Cations alkylammonium

POMs form by a self-assembly process, typically in an acidic aqueous solution and can be isolated as powder or crystals with counter-cations. Appropriate selection of counter-cations can control the solubility of POMs in various reaction media. For homogeneous system, alkylammonium cations, generally TBA, are selected as counter-cations of POM anions for the dissolution in organic solvents such as acetonitrile, DMF, DMSO and 1,2-dichloroethane. POMs with metal counter-cations such asNa +, K+,Rb+,Cs + and Ag + are not soluble in common organic solvents. 

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The results obtained indicate that the ion-exchanger nature, generally not taken into account when developing ISEs for alkylammonium cations, actually influences strongly the selectivity of such ISEs and should be paid attention to when choosing optimal membrane composition. These data will be useful for finding ways to control the ISEs selectivity by rational choice of the membrane composition. 

Adsorption of aliphatic alcohols and tetra-alkylammonium cations from Na2S04 + HjO solutions on Sb electrodes has been investi-gated.721 724 Splitting of the adsorption-desorption peak into two independent maxima has been found725,726 for cyclohexanol adsorption at an electrochemically polished pc-Sb electrode accordingly, the difference between the [Pg.120]

There are large cations in these cells, e.g., tetra-alkylammonium cations in the organic phase and the interfacial ion exchange involves only so-called critical ions, here X and LX ions are practically not transferred through the organic phase. Both liquid interfaces are reversible with respect to the appropriate anion, X or L. EMF is, in practice, also influenced by the diffusion potential in the organic phase, and in the case of cells of the type in Scheme 11 - by the difference of standard transfer energies of both ions (Section III.A)... 

The arrangement of zinc and sulfur atoms in the Zn4S core is similar to the observed Zn40. Theoretical calculations demonstrated that the compound is a poor model of extended metal chalcogenide semiconductors (ZnS). Octanuclear zinc compounds have also been structurally characterized with this core. In the presence of an alkylammonium cation, a sulfide containing octanuclear zinc species was formed [BzEt3N]2[Zng(S)(SBz)i6].126 The complexes with benzylthiolate... 

Brighteners are applied to cotton by methods similar to direct dyes. By far the most common are triazinyl derivatives of diaminostilbenedisulphonic acid (DAS) of general formula 11.5, where M is an alkali metal, ammonium or alkylammonium cation. Examples of groups Ilj and R2 are shown in Table 11.1. Most suppliers of FBAs market such compounds, often called DAST brighteners. Products in this class have sometimes been marketed because the supplier needed to offer something different for commercial reasons, or to avoid infringing a competitor s patent, rather than for any real technological necessity. 

Except for the PBS/SAP-qC16 (n-hexadecyl tri-n-butyl phosphonium cation modified saponite) system, the degree of degradation is the same for other samples. This indicates that MMT or alkylammonium cations, and at the same time other properties, have no effect on the biodegradability of PBS. The accelerated degradation of PBS matrix in the presence of SAP-qC16 may be due to the presence of alkylpho-sphonium surfactant. This kind of behavior is also observed in the case of PLA/MMT-based nanocomposite systems. 

Theng BKG, Greenland DJ, Quirk JP (1967) Adsorption of alkylammonium cations by montmorillonite. Clay Miner 7 1-17... 

The electrostatic and steric effects can be combined to stabilize nanoparticles in solution. This type of stabilization is generally provided by means of ionic surfactants such as alkylammonium cations (Scheme 9.3). These compounds bear both a polar head group which is able to generate an electrical double layer, and a lipophilic side chain which is able to provide steric repulsion [14, 15]. 

However, styrene and cyclohexene gave complex product mixtures, and 1-octene did not react under the same reaction conditions. Thus, the activity of this catalyst is intrinsically low. Jacobs and co-workers [159,160] applied Veturello s catalyst [PO WCKOj ]3- (tethered on a commercial nitrate-form resin with alkylammonium cations) to the epoxidation of allylic alcohols and terpenes. The regio- and diastereoselectivity of the parent homogeneous catalysts were preserved in the supported catalyst. For bulky alkenes, the reactivity of the POM catalyst was superior to that of Ti-based catalysts with large pore sizes such as Ti-p and Ti-MCM-48. The catalytic activity of the recycled catalyst was completely maintained after several cycles and the filtrate was catalytically inactive, indicating that the observed catalysis is truly heterogeneous in nature. 

