High repetition rate mid-infrared laser source

An efficient, high-power mid-infrared laser source based on ZnGeP₂ (ZGP) optical parametric oscillator (OPO) is presented. Using a Q-switched Ho:YAG laser as the pump source a total output power of 10.6 W was obtained in the 3–5 μm band at 10 kHz and 8.5 W at 20 kHz. The Ho:YAG laser was pumped by two diode-pumped polarization coupled Tm:YLF lasers. Optical-to-optical efficiency achieved is >8.8% (laser-diode 792 nm to mid-IR 3–5 μm). With a commercial PtSi infrared camera (256×256 pixel focal plane array, 24 μm pitch) the pointing stability of Ho pump, signal and idler beam was measured to be better than 30 μrad. Whilst propagating the OPO beams over 100 m, little absorption for the idler beam was observed, resulting in a significant higher peak-to-peak value of ±22%, whereas the peak-to-peak stability of the signal pulses remained unchanged (±13%). To cite this article: M. Schellhorn et al., C. R. Physique 8 (2007).     

Calcifications in human osteoarthritic articular cartilage: ex vivo assessment of calcium compounds using XANES spectroscopy

Calcium (Ca²⁺)‐containing crystals (CCs), including basic Ca²⁺ phosphate (BCP) and Ca²⁺ pyrophosphate dihydrate (CPPD) crystals, are associated with severe forms of osteoarthritis (OA). Growing evidence supports a role for abnormal articular cartilage mineralization in the pathogenesis of OA. However, the role of Ca²⁺ compounds in this mineralization process remains poorly understood. Six patients, who underwent total knee joint replacement for primary OA, have been considered in this study. Cartilage from femoral condyles and tibial plateaus in the medial and lateral compartments was collected as 1 mm‐thick slices cut tangentially to the articular surface. First, CCs presence and biochemical composition were assessed using Fourier transform infrared spectroscopy (FT‐IR). Next, Ca²⁺ compound biochemical form was further assessed using X‐ray absorption spectroscopy (XAS) performed at the Ca²⁺K‐absorption edge. Overall, 12 cartilage samples were assessed. Using FT‐IR, BCP and CPPD crystals were detected in four and three out of 12 samples, respectively. Ca²⁺ compound biochemical forms differed between areas with versus without CCs, when compared using XAS. The complete set of data shows that XANES spectroscopy can be used to accurately characterize sparse CCs in human OA cartilage. It is found that Ca²⁺ compounds differ between calcified and non‐calcified cartilage areas. In calcified areas they appear to be mainly involved in calcifications, namely Ca²⁺ crystals.     

Identification of iron(III) peroxo species in the active site of the superoxide reductase SOR from Desulfoarculus baarsii

The active site of superoxide reductase SOR consists of an Fe2+ center in an unusual [His4 Cys1] square-pyramidal geometry. It specifically reduces superoxide to produce H2O2. Here, we have reacted the SOR from Desulfoarculus baarsii directly with H2O2. We have found that its active site can transiently stabilize an Fe3+-peroxo species that we have spectroscopically characterized by resonance Raman. The mutation of the strictly conserved Glu47 into alanine results in a stabilization of this Fe3+-peroxo species, when compared to the wild-type form. These data support the hypothesis that the reaction of SOR proceeds through such a Fe3+-peroxo intermediate. This also suggests that Glu47 might serve to help H2O2 release during the reaction with superoxide.     

Development of new camphor based N,S chiral ligands and their application in transfer hydrogenation

A new class of N,S-containing chiral compounds based on the camphor scaffold have been synthesised and evaluated as chiral catalysts in the transfer hydrogenation of acetophenone. The best results were achieved using compound 6a as the ligand and [Ir(COD)Cl](2) as the metal precursor.     

Toxicological classification of urine samples using pattern recognition techniques and capillary electrophoresis

In toxicology, hazardous substances detected in organisms may often lead to different pathological conditions depending on the type of exposure and level of dosage; hence, further analysis on this can suggest the best cure. Urine profiling may serve the purpose because samples typically contain hundreds of compounds representing an effective metabolic fingerprint. This paper proposes a pattern recognition procedure for determining the type of cadmium dosage, acute or chronic, administrated to laboratory rats, where urinary profiles are detected using capillary electrophoresis. The procedure is based on the composition of a sample data matrix consisting of areas of common peaks, with appropriate pre-processing aimed at reducing the lack of reproducibility and enhancing the potential contribution of low-level metabolites in discrimination. The matrix is then used for pattern recognition including principal components analysis, cluster analysis, discriminant analysis and support vector machines. Attention is particularly focussed on the last of these techniques, because of its novelty and some attractive features such as its suitability to work with datasets that are small and/or have low samples/variable ratios. The type of cadmium administration is detected as a relevant feature that contributes to the structure of the sample matrix, and samples are classified according to the class membership, with discriminant analysis and support vector machines performing complementarily on a training and on a test set.     

