Design and Synthesis of a More Highly Selective Ammonium Ionophore Than Nonactin and Its Application as an Ion-Sensing Component for an Ion-Selective Electrode

Abstract

A novel ammonium ionophore, which exhibits superior NH4+ selectivity compared with that of the natural antibiotic nonactin, was successfully designed and synthesized based on a 19-membered crown compound (TD19C6) having three decalino subunits in the macrocyclic system. This bulky decalino subunit is effective for (1) increasing the structural rigidity of the cyclic compound, (2) introducing the "block-wall effect", which prevents forming a complex with a large ion, and (3) increasing the lipophilicity of the ionophore molecule. In the ammonium ionophore design, the first factor contributes to increasing the NH4+ selectivity relative to smaller ions such as Li+, Na+, or even the closest size, K+, and the second factor increases the NH4+ selectivity over larger ions such as Rb+ and Cs+. The X-ray structural analysis proved that TD19C6 forms a size-fit complexwith NH4+ in its crown ring cavity. As an application of this ionophore, an ion sensor (ion-selective electrode) was prepared, which exhibited NH4+ to K+ and Na+ selectivity of 10 and 3,000 times, respectively. This electrode showed a better performance compared to the electrode based on nonactin, which is the only ammonium ionophore presently used in practical applications.

Theoretical Studies on Selectivity of Dibenzo-18-Crown-6-Ether for Alkaline Earth Divalent Cations

“…This simple molecular recognition system has drawn much attention of many researchers and been utilized in various fields such as phasetransfer catalysis, ion-selective electrode, fluorophore, and ionophore. [1][2][3][4] Since the cavity size is proportional to the ring size, it is believed that crown ethers show selectivity in binding depending on cavity and ion size. However selectivity is not governed simply by cavity size relationship, but by interplay of interactions among cations, crown ethers, and solvents.…”

Ammonium secretion by Malpighian tubules ofDrosophila melanogaster: application of a novel ammonium-selective microelectrode

“…The cocktail that had the highest selectivity contained 1% of the ionophore TD19C6, 0.25% of the lipophilic salt potassium tetrakis [3,5-bis-(trifluoromethyl) progressively reduced the slope of the ammonium microelectrode (Table1). A previous study determined selectivity coefficients for the ionophore TD19C6 incorporated into macroelectrodes containing polyvinyl chloride (Suzuki et al, 2000). However, selectivity coefficients are not always similar in macroelectrodes and microelectrodes, or in liquid-membrane electrodes that do not contain polyvinyl chloride.…”

“…Use of electrodes based on nonactin in physiological solutions typically requires compensation for interference from both Na + and K + . Studies with macroelectrodes have shown that membranes containing polyvinyl chloride and a novel ionophore based on a 19-membered crown compound 2,5,12,15,22,26-hexaoxaheptacyclo[25.4.4.4 6.11 4 16.21 .0 1.27 .0 6.11 .0 16.21 ]-tritetracontane (TD19C6) have much greater selectivity towards sodium than do membranes based on nonactin (Suzuki et al, 2000). Thus, use of NH 4 + -selective microelectrodes based on this compound offers the possibility that a complex calculation to correct for the effects of interfering ions could be reduced to one in which only interference from K + needs to be considered.…”

Spectrophotometric Characterization of Diazacrown Ethers Having Two Carbodithioate Groups

“…Analytical investigations have proved their potential in analytical chemistry. [13][14][15][16][17][18][19][20] For example, a modification of crown ethers, i.e. the introduction of a side chain into a crown ring, has already been investigated for improving crown-ring selectivity and stimulating new chromoionophore development.…”

“…the introduction of a side chain into a crown ring, has already been investigated for improving crown-ring selectivity and stimulating new chromoionophore development. Suzuki et al [18][19][20] introduced bulky groups as "block" subunits into crown compounds to improve their recognition ability for alkali metal ion or ammonium ion as ionophores of ion-selective electrodes. Takagi et al [7][8][9] combined a crown ether and a chromophore to synthesize a chromoionophore for alkali-metal ions or alkaline earth-metal ions.…”