Electrochemically switchable calixarene ionophores.
The synthesis of a series of p-tert-butylcalixI4Iarcne based, electrochemically
switchable, ionophores (1), (2), (3), (4) and (5) is described. Their electrochemical
properties were investigated in the presence of added Croup I metal perchloratcs. Both
compounds (1) and (2) displayed no enhancement of binding for metal ions, due to
electrostatic interactions, upon electrochemical reduction. This behaviour is explained on
steric grounds, as deduced by molecular modelling. Compounds (3), (4) and (5) all display
significant enhancements of metal ion binding upon electrochemical reduction. Compounds
(4) and (5) appear to display a high selectivity for sodium ions over other Croup I metal
ions. Compound (3) displayed the highest binding enhancements yet recorded for both
sodium (3.138 x loS) and potassium (1.398 x 103) ions.
Compound (6) (from which (3), (4) and (5) were malic) could be converted to m,my
other compounds in which the side arms bear difierent functional groups in an eiiort to
control selectivity. For example thio esters or thin arnides for silver, ethyl groups tor