Allosteric Binding of Alkali Metal Ions to a Pseudocryptand Formed by a Tripodal Heterocyclic Hexadentate Ligand and Ga(III) †

Abstract

A new tripodal heterocyclic hexadentate ligand, in which three sets of 3-hydroxy-4(1 H)-pyridinone and ethyleneoxy chain are linked to tris(carboxyethoxymethyl)ethane, was synthesized. UV-Vis spectroscopic analysis in aqueous solution indicated 1:1 stoichiometric complexation of the hexadentate ligand with iron(III) ( λ max 460 nm and ε 5100 M −1 cm −1; the relative stability constant log K=32.9). Allosteric binding of alkali metal ions to a pseudocryptand formed by the tripodal hexadentate ligand and Ga(III) was examined in CDCl 3–CD 3CN (1:1) mixture by means of 1H NMR spectroscopy. The pseudocryptand formed 1:1 complexes with Na + and K + ions, and the binding constant was estimated to be almost the same ( K=5.9×10 2 for Na + and 5.8×10 2 M −1 for K +).