Search results for "element"
showing 10 items of 13601 documents
Studies on the natural hemolytic system of the annelid worm Spirographis spallanzanii viviani (Polychaeta).
1981
Abstract Hemolytic activity in the hemolymph of Spirographis spallanzanii was estabilished against Bufo, sheep, calf, rabbit, rat, human A, B, O erythrocytes. Chemico-physical treatments suggest that the hemolytic factor could be a thermo-labile protein whose activity requires calcium ions and which is active over broad pH and temperature ranges. Some of these properties and the sigmoidal curve obtained by plotting the quantity of hemolymph against the percentage of hemolysis, produce some analogies with the mammalian lytic system.
Dynamics of F-center annihilation in thermochemically reduced MgO single crystals
2001
Optical absorption measurements were used to monitor the thermal annihilation of oxygen vacancies (F-centers) in thermochemically reduced MgO crystals. The annihilation characteristics were sample-dependent and varied strongly with the F-center concentration. Different mechanisms for the destruction of F centers are suggested depending on their concentration.
3,4-Dihydro-2H-pyrrole-2-carbonitriles: Useful Intermediates in the Synthesis of Fused Pyrroles and 2,2′-Bipyrroles
2016
Various heterocyclic structures containing the pyrrole moiety have been synthesized from easily accessible 3,4-dihydro-2H-pyrrole-2-carbonitriles in one-pot procedures. 5,6,7,8-Tetrahydroindolizines, 2,3-dihydro-1H-pyrrolizines as well as 6,7,8,9-tetrahydro-5H-pyrrolo[1,2-a]azepines were obtained from these precursors in high yields in an alkylation/annulation sequence. The same conditions were applied in the synthesis of a 5,8-dihydroindolizine, which could easily be transformed to the corresponding indolizine by dehydrogenation. Furthermore, oxidative couplings of 3,4-dihydro-2H-pyrrole-2-carbonitriles with copper(II)-salts furnished 2,2'-bipyrroles as well as 5,5'-bis(5-cyano-1-pyrroline…
Photoelectrochemical evidence of nitrogen incorporation during anodizing sputtering--deposited Al-Ta alloys.
2015
Anodic films were grown to 20 V on sputtering-deposited Al–Ta alloys in ammonium biborate and borate buffer solutions. According to glow discharge optical emission spectroscopy, anodizing in ammonium containing solution leads to the formation of N containing anodic layers. Impedance measurements did not evidence significant differences between the dielectric properties of the anodic films as a function of the anodizing electrolyte. Photoelectrochemical investigation allowed evidencing that N incorporation induces a red-shift in the light absorption threshold of the films due to the formation of allowed localized states inside their mobility gap. The estimated Fowler threshold for the intern…
Kinetics of coloration of anodic electrochromic films of WO3·H2O
1980
Polycrystalline layers of WO3·H2O are obtained by anodization of tungsten in 1 N H2SO4 at 70° C. The cathodic reduction of these layers in acid solutions causes the formation of blue WO3−x·H2O (0<x⩽:0.12) oxides. The kinetics of coloration are investigated by galvanostatic and potentiostatic techniques. The experimental results are compared with the theoretical data obtained by solving the diffusion equation for a constant flow of oxygen vacancies and for a time-dependent surface vacancy concentration. Except in the initial stage of coloration, the process controlling rate can be ascribed to the diffusion of oxygen vacancies from the oxide-electrolyte interface into the bulk of the layers. …
Microporous alumina membranes electrochemically grown
2003
Abstract The electrochemical fabrication of alumina membranes by anodizing of aluminium in phosphoric acid and oxalic acid solutions, in the temperature interval from −1 to 16 °C, was investigated in order to study the influence of different parameters (initial treatment of aluminium surface, nature and composition of electrolyte, temperature) on the final characteristics of the membranes. Porous layers were grown using a linear potential scan at 0.2 V s −1 up to 160 V in H 3 PO 4 solution and 70 V in oxalic acid solution. The efficiency of porous layer formation was calculated by using Faraday's law and weight measurements. Pore size distribution and porosity of membranes prepared in 0.4 M…
Tin(IV) catalyzed D-galacturonic acid anomerization
2008
A comparative kinetic study of anomerization between the four main forms (alpha/beta-pyranosides and alpha/beta-furanosides) of D-galacturonic acid (GalAH(2), 1) and tin(IV) complexed D-galacturonate ([Sn(CH(3))(2)(GalA)(H(2)O)(2)], 2) in D(2)O, is reported. Important differences are shown by pD vs. mutarotation rate profiles of 1 and 2. Coordination, in fact, causes: i) a spectacular increase of the rate due to kinetic template assistance of the carboxylic tail holding the metal in close proximity to the reactive centre and ii) a change in the dependence of the rate on the pD. Entropic and enthalpic factors contribute to the huge activation energy decrease in 2. Anomerization rates of the …
Dinuclear and tetranuclear complexes of copper coordinated by an anthracene-based new μ-bis(tridentate) ligand: Synthesis, structure, spectroscopy an…
2016
Abstract Copper(II) complexes of an anthracene-based new μ-bis(tridentate) ligand, N,N′-bis[anthracene-2-ylmethyl]-N,N′-bis[carboxymethyl]-1,3-diaminopropan-2-ol (H3acdp) with mixed donating groups, have been studied in solid state as well as in solution. The reaction of stoichiometric amounts of CuSO4·5H2O and the ligand H3acdp in the presence of NaOH at ambient temperature in methanol-dichloromethane, afforded a new dinuclear copper complex, [Cu2(acdp)(MeO)(MeOH)2] (1). On the other hand, the reaction of stoichiometric amounts of Cu(OAc)2·H2O and the ligand H3acdp in the presence of NaOH at ambient temperature in methanol-dichloromethane yielded, a novel tetranuclear copper complex, [Cu4(…
Palladium-Catalysed Amination of 1,8- and 1,5-Dichloroanthracenes and 1,8- and 1,5-Dichloroanthraquinones
2005
Diamino derivatives of anthracene and anthraquinone have been synthesised by palladium-catalysed coupling of 1,8-dichloroanthracene and 1,8-dichloroanthraquinone with a wide range of aliphatic and aromatic primary and secondary amines. The use of polyamines gave rise to a large number of new nitrogen- and oxygen-containing macrocycles incorporating anthracene or anthraquinone moieties. The method has also been employed for the preparation of bismacrocycles in which two cyclam or azacrown units are linked together by an anthracene bridge through C(sp2)−N bonds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Highly selective fluorescence detection of hydrogen sulfide by using an anthracene-functionalized cyclam-CuII complex
2013
An anthracene-functionalised cyclam-copper(II) complex for the detection of HS- in aqueous environments has been prepared. This probe displays poor fluorescence but can selectively and sensitively detect HS- anions in water over other anions, biothiols and common oxidants such as H2O2 through remarkably enhanced emission. This turn-on response in the presence of the HS- anion is ascribed to a demetallation reaction that inhibits emission quenching observed in the initial complex as a result of the presence of the paramagnetic Cu2+ centre. Moreover, real-time fluorescence imaging measurements confirm that probe [Cu(1)](2+) can be easily used to detect intracellular HS- at micromolar concentr…