Micellar cation exchange

Other studies have been concerned with trapping the C0-O2 monomeric complex in an environment where dimerisation is impossible. Nakamoto and co-workers have published a series of papers on Co(II) complexes trapped in 02-doped argon matrices " and a report has appeared of Co " complexed by a nitrogen macrocycle in a micellar phase . Co complexed by ethylenediamine in zeolite cages forms an 1 mononuclear complex at low concentration but j/ dinuclear complexes are observed at higher concentrations. There is some evidence for formation of free Of ion Similar results were found for Go(II) ethylenediamine complexes absorbed on a cation exchange resin ... 

Cation Exchange, Surfactant Precipitation, and Adsorption in Micellar Flooding... 

More recently Smith (8), and Hill and Lake (14) studied cation exchange as it affected the behavior of micellar slugs in typical reservoir cores. These authors found that cation exchange in cores was quite complex, but that calcium and magnesium could, for all practical purposes, be treated as a single species. Moreover, they found that pre-flushing of a core reduced surfactant losses in most cases. Hill and Lake found that surfactant adsorption in cores was reduced by dissolution of carbonate minerals and by converting the clays to their sodium form. 

K. Mori, Cation-Exchange Chromatography of Catecholamines with Micellar Mobile Phases, J Pharmacobio-Dyn., 7 5 (1984). 

The protonation of the triplet jtjt state of 3-bromonitrobenzene is shown to be responsible for the acid-catalysed promotion of halogen exchange which follows a S y23Ar mechanism26 (equation 23). Cationic micellar effects on the nucleophilic aromatic substitution of nitroaryl ethers by bromide and hydroxide ions have also been studied27. The quantum efficiency is dependent on the chain length of the micelle. The involvement of counter ion exchanges at the surface of ionic micelles is proposed to influence the composition of the Stem-layer. 

Surface-active agents used as adjuvants in pharmaceutical preparations to improve drug dissolution may affect the stability of /3-lactams. Thus, the presence of micelles of cetyl(trimethyl)ammonium bromide (CTAB) enhanced up to 50-fold the rate of alkaline hydrolysis of penicillins [140]. In the case of cephalosporins, micelle-promoted catalysis of the intramolecular degradation process (see Sect 5.2.2) was also observed [85][141], It has been proposed that the negatively charged penicillins and cephalosporins are attracted by the cationic micelles. This attraction increases substrate concentration in the micellar phase, in turn accelerating the rate of HO- ion attack. Ion exchange at the micellar surface and electrostatic stabilization of the transition state may also contribute to the increased rate [142][143],... 

For a surface active betaine ester the rate of alkaline hydrolysis shows significant concentration dependence. Due to a locally elevated concentration of hydroxyl ions at the cationic micellar surface, i.e., a locally increased pH in the micellar pseudophase, the reaction rate can be substantially higher when the substance is present at a concentration above the critical micelle concentration compared to the rate observed for a unimeric surfactant or a non-surface active betaine ester under the same conditions. This behavior, which is illustrated in Fig. 10, is an example of micellar catalysis. The decrease in reaction rate observed at higher concentrations for the C12-C18 1 compounds is a consequence of competition between the reactive hydroxyl ions and the inert surfactant counterions at the micellar surface. This effect is in line with the essential features of the pseudophase ion-exchange model of micellar catalysis [29,31]. 

Electron transfer can be accomplished by quenching of a micelle trapped chromophore by ions capable of ion pairing with the micelle surface. For example, excited N-methylphenothiazine in sodium dodecylsulfate (SDS) micelles can exchange electrons with Cu(II). The photogenerated Cu(I) is rapidly displaced by Cu(II) from the aqueous phase so that intramicellar recombination is averted, Fig. 5 (266). Similarly, the quantum yield for formation of the pyrene radical cation via electron transfer to Cu(II) increases with micellar complexation from 0.25 at 0.05 M SDS to 0.60 at 0.8 M SDS (267). The electron transfer quenching of triplet thionine by aniline is also accelerated in reverse micelles by this mechanism (268). 

An example of exchange with an oxygen-containing functional group is given which utilises a micellar system. Cationic micelles of cetyltrimethylammonium chloride and bromide, and tetradecyltrimethylammonium chloride and bromide, accelerate the reaction of 2-(4-nitro-phenoxy)quinoxaline with hydroxide ion to give quinoxalin-2(l/f)-one. ... 

T. Okada, Interpretation of retention behavior of transition-metal cations in micellar chromatography using an ion-exchange model, Anal. Chem. 64 589 (1992). 

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