Fe(CO)5 thin films adsorbed on Au(111) and on self-assembled organic monolayers: II. Thermal transformations

The thermal transformations of as-deposited Fe(CO)(5) films adsorbed on Au(111)/mica and C(4), C(8), C(12), and C(16) self-assembled methyl-terminated monolayer organic surfaces have been studied using infrared spectroscopy to probe how the physical restructuring influences the sensitivity of these systems to low-energy electron beams. A companion publication shows that the as-deposited monolayers are composed of molecules physisorbed with one axial and two equatorial carbonyl groups directed toward the substrate; subsequent layers are preferentially oriented with the C(3) molecular axis aligned perpendicular to the substrate (i.e., one axial carbonyl group directed toward the substrate). In this work, we show that the as-deposited films are structurally unstable above 125 K on Au(111)/mica surfaces and above 100 K on the organic self-assembled monolayers. Above these thresholds, the layered structures transform into three-dimensional aggregates, implying strongly nonwetting behavior for Fe(CO)(5) on each of these substrates; molecular desorption from this aggregate structure takes place between 140 and 160 K. The irreversibility of this temperature-induced transformation demonstrates that the as-deposited layered films do not represent a thermodynamically well-defined phase; this key feature of the as-deposited films is believed to be the cause of the discrepancies in previous attempts to understand Fe(CO)(5)/surface structures based on infrared results. Moreover, the thermally induced transformation to 3D aggregate structures is shown to decrease the apparent sensitivity of the adsorbed Fe(CO)(5) to low-energy electron-induced decarbonylation (0-10 eV) by over 3 orders of magnitude.     

Alpha,beta-D-CNA induced rigidity within oligonucleotides

Introduction of alpha,beta-D-CNA featuring canonical values of the torsional angles alpha and beta within oligonucleotides leads to an overall stabilization and improved rigidity of the duplex DNA as demonstrated by UV experiments, circular dichroism and corroborated by molecular dynamics simulations.     

Characterization of low-density silica xerogel formed into microspheres

Low-density silica xerogels were formed into spherical pellets using a process in which a xerogel suspension containing sodium alginate was solidified through free fall in a solution of divalent ions that induce the droplet solidification. Pellet preparation was also carried out at laboratory scale by using a syringe instead of the material-consuming unit used for scaling up. When beads are made from a suspension of dried-and-calcined xerogel material, the textural properties such as porosity and surface area are significantly altered. Both properties are reduced by 30-50% compared to the starting reference material. Properties were improved when a suspension of dried xerogel that is less sensitive to contact with water was used: specific surface area was maintained at its initial level and porosity decreased by 25%.     

Adsorption of Hexavalent Chromium Using Activated Carbon Produced from Sargassum ssp.: Comparison between Lab Experiments and Molecular Dynamics Simulations

Adsorption is one of the most successful physicochemical approaches for removing heavy metal contaminants from polluted water. The use of residual biomass for the production of adsorbents has attracted a lot of attention due to its cheap price and environmentally friendly approach. The transformation of Sargassum—an invasive brown macroalga—into activated carbon (AC) via phosphoric acid thermochemical activation was explored in an effort to increase the value of Sargassum seaweed biomass. Several techniques (nitrogen adsorption, pH_PZC, Boehm titration, FTIR and XPS) were used to characterize the physicochemical properties of the activated carbons. The SAC600 3/1 was predominantly microporous and mesoporous (39.6% and 60.4%, respectively) and revealed a high specific surface area (1695 m²·g⁻¹). To serve as a comparison element, a commercial reference activated carbon with a large specific surface area (1900 m²·g⁻¹) was also investigated. The influence of several parameters on the adsorption capacity of AC was studied: solution pH, solution temperature, contact time and Cr(VI) concentration. The best adsorption capacities were found at very acid (pH 2) solution pH and at lower temperatures. The adsorption kinetics of SAC600 3/1 fitted well a pseudo-second-order type 1 model and the adsorption isotherm was better described by a Jovanovic-Freundlich isotherm model. Molecular dynamics (MD) simulations confirmed the experimental results and determined that hydroxyl and carboxylate groups are the most influential functional groups in the adsorption process of chromium anions. MD simulations also showed that the addition of MgCl₂ to the activated carbon surface before adsorption experiments, slightly increases the adsorption of HCrO₄⁻ and CrO₄²⁻ anions. Finally, this theoretical study was experimentally validated obtaining an increase of 5.6% in chromium uptake.