Recognition of primary amines in water by a zinc funnel complex based on calix[6]arene

Abstract

A water-soluble calix[6]arene-based tris(imidazole) ligand behaves as a highly selective receptor for primary amines in the presence of Zn(II) in water near physiological pH. It represents the first compound of this family of ligands that binds a Zn dication and an organic guest in water, thus giving rise to a stable host–guest adduct in spite of the highly competitive medium. The herein described self-assembly process displays a remarkable set of biomimetic properties. The ternary system (calix/Zn/amine) is formed in a very synergistic and allosteric manner and stabilizes the neutral form of the amino guest with a spectacular pseudo-pK_a shift of ca. 7 units. This system constitutes an interesting structural model of metalloenzymes in aqueous solution.