Cyclitol-Based Metal-Complexing Agents. Effect of the Relative Orientation of Oxygen Atoms in the Ionophoric Ring on the Cation-Binding Ability ofmyo-Inositol-Based Crown Ethers

Abstract

myo-Inositol-derived crown ethers having varying relative orientations (1,3-diaxial, 1,2-diequatorial, and 1,2-axial-equatorial) of the oxygen atoms in the ionophoric ring were synthesized and the extent of their binding with picrates of alkali metals, ammonia, and silver were estimated. These crown ethers bind very well with potassium and silver picrates and show good to moderate binding toward lithium, sodium, cesium, and ammonium picrates. These myo-inositol-derived crown ethers exhibit very strong binding for silver, even though they do not have sulfur or nitrogen coordinating sites in them, which are known to have high affinity for silver. The ratio of binding constants for silver to other ions tested varies from 10(2) to 10(5). The ion selectivity and the strength of binding are dependent on the relative orientation of the oxygen atoms in the ionophoric ring as well as on the size of the macrocyclic ring.