Molecular machines based on metal ion translocation.

Transition metal ions can be moved reversibly between the two coordinatively unequivalent compartments A and B of a ditopic ligand, using as an input the variation of a bulk solution parameter, either pH or redox potential. In a redox-driven translocation, the metal moves reversibly from A to B on cycling between two consecutive oxidation states (e.g., Cu(II)/Cu(I); Fe(III)/Fe(II)) by means of auxiliary oxidation and reduction reactions. In a pH-driven process, one compartment displays also acid-base properties (AH(n)() left arrow over right arrow A(n)(-) + nH(+)), and the M(n)(+) ion is translocated between B and A(n)(-) through consecutive addition of base and acid.