Comparison of Two Molecular Design Strategies for the Development of an Ammonium Ionophore More Highly Selective than Nonactin

• Published in: Analytical chemistry (Washington) Vol. 74; no. 18; pp. 4845 - 4848
• Main Authors: Sasaki, Shin-ichi, Amano, Tsuyoshi, Monma, Gou, Otsuka, Takeshi, Iwasawa, Naoko, Citterio, Daniel, Hisamoto, Hideaki, Suzuki, Koji
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.09.2002
• Subjects: Analytical chemistry; Chemical reactions; Chemistry; Design; Electrochemical methods; Exact sciences and technology; Ions; Ion selective electrode; Ionic selectivity; Tripod; Cyclic compound; Crown ethers; Chemical structure; Ammonium ion; Ionophore; Comparative study
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac025713+

A series of ionophores for ammonium ion-selective electrodes was designed and synthesized, and their characteristics were examined. The design of the ionophores is based on two different strategies:  (1) introduction of bulky blocking subunits (decalino groups) in 20- or 21-membered crown ethers (TD20C6 and TD21C6), the ring size of which is expected to be suitable for selective NH4 + recognition, as compared to the slightly smaller K+; and (2) preorganized tripodal ionophores based on a 6-fold substituted benzene ring in order to complementarily recognize the tetrahedral NH4 +, in contrast to the spherical K+. Compared to nonactin, a natural product that is used as a representative NH4 + ionophore, the newly developed TD20C6 showed higher NH4 + selectivity over K+ while retaining the selectivity over Na+ (log = −1.5 and log = −2.5). On the other hand, a tripodal ionophore with pyrazole nitrogen atoms as NH4 + binding sites showed high NH4 +/K+ selectivity but suffered from increased Ca2+ interference (log = −2.1 and log = −1.6). As an overall conclusion, the cyclic ionophores TD19C6 and TD20C6 are the best ammonium-selective ionophores developed to date.