A ditopic calix[6]arene ligand with N-methylimidazole and 1,2,3-triazole substituents: synthesis and coordination with Zn(II) cations

The first member of a new class of ditopic calix[6]arene has been synthesized, which is decorated with three N-methylimidazoles at the small rim and three 1,4-disubstituted-1,2,3-triazoles at the large rim. The coordination of a first Zn(II) cation selectively takes place at the small rim. Addition of a second equivalent results in the complexation of the three triazoles, providing a rare example of 1,2,3-triazole ligands embedded within a supramolecular system.     

Synthesis, ionisation potentials and electron affinities of hexaazatrinaphthylene derivatives

Several hexaazatrinaphthylene derivatives and a tris(thieno)hexaazatriphenylene derivative have been synthesised by reaction of the appropriate diamines with hexaketocyclohexane. The crystal structure of 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene has been determined by X-ray diffraction; this reveals a molecular structure in good agreement with that predicted by density functional theory (DFT) calculations and pi-stacking with an average spacing between adjacent molecular planes of 3.18 A. Solid-state ionisation potentials have been measured by using UV photoelectron spectroscopy and fall in the range of 5.99 to 7.76 eV, whereas solid-state electron affinities, measured using inverse photoelectron spectroscopy, vary in the range -2.65 to -4.59 eV. The most easily reduced example is a tris(thieno)hexaazatriphenylene substituted with bis(trifluoromethyl)phenyl groups; DFT calculations suggest that the highly exothermic electron affinity is due both to the replacement of the outermost phenylene rings of hexaazatrinaphthylene with thieno groups and to the presence of electron-withdrawing bis(trifluoromethyl)phenyl groups. The rather exothermic electron affinities, the potential for adopting pi-stacked structures and the low intramolecular reorganisation energies obtained by DFT calculations suggest that some of these molecules may be useful electron-transport materials.     

Gas chromatography/mass spectrometry characterization of historical varnishes of ancient Italian lutes and violin

The organic constituents of historical vanishes from two ancient Italian lutes and a Stradivari violin, kept in the Musée de la musique in Paris, have been characterized using gas chromatography-mass spectrometry. Results have been compared with the chromatograms and mass spectra of recent as well as old naturally aged reference materials. The three historical varnishes analyzed have been shown to be oil varnishes, probably mixtures of linseed oil with resins. Identification of diterpenoids and triterpenoids compounds, and of the resins that may have been ingredients of the varnishes, are discussed in this paper.     

Colloidal phase separation of concentrated PNIPAm solutions

In the concentration range of 1-6 wt %, solutions of a thermosensitive polymer (poly-N-isopropylacrylamide (PNIPAm), Mw = 1.4 x 10(5) g.mol(-1)) are shown to phase separate in the form of dense stable colloids of nearly pure polymer. Diffuse wave spectroscopy and small-angle neutron scattering both provide consistent measurements of the colloidal size as a function of temperature. Results are in agreement with a Cahn regime of spinodal decomposition blocked at an early stage, prior to a growth that would lead to a macroscopic phase separation. [Early results of this work were presented at the 231st American Chemical Society National Meeting, Symposium on Amphiphilic Polymers, Atlanta, GA, 2006, March 26-30.].     

Tailoring the Flow Properties of Soft Colloidal Dispersions

Summary: The dynamics and the non-linear rheology of concentrated dispersions of soft particles are shown to exhibit generic properties. They display both solid-like and liquid-like properties depending on the applied stress. Below the yield point, dispersions exhibit history-dependent phenomena that have all the hallmarks of ageing in glasses. The close-packed disordered structures of the dispersions lie at the heart of this behaviour. Other properties such as the propensity of pastes to slip on solid surfaces appear to be governed by specific contact interactions between the squeezed particles.     

Development of Sustainable Chemistry in Madagascar: Example of the Valuation of CNSL and the Use of Chromones as an Attractant for Mosquitoes

This article describes a part of the results obtained from the cooperation between the University of Lyon1 (France) and the University of Antananarivo (Madagascar). It shows (among others) that useful research can be carried out in developing countries of the tropics if their social, technical, and economic conditions are taken into account. The concepts and methods associated with so-called “green chemistry” are particularly appropriated for this purpose. To illustrate this approach, two examples are shown. The first deals with industrial ecology and concerns waste transformation from the production of cashew nut into an amphiphilic product, oxyacetic derivatives. This product was obtained with a high yield and in a single step reaction. It exhibited an important surfactant property similar to those of the main fossil-based ones but with a much lower ecological impact. The second talks about chemical ecology as an alternative to insecticides and used to control dangerous mosquito populations. New substituted chromones were synthesized and showed biological activities toward Aedes albopictus mosquito species. Strong repellent properties were recorded for some alkoxylated products if others had a significant attractant effect (Kairomone) depending on their stereochemistry and the length of the alkyl chain.     

Confined viscoplastic flows with heterogeneous wall slip

The steady, pressure-driven flow of a Herschel-Bulkley fluid in a microchannel is considered, assuming that different power-law slip equations apply at the two walls due to slip heterogeneities, allowing the velocity profile to be asymmetric. Three different flow regimes are observed as the pressure gradient is increased. Below a first critical pressure gradient G ₁, the fluid moves unyielded with a uniform velocity, and thus, the two slip velocities are equal. In an intermediate regime between G ₁ and a second critical pressure gradient G ₂, the fluid yields in a zone near the weak-slip wall and flows with uniform velocity near the stronger-slip wall. Beyond this regime, the fluid yields near both walls and the velocity are uniform only in the central unyielded core. It is demonstrated that the central unyielded region tends towards the midplane only if the power-law exponent is less than unity; otherwise, this region rends towards the weak-slip wall and asymmetry is enhanced. The extension of the different flow regimes depends on the channel gap; in particular, the intermediate asymmetric flow regime dominates when the gap becomes smaller than a characteristic length which incorporates the wall slip coefficients and the fluid properties. The theoretical results compare well with available experimental data on soft glassy suspensions. These results open new routes in manipulating the flow of viscoplastic materials in applications where the flow behavior depends not only on the bulk rheology of the material but also on the wall properties.