Lonophores neutral

Solutions of non-electrolytes contain neutral molecules or atoms and are nonconductors. Solutions of electrolytes are good conductors due to the presence of anions and cations. The study of electrolytic solutions has shown that electrolytes may be divided into two classes ionophores and ionogens [134]. lonophores (like alkali halides) are ionic in the crystalline state and they exist only as ions in the fused state as well as in dilute solutions. Ionogens (like hydrogen halides) are substances with molecular crystal lattices which form ions in solution only if a suitable reaction occurs with the solvent. Therefore, according to Eq. (2-13), a clear distinction must be made between the ionization step, which produces ion pairs by heterolysis of a covalent bond in ionogens, and the dissociation process, which produces free ions from associated ions [137, 397, 398]. 

Cation-n Interactions, p. 214 Crown Ethers, p. 326 Fluorescent Sensors, p. 572 lonophores, p. 760 Organic Zeolites, p. 996 Platonic and Archimedean Solids, p. 1100 Protein Supramolecular Chemistry, p. 1161 Simultaneous Binding of Cations and Neutral Molecules, p. 1295... 

The lonophores thus far described lack lonlzable groups and are collectively classified as neutral lonophores their complexes acquire the net charge of whatever ion is complexed. We shall now examine two representatives of the carboxylic subclass of lonophores. Only the anionic form of these lonophores complex cation hence they form electrically neutral zwitterlonic complexes. This distinction is fundamental for explaining the profound differences in biological behavior of the lonophore subclasses, hence we prefer carboxylic lonophore to the term polyether antibiotic used by Westley O). The latter term, furthermore, leads to functional ambiguity with the ethereal macrolide nactlns and crown polyethers which are neutral lonophores. 

Neutral lonophores. The relationship between equilibrium ionophore affinities and dynamic biological transmembrane transport is detailed in Figure 2. The transport cycle catalyzed by neutral ionophores is given on the left. Ionophore added to a biological membrane partitions predominately into the membrane. A portion of the ionophore diffuses to the membrane Interface where it encounters a hydrated cation. A loose encounter complex is formed followed by replacement of the cationic hydration sphere by engulfment of the cation by the ionophore. The dehydrated complex is lipid-soluble and hence can diffuse across the membrane. The cation is then rehydrated, released, and the uncomplexed lono-phore freed to return to its initial state within the membrane. 

Two Independent factors determine the thermodynamic gradient governing net transport by neutral lonophores the membrane potential, i.e. AE, and the concentration gradient,... 

Carboxylic lonophores. Carboxylic ionophore-medlated transport is detailed on the left of Figure 2. The form assumed within the membrane at the start of the transport cycle is an electrically neutral zwltterlon, rf " anionic free I is presumably too polar to be stable at that locus. When this species diffuses to the membrane Interface, it is subject to solvation the cation can be hydrated and removed from the complex. The resultant highly polar I is obliged to remain at the interface until a new charge partner, represented by IT H20, arrives. Once in position,... 

Pharmacological Effects. Although both neutral and carboxylic lonophores have been extensively employed as tools for In vitro studies of biological systems for the reasons detailed previously, only the carboxylic lonophores are sufficiently tolerated by intact animals to produce well defined pharmacological responses. We initially examined the cardiovascular effects of lasalocld because of its ability to transport the key biological control agents, Ca2+ and catecholamines (20,21). However, we later discovered that carboxylic lonophores selective for alkali ions were even more potent in evoking the same responses (22). 

The so-called ionophoreSy which are known under the name neutral carriers if used in ISEs, became meaningful also for optodes. lonophores which carry a chromogenic group are called chromoionophores. However, this term is sometimes used for the combination of ion-exchanging ligand and lipohilic colour indicator. 

Lipophilic, electrically neutral lonophores are also called ion carriers because of their capability of selectively transporting ions across artificial membranes. They are chemical components that are key to achieving high selectivity with liquid or polymer membrane based ISEs. 

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