One of the earliest reports on the use of dendrimers in catalysis is the unimolecu-lar decarboxylation of 6-nitro-benzisoxazole-3-carboxylate in the presence of a dendrimer comprising ether dendrons which are functionalized at their periphery with tetra-alkylammonium cations (e.g. 20, Scheme 21) [30]. In aqueous media, the quaternary ammonium groupings promote the reactivity of organic anions which presumably bind in high concentration to the polycationic periphery of the dendrimer. The latter species enhances the rate of the bimolecular hydrolysis of p-nitrophenyl diphenyl phosphate catalyzed by o-iodosobenzoate ion. 

Most of the work on chiral recognition in the ground state deals with salts having chiral, primary alkylammonium cations. Another approach is the chiral discrimination between two enantiomeric anions present as counterions in metal-cation complexes (Lehn et al., 1978). Discrimination between enantiomeric transition states will be dealt with in the next section together with non-chiral mimicry of enzymic catalysis. 

Compounds [54] and [55] have been shown to complex group 1 and 2 metal cations and also ammonium and alkylammonium cations by nmr and UV/Vis spectroscopies and also by a number of solid-state X-ray crystallographically determined structures. The quinone moieties in these molecules constitute not only the coordination site but also the redox-active centre. The complexation... 

Miura and Yoshida also investigated the changes in the microstructure of 1100 EW Nafion sulfonate membranes, in alkali, ammonium, and alkylammonium cation forms, that were induced by swelling in ethanol using DSC, dynamic mechanical analysis (DMA), SAXS, and electron probe microanalysis (EPMA). These studies were performed within the context of liquid pervaporation membranes that could potentially be used to separate ethanol from water... 

ILs based on the l-alkyl-3-methyIimidazoIium cation, [C CiIm] , or tetra-alkylammonium cation, [(C )4N]l are among the most popular and commonly studied or used in technological improvements. As for the anions, l7is(trifluoromethylsulfonyl)imide, [Tf2N], and alkylsulfate, [C S04] (n = 1, ll 8), are much superior compared to the more commonly investigated hexafluorophosphate, [PFg] , and tetrafluoroborate, [BF4], being hydrolytically stable and less viscous. Comparing the results of the solubility of ILs in typical solvents from different publications, it can be concluded that the miscibility gap in the liquid phase increases in the order alcohol < aromatic hydrocarbon < cycloalkane < n-alkane [50-54,66,78,79,95-100,127-136]. 

H and 13C NMR have also been widely used to study the binding of alkylammonium cations to crown ethers. The shift in substrate proton resonances can give detailed information of the preferred structure of the complex. This is particularly important in the study of chiral recognition by asymmetric receptors (79CSR85) (Section 5.21.3.2.2) and also the development of bioorganic models and catalysts (Section 5.21.5.1.1). 

Recently a number of coreceptors containing two potential RNH3+ binding sites have been prepared, e.g. (19). These systems can complex either two alkylammonium cations (20) or one alkyldiammonium dication (21) inside the cavity (80TL941,81CC990,82CC557) and hold considerable potential as models of enzyme binding sites (Section 5.21.5.1.1). 

The ability of cyclic ethers to complex biologically important alkylammonium cations makes the choice of crown ethers as enzyme binding site models a natural one. In recent years a number of molecules containing both a crown ether-based substrate binding site and a potentially reactive group have been prepared as models for enzyme active sites (79PAC979, B-82MI52100). 

Apart from alkali metal cations [18]crown-6 derivatives can complex and transport primary alkylammonium cations across chloroform membranes <80JCR(S)136). This process is particularly relevant as many amines (e.g. amphetamine) are physiologically important species. 

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