“…Noncyclic Amide Ionophores. As in the case of Li + ISEs, the first class of fully synthetic ionophores that was investigated were the noncyclic di- and triamides. − One of the most successful diamides was ETH 157 ( Na + -2 , log P TLC 4.6: 48 log
−0.3; PL-4 as plasticizer). − Even though the discrimination of K + is poor, it can be used for measurements in extracellular fluids and has been applied in clinical analyzers. Whereas efforts to improve its selectivity by introducing substituents to the central aromatic ring were not successful, the use of a 1,8-naphthalenediol ( Na + -3 ) instead of the catechol unit improved log
(SSM) to −0.7 and, upon further replacing the substituents on the nitrogens by cyclohexyl groups, to −1.3 ( Na + -4 , bis(1-butylpentyl)adipate) …”