A new class of infrared transmitting glass-ceramics based on controlled nucleation and growth of alkali halide in a sulphide based glass matrix

Oxides-based glass-ceramics have been intensively studied and while they exhibit exceptional thermo-mechanical properties, their transparency in the infrared is limited to the 3 μm region. In this paper we describe a new type of glass-ceramics which are transparent up to 11 μm and based on the controlled nucleation and crystallization of cesium chloride sub-micron particles inside a Ge-Sb-S glass matrix. The evolution of the optical transmission versus annealing time and temperature has been investigated. Observations under scanning electronic microscopy as well as X-ray diffraction indicate that the crystalline phase is a primitive cubic cell with a parameter slightly inferior to that of pure CsCl and that the grain sizes are about 100 nm. A preliminary test on fracture propagation shows a much better resistance of glass-ceramics to cracks than the corresponding pure glass matrix.     

Use of the Fluorescent Nucleoside Analogue Benzo[g]quinazoline 2′‐O‐Methyl‐β‐D‐ribofuranoside to Monitor the Binding of the HIV‐1 Tat Protein or of Antisense Oligonucleotides to the TAR RNA Stem‐Loop

The Tat protein is an essential trans‐activator of HIV gene expression. It interacts with its RNA recognition sequence, the trans‐activation responsive region TAR, as well as cellular factors. These interactions are potential targets for drug discovery against HIV infection. We have developed a new and sensitive assay for the measurement of Tat binding to TAR in solution under equilibrium conditions based on the change of fluorescence of the base analogue benzo[g]quinazoline‐2,4(1H,3H)‐dione (BgQ) incorporated into the chemically synthesized model TAR stem‐loop 2 to which was added Tat‐[37‐72] peptide ( 3 ). The results show that Tat‐TAR binding strength is 2 – 3‐fold stronger than has previously been determined by mobility‐shift analysis. Changes of fluorescence were used also to measure the binding of antisense 2′‐O‐methyloligonucleotides to TAR 2 .     

The uptake of Mn-DPDP by hepatocytes is not mediated by the facilitated transport of pyridoxine

Manganese-dipyridoxal diphosphate (Mn-DPDP) is a liver-selective contrast agent selectively taken up by the hepatocytes. Because of the analogy of structure with pyridoxine (vitamin B₆), it was previously suggested that this compound can be selectively taken up by the facilitated transport of vitamers B₆. To understand the uptake mechanism, an in vivo binding study was performed based on a competition between ⁵⁴Mn-DPDP and pyridoxine on the one hand, and Mn-DPDP and [³H]pyridoxine on the other. We found that the [³H]pyridoxine levels in the liver were not significantly different 5 min after intravenous administration of several doses of Mn-DPDP (5 nmol/kg to 50 μmol/kg): 5.0 ± 0.3% of the injected dose/g tissue. The content of ⁵⁴Mn (administered as ⁵⁴Mn-DPDP) in the liver was not affected by a saturation dose of pyridoxine (1 mmol/kg) and was found to be constant (±10% of the injected dose/g tissue) for 60 min. These experiments showed that the uptake of Mn-DPDP is not mediated by the transporter of pyridoxine.     

Adsorption of stereoregular poly(methyl methacrylates) on γ-alumina: Spectroscopic analysis

ABSTRACTS: Three poly(methyl methacrylates) (PMMA) with a racemic fraction ranging from 0.25 to 0.91 have been adsorbed from a chloroform solution on γ-alumina and studied by diffuse reflectance infrared spectroscopy (DRIFT) and solid-state ¹³C NMR spectroscopy. From DRIFT spectra, it is seen that the fraction of carbonyl groups bonded to the surface goes from 0.29 for s-PMMA to 0.41 for i-PMMA, but there is a larger amount of s-PMMA retained on the surface (at any given solution concentration). NMR spectroscopy indicates, from shifts of the methylene and α-methyl carbon peaks (due to the γ-gauche effect), that the adsorption is accompanied by changes in conformation, with an increase in the number of trans conformers, particularly with i-PMMA. These results indicate that s-PMMA adsorbs on γ-alumina in a brush-like configuration, with a relatively small number of groups attached to the surface, and tails and loops sticking out of the surface, whereas i-PMMA adsorbs in a sheet-like configuration, with a greater number of interacting groups. In both cases, the adsorption is accompanied with an increase in the number of trans conformers as compared to the bulk conformation. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2985–2995, 1999     

A distributed Lagrange multiplier/fictitious domain method for flows around moving rigid bodies: Application to particulate flow

This article discusses the application of a Lagrange multiplier‐based fictitious domain method to the numerical simulation of incompressible viscous flow modeled by the Navier–Stokes equations around moving rigid bodies; the rigid body motions are due to hydrodynamical forces and gravity. The solution method combines finite element approximations, time discretization by operator splitting and conjugate gradient algorithms for the solution of the linearly constrained quadratic minimization problems coming from the splitting method. The study concludes with the presentation of numerical results concerning four test problems, namely the simulation of an incompressible viscous flow around a NACA0012 airfoil with a fixed center but free to rotate, then the sedimentation of 200 and 1008 cylinders in a two‐dimensional channel, and finally the sedimentation of two spherical balls in a rectangular cylinder. Copyright © 1999 John Wiley & Sons, Ltd.     

