Aerobic anoxygenic phototrophic bacteria

The aerobic anoxygenic phototrophic bacteria are a relatively recently discovered bacterial group. Although taxonomically and phylogenetically heterogeneous, these bacteria share the following distinguishing features: the presence of bacteriochlorophyll a incorporated into reaction center and light-harvesting complexes, low levels of the photosynthetic unit in cells, an abundance of carotenoids, a strong inhibition by light of bacteriochlorophyll synthesis, and the inability to grow photosynthetically under anaerobic conditions. Aerobic anoxygenic phototrophic bacteria are classified in two marine (Erythrobacter and Roseobacter) and six freshwater (Acidiphilium, Erythromicrobium, Erythromonas, Porphyrobacter, Roseococcus, and Sandaracinobacter) genera, which phylogenetically belong to the alpha-1, alpha-3, and alpha-4 subclasses of the class Proteobacteria. Despite this phylogenetic information, the evolution and ancestry of their photosynthetic properties are unclear. We discuss several current proposals for the evolutionary origin of aerobic phototrophic bacteria. The closest phylogenetic relatives of aerobic phototrophic bacteria include facultatively anaerobic purple nonsulfur phototrophic bacteria. Since these two bacterial groups share many properties, yet have significant differences, we compare and contrast their physiology, with an emphasis on morphology and photosynthetic and other metabolic processes.     

Sites of alcohol and volatile anaesthetic action on GABA(A) and glycine receptors

Volatile anaesthetics have historically been considered to act in a nonspecific manner on the central nervous system. More recent studies, however, have revealed that the receptors for inhibitory neurotransmitters such as gamma-aminobutyric acid (GABA) and glycine are sensitive to clinically relevant concentrations of inhaled anaesthetics. The function of GABA(A) and glycine receptors is enhanced by a number of anaesthetics and alcohols, whereas activity of the related GABA rho1 receptor is reduced. We have used this difference in pharmacology to investigate the molecular basis for modulation of these receptors by anaesthetics and alcohols. By using chimaeric receptor constructs, we have identified a region of 45 amino-acid residues that is both necessary and sufficient for the enhancement of receptor function. Within this region, two specific amino-acid residues in transmembrane domains 2 and 3 are critical for allosteric modulation of both GABA(A) and glycine receptors by alcohols and two volatile anaesthetics. These observations support the idea that anaesthetics exert a specific effect on these ion-channel proteins, and allow for the future testing of specific hypotheses of the action of anaesthetics.     

Fluorination of pressure-polymerized C60 phases

The reactivity of O-, T- and R-phases of the high pressure-high temperature (HPHT) polymerized C₆₀ towards gaseous fluorine in the temperature range of 50-250 °C was investigated. The reaction products were characterized by FTIR, powder X-ray diffraction, SEM, EDX, and VTP-EIMS to determine the bulk stoichiometries, bonding patterns, phase compositions, crystalline structures and thermal decomposition behavior of the fluorinated polymers. At 1 h isothermal treatment duration, fluorinated products with various bulk stoichiometries were obtained from different polymer phases with the R-phase showing the highest fluorine uptake. At 250 °C, all C₆₀ polymers showed partial decomposition to unfluorinated C₆₀ monomer under fluorine atmosphere. At 200 °C, the fluorination of R-phase yielded a pure fluoropolymer most likely having a {C₆₀F_x}_n (x = 36-44) composition. The same fluoropolymer was presumably obtained from O- and T-phases in lower yields. The linear chain structure was suggested for this new fluorocarbon polymer in agreement with the molecular mechanics modeling calculations.     

Synthesis, Characterization and Photocatalytic Activity of Titania Loaded Cd-MCM-41

Catalysts consisting of cadmium incorporated into MCM-41 mesoporous molecular sieves (Cd-MCM-41) with Si/Cd = 80 have been synthesized by the hydrothermal method using cadmium acetate as the source of cadmium. This was then loaded with titania via the sol-gel method to explore the photoactivity in UV light. These two materials were characterized by various physicochemical techniques such as N₂ physisorption, O₂ chemisorption, diffuse reflectance UV-vis, X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The pore size of the Cd-MCM-41 was higher and the BET surface area was lower than those commonly found in our siliceous MCM-41. This is due to the partial pore breakage, as recorded by pore size distribution analysis. The oxygen chemisorption results shows that the dispersion of cadmium is quite high, and decreased after loading of titania. The XRD patterns of Cd-MCM-41 and 25%TiO₂/Cd-MCM-41 are similar to those of siliceous MCM-41; however, the intensity of the d ₁₀₀ peak is decreased and the unit-cell parameter increased with titania loading. Raman spectra could not detect any peaks, whereas peaks were detected at 144, 397, 518 and 641 cm_-1 with loading of titania, these peaks being associated with the anatase phase of titania. The surface composition and binding energy of the Cd 3d_5/2 peak for Cd-MCM-41 and 25%TiO₂/Cd-MCM-41 was analyzed by XPS and showed considerable infusion of cadmium ions on to the surface upon loading of titania. The Cd/Si surface atomic ratio measured by XPS increases 10 times with loading of titania on Cd-MCM-41, indicating that the two separate surface electronic levels such as Cd-O-Si and Cd-O-Ti were found for 25%TiO₂/Cd-MCM-41. The 25%TiO₂/Cd-MCM-41 showed higher activity than 25%TiO₂/MCM-41 for photocatalytic degradation of formic acid. The activity results are compared with the pure titania based on the transformation per site of Ti.     

Solution to the Problem of Cleaning Autoclaves for Growing Synthetic Quartz

Refractories and Industrial Ceramics - An experimental study was performed to break down a sample of a by-product of the autoclave production of artificial quartz crystals using a pilot...     

Polyaniline–13X zeolite composite‐supported platinum electrocatalysts for direct methanol fuel cell applications

We successfully synthesized 13X zeolite using a hydrothermal method. Then, composites of polyaniline (PANI) with 13X zeolite and PANI–13X with platinum were prepared by chemical oxidative polymerization and chemical reduction, respectively. Field emission scanning electron microscopy, X‐ray diffraction, Raman spectroscopy and Brunauer–Emmett–Teller techniques were used to characterize the PANI–Pt and PANI–Pt–13X composites. Further, the electrocatalytic activity towards methanol oxidation of the synthesized catalysts was explored using cyclic voltammetry in 1 mol L^?1 CH₃OH + 0.5 mol L^?1 H₂SO₄ solution. From the obtained results, PANI–Pt–13X shows superior performance compared to PANI–Pt towards methanol oxidation and electrical conductivity. Hence, the 13X zeolite‐incorporated PANI–Pt composite could be an efficient catalyst for direct methanol fuel cell applications. © 2019 Society of Chemical Industry