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Ammonium Moieties (ammonium + moiety)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Electrochemically-Induced Deposition of Amine-Functionalized Silica Films on Gold Electrodes and Application to Cu(II) Detection in (Hydro)Alcoholic Medium

ELECTROANALYSIS, Issue 19 2005
Alain Walcarius
Abstract Well-adherent amine-functionalized porous silica films have been deposited on gold electrodes by combining the self-assembly technology, the sol,gel process, and the electrochemical modulation of pH at the electrode/solution interface. A partial self-assembled monolayer of mercaptopropyl-trimethoxysilane (MPTMS) was first formed on disposable gold electrodes from recordable CDs (Au-CDtrodes). The so pretreated MPTMS-Au-CDtrodes were immersed in a stable sol solution (pH,3) containing (3-aminopropyl)-triethoxysilane (APTES) and tetraethoxysilane (TEOS). Polycondensation of the APTES and TEOS precursors was then achieved by applying a negative potential for a given period of time to generate a local pH increase at the electrode/solution interface and promote the deposition of the amine functionalized silica film adhering well to the electrode surface owing to the MPTMS monolayer acting somewhat as a "molecular glue". Various parameters affecting the electrodeposition process have been studied and the film permeability to redox probes in solution was characterized by cyclic voltammetry. The amine-functionalized silica film electrodes were then applied to the preconcentration of copper(II) species prior to their electrochemical detection by anodic stripping differential pulse voltammetry. Getting high sensitivity has however required the application of an electrochemical pre-activation step as the majority of the organo-functional groups were in the form of ammonium moieties (because the film was prepared from an acidic sol). This was achieved by applying a sufficiently negative potential to the electrode surface to reduce protons and increase consequently the amine-to-ammonium ratio within the film and, thus, the efficiency of the precocentration process. The resulting device was then optimized for copper(II) determination in hydroalcoholic medium, giving rise to a linear response in the 0.1,10,,M concentration range. [source]

Polystyrene nanocomposite materials by in situ polymerization into montmorillonite,vinyl monomer interlayers

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007
Ahmed Akelah
Abstract A different series of new polystyrene,clay nanocomposites have been prepared by grafting polymerization of styrene with vinyl-montmorillonite (MMT) clay. The synthesis was achieved through two steps. The first step is the modification of clay with the vinyl monomers, such as N,N -dimethyl- n -octadecyl-4-vinylbenzyl-ammonium chloride, n -octadecyl-4-vinylbenzyl-ammonium chloride, triphenyl-4-vinylbenzyl-phosphonium chloride, and tri- n -butyl-4-vinylbenzyl-phosphonium chloride. The second step is the polymerization of styrene with different ratios of vinyl-MMT clay. The materials produced were characterized by different physical and chemical methods: (1) IR spectra, confirming the intercalation of the vinyl-cation within the clay interlayers; (2) thermogravimetric analysis (TGA), showing higher thermal stability for PS,nanocomposites than polystyrene (PS) and higher thermal stability of nanocomposites with of phosphonium moieties than nanocomposites with ammonium moieties; (3) swelling measurements in different organic solvents, showing that the swelling degree in hydrophobic solvents increases as the clay ratio decreases; (4) X-ray diffraction (XRD), illustrating that the nanocomposites were exfoliated at up to a 25 wt % of organoclay content; and (5) scanning electron microscopy (SEM), showing a complete dispersion of PS into clay galleries. Also, transmission electron microscopy (TEM) showed nanosize spherical particles of , 150,400 nm appearing in the images. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3739,3750, 2007 [source]

Synthesis of an Inherently Chiral Calix[4]arene Amino Acid and Its Derivatives: Their Application to Asymmetric Reactions as Organocatalysts

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2009
Seiji Shirakawa
Abstract The synthesis of an inherently chiral calix[4]arene amino acid as a chiral building block has been achieved in order for subsequent transformation to various types of inherently chiral calix[4]arenes. The optically pure, inherently chiral calix[4]arene amino acids were prepared by the separation of a diastereomeric mixture of calix[4]arene amino acid derivatives bearing a (R)-BINOL moiety. The separated optically pure calix[4]arene amino acid derivatives with a (R)-BINOL moiety were easily transformed to novel inherently chiral calix[4]arenes containing an amino alcohol structure or a quaternary ammonium moiety. These optically pure chiral calix[4]arenes were applied to asymmetric reactions as organocatalysts.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Multirotations of (Anilinium)([18]Crown-6) Supramolecular Cation Structure in Magnetic Salt of [Ni(dmit)2],

CHEMISTRY - AN ASIAN JOURNAL, Issue 9 2007
Sadafumi Nishihara Dr.
Abstract A solid-state dynamic supramolecular structure consisting of (anilinium)([18]crown-6) was arranged as the cation in a salt of [Ni(dmit)2], (dmit=2-thioxo-1,3-dithiole-4,5-dithiolate). With the ammonium moiety of anilinium located within the cavity of [18]crown-6, a hydrogen-bonded supramolecular structure is formed, with an orthogonal arrangement between the ,,plane of anilinium and the mean O6 plane of [18]crown-6. In this supramolecular cation, both anilinium and [18]crown-6 act as dynamic units with different rotational modes in the solid state. The uniform stacks of cations form an antiparallel arrangement, thus producing a layer structure. Sufficient space for the 180° flip-flop motion of the phenyl ring and the rotation of [18]crown-6 was observed in the cation layer. Thermally activated 180° flip-flop motions, with a frequency of 6,MHz at room temperature and an activation energy of 31,kJ,mol,1, were confirmed by temperature-dependent 2H,NMR spectra of ([D5]anilinium)-([18]crown-6)[Ni(dmit)2]. A double-minimum potential for the molecular rotation of anilinium, with a barrier of approximately 40,kJ,mol,1, was indicated by ab,initio calculations. The wide-line 1H,NMR spectra indicated a thermally activated rotation of [18]crown-6 at temperatures above 250,K. Therefore, multiple molecular motions of the 180° flip-flop motion of the phenyl ring and the rotation of [18]crown-6 occur simultaneously in the solid state. The temperature-dependent dielectric constants revealed that the molecular motion of [18]crown-6, other than the flip-flop motion, dominates the dielectric response in the measured temperature and frequency range. [source]