Allosteric binding of amino alcohols and diamines by dimeric zinc biladienone

A zinc complex of biladienone forms a dimer in toluene and dichloromethane. Binding of two molecules of amino alcohols and diamines to the dimer occurs cooperatively, with the first binding constant being two orders or three orders of magnitude smaller than the second binding constant. Simple amines such as butylamine did not show such cooperative binding. We suggest the mechanism of cooperative binding, where the amino or hydroxyl group in amino alcohols or diamines prevents the dimer dissociation to result in the less tight binding for the first guest, while the binding of the second ligand caused dimer dissociation to release strain in the intermediate complex.