Cation-selective receptors

Owing to the unique host-guest properties of calixarene macrocycles, calixarene-functionalized silica particles were used as cation-selective receptor colloids [81], and separator of lanthanides and actinides [82]. Calixarenes were also used for the syntheses of Ru, Pt and Pd NPs [83-85]. Furthermore, photoluminescence and charge-transfer complexes of calixarenes and calix[4]arene-based glycoclusters were grafted onto the surface of Ti02 NPs [64, 86]. 

Based on these observations a selective receptor for lithium 117 has been synthesized from a smaller diazadioxa macrocycle [160]. Ligands 110 and 117 may be regarded also as binucleating ligands capable of binding two cations at a time. 

Ammonium cation-selective redox-active receptors... 

Several different types of serotonin receptor (for example, S-HTi / 5-HT2A/ 5-HT2C/ 5-HTib/id) have been associated with the motor side effects of the SSRIs which may arise should these drugs be administered in conjunction with a monoamine oxidase inhibitor. The 5-HT3 receptor is an example of a non-selective cation charmel receptor which is permeable to both sodium and potassium ions and, because both calcium and magnesium ions can modulate its activity, the 5-HT3 receptor resembles the glutamate-NMDA receptor. Antagonists of the 5-HT3 receptor, such as ondansetron, are effective antiemetics and are particularly useful when... 

For the alkoxy receptor 12, which can also form 1 1 complexes with guanine nucleotides, the influence of the cationic site/receptor ratio on the EMF selectivity was determined (Table 2). Electrodes based on 12 and 210 mol% 9 gave similar, Nemstian responses to both 5 -GMP and 5 -AMP, as expected for an excess of cationic sites. Due to the high concentration of cation 9, the concentration of uncomplexed nucleotides in these membrane is high and a selectivity typical for a... 

Nicotinic receptors are part of a transmembrane polypeptide whose subunits form cation-selective ion channels (see Figure 2-9). These receptors are located on plasma membranes of postganglionic cells in all autonomic ganglia, of muscles innervated by somatic motor fibers, and of some central nervous system neurons (see Figure 6-1). 

Anion-selective receptor design is still less developed than that reported for its cation counterpart. This lack of development can be related to the various differences that exist between anions/cations and include ... 

The majority of the devices mentioned thus far rely on the Hofmeister series for anion selectivity. However, for anions that deviate from this series, organometallic receptors can be utilised. The type of ligand or metal centre will influence the sensor selectivity due to the characteristics of the electron acceptance of the complex. An interesting development that is being explored here is the use of calixarenes. These have previously found use as cation-selective species, but with suitable substitution are now being incorporated within anion-selective devices. Compounds suitable as receptors for halides [61],benzoate [61] and acetate [62] have been developed. Reinhoudt and his co-workers have reported the production of a POj-selective CHEMFET based on a uranyl cation immobilised within a salophene ligand (Fig. 5), which shows selectivity over more lipophilic anions such as Br" and NOj [63]. 

Keramidas A, Moorhouse AJ, French CR, Schofield PR, Barry PH. M2 pore mutations convert the glycine receptor channel from being anion- to cation-selective. Biophys J 2000 79(l) 247-259. 

In this chapter our work is described that deals with the development of chemically modified Field Effect Transistors (CHEMFETs) that are able to transduce chemical information from an aqueous solution directly into electronic signals. The emphasis of this part of our work will be on the materials that are required for the attachment of synthetic receptor molecules to the gate oxide surface of the Field Effect Transistor. In addition the integration of all individual components into one defined chemical system will be described. Finally, several examples of cation selective sensors that have resulted from our work will be presented. 

By conditioning of the poIyHEMA layer in a buffer of fixed pH and primary ion concentration prior to use, the activity of the ions (u,) in the polyHEMA layer is constant. This fixes the inner boimdary potential of the ion sensitive membrane Fot an accurate measurement of an unknown activity of the primary ion in the sample solution based on Nemst law, it is essential that the primary ion activity in the membrane phase (a,) remains constant. This can be achieved by the introduction of proper amounts of primary ion-selective receptor molecules (ligands, L) in the membrane. The extraction of a particular ion in the membrane phase is then determined by the product of the partition of the ion over membrane and aqueous phase (/fp) and the association constant of the ion ionophore complex in the membrane (, ). The association constant /I, determines the free cation activity in the membrane ... 

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