Search results for "cyclic"
showing 10 items of 2439 documents
Thermal behaviour and electrochemical properties of bis(trifluoromethanesulfonyl)amide and dodecatungstosilicate viologen dimers
2012
We report the synthesis and characterization of dimeric viologen salts (1',1''-(alkane-1,n-diyl)bis(1-ethyl-4,4'-bipyridinium) with n = 4-10) with bis(trifluoromethanesulfonyl)amide (bistriflimide, Tf(2)N(-)) as a counteranion. For n = 4, 5 and 6, and for the nonylviologen cation (1,1'-dinonyl-4,4'-bipyridinium) we also prepared salts with the totally inorganic dodecatungstosilicate anion, SiW(12)O(40)(4-), featuring a poly-charged surface and nanosized dimensions. The materials have been characterized by means of calorimetric techniques, X-ray diffraction and solid state NMR and a comparison is made with analogous monomeric viologen salts exhibiting smectic mesophases. A strong odd-even ef…
Stabilizing Lead Cathodes with Diammonium Salt Additives in the Deoxygenation of Aromatic Amides
2014
Lead is efficiently protected against cathodic corrosion by the addition of diammonium salts in the electrolyte. The cationic coating of the cathode allows the efficient electroreduction of benzamides to benzylamines. The electrochemical deoxygenation of the amide is achieved without the use of oxophilic agents or sacrificial anodes. The surface of the lead cathode stays smooth and the cathode can be reused for multiple runs, providing <2.5 ppm of the crude product. Cyclic voltammetry studies reveal a shift in the onset potential of the hydrogen evolution reaction by −157 mV.
Electrosynthesis of Poly(alanine)-Like Peptides in Concentrated Alanine Based Electrolytes, Characterization Coupled to DFT Study and Application to …
2014
The anodic oxidation of concentrated l-alanine on smooth electrodes such as platinum and glassy carbon electrodes was studied. Contrary to the previous studies performed up to now with diluted l-alanine, the electrochemical process generated here results in a completely different situation. The oxidation on smooth platinum was carried out by electrochemical quartz crystal microbalance (EQCM) coupled to cyclic voltammetry technique. The effects of concentration, scan rate, and pH (zwitterion at pH = 6 and alkaline media at pH = 13) on potential values were examined. Glassy carbon and smooth gold electrodes showed the same behavior as on smooth platinum electrode. Spectroscopic analysis such …
3D-transition metal mono-substituted Keggin polyoxotungstate with an antenna molecule: synthesis, structure and characterization
2008
Three new organic-inorganic hybrid complexes based on 3d-transition metal monosubstituted Keggin polyoxometalates (POMs) with imidazole (Im) as pendant ligands, formulated as (HIm)(6-)[SiW11O39NiIm]0.8[SiW11O39Ni(H2O)]0.2.7H2O (1), (Im)4Na6[SiW11O39MnIm]0.69[SiW11O39Mn(H2O)]0.31.7.5H2O (2) and (HIm)6[SiW11O39CoIm]0.63[SiW11O39Co(H2O)]0.37.7H2O (3), have been synthesized and characterized by IR spectroscopy, UV-visible spectroscopy, elemental analysis, TG analysis, cyclic voltammetry, magnetic properties, EPR and single-crystal/powder X-ray diffraction. The structural analyses indicate that the 3d metal atoms are incorporated into the vacancy of the alpha-[SiW11O39](8-) (SiW11). Complexes 1-…
Electrochemistry of copper complexes with polyaza[n]paracyclophanes. Influence of ATP as an exogen ligand on the relative stability of the Cu(II) and…
2000
Abstract Interaction of Cu 2+ with the macrocycle 2,6,9,13-tetraaza[14]paracyclophane (L) and ATP has been followed by pH-metric titration, cyclic voltammetry and differential pulse voltammetry (DPV). Mixed adduct species with various degrees of protonation were found to be stable for pH>4. In neutral and alkaline media reduction of mixed complexes occurs in a two-electron quasi-reversible step in contrast with binary Cu 2+ L complexes which display two successive one-electron couples. The potentiometric and voltammetric data suggest that in ternary adducts ATP binds to Cu 2+ ions through the phosphate chain and one N-site of the adenine ring system.
