Synthesis, microwave spectrum, and dipole moment of allenylisocyanide (H2C═C═CHNC), a compound of potential astrochemical interest

An improved synthesis of a compound of potential astrochemical interest, allenylisocyanide (H(2)C═C═CHNC), is reported together with its microwave spectrum, which has been investigated in the 8-120 GHz spectral range to facilitate a potential identification in interstellar space. The spectra of the ground vibrational state and of five vibrationally excited states belonging to three different vibrational modes have been assigned for the parent species. A total of 658 transitions with a maximum value of J = 71 were assigned for the ground state and accurate values obtained for the rotational and quartic centrifugal distortion constants. The spectra of five heavy-atom ((13)C and (15)N) isotopologues were also assigned. The dipole moment was determined to be μ(a) = 11.93(16) × 10(-30) C m, μ(b) = 4.393(44) × 10(-30) C m, and μ(tot) = 12.71(16) × 10(-30) C m. The spectroscopic work has been augmented by theoretical calculations at the CCSD/cc-pVTZ and B3LYP/cc-pVTZ levels of theory. The theoretical calculations are generally in good agreement with the experimental results.     

Quantitative analysis of the dynamic behaviour of photochromic systems

The good understanding of a photochromic reaction mechanism requires the establishment of the list of all the transient species and the definition of their connecting processes. The purpose of kinetic studies is the determination of the main photochromic parameters, such as the quantum yields of photoisomerization, rate constants of thermal relaxation and spectra of transient species. These data allow the establishment of structure properties relationships in order to select the best substituents to improve photochromic performances within a given series. In this review, we describe the dynamic behaviour of various photochromic systems during thermal relaxation after irradiation, from the simplest mono-exponential decay to the more complicated multi-exponential dynamics. Then, we analyse the evolution of the long-lived isomers under continuous irradiation. Several pedagogical examples and tricks to perform easy kinetic analysis are given in the appendices.     

Local shrinkage and stress induced by thermo-oxidation in composite materials at high temperatures

The paper is concerned with the modelling, simulation and experimental characterisation of local shrinkage strains and stresses induced by thermo-oxidation phenomena in the IM7/977-2 carbon/epoxy composite material at elevated temperatures. The oxygen concentration and mechanical fields were established through a coupled model constructed from a unified multiphysical approach and the thermodynamics of irreversible processes. The model was implemented in the ABAQUS^® finite element commercial code. Simulations of thermo-oxidation-induced matrix shrinkage were run at a local scale, i.e., the scale of the elementary constituents of the composite, the fibre and the matrix. The experimental assessment was done at the same scale, and the local matrix shrinkage profiles were measured by confocal interferometric microscopy.A good agreement was found between the simulated and measured profiles, validating the unified model. The thermo-oxidation induced stress field was analysed to understand the influence of the environment on the onset of damage in composite materials at elevated temperature.     

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.     

From calcium interaction to calcium electrochemical detection by [(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] and its two novel structurally characterized derivatives

[(C(5)H(5))Fe(C(5)H(4)COCH=CHC(6)H(4)NEt(2))] (1) has been electrochemically evaluated toward different cations in solution. Calcium sensing by this compound and its two new derivatives [(C(5)H(5))Fe(C(5)H(4)CO(CH=CH)(2)C(6)H(4)NMe(2))] (2) and [(C(5)H(5))Fe(C(5)H(4)CH=CHCOCH=CHC(6)H(4)NEt(2))] (3) that exhibit a conjugated link between the ferrocene unit and the nitrogen atom has been thoroughly examined. Compounds 2 and 3 have been structurally characterized by single-crystal X-ray diffraction studies. The three related protonated species [1H][BF(4)] (4), [2H][BF(4)] (5), and [3H][BF(4)] (6) have been isolated in a good yield. NMR experiments clearly established that calcium interaction occurs in the vicinity of the carbonyl group, and mass spectrometry studies confirmed that this interaction, which involves several ligand-Ca(2+) adducts, is complex. A combination of electrochemical and NMR experiments highlighted an original salt influence on the electrochemical calcium sensing result.     

