Search results for "ACID"
showing 10 items of 13107 documents
Phosphorylation of the Goodpasture antigen by type A protein kinases.
1995
Collagen IV is the major component of basement membranes. The human alpha 3 chain of collagen IV contains an antigenic domain called the Goodpasture antigen that is the target for the circulating immunopathogenic antibodies present in patients with Goodpasture syndrome. Characteristically, the gene region encoding the Goodpasture antigen generates multiple alternative products that retain the antigen amino-terminal region with a five-residue motif (KRGDS). The serine therein appears to be the major in vitro cAMP-dependent protein kinase phosphorylation site in the isolated antigen and can be phosphorylated in vitro by two protein kinases of approximately 50 and 41 kDa associated with human …
Enhanced Heterogeneous Catalytic Conversion of Furfuryl Alcohol into Butyl Levulinate
2014
We study the catalytic condensation of furfuryl alcohol with 1-butanol to butyl levulinate. A screening of several commercial and as-synthesized solid acid catalysts shows that propylsulfonic acid-functionalized mesoporous silica outperforms the state-of-the-art phosphotungstate acid catalysts. The catalyst is prepared via template-assisted sol-gel polycondensation of TEOS and MPTMS. It gives 96 % yield (and 100 % selectivity) of butyl levulinate in 4h at 110 °C. Reaction profiles before and after a hot filtration test confirm that the active catalytic species do not leach into the solution. The catalyst synthesis, characterization, and mode of operation are presented and discussed. Sour ca…
A DFT study of the Diels–Alder reaction between methyl acrolein derivatives and cyclopentadiene. Understanding the effects of Lewis acids catalysts b…
2006
Abstract The effects of Lewis acid catalysts based on sulfur containing boron heterocycles on the Diels–Alder reactions of two methyl acroleins with cyclopentadiene have been studied using DFT methods. These reactions take place along highly asynchronous concerted processes. While the reaction with crotonaldehyde leads to the expected endo adduct, the reaction with methacrolein leads to exo one in agreement with the experiments. The catalytic effect can be explained through the analysis of the electrophilicity index (ω) of the reagents, and the molecular structure of the corresponding transition structures.
Effects of NH3 and alkaline metals on the formation of particulate sulfate and nitrate in wintertime Beijing
2020
Sulfate and nitrate from secondary reactions remain as the most abundant inorganic species in atmospheric particle matter (PM). Their formation is initiated by oxidation (either in gas phase or particle phase), followed by neutralization reaction primarily by NH3, or by other alkaline species such as alkaline metal ions if available. The different roles of NH3 and metal ions in neutralizing H2SO4 or HNO3, however, are seldom investigated. Here we conducted semi-continuous measurements of SO4 2−, NO3 −, NH4 +, and their gaseous precursors, as well as alkaline metal ions (Na+, K+, Ca2+, and Mg2+) in wintertime Beijing. Analysis of aerosol acidity (estimated from a thermodynamic model) indicat…
Ammonium adsorption, desorption and recovery by acid and alkaline treated zeolite
2021
In this study, the suitability of zeolite as a possible medium for ammonium adsorption, desorption and recovery from wastewater was investigated. Specifically, batch adsorption and desorption studies with solutions enriched in NH$_4^+$ were conducted employing zeolite to evaluate how the chemical treatment and contact time affect adsorption and desorption. Several experimental tests were carried out considering both untreated and treated zeolite. Untreated and HCl-Na treated zeolite adsorbed up to 11.8 mg NH$_4^+$ g$^{-1}$ and showed the highest efficiency in recovering NH$_4^+$ from aqueous solution. Regardless of pre-treatment, treatments with NaCl resulted in higher and faster adsorption…
AlTf-UVM-7—Highly active catalysts for the synthesis of long chain symmetrical ethers and non-ionic surfactant structures
2010
New Lewis acid AlTf-UVM-7 catalysts with bimodal pore system and different Si to Al ratios were prepared in a two-step synthesis in which triflic acid (Tf) was incorporated into previously synthesized mesoporous aluminum-containing silica. The Al incorporation inside the pore walls was carried out through the Atrane method. The characterization of the resulted catalysts showed that the triflic acid treatment step did not damage the texture or the structure of the catalysts. These materials were used as green catalysts for the etherification of fatty alcohols and the conversion of ethylene glycol (EG) with n-octanol resulting in mixtures of short ethoxylated structures with a large distribut…
The genus thiobacillus: Physiology and industrial applications
1983
This review deals with different aspects concerning the genus Thiobacillus as an obligat chemoautotroph able to oxidize reduced anorganic sulphur compounds. There are given the following topics: physiology of the genus (nutritional requirements, enzymatic complexes for sulphur oxidation, energy generation, reductive CO2 assimilation and growing in presence of organic compounds). The ecological significance of Thiobacilli in the sulphur cycle in Nature is presented. The industrial applications of Thiobacilli in respect to the leaching processes that allow the recovery of metals through oxidation and solubilization from low-grade ores are discussed, with special reference to copper and uraniu…
Recent Advances in Halogen Bonded Assemblies with Resorcin[4]arenes
2020
Resorcinarenes are cavity-containing compounds when in the crown conformation, from the calixarene family of concave compounds. These easy to synthesize macrocycles can be decorated at the upper rim through the eight hydroxyl groups and/or the 2-position of the aromatic ring. They are good synthons in supramolecular chemistry leading to appealing assemblies such as open-inclusion complexes, capsules and tubes through multiple weak interactions with various guests. Halogen bonding (XB) is a highly directional non-covalent interaction by an electron-deficient halogen atom as a donor that interacts with a Lewis base, the XB acceptor. This tutorial review provides an overview of recent advances…
Combined NC-AFM and DFT study of the adsorption geometry of trimesic acid on rutile TiO2(110)
2010
The adsorption behavior of trimesic acid (TMA) on rutile TiO(2)(110) is studied by means of non-contact atomic force microscopy (NC-AFM) and density-functional theory (DFT). Upon low-coverage adsorption at room temperature, NC-AFM imaging reveals individual molecules, centered above the surface titanium rows. Based on the NC-AFM results alone it is difficult to deduce whether the molecules are lying flat or standing upright on the surface. To elucidate the detailed adsorption geometry, we perform DFT calculations, considering a large number of different adsorption positions. Our DFT calculations suggest that single TMA molecules adsorb with the benzene ring parallel to the surface plane. In…
The role of H2O in the photocatalytic oxidation of toluene in vapour phase on anatase TiO2 catalyst
1999
Abstract Photocatalytic oxidation of toluene has been carried out in a gas–solid regime by using polycrystalline anatase TiO2 in a fixed-bed continuous reactor. Air containing toluene and water vapours in various molar ratios was fed to the photoreactor irradiated by a medium pressure Hg lamp. Toluene was mainly photo-oxidised to benzaldehyde, and small amount of benzene, benzyl alcohol and traces of benzoic acid and phenol were also detected. In the presence of water, no decrease of photoreactivity was observed at steady-state conditions. By removing water vapour from the feed, the conversion of toluene to benzaldehyde was almost completely inhibited, and an irreversible deactivation of th…