An Iron-Based Molecular Redox Switch as a Model for Iron Release from Enterobactin via the Salicylate Binding Mode
2001
The iron release mechanism from protonated ferric enterobactin [Fe(III)(enterobactinH(3))] via the salicylate binding mode was probed. For this purpose, a tripodal dodecadentate ligand incorporating three salicylamide (OO) and three bipyridine (NN) binding sites was synthesized as well as iron complexes thereof. It was shown that a ferric ion coordinates selectively to the hard salicylamides and a ferrous ion binds to the softer bipyridines. Upon reduction or oxidation, the iron translocates reversibly and intramolecularly from one site to the other, thus displaying switchlike properties. Both states were characterized by cyclic voltammetry and visible and Mössbauer spectroscopy. The Mössba…
Extending Limits of Chlorine Kinetic Isotope Effects
2012
Chlorine kinetic isotope effects exceeding semiclassical limits were observed in enzyme-catalyzed reactions, but their source has not been yet identified. Herein we show that unusually large chlorine kinetic isotope effects are associated with reactions in which chlorine is the central atom that is being passed between two heavy atoms. The origin of these large values is the ratio of imaginary frequencies for light-to-heavy species (the so-called temperature-independent factor).
Selective, Sensitive, and Rapid Analysis with Lateral-Flow Assays Based on Antibody-Gated Dye-Delivery Systems: The Example of Triacetone Triperoxide
2013
[EN] Antibodygated MSNs that are loaded with a rhodamine dye and that can be used for the determination of the presence of peroxide-based explosive TATP with a lateral-flow fluorescence reader have been designed and prepared, thereby allowing for detection limits in the lower ppb range. The mechanism of the detection relies on a displacement of the antibody from the surface of the hybrid material because of highly affine antibody-TATP interactions, which release a much larger number of entrapped dye molecules from the pores than antibodies are displaced. The high selectivity of the antibody is retained in the gated material, thus allowing for a remarkable discrimination against H2O2. System…
Über die Synthese von o-Acylamino-β-dimethylaminopropiophenonen Mitt.: Aminomethylierung von 2-Nitro-5-methoxy-und 2-Nitro-5-benzyloxyacetophenon
1971
Der von Makino und Takahashi sowie Joh als 2-Nitro-5-methoxy-β-dimethylamino-propiophenon bezeichnete Korper wurde als 2-Nitro-5-methoxy-α-dimethylaminomethyl-acrylophenon identifiziert. Nach einer fruher beschriebenen Methode zur Darstellung von 2-Nitro-β-dimethylamino-propiophenon war es moglich, 2-Nitro-5-methoxy- und 2-Nitro-5-benzyloxy-acetophenon normal zu aminomethylieren. –Die Synthese von 2-Amino-5-methoxy-, 2-Amino-5-benzyloxy- und 2-Amino-5-hydroxy-β-dimethylamino-propiophenon sowie ihrer Acetylderivate wird beschrieben. Synthesis of o-Acylamino-β-dimethylamino-propiophenones The compound synthetized by Makino and Takahashi and by Joh described as 2-nitro-5-methoxy-β-dimethylamin…
Using theozymes for designing transition-state analogs for the intramolecular aldol reaction of δ-diketones
2001
Two theozymes for the intramolecular aldol reaction of δ-diketones have been studied using ab initio methods. The presence of both acid/base residues favors several steps of the aldol reaction. The appropriate positioning of these residues can accelerate one of two diastereromeric reaction pathways, the catalyzed aldol reaction being highly stereoselective. Analysis of the geometrical parameters, charge distribution, and the shape of molecular electrostatic potential for the corresponding acid/base catalyzed transition structure allows us to design adequate transition-state analogs to favor a reactive channel of this intramolecular aldol reaction. © 2001 John Wiley & Sons, Inc. Int J Quant …