Etude par diffraction X et microscopie electronique du système CaTiO3---Ca2Fe2O5

In order to check the extended defect model previously proposed for the nonstoichiometric perovskite A_nM_nO_3n−1 (n 2), the Ca₂Ti_2−2xFe_2xO_6−x solid solution has been studied by means of X-ray diffraction and electron microscope investigations. The results show the existence of a continuous evolution (0 x 1) with two different regions. Close to the CaTiO₃ composition (0 x 0.40) the oxygen vacancies seem to be randomly distributed and the symmetry remains pseudocubic. In the composition range 0.55 x 1, the electron microscope patterns show an ordering of the defects: the oxygen vacancies are ordered in the (0k0) planes in strings parallel to the [101] direction. It is concluded from these observations that perpendicular to the Oy direction isolated planes of tetrahedra arranged in rows separate planes of corner-linked octahedra. The n = 2; 2.5; 3, et 4 terms of the A_nM_nO_3n−1 series have been identified. C.S. planes characteristic of classical nonstoichiometric oxides with small cations do not appear: instead, tetrahedra planes succeed to the previous octahedra planes as the degree of nonstoichiometry increases.

Résumé

Afin de vérifier le modèle de non-stoechiométrie proposé dans un travail précédent pour les perovskites lacunaires A_nM_nO_3n−1 (n 2), la solution solide Ca₂Ti_2−2xFe_2xO_6−x a été, étudiée par diffraction X et microscopie électronique. Les résultats montrent l'existence d'une évolution continue (0 x 1) avec deux domaines différents. Pour les compositions proches de CaTiO₃ (0 x 0.40), les lacunes oxygénées semblent être distribuées statistiquement et la symétrie demeure pseudocubique. Dans le domaine de compositions 0.55 x 1, les images de microscopie électronique montrent un ordre des défauts: les lacunes d'oxygène sont ordonnées dans les plans (0k0) en rangées parallèles à la direction [101]. Ces observations ont permis de conclure que perpendiculairement à la direction Oy des plans isolés de files de tétraèdres séparent des plans d'octaèdres liés par leurs sommets. Les termes n = 2; 2.5; 3 et 4 des séries A_nM_nO_3n−1 ont été identifiés. Des plans de cisaillement rencontrés dans les oxydes non-stoechiométriques classiques de petits cations n'ont pas été mis en évidence: par contre, des plans de tétraèdres se substituent aux plans d'octaèdres initiaux lorsque le degré de non-stoechiométrie augmente.     

Luminescence-detected phase transitions in lanthanide-containing liquid crystals

Complexes between lanthanide nitrates and a pro-mesogenic 18-membered diaza-substituted coronand are luminescent both as powders and liquid crystals (between 87 and 195 degrees C), and the phase transitions are detected by monitoring luminescence intensity and lifetime.     

Anionic copper complex fragmentations from enkephalins under low-energy collision-induced dissociation in an ion trap mass spectrometer

Peptide metallation with Cu2+ was explored in the negative ESI mode using an ion trap mass spectrometer. Under these conditions, the [(M-3H) + CuII]- species formed were investigated under low-energy collision-induced dissociation conditions. MS2 experiments indicate a very different behavior of CuII metallated complexes compared with [M-H]- species. CuII induces an easy loss of CO2 and specific side-chain cleavages (by radical losses) at the C-terminal residue, as observed previously by prompt 'in source' dissociation experiments. The loss of CO2 yields an unstable carbylide that leads to further dissociations involving the migration of a proton or a hydrogen radical (through the reduction of CuII). Multistage MS3 experiments were carried out to rationalize this behavior. Fragmentation pathways are proposed in order to explain the product ions observed. The side-chain radical loss at the C-terminus was demonstrated to be a consecutive process. Finally, evidence is provided that the specific side-chain cleavages can be used for the differentiation of Leu/Ile and Gln/Lys residues when they are located at the C-terminus. The existence of a zwitterionic form in the case of the anionic YGGFK-CuII complex is proposed.     

Helical self-organization and hierarchical self-assembly of an oligoheterocyclic pyridine-pyridazine strand into extended supramolecular fibers

The synthesis and characterization of an alternating pyridine-pyridazine strand comprising thirteen heterocycles are described. Spontaneous folding into a helical secondary structure is based on a general molecular self-organization process enforced by the conformational information encoded within the primary structure of the molecular strand itself. Conformational control based on heterocyclic "helicity codons" illustrates a strategy for designing folding properties into synthetic oligomers (foldamers). Strong intermolecular interactions of the highly ordered lock-washer subunits of compound 3 results in hierarchical supramolecular self-assembly into protofibrils and fibrils. Compound 3 also forms mechanically stable two-dimensional Langmuir-Blodgett and cast thin films.