Neutral lonophores having extraordinary Ca2+ binding strengths and Ca2+/Na+ selectivities in aqueous solution

Abstract

The highest divalent calcium cation binding constants and Ca²⁺/Na⁺ selectivities ever observed in aqueous solution for neutral crown ether derivatives are reported: for 4, 13-diaza-18-crown-6 derivatives having -gly-gly-OCH₂CH₃ or -gly-ala-OCH2CH3 sidearms, K_S values in water are, respectively, 10^6.6 and 10^7.8 and the Ca²⁺/Na selectivities in water for these two compounds are, respectively, >10⁴ and >10⁵.