Functional supramolecular systems with highly cooperative and responding properties

The dynamic processes of host-guest interactions contribute to the multistep regulation of various molecular functions such as the catalysis of chemical reactions, transport of materials, control of reaction pathways, and cooperative and responsive phenomena particularly in biological systems. In this review, we describe artificial metallo-supramolecular systems, which exhibit highly cooperative and responsive functions to external stimulus, by utilizing formation of the metal complexes and their characteristic properties. Pseudomacrocycles such as pseudocrown ethers and pseudocryptands have been synthesized to control macrocyclic and macrobicyclic effects on guest recognition by using a metal ion as an effector, and remarkably positive and allosteric effects have been achieved. Highly cooperative stepwise regulation of the affinity to anions has also been achieved by a pseudocryptand and a salt-binding host. The electrostatic interactions between the anions and cations are important for the combination specificity of the salts. We also introduce a linear bis-salamo ligand as a precursor for a novel multimetal cooperative host. A trinuclear zinc complex was formed cooperatively and only the central zinc ion was replaced by lanthanide and calcium ions in a transmetalation way. (C) 2008 the Japan Chemical Journal Forum and Wiley Periodicals, Inc.