Ferrocene and Porphyrin Monolayers on Si(100) Surfaces: Preparation and Effect of Linker Length on Electron Transfer

The missing link : Ferrocene and porphyrin monolayers are tethered on silicon surfaces with short (see picture, left) or long (right) linkers. Electron transfer to the silicon substrate is faster for monolayers with a short linker.

     

NMR studies of the reaction between amino-phenylene vinylene thiophene and tetracyanoethylene

Amino tricyanovinyl thiophene chromophores (A-TCVT) are prepared by a substitution reaction of amino-phenylene vinylene thiophene (A-PVT) with tetracyanoethylene (TCNE). This reaction does not occur directly. The vinylene double bond in the PVT unit first reacts rapidly with TCNE to form a [2+2] cycloaddition product. It is then reverted to PVT unit prior to the subsequent substitution at 50 °C. This reversible cycloaddition converts the cis-isomer of PVT units into the trans-counterparts, thus the final TCNE substituted products can be expected for a better performance as non-linear optical materials.     

Refinements to the diastereoisomer-specific method for the analysis of hexabromocyclododecane

The emergence of hexabromocyclododecane (HBCD) as a bromine-based flame retardant of concern is partly attributable to recent measurements on the environmental occurrence of the individual diastereoisomers (alpha, beta and gamma). These measurements were fuelled by a newly developed liquid chromatography/tandem mass spectrometric (LC/MS/MS)-based analytical method. However, in the course of our recent studies on the environmental fate and behaviour of the diastereoisomers of HBCD, some interesting features of the LC/MS/MS method became apparent. For example, the ion signal of the native ions was found to be dependent on the final extract volume. This was true for both biotic and sediment samples and was found to arise from the suppression of the ion signal due to endogenous material in the extracts that escape clean-up. We have also found differences in the stability of the diastereoisomers in different solvents. If left unaccounted for, both factors can compromise analytical measurement data. By way of a series of controlled experiments conducted at our two laboratories [Department of Fisheries & Oceans Canada (DFO) and Environment Canada (EC)], we illustrate these features and demonstrate that use of newly synthesized labelled HBCD isomers [(13-carbon (13C) and deuterium (d18)] can minimize and often circumvent matrix-related effects.     

Experimental and numerical study of shock wave propagation in water generated by pulsed arc electrohydraulic discharges

The objective of this study is to simulate the propagation of the shock wave in water due to an explosion. The study is part of a global research program on the development of an alternative stimulation technique to conventional hydraulic fracturing in tight gas reservoirs aimed at inducing a distributed state of microcracking of rocks instead of localized fracture. We consider the possibility of increasing the permeability of rocks with dynamic blasts. The blast is a shock wave generated in water by pulsed arc electrohydraulic discharges. The amplitude of these shock waves is prescribed by the electrohydraulic discharges which generate high pressures of several kilobars within microseconds. A simplified method has been used to simulate the injected electrical energy as augmentation of enthalpy in water locally. The finite element code EUROPLEXUS is used to perform fluid fast dynamic computation. The predicted pressure is consistent with the experimental results. In addition, shock wave propagation characteristics predicted with simulation can be valuable reference for design of underwater structural elements and engineering of underwater explosion.     

Calcul d'un Invariant de Star-Produit Fermé sur une Variété Symplectique

Let M be a symplectic manifold over $ℝ. In [CFS] the authors construct an invariant ϕ in the cyclic cohomology of M for any closed star-product. They compute this invariant in the de Rham complex of M when M=T ^* V. We generalize this result by computing the image of ϕ in the de Rham complex for any symplectic manifold and any star-product and we show how this invariant is related to the general classification of Kontsevich. The proof uses the Riemann–Roch theorem for periodic cyclic chains of Nest–Tsygan.

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Calcul d'un Invariant de Star-Produit Fermé sur une Variété Symplectique

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Received: 30 November 1998 / Accepted: 15 February 1999     

Effect of chitosan and thiolated chitosan coating on the inhibition behaviour of PIBCA nanoparticles against intestinal metallopeptidases

Surface modified nanoparticles composed of poly(isobutylcyanoacrylate) (PIBCA) cores surrounded by a chitosan and thiolated chitosan gel layer were prepared and characterized in previous works. The presence of such biopolymers on the nanoparticle surface conferred those nanosystems interesting characteristics that might partially overcome the gastrointestinal enzymatic barrier, improving the oral administration of pharmacologically active peptides. In the present work, the antiprotease behaviour of this family of core–shell nanoparticles was in vitro tested against two model metallopeptidases present in the gastrointestinal tract (GIT): Carboxypeptidase A -CP A- (luminal protease) and Leucine Aminopeptidase M -LAP M- (membrane protease). As previous step, the zinc-binding capacity of these nanoparticles was evaluated. Interestingly, an improvement of both the zinc-binding capacity and the antiprotease effect of chitosan was observed when the biopolymers (chitosan and thiolated chitosan) were used as coating component of the core–shell nanoparticles, in comparison with their behaviour in solution, thanks to the different biopolymer chains rearrangement. The presence of amino, hydroxyl and thiol groups on the nanoparticle surface promoted zinc binding and hence the inhibition of the metallopeptidases analysed. On the contrary, the occurrence of a cross-linked structure in the gel layer surrounding the PIBCA cores of thiolated formulations, due to the formation of interchain and intrachain disulphide bonds, partially limited the inhibition of the proteases. The low accessibility of cations to the active groups of the cross-linked polymeric shell was postulated as a possible explanation of this behaviour. Results obtained in this work make this family of surface-modified nanocarriers promising candidates for the successfull administration of pharmacologically active peptides and proteins by the oral route.     

Etude comparative des proprietes magnetiques des oxydes lamellaires ACrO2 (A = Li,Na, K)—I: Etude par effet Mössbauer de LiCrO2 dope par le fer

A Mössbauer study of the dimensionality of magnetic interactions in the layer oxide LiCr_0.99Fe_0.01O₂ shows a 2-D behaviour.