which all lead to a family of concentration distributions stable by self-convolution. To cite this article: E. Villermaux, J. Duplat, C. R. Mecanique 331 (2003).     

Short and efficient access to imidazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives

Access to N-protected or N-free imidazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives as potential antiviral compounds was achieved in good yields from N-protected 7-amino-8-halo-2-methylimidazo[1,2-a]pyridines by catalytic coupling of terminal acetylenes under mild conditions using [PdCl₂(PPh₃)₂] or [Cu(Phen)(PPh₃)₂]NO₃.