Design and synthesis of highly selective ammonium ion ionophores and the preoaration of high performance ammonium ion selective sensors based on the ionophores

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We found that the membrance electrode based on dibenzyl ether (DBC) exhibited a high selectivity to ammonium ion (NH_4^+) over K^+ and Na^+. Here we proposed a model for the complexation of DBE and NH_4^+, that is, the formation of a 4 : 1 complex by hydrogen bonds. Our investigation was directed to determine the factors that affect the complexation of the ammonium ion by benzyl ether, by studying the effect of the introduction of electron donating groups and electron withdrawing groups in the para position of the benzyl group. The participation of phenyl group and the influence of the flexibility of the ionophore through the methylene units of the benzyl group was also discussed.The ammonium ion selectivity behavior of dibenzyl ether was mainly thought to be born by the ether oxygen atom as the central donor atom. Flexibility of the methylene unit in the benzyl unit was important to facilitate the phenyl units free movement to accommodate the size of the ion and the charge distributio … More n and orientation of the ammonium ion. Introduction of electron-donating groups or electron-withdrawing groups in the benzyl units affected the ammonium ion selectivity of the synthesized compounds. The aromatic system of benzyl units was also found to take part in the complexation of the ammonium ion, whereas the pi-electron of the allyl groups were evident not as effective as the benzyl units.The di-and tetra-ether compounds were designed and synthesized, which were expected to form more stable complexes with the ammonium ion compared to the mono-ether such as DBE,because they have a higher number of donor atoms compared with the mono-ether. Connecting the two dibenzyloxy units with the alkyl chain increased the ammonium ion selectivity of the ionophore. The butylene bridge unit was the best suited for such a purpose. The introduction of a tetramethyl unit in the carbon atoms adjacent to the ether oxygen atoms produced structural rigidity of the synthesized ionophore. The tetramethyl units were also thought to serve as 'blocking units' to prevent other ions from forming complexes with the ionophore. The ionophore bearing combination of the benzyl unit, the tetramethyl blocking unit at the butylene bridge section in the ionophore molecule exhibited higher ammonium selectivity over K^+. finally we obtained the novel de-ether ionophore, dibenzyl-1,1,4,4-tetramethylbutyl ether, which gave the highest ammonium ion selectivity among all the ammonium ionophores developed to date. Less