Ag+-Specific Pyridine Podands: Effects of Ligand Geometry and Stereochemically Controlled Substitution on Cation Complexation and Transport Functions

A new series of acyclic podands was designed so that three pyridine moieties cooperatively bind a guest Ag + . Liquid−liquid extraction, NMR binding, and computer calculation experiments reveal that podands with three pyridine donors in a proper geometry exhibit a perfect Ag + specificity. They selectively extracted Ag + in the presence of equimolar Pb 2+, Cu 2+, Ni 2+, Co 2+, and Zn 2+ . Introduction of two chiral centers close to the pyridine binding sites surprisingly influences the Ag + -binding ability of the podand. Fourteen new pyridine podands were evaluated as carriers in a liquid membrane transport system. A combination of ligand geometry and stereocontrolled substitution provides excellent Ag + -specific transport.