Characterisation of the anodic layers formed on 2024 aluminium alloy, in tetraborate electrolyte containing molybdate ions

Anodic layer growth on 2024 aluminium alloy at 70 °C, under 40 V, during 60 min, in 50 g L⁻¹ di-sodium tetraborate solution containing di-sodium molybdate from 0.1 to 0.5 M (pH 10) is examined. Anodising behaviours strongly depend on additive concentration. Development of anodic films is favoured with weak molybdate additions (<0.3-0.4 M). The film thicknesses increase and the porosity of anodic layers decreases. Molybdenum (+VI), detected by X-ray photoelectron spectroscopy (XPS) analysis, is present in the anodic films and the Mo incorporation, studied by energy dispersive spectroscopy (EDS) analysis, increases with molybdate concentration. However, for high molybdate concentrations (>0.4 M), anodising behaviour becomes complex with the formation of a blue molybdenum oxide at the cathode. The growth of aluminium oxide is hindered. As the anodic layers are thinner, the Mo(+VI) incorporation significantly decreases. These two configurations implicate different corrosion performances in 5% sodium chloride solution at 35 °C. As the alkaline anodic layer formed with 0.3 M molybdate species is the thickest and the Mo incorporation is the more pronounced, its corrosion resistance is the highest. The effect of morphology and composition of anodic films on pitting corrosion is also discussed.     

Synthesis of aaptamine,a novel marine alkaloid

The novel sponge alkaloid aaptamine has been synthesized for the first time by an efficient route starting from 6-methoxy-7-hydroxy-3,4-dihydrolsoquinoline.     

Hamiltonian location problems

Exact algorithms for a series of simultaneous location and routing problems are developed. Problems are formulated as integer programs which are solved by a constraint relaxation procedure. Numerical results are reported.     

Effect of the polar headgroup of phospholipids on their interaction with actin

It is generally admitted that actin filaments are anchored to a membrane by membranar actin-binding-proteins. However, we found that actin may also interact directly with membrane phospholipids. The actin-phospholipid complex has been investigated at the air-water interface using a film balance technique. In order to probe the effect of the phospholipid headgroup on the actin-phospholipid interaction, we focus mainly on phospholipids that have the same acyl chain length but different headgroups. For all the phospholipids, the apparent area per molecule (the total surface divided by the number of lipid molecules) increases after the injection of the protein into the subphase, which suggests an intercalation of actin between the phospholipid molecules. This effect seems to be more important for DMPE and DMPS than for DMPG, suggesting that the headgroup plays an important role in this intercalation. The critical surface pressure associated to the liquid expanded-liquid condensed (LE-LC) phospholipid transition increases with the concentration of G-actin and thus suggests that G-actin acts as an impurity, simply competing as a surfactant at the air-water interface. On the other hand, F-actin affects the LE to LC transition of phospholipids differently. In this case, the LE to LC transition is broader and F-actin slightly decreases the critical surface pressure, which suggests that electrostatic interactions are involved.     

Informative barycentres in statistics

Barycentres of a discrete probability measure on a dually flat statistical manifold are introduced. They are shown to be unique and to behave as barycentres in Euclidean space. The estimation of these barycentres is studied. Potential applicative usefulness of informative barycentres include the problem of interpolating a statistical manifold valued map and the problem of model merging, which consists in merging several statistical models into a unique one. The results are illustrated on the exponential family, for which a projection theorem is proved.     

The fate of mercury species injected into coelomic fluid of starfish Leptasterias polaris

Mature starfish Leptasterias polaris, collected in the St Lawrence Estuary (eastern Canada), were exposed to two mercury species (HgCI₂ and CH₃HgCI) via injections into the coelomic fluid. In vivo effects of some complexing agents (glutathione, mercaptoethanol and EDTA) on the distribution of ²⁰³Hg-labelled species in starfish organs and tissues and their possible role in mercury transport through membranes were studied over a 24 h period. The excretion of ammonia and mercury was also measured. When injected alone, inorganic mercury and methylmercury [CH₃Hg(II)] were distributed in all organs, with a preferential adsorption in gonads, pyloric caeca and stomach. Mercury excretion was very low under all conditions studied. Mercaptoethanol, a small thiol ligand, was very efficient in reducing both mercury species in the coelomic fluid and seems to have promoted translocation towards most organs of the starfish. Its action is attributed to the formation of small and neutral complexes, HgL₂ and CH₃HgL, which can diffuse through membranes preserving their integrity. Glutathione increased the translocation of CH₃Hg(II) towards surrounding organs, but had no apparent effect on inorganic mercury. EDTA promoted the transport of inorganic mercury only. These results highlight (1) the particular interest of starfish to workers studying in vivo chemical complexation of mercury species, and (2) the potential role of complexing molecules in the biotransport of mercury species through living membranes.     

Mild and adaptable silver triflate-assisted method for trityl protection of alcohols in solution with solid-phase loading applications

Trityl ethers were prepared in solution in a matter of minutes by treating trityl chloride with silver triflate in the presence of alcohols. Yields were comparable or better than known literature methods. The method was compatible with the base-labile Fmoc protecting group of amino alcohols and adapted for trityl protection of halo-containing alcohols. These base- and nucleophile-sensitive intermediates were anchored on trityl resin and further functionalized, displaying the utility of this approach for future combinatorial applications.     

Numerical simulation of flat-tip micro-indentation of glassy polymers: Influence of loading speed and thermodynamic state

Flat-tip micro-indentation tests were performed on quenched and annealed polymer glasses at various loading speeds. The results were analyzed using an elasto-viscoplastic constitutive model that captures the intrinsic deformation characteristics of a polymer glass: a strain-rate dependent yield stress, strain softening and strain hardening. The advantage of this model is that changes in yield stress due to physical aging are captured in a single parameter. The two materials studied (polycarbonate (PC) and poly(methyl methacrylate) (PMMA)) were both selected for the specific rate-dependence of the yield stress that they display at room temperature. Within the range of strain rates experimentally covered, the yield stress of PC increases linearly with the logarithm of strain rate, whereas, for PMMA, a characteristic change in slope can be observed at higher strain rates. We demonstrate that, given the proper definition of the viscosity function, the flat-tip indentation response at different indentation speeds can be described accurately for both materials. Moreover, it is shown that the model captures the mechanical response on the microscopic scale (indentation) as well as on the macroscopic scale with the same parameter set. This offers promising possibilities of extracting mechanical properties of polymer glasses directly from indentation experiments.     

Cinnamoyl inhibitors of tissue transglutaminase

Transglutaminases (TGases) catalyze the intermolecular cross-linking of certain proteins and tissue TGases (TG2) are involved in diverse biological processes. Unregulated, high TGase activities have been implicated in several physiological disorders, but few reversible inhibitors of TG2 have been reported. Herein, we report the synthesis of a series of novel trans-cinammoyl derivatives, discovered to be potent inhibitors of guinea pig liver transglutaminase. The most effective inhibitors evaluated can be sorted into two subclasses: substituted cinnamoyl benzotriazolyl amides and the 3-(substituted cinnamoyl)pyridines, referred to more commonly as azachalcones. Kinetic evaluation of both of these subclasses revealed that they display reversible inhibition and are competitive with acyl donor TGase substrates at IC50 values as low as 18 microM. An analysis of structure-activity relationships within these series of inhibitors permitted the identification of potentially important binding interactions. Further testing of some of the most potent inhibitors demonstrated their selectivity for TG2 and their potential for further development.