Lipophilic ions neutral ionophores

Lipophilic, electrically neutral ionophores, also called ion carriers because of their... 

M 644.9, m 156-158". Purified by chromatography on a Kieselgel column and eluted with CH2Cl2-EtOAc (5 1), and recryst from EtOH-Me2CO as colourless crystals. It is an electrically neutral ionophore with high selectivity for Ba " ions and with high lipophilicity. [Chem Ber 118 1071 1985.]... 

Fig. 2 The model of ion extraction/ion exchange for an optode based on a neutral ionophore and a lipophilic cationic dye in relation to the ion-optode response mechanism i+ cation to be extracted, H+ proton, S neutral ionophore, R lipophilic cationic additive, D color-changeable dye. The subscripts o and w represent the organic phase and the water phase, respectively)...

Liquid membrane electrodes are three (or four) component membrane based devices with positively charged, negatively charged, or electrically neutral ionophores. The main component of the liquid membrane is the ionophore, or mobile carrier—a compound with binding properties to different ions and responsible for the ion selectivity. The carriers are incorporated into membrane matrices, most commonly into plasticized poly(vinyl chloride). Liquid membranes often contain lipophilic salt additives also to enhance the permselectivity of hte membrane. 

Ion determination can essentially be carried out by detection of the protonation/ deprotonation process of a single lipophilic anionic dye in the organic phase. Therefore, no special color-responsive chelating reagents are required for the measurement of another kind of analyte ion. One only need to alter the neutral ionophore for different ion-selective ionophores. From the viewpoint of optical instrumentation, this merit is... 

Table 2 Optimum concentration ratio of lipophilic anionic sites to neutral ionophore giving optimal selectivity for the analyte ion over...

Tab. 3 Optimum concentration ratio of lipophilic anionic sites to neutral ionophore, giving highest selectivity for the analyte ion over an interfering ion. The optimum ratios are dependent on the charges of both ions and the respective complex stoichiometries (number of ligands per ion) in the membrane...

Neutral carrier-based membranes require the addition of a lipophilic ion-exchanger for proper functioning. This ion-exchanger forms the counterion of the complexed analyte ion in the membrane. Its concentration should not be too large in order to allow for a substantial concentration of unbound ionophore in the membrane. Eor instance, a cation-selective membrane may contain the ionophore and the lipophilic tetraphe-nylborate derivative cation-exchanger potassium tetrakis(4-chlorophenyl)borate, while anion-selective membranes may be doped with tridodecylmethylammonium chloride as anion-exchanger in addition to the ionophore. 

For this reason, membranes containing neutral ionophores must also contain a lipophilic ion-exchanger whose charge is opposite that of the analyte ion. It then dictates via electroneutrality condition the concentration of the /L+ complex in the membrane. 

Cholanic acid also possesses the ability of transporting cations across a lipophilic membrane but the selectivity is not observed because it contains no recognition sites for specific cations. In the basic region, monensin forms a lipophilic complex with Na+, which is the counter ion of the carboxylate, by taking a pseudo-cyclic structure based on the effective coordination of the polyether moiety. The lipophilic complex taken up in the liquid membrane is transferred to the active region by diffusion. In the acidic region, the sodium cation is released by the neutralization reaction. The cycle is completed by the reverse transport of the free carboxylic ionophore. 

Recently, Shinkai and Manabe achieved the active transport of K+ using a new type of carrier 39 derived from diaza crown ether43, 44). The ionophore forms the zwitter-ionic species 39b, which is most lipophilic among other species (39a, 39c), at about neutral pH region, and it acts as effective ion carrier in the active transport... 

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