Ionophores noncyclic

In mimicking this type of function, noncyclic artificial carboxylic ionophores having two terminal groups of hydroxyl and carboxylic acid moieties were synthesized and the selective transport of alkali metal cations were examined by Yamazaki et al. 9 10). Noncyclic polyethers take on a pseudo-cyclic structure when coordinating cations and so it is possible to achieve the desired selectivity for specific cations by adjusting the length of the polyether chain 2). However, they were not able to observe any relationship between the selectivity and the structure of the host molecules in an active transport system using ionophores 1-3 10). (Table 1)... 

Okahara, M., and Nakatsuji, Y. Active Transport of Ions Using Synthetic Ionophores Derived from Cyclic and Noncyclic Polyoxyethylene Compounds. 128, 37-59 (1985). 

Many other cyclic and noncyclic organic carriers with remarkable ion selectivities have been used successfiilly as active hosts of various liquid membrane electrodes. These include the 14-crown-4-ether for lithium (30) 16-crown-5 derivatives for sodium bis-benzo-18-crown-6 ether for cesium the ionophore ETH 1001 [(R,R)-AA -bisd l-ethoxycarbonyl)undecyl-A,yVl-4,5-tctramcthyl-3,6-dioxaoctancdiamide] for calcium the natural macrocyclics nonactin and monensin for ammonia and sodium (31), respectively the ionophore ETH 1117 for magnesium calixarene derivatives for sodium (32) and macrocyclic thioethers for mercury and silver (33). 

The parent bicyclic compound (65), prepared from (9o) and cyclopentadiene, has been elaborated in only a few steps into the noncyclic ionophore (121), which transports Ca + efficiently. Its 2,4-dimethyl-ated homolog (64) has been used by Wierenga et al. as the starting material to prepare functionali barbaralanes (124) (Scheme 29) ... 

Nakatsuji Y, Inoue M, Matsumoto M, Masuyama A, and Kida T. Selective transport of lithium ion using noncyclic proton-ionizable ionophores through bulk and emulsion liquid membranes. J Mem Sci, 1995 104(1-2) 165-172. 

Any classification scheme is necessarily arbitrary, but ionophores are often divided into two groups naturally occurring and synthetic. A subclassification distinguishes on the basis of open-chained (noncyclic) versus cyclic. Examples of the latter typically exceed the former because binding site preorganization and geometric complementarity are usually easier to achieve or ensure in a cyclic structure when the goal is to complex a spherical ion. 

Despite their apparently low level of host preorganization, the noncyclic amide ionophores (ETH... 

The structures of the most successful Mg + ionophores have a strong resemblance to those of Ca + ionophores. While early work with diamide ionophores for Mg + was also performed, the most selective noncyclic ionophores for Mg + are the triamides and Mg2+.j ii4,ii5... 

Wierenga, Wendell, Evans, Bruce R. and Woltersom, John A. 1979 Synthesis of new, noncyclic ionophores exhibiting efficient Ca transport J. Am. Chem. Soc. 101,1334-1336. 

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