نتایج جستجو برای: quaternary ammonium compounds
تعداد نتایج: 259839 فیلتر نتایج به سال:
The microwave synthesis of several quaternary ammonium salts is described. The synthesis provides comparable or better yields than published methods with reduced reaction times and in the absence of solvent.
Quaternary ammonium blockers inhibit many voltage-activated potassium (K+) channels from the intracellular side. When applied to Drosophila Shaker potassium channels expressed in mammalian cells, these rapidly reversible blockers produced use-dependent inhibition through an unusual mechanism--they promoted an intrinsic conformational change known as C-type inactivation, from which recovery is s...
Polymeric maleimido-quaternary ammonium (QA) compounds have been shown to function as molecular tape measures when covalently tethered to external cysteine residues of a Shaker K(+) channel (Blaustein R.O., P.A. Cole, C. Williams, and C. Miller. 2000. Nat. Struct. Biol. 7:309-311). For sufficiently long compounds, the cysteine-maleimide tethering reaction creates a high concentration, at the ch...
A new series of ester functionalized cationic gemini surfactants having different cationic headgroups (i.e. piperidinium, pyrrolidinium, morpholinium and quaternary ammonium) have been synthesized and characterized using NMR and Mass spectroscopy. These new gemini surfactants were investigated for their micellization and viscosity properties using surface tension, conductivity, fluorescence and...
Emulsions comprising a dual-surfactant system of a long-chain amidoamine derivative and a quaternary ammonium salt developed an iridescent color at a specific temperature region. The emulsions underwent phase inversion on heating from an O/W emulsion to a W/O emulsion, passing through a periodical lamellar structure which developed a characteristic interference color. Interestingly, the color a...
An efficient C-O, C-S and C-C bond-forming sequence leads to functionalised compounds bearing sulfur-substituted quaternary carbons. Ynamides are employed as diazo-equivalents to access the [2,3]-sigmatropic rearrangements of allyl sulfonium ylides by a three-component chemoselective oxidation and intermolecular ylide formation.
Late Quaternary megafauna extinctions impoverished mammalian diversity worldwide. The causes of these extinctions in Australia are most controversial but essential to resolve, because this continent-wide event presaged similar losses that occurred thousands of years later on other continents. Here we apply a rigorous metadata analysis and new ensemble-hindcasting approach to 659 Australian mega...
Microfossils present in Quaternary micrites from Serra da Bodoquena, Mato Grosso do Sul State, Brazil, are here described for the first time. The studied taxa are: a) ostracods: Candona sp., Candonopsis sp., Cyclocypris sp., Cypria sp., Cypridopsis sp., Notodromas sp., Ilyocypris sp., Cyprideis sp., Wolburgiopsis cf. chinamuertensis (Musacchio 1970), Darwinula sp. and 5 morphotypes; b) microgas...
The enantiomeric enrichment of racemic 1-benzylated Reissert compounds under organocatalytic biphasic conditions is presented. The enrichment is the consequence of an asymmetric destruction of the racemic compounds resulting in the formation of the corresponding 1-benzylated isoquinolines. The highest selectivity has been achieved using quaternary cinchona alkaloids as phase-transfer catalysts....
Mycobacterium tuberculosis has enjoyed the distinction, among the nonspore bearing organisms, of being one of the most resistant to chemical disinfection. Quaternary ammonium compounds, widely used as effective germicides against gram positive organisms, have generally proved to be without effect on the tubercle bacillus (Lawrence and Grover, 1951; Smith et al., 1950). Recently, it has been rep...
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