Anion selectivity

Another example of vims clearance is for IgM human antibodies derived from human B lymphocyte cell lines where the steps are precipitation, size exclusion using nucleases, and anion-exchange chromatography (24). A second sequence consists of cation-exchange, hydroxylapatite, and immunoaffinity chromatographies. Each three-step sequence utilizes steps based on different properties. The first sequence employs solubiUty, size, and anion selectivity the second sequence is based on cation selectivity, adsorption, and selective recognition based on an anti-u chain IgG (24). 

The anion-selective (AX) membranes (Eig. 2b) also consist of cross-linked polystyrene but have positively charged quaternary ammonium groups chemically bonded to most of the phenyl groups in the polystyrene instead of the negatively charged sulfonates. In this case the counterions are negatively... 

Silver alone on a support does not give rise to a good catalyst (150). However, addition of minor amounts of promoter enhance the activity and the selectivity of the catalyst, and improve its long-term stabiHty. Excess addition lowers the catalyst performance (151,152). Promoter formulations have been studied extensively in the chemical industry. The most commonly used promoters are alkaline-earth metals, such as calcium or barium, and alkaH metals such as cesium, mbidium, or potassium (153). Using these metals in conjunction with various counter anions, selectivities as high as 82—87% were reported. Precise information on commercial catalyst promoter formulations is proprietary (154—156). 

Reductive amination ol aldehydes or ketones by cyanoborohydride (or tnacetoxyborohydride) anion Selective reduction of carbonyls to alcohol, oximes to N alkylhydroxylarmnes, enamines to amines... 

C — Cation Selective Membrane A — Anion Selective Membrane... 

Transition metal complexes with 2,2 -bipyridine ligands in anion-selective recognition and optical/electrochemical sensing 96CC689. 

The transmembrane potential derived from a concentration gradient is calculable by means of the Nemst equation. If K+ were the only permeable ion then the membrane potential would be given by Eq. 1. With an ion activity (concentration) gradient for K+ of 10 1 from one side to the other of the membrane at 20 °C, the membrane potential that develops on addition of Valinomycin approaches a limiting value of 58 mV87). This is what is calculated from Eq. 1 and indicates that cation over anion selectivity is essentially total. As the conformation of Valinomycin in nonpolar solvents in the absence of cation is similar to that of the cation complex 105), it is quite understandable that anions have no location for interaction. One could with the Valinomycin structure construct a conformation in which a polar core were formed with six peptide N—H moieties directed inward in place of the C—O moieties but... 

Dutzler R, Campbell EB, Cadene M et al (2002) X-ray structure of the C1C chloride channel at 3.0 A resolution molecular basis of anion selectivity. Nature 415 287—294... 

FIGURE 5-14 Structures of some chemical species useful for designing anion-selective electrodes (a) Mn(III) porphyrin (b) vitamin Bi2 derivative (c) tri-n-octyltin chloride (d) lipophilic polyamine macrocyclic compound. 

Anion selective electrodes, 156, 158 Anodic shipping voltammetry, 76 Antibody, 183 Antimony, 85... 

Figure 6. Bipolar precipitates consisting of an inner anion-selective layer and an outer cation-selective layer.19 When the electrode is polarized to the more noble side, protons and chloride ions are kept from permeating through the film, so that anodic dissolution of the substrate metal is blocked. (Reproduced from N. Sato, Corrosion, 45 354, 1989, Fig. 24 with permission of NACE International.)...

Metallocarboranes and metalloboranes, discussed in 6.5.4, may be prepared from metal halides and carborane anions. Selected examples of complexes formed by thermal—or otherwise—induced polyhedral rearrangements of existing metallocarboranes are given in a few equations, and some other individual compounds are listed in tables. 

Miscellaneous Reactions Reactions of Phosphonate Anions Selected Applications in Synthesis... 

The regions involved in the cation vs. anion selectivity are not well defined, as they are for the nAChR. However, in contrast to the nAChR, the residues within the pore contribute to the selectivity, as receptors formed from fully edited AMPA or kainate receptors (e.g., having an R at the Q/R site) are also permeable to chloride. 

Nystatin applied to both sides of a bilayer produces channels which are anion selective, whereas application to one side gives cation selectivity. This remarkable difference is in accord with the double channel having identical head ends, whereas the single channel has dissimilar ends 199). 

Tan S.S.S., Hauser P.C., Chaniotakis N.A., Suter G., Simon W., Anion-selective optical sensors based on a coextraction of anion-proton pairs into a solvent-polymeric membrane, Chimia 1989 43 257. 

Wang E., Meyerhoff M.E., Anion selective optical sensing with metalloporphyrin-doped polymeric films, Anal. Chim. Acta 1993, 283 673. 

Ionophore-based solvent polymeric membranes were used as sensing layers for the development of LAPS selective for lithium [70], potassium and calcium ions [71]. Anion-selective LAPS for the determination of nitrate and sulfate ions were described [72],... 

Y. Mourzina, Y. Ermolenko, T. Yoshinobu, Y. Vlasov, H. lwasaki, and MJ. Schoning, Anion-selective light-addressable potentiometric sensors (LAPS) for the determination of nitrate and sulphate ions. Sens Actuators, B 91, 32—38 (2003). 

A. Malon, A. Radu, W. Qin, Y. Qin, A. Ceresa, M. Maj-Zurawska, E. Bakker, and E. Pretsch, Improving the detection limit of anion-selective electrodes an iodide-selective membrane with a nanomolar detection limit. Anal. Chem. 75, 3865-3871 (2003). 

Fig. 30. Two compartment (A) and three-compartment (B) cell for salt splitting [135] A.S.M. = anion selective membrane C.S.M. = cation selective membrane...

A-S = Anion-selective membrane C-S = Cation-selective membrane... 

Typically, functional porins are homotrimers, which assemble from monomers and then integrate into the outer membrane. The general porins, water-filled diffusion pores, allow the passage of hydrophilic molecules up to a size of approximately 600 Daltons. They do not show particular substrate specificity, but display some selectivity for either anions or cations, and some discrimination with respect to the size of the solutes. The first published crystal structure of a bacterial porin was that of R. capsulatus [48]. Together with the atomic structures of two proteins from E. coli, the phosphate limitation-induced anion-selective PhoE porin and the osmotically regulated cation-selective OmpF porin, a common scheme was found [49]. Each monomer consists of 16 (3-strands spanning the outer membrane and forming a barrel-like structure. 

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