Self-assembly of solid-supported membranes using a triggered fusion of phospholipid-enriched proteoliposomes prepared from the inner mitochondrial membrane

A general procedure for the formation ofsolid-supported artificial membranes containing transmembrane proteins is reported. The main objective was to directly use the pool of proteins of the native biomembrane (here the inner membrane from mitochondria of human carcinogenic hepatic cells) and to avoid purification steps with detergent. Proteoliposomes of phospholipid-enriched inner membranes from mitochondria were tethered and fused onto a tailored surface via a streptavidin link. The failure of some preliminary experiments on membrane formation was attributed to strong nonspecific interactions between the solid surface and the protuberant hydrophilic parts of the transmembrane complexes. The correct loading of uniform membranes was performed after optimization of a tailored surface, covered with a grafted short-chain poly(ethylene glycol), so that nonspecific interactions are reduced. Step-by-step assembly of the structure and triggered fusion of the immobilized proteoliposomes were monitored by surface plasmon resonance and fluorescence photobleaching recovery, respectively. The long-range lateral diffusion coefficient (at 22 degrees C) for a fluorescent lipid varies from 2.5 x 10(-8) cm2 s(-1) for a tethered lipid bilayer without protein to 10(-9) cm2 s(-1) for a tethered membrane containing the transmembrane proteins of the respiratory chain at a protein area fraction of about 15%. The decrease in the diffusion coefficient in the tethered membrane with increase in protein area fraction was too pronounced to be fully explained by the theoretical models of obstructed lateral diffusion. Covalent tethering links with the solid are certainly involved in the decrease of the overall lateral mobility of the components in the supported membrane at the highest protein-to-lipid ratios.     

MeV dark matter: has it been detected?

We discuss the possibility that the recent detection of 511 keV gamma rays from the galactic bulge, as observed by INTEGRAL, is a consequence of low mass (1-100 MeV) particle dark matter annihilations. We discuss the type of halo profile favored by the observations as well as the size of the annihilation cross section needed to account for the signal. We find that such a scenario is consistent with the observed dark matter relic density and other constraints from astrophysics and particle physics.     

Photosensitivity of As2S3 chalcogenide thin films at 1.5 microm

Chalcogenide glasses are promising candidates for all-optical switching and various nonlinear applications. However, we show that As2S3 thin films are photosensitive at wavelengths in the 1.5-microm telecommunication window. This sensitivity is evidenced by the formation of self-written waveguides in slabs, where channels as narrow as 1 microm are created. We also show the detrimental effects of such photosensitivity in ridge waveguides. This photosensitivity seems to occur only in thin-film form and not in bulk samples or fibers.     

Improved image contrast with mangafodipir trisodium (MnDPDP) during MR-guided percutaneous cryosurgery of the liver

The present study was undertaken to measure the gain observed in the liver-to-tumor contrast of perioperative images when using mangafodipir trisodium, a liver-specific contrast agent, during percutaneous cryosurgery of the liver performed under the guidance of magnetic resonance images. Retrospective quantitative analyses of MR images were performed on eleven patients having a total of 30 liver tumors treated by MR-guided percutaneous cryosurgery. An initial group of four patients were treated with no contrast agent, and was compared with a second group of 7 patients who received an intravenous injection of 5 microM/kg of mangafodipir for their cryosurgery. The percutaneous cryosurgery was monitored under the near-real-time-imaging mode of a 0.5T open-configuration MRI system using a T(1)-weighted Gradient-recalled echo pulse sequence. A significant improvement in the liver-to-tumor contrast-to-noise ratio was observed with mangafodipir (p < 0.05, paired t test) in 0.5T preoperative images. Along with the stability of the mangafodipir contrast enhancement during the entire cryosurgical procedure, the resulting gain in contrast allowed for better visualizing the presence of residual untreated tumor margins at the periphery of the cryosurgery iceball directly from perioperative images acquired with patients under narcosis. Consequently, it not only became easier for the interventionalist to determine the need for an additional cryoprobe to increase the size of the iceball during the procedure, but also to decide on the appropriate end point of the cryosurgery.     

New chemical synthesis of functionalized arylzinc compounds from aromatic or thienyl bromides under mild conditions using a simple cobalt catalyst and zinc dust

A new chemical method for the preparation of arylzinc intermediates is described in acetonitrile, on the basis of the activation of aryl bromides by low-valent cobalt species arising from the reduction of cobalt halide by zinc dust. This procedure allows for the synthesis of a variety of functionalized aryl- and thienylzinc species in good to excellent yields. The versatility and the simplicity of that original method represent an alternative to most known procedures.     

Renormalization of the 2-Point Function of the Hubbard Model at Half-Filling

We prove that the Hubbard model at finite temperature T and half-filling is analytic in its coupling constant λ for where c is some numerical constant. We also bound the self-energy and prove that the Hubbard model at half-filling is not a Fermi liquid (in the mathematically precise sense of Salmhofer), modulo a simple lower bound on the first non-trivial self-energy graph, which will be published in a companion paper.submitted 09/09/04, accepted 20/12/04     

New and simple one-step cobalt-catalyzed preparation of functionalized arylstannanes from the corresponding aryl bromides or iodides

A variety of functionalized arylstannanes are obtained in moderate to excellent yields by a one-step chemical procedure from corresponding halides and tributylstannyl chloride via cobalt catalysis.     

Surface-directed capillary system; theory, experiments and applications

We present a capillary flow system for liquid transport in microsystems. Our simple microfluidic system consists of two planar parallel surfaces, separated by spacers. One of the surfaces is entirely hydrophobic, the other mainly hydrophobic, but with hydrophilic pathways defined on it by photolithographic means. By controlling the wetting properties of the surfaces in this manner, the liquid can be confined to certain areas defined by the hydrophilic pathways. This technique eliminates the need for alignment of the two surfaces. Patterned plasma-polymerized hexafluoropropene constitutes the hydrophobic areas, whereas the untreated glass surface constitutes the hydrophilic pathways. We developed a theoretical model of the capillary flow and obtained analytical solutions which are in good agreement with the experimental results. The capillarity-driven microflow system was also used to pattern and immobilize biological material on planar substrates: well-defined 200 microm wide strips of human cells (HeLa) and fluorescence labelled proteins (fluorescein isothiocyanate-labelled bovine serum albumin, i.e., FITC-BSA) were fabricated using the capillary flow system presented here.     

Détermination d'un champ de forces de valence pour le thiazole et ses dérivés deutériés: Étude du méthyl-2 et chloro-2 thiazole

The vibrational frequencies of thiazole and its deuterated derivatives have been used in valence force field calculations. The transferability of the force field is verified by the study of 2-chloro- and 2-methyl-thiazole. Previous assignments are discussed.