Ion coupling

The halogen displacement polymerization proceeds by a combination of the redistribution steps described for oxidative coupling polymerization and a sequence in which a phenoxide ion couples with a phenoxy radical (eq. 11) and then expels a bromide ion. The resultant phenoxy radical can couple with another phenoxide in a manner that is analogous to equation 11 or it can redistribute with other aryloxy radicals in a process analogous to equations 7 and 8. 

Diazo coupling is expected to occur only with highly reactive systems, and experiment bears this out. Diazonium ions couple with the anions of N-unsubstituted imidazoles at the 2-position (e.g. 125 yields 126) and with indazoles (127) in the 3-position. In general, other azoles react only when they contain an amino, hydroxyl, or potential hydroxyl group, e.g. the 4-hydroxypyrazole (128), the triazolinone (129) and the thiazolidinedione (130) (all these reactions occur on the corresponding anions). 

Samal et al. [25] reported that Ce(IV) ion coupled with an amide, such as thioacetamide, succinamide, acetamide, and formamide, could initiate acrylonitrile (AN) polymerization in aqueous solution. Feng et al. [3] for the first time thoroughly investigated the structural effect of amide on AAM polymerization using Ce(IV) ion, ceric ammonium nitrate (CAN) as an initiator. They found that only acetanilide (AA) and formanilide (FA) promote the polymerization and remarkably enhance Rp. The others such as formamide, N,N-dimethylformamide (DMF), N-butylacetamide, and N-cyclohexylacetamide only slightly affect the rate of polymerization. This can be shown by the relative rate (/ r), i.e., the rate of AAM polymerization initiated with ceric ion-amide divided by the rate of polymerization initiated with ceric ion alone. Rr for CAN-anilide system is approximately 2.5, and the others range from 1.04-1.11. 

The gel permeation chromatogram shown in Fig. 6 illustrates the purity of a block copolymer obtained by ion coupling. It is seen that about 5% of uncoupled block copolymer contaminates a triblock copolymer of narrow molecular weight distribution. The synthesis of star block polymers owes its recent development to the use of new coupling agents412. ... 

Ion coupling of anionic and cationic living polymers is an interesting procedure for the synthesis of a well-defined block copolymer. Attempted coupling of the polystyrene anion with the poly-THF cation initiated by triethyloxonium tetrafluoro-borate yielded a block copolymer mixed with homopolymers394. The block ef-... 

Fig. 7. Effect of the molar ratio of initiators on the Mn of the block copolymer (THF-MS n produced by ion coupling ---------observed ---------calculated...

Term wavefunctions describe the behaviour of several electrons in a free ion coupled together by the electrostatic Coulomb interactions. The angular parts of term wavefunctions are determined by the theory of angular momentum as are the angular parts of one-electron wavefunctions. In particular, the angular distributions of the electron densities of many-electron wavefunctions are intimately related to those for orbitals with the same orbital angular momentum quantum number that is. 

Independently of this, chronoabsorptiometric measurements by Genies et al. have proved that PPy films grow in timer linear to t and not to j/t. In the opinion of the authors this implies that the rate-determining step during film growth is a radical ion coupling and not the diffusion of the uncharged monomer towards the electrode surface. The attested phenomenon that PPy polymerizes... 

Precellular solute ionization dictates membrane permeability dependence on mucosal pH. Therefore, lumenal or cellular events that affect mucosal microclimate pH may alter the membrane transport of ionizable solutes. The mucosal microclimate pH is defined by a region in the neighborhood of the mucosal membrane in which pH is lower than in the lumenal fluid. This is the result of proton secretion by the enterocytes, for which outward diffusion is slowed by intestinal mucus. (In fact, mucosal secretion of any ion coupled with mucus-restricted diffusion will provide an ionic microclimate.) Important differences in solute transport between experimental systems may be due to differences in intestinal ions and mucus secretion. It might be anticipated that microclimate pH effects would be less pronounced in epithelial cell culture (devoid of goblet cells) transport studies than in whole intestinal tissue. 

The laccases, classed as polyphenol oxidases, catalyze the oxidation of diphenols, polyamines, as well as some inorganic ions, coupled to the four-electron reduction of oxygen to water see Fig. 12.4 for the proposed catalytic cycle. Due to this broad specificity, and the recognition that this specificity can be extended by the use of redox mediators [27], laccases show promise in a range of applications [28], from biosensors [29-32], biobleaching [27, 33-35] or biodegradation [36], to biocatalytic fuel cells [1-3, 18, 26, 37-42]. 

Kanner, B. I. and Bendahan, A. (1982) Binding order of substrates to the sodium and potassium ion coupled L-glutamic acid transporter from rat brain. Biochemistry 21,6327-6330. 

Williams, K. A. (2000) Three-dimensional structure of the ion-coupled transport protein NhaA. Nature 403,112-115. 

Eukaryotic ABC transport system Phosphotransferase system (PTS) Ion-coupled transport system Signal Transduction Two-component system Bacterial chemotaxis MAPK signaling pathway Second messenger signaling pathway Ligand-Receptor Interaction G-protein-coupled receptors Ion-channel-linked receptors Cytokine receptors Molecular Assembly Ribosome assembly Flagellar assembly Enzyme assembly... 

Auger transitions are due to the transfer of a solid electron to the ion, coupled with the excitation of a second electron into an Auger state of energy in the solid. Thus, the TDAN Hamiltonian is augmented by the terms ... 

Let us now imagine a redox process involving two metal-ion couples ... 

Metal/Metal-Ion Couple Electrode Reaction Standard Value (V)... 

Electrodimerization of activated alkenes in aprotic solvents occurs by radical-ion, radical-ion coupling. There is ample evidence for steric inhibition to this process. In contrast to the low reactivity of 11,4-methylbenzabnalononitriIe radical-ion dimeiises with a rate constant of 5.8 x 10 M s in dimethylformamide containing tetraalkylammonium ions [48]. Dimethyl maleate radical-anion diraerises faster than dimethylftimarate radical-anion by a factor of lO in dimethylformamide [49]. 

Evidence in support of a carbonium ion type of mechanism for low temperature polymerization was also obtained in an investigation of the kinetics of the homogeneous liquid phase polymerization of propene in the presence of aluminum bromide and hydrogen bromide at about —78° (Fontana and Kidder, 89). The rate of reaction is approximately proportional to the concentration of the promoter, no polymerization occurring in its absence. During the main portion of the reaction, the rate is independent of the monomer concentration toward the end, it decreases, due apparently to the low-concentration of the monomer, addition of more olefin resulting in an increase in the rate. It was concluded that the reaction involves an active complex, which may be regarded as a carbonium ion coupled with an anion ... 

Mecfianism of Action A skeletal muscle relaxant that reduces muscle contraction by interfering with release of calcium ion. Reduces calcium ion concenfrafion. Therapeutic Effect Dissociafes excitation-conf racf ion coupling. Interferes wifh catabolic process associated with malignant hyperthermic crisis. 

As in other transition metal oxides such as NiO, the spins on the transition metal ions are coupled via the oxide ions. The Mn " ions couple antiferromagnetically with each other via superexchange as in NiO. The coupling of the Mn " ions varies and can be ferro- or antiferro-magnetic. Mn " ions couple to Mn " ions in a process known as double exchange. In this process, a simultaneous hop of an electron from Mn " to an 0 Ip orbital and from the 0 2p orbital to an Mn ion takes place. 

The process at more negative potentials must correspond to the reduction of Fe + ions coupled with the insertion of K+ ions from the electrolyte ... 

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