Advances in the Function and Regulation of Hydrogenase in the Cyanobacterium Synechocystis PCC6803

In order to use cyanobacteria for the biological production of hydrogen, it is important to thoroughly study the function and the regulation of the hydrogen-production machine in order to better understand its role in the global cell metabolism and identify bottlenecks limiting H₂ production. Most of the recent advances in our understanding of the bidirectional [Ni-Fe] hydrogenase (Hox) came from investigations performed in the widely-used model cyanobacterium Synechocystis PCC6803 where Hox is the sole enzyme capable of combining electrons with protons to produce H₂ under specific conditions. Recent findings suggested that the Hox enzyme can receive electrons from not only NAD(P)H as usually shown, but also, or even preferentially, from ferredoxin. Furthermore, plasmid-encoded functions and glutathionylation (the formation of a mixed-disulfide between the cysteines residues of a protein and the cysteine residue of glutathione) are proposed as possible new players in the function and regulation of hydrogen production.     

Microstructure evolution and electromechanical properties of (K,Na) NbO3-based thick films

This study investigated an unconventional method of electrophoretic deposition (EPD) for the processing of environmentally benign (K_0.5Na_0.5)_0.99Sr_0.005NbO₃ (KNNSr) thick films on Pt/alumina substrate. EPD allows rapid, economical, and low-waste processing of thick films and thus offers an integration advantage for electronics manufacturing. To understand the functional response of the KNNSr thick films, the effect of the sintering temperature and atmosphere on their structure, microstructure, and electromechanical properties was investigated. KNNSr thick films densify in constrained conditions in a very narrow temperature range only a few 10°C below the melting temperature of 1140°C. Up to 1100°C the relative density increases to 80%, upon further heating to 1110°C we observed only the grain growth and pore coalescence. The densification is not affected significantly by the atmosphere. The local domain structure of 25-33 μm thick KNNSr films was similar, while the dielectric and electromechanical properties increased with the increasing sintering temperature. KNNSr thick film sintered at 1100°C has a thickness-coupling factor k_t of 0.4, comparable to that of bulk. The results reveal that the EPD enables the economic processing of high-performance thick films on complex-shape substrates that are difficult to fabricate using conventional thick-film methods.     

Novel Application of Cyclolipopeptide Amphisin: Feasibility Study as Additive to Remediate Polycyclic Aromatic Hydrocarbon (PAH) Contaminated Sediments

To decontaminate dredged harbor sediments by bioremediation or electromigration processes, adding biosurfactants could enhance the bioavailability or mobility of contaminants in an aqueous phase. Pure amphisin from Pseudomonas fluorescens DSS73 displays increased effectiveness in releasing polycyclic aromatic hydrocarbons (PAHs) strongly adsorbed to sediments when compared to a synthetic anionic surfactant. Amphisin production by the bacteria in the natural environment was also considered. DSS73's growth is weakened by three model PAHs above saturation, but amphisin is still produced. Estuarine water feeding the dredged material disposal site of a Norman harbor (France) allows both P. fluorescens DSS73 growth and amphisin production.     

5',6'-nucleoside phosphonate analogues architecture: synthesis and comparative evaluation towards metabolic enzymes

Nucleoside phosphonates have been designed as stable 5'-mononucleotide mimics and are nowadays considered a potent class of antiviral agents. Within cells, they must be metabolised to the corresponding diphosphate to exert their biological activity. In this process, the first phosphorylation step, catalysed by nucleoside monophosphate kinases (NMP kinases), has been proposed as a bottleneck. Herein, we report the synthesis of a series of ribonucleoside phosphonate derivatives isosteric to 5'-mononucleotides, with different degrees of flexibility within the 5',6'-C-C bond, as well as different polarities, through the introduction of hydroxy groups. The influence of these modifications on the capacity of the compounds to act as substrates for appropriate human NMP kinases, involved in nucleic acids metabolism, has been investigated. Low flexibility, as well as an absence of hydroxy groups within the ribose-phosphorus architecture, is critical for efficient phosphotransfer. Among the series of pyrimidine analogues, one derivative was shown to be phosphorylated by human UMP-CMP kinase, with rates similar to those of dUMP and even better than dCMP.     

