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.     

Dynamic mechanical relaxation and thermal creep of high-entropy La30Ce30Ni10Al20Co10 bulk metallic glass

Spatial frequency shift(SFS) microscopy with evanescent wave illumination shows intriguing advantages, including large field of view(FOV), high speed, and good modularity. However, a missing band in the spatial frequency domain hampers the SFS superresolution microscopy from achieving resolution better than 3 folds of the Abbe diffraction limit. Here, we propose a novel tunable large-SFS microscopy, making the resolution improvement of a linear system no longer restricted by the detection numerical aperture(NA). The complete wide-range detection in the spatial frequency domain is realized by tuning the illumination spatial frequency actively and broadly through an angle modulation between the azimuthal propagating directions of two evanescent waves. The vertical spatial frequency is tuned via a sectional saturation effect, and the reconstructed depth information can be added to the lateral superresolution mask for 3D imaging. A lateral resolution of λ/9, and a vertical localization precision of ~λ/200(detection objective NA = 0.9) are realized with a gallium phosphide(GaP) waveguide. Its unlimited resolution enhancing capability is demonstrated by introducing a designed metamaterial chip with an unusual large refractive index. Besides the great resolution enhancement, this method shows better anti-noise capability than classical structured illumination microscopy without SFS tunability. This method is chip-compatible and can potentially provide a massproducible illumination chip module achieving the fast, large-FOV, and deep-subwavelength 3D nanoscopy.     

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.     

Hepatic butyltin concentrations in beluga whales (Delphinapterus leucas) from the St Lawrence Estuary and northern Quebec,Canada

Butyltin (tributyltin TBT; dibutyltin DBT and monobutyltin MBT) speciation was measured in the liver of beluga whales from the St Lawrence Estuary and Hudson Strait (northern Quebec). Using GC–MS, liver samples were analysed from 21 beluga whales found dead, stranded along the shores of the St Lawrence during the period 1995–1998. In all cases, including a neonate specimen, the liver was contaminated with butyltin compounds with concentrations in the range 0.04–2.1 mg Sn kg⁻¹ on a dry weight basis. Liver samples of five beluga whales from Hudson Strait obtained in the summer of 1998 were also analysed. For these animals, hepatic butyltin concentrations were consistently below the detection limit (<0.5 ng Sn g⁻¹ for MBT and <0.2 ng Sn g⁻¹ for DBT and TBT). Compared with published data on the contamination by TBT of the marine mammals of the St Lawrence in 1988, these contemporary results clearly indicate that the level of contamination of the beluga whales in this coastal marine ecosystem has not decreased ten years after regulating the use of TBT‐based antifoulants on small craft. Copyright © 2000 John Wiley & Sons, Ltd.     

An adaptive finite element method for forced convection

This paper presents an adaptive finite element method to solve forced convective heat transfer. Solutions are obtained in primitive variables using a high-order finite element approximation on unstructured grids. Two general-purpose error estimators are developed to analyse finite element solutions and to determine the characteristics of an improved mesh which is adaptively regenerated by the advancing front method. The adaptive methodology is validated on a problem with a known analytical solution. The methodology is then applied to heat transfer predictions for two cases of practical interest. Predictions of the Nusselt number compare well with measurements and constitute an improvement over previous results. © 1997 John Wiley & Sons, Ltd.