A Validated HPLC-PDA-HRMS Method to Investigate the Biological Stability and Metabolism of Antiparasitic Triterpenic Esters

Pentacyclic triterpenes (PTs) are commonly found in medicinal plants with well-known antiparasitic effects. Previous research on C-3 and C-27 triterpenic esters showed effective and selective in vitro antiparasitic activities and in vivo effectiveness by parenteral routes. The aim of this study was to determine triterpenic esters’ stability in different biological-like media and the main microsomal degradation products. An HPLC-PDA method was developed and validated to simultaneously analyze and quantify bioactive triterpenic esters in methanol (LOQ: 2.5 and 1.25–100 µg/mL) and plasma (LOQ: 5–125 µg/mL). Overall, both triterpenic esters showed a stable profile in aqueous and buffered solutions as well as in entire plasma, suggesting gaining access to the ester function is difficult for plasma enzymes. Conversely, after 1 h, 30% esters degradation in acidic media was observed with potential different hydrolysis mechanisms. C-3 (15 and 150 µM) and C-27 esters (150 µM) showed a relatively low hepatic microsomal metabolism (<23%) after 1 h, which was significantly higher in the lowest concentration of C-27 esters (15 µM) (>40% degradation). Metabolic HPLC-PDA-HRMS studies suggested hydrolysis, hydroxylation, dehydration, O-methylation, hydroxylation and/or the reduction of hydrolyzed derivatives, depending on the concentration and the position of the ester link. Further permeability and absorption studies are required to better define triterpenic esters pharmacokinetic and specific formulations designed to increase their oral bioavailability.     

Recent developments in rubber processing,leading to new applications such as the “green tyre”

Rubber articles derive most of their mechanical properties from the admixture of reinforcing fillers. Most commonly, carbon black is used as reinforcing filler. If silica is used instead, tyres made with such rubber compounds may exhibit a rolling resistance reduction by ca. 30%, which translates in substantial fuel savings of a car. Such silicas are far more difficult to mix with rubber than carbon black. Coupling agents are used as a surface modification of the filler to enhance compatibility with the polymer. Additionally they improve the ease of mixing with the rubber. The development of proper coupling agents combined with improved mixing techniques has contributed to the final break-through of the silicareinforced “Green Tyre”.     

Mass-selected reagent ion chemical ionization and multiple tandem mass spectrometry techniques in an ion trap mass spectrometer for structural analysis

Mass-selected reagent ion chemical ionization (CI) performed in an ion trap instrument is an efficient tool to investigate gas-phase ion reactivities and therefore to find out new and/or optimized applications for structural analysis. For instance, it was shown that the C₃H₆O^{+ .} (58 mass units) molecular ion originated from vinyl methyl ether (VME) should necessarily be used alone (i.e. unit-mass selected) to produce significant diagnostic-ions for double bond location in aliphatic alkenes. Regarding the assignment of epoxides, the previous NO⁺/CI method was adapted for an optimal use in the trap through isolation of NO⁺ cation from N₂O (instead of NO) plasma and production of the acylium diagnostic-ions via CID of [M − H]⁺ formed by NO⁺-induced hydride abstraction. New alkylation ion-products, e.g. RCH = O⁺-al , were also found to characterize isomeric epoxides as a result of either an initial electrophilic addition of the C₂H₅⁺ cation (with saturated epoxides) or a methyl-transfer from [VME]^{+ .} (with α,β-unsaturated epoxides). The multiple tandem mass spectrometry (MSⁿ) capabilities of the ion trap were essential to achieve reagent ion mass-selection, structural assignment of the diagnostic-ions, or to provide further selectivity. © 1997 John Wiley & Sons, Ltd.     

Paul Havrez und seine Benzolformel

The belgian chemist Paul Havrez (1838–1875) proposed two highly symmetrical, space-filling models for the benzene molecule, only a few months after Kekulé's seminal proposal of a cyclic benzene structure. One of these models is characterized by the revolutionary assumption of equal 3/2 bonds between all neighbouring carbon atoms, in sharp contrast to Kekulé's formula with alternating double and single bonds. With Considerable hind-sight, Havrez's model could be considered as a forerunner of the benzene structure with delocalized π bonds.