Super-crosslinked ionic liquid-intercalated montmorillonite/epoxy nanocomposites: Cure kinetics,viscoelastic behavior and thermal degradation mechanism

Super-crosslinked epoxy nanocomposites containing N-octadecyl-N′-octadecyl imidazolium iodide (IM)-functionalized montmorillonite (MMT-IM) nanoplatelets were developed and examined for cure kinetics, viscoelastic behavior and thermal degradation kinetics. The structure and morphology of MMT-IM were characterized by FTIR, XRD, TEM, and TGA. Synthesized MMT-IM revealed synergistic effects on the network formation, the glass transition temperature (T_g) and thermal stability of epoxy. Cure and viscoelastic behaviors of epoxy nanocomposites containing 0.1 wt% MMT and MMT-IM were compared based on DSC and DMA, respectively. Activation energy profile as a function of the extent of cure was obtained. DMA results indicated a strong interface between imidazole groups of MMT-IM and epoxy, which caused a significant improvement in storage modulus and the T_g of epoxy. Network degradation kinetics of epoxy containing 0.5, 2.0, and 5.0 wt% MMT and MMT-IM were compared by using Friedman, Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and the modified Coats-Redfern methods. Although addition of MMT to epoxy was detrimental to the T_g value, as featured by a fall from 94.1°C to 89.7°C detected by DMA method, and from 103.3°C to 97.9°C by DSC method, respectively. By contrast, meaningful increase in such values were observed in the same order from 94.1°C to 94.7°C and from 103.3°C to 104.7°C for super-crosslinked epoxy/MMT-IM systems.     

X-ray imaging of a high-temperature furnace applied to glass melting

The dynamics of soda-lime-silica glass grain melting is investigated experimentally using a nonintrusive technique. A cylindrical alumina crucible is filled with glass cullet and placed into a furnace illuminated by an X-ray source. This glass granular bed is gradually heated up to 1100°C, leading to its melting and the generation of a size-distributed population of bubbles rising in the molten glass. An image processing algorithm of X-ray images of the cullet bed during melting allows the characterization of bubbles size distribution in the crucible as well as their velocity. The introduction of tin dioxide μ-particles in the glass matrix before melting enhances the texture of the images and makes possible the determination of the bubble-induced molten glass velocity field by an optical flow technique. The bubble size distribution can be fitted by a log-normal law, suggesting that it is closely related to the initial size distribution in the cullet bed. The liquid motion induced by the bubbles in Stokes' regime is strongly affected by the flow confinement and the determination of bubble rising velocity along its trajectory unveils the existence of local tiny temperature fluctuations in the crucible. Overall, the measuring techniques developed in this work seem to be very promising for the improvement of models and optimization of industrial glass furnaces.     

Selective reduction of NOx by hydrogen and methane in natural gas stationary sources over alumina-supported Pd, Co and Co/Pd catalysts: Part A. On the effect of palladium precursors and catalyst pre-treatment

The aim of the present work is to study the selective reduction of NO_x from natural gas sources. The unburned methane can be used as reductant. Another reductant such as hydrogen can be created in situ, using a microreformer. The results suggest that the NO_x are reduced by H₂ at low temperature, when methane is not activated and at higher temperature the methane is then the main reductant. However, the catalytic behaviour depends on the metal precursor and the catalyst treatment. The most prominent result is obtained on the palladium catalyst prepared from Pd(NH₃)₄(NO₃)₂ precursor. Comparing the reduction and the calcination step in the course of catalyst preparation, one can conclude that calcination lead to the higher activity in deNO_x, since reduced catalysts are oxidized during the deNO_x process.     

Stainless steel patterning by combination of micro-patterning and driven strain produced by plasma assisted nitriding

Plasma-assisted nitriding treatments on austenitic stainless steel at low temperature produce the so called “expanded austenite”. The expansion of the nitrided layer that occurs from the initial surface of the substrate in a direction perpendicular to the surface is used here as a mean to produce patterned surfaces by selective nitrogen diffusion through masks. Using grids, a network of well defined square dots can be obtained. In this communication, the results of nitriding treatments on austenitic stainless steel substrates previously covered by a patterned silicon oxide layer are presented. The interactions mechanisms at the interface between fixed silicon oxide mask with several different shapes (circular and square dots) and the expanded austenite are also described. The role of nitrogen diffusion, consistent with the experimental conditions and the mask characteristics, is shown to be very important. Depending on the size of the dots, it leads to a simple uniform mask deformation or to a significant mask deformation with strong distortions at the edges. This phenomenon is noted as a toroidal-shell shape distortion. Optical cross-section seems to prove that it is only the result of the vertical force due to the austenite expansion induced by nitrogen diffusion just under the mask edges.