Similar to
crown ethers and
ionophores, these
macrocyclic molecules show good selectivity for metal
ions and can transport them across
membranes. They are made by making the
2D, flat crown ether into a
3D cage for the metal ion. The simplest method is adding a bridge to make a
bicyclic molecule, with nitrogens usually. This adds more
ligands to the molecule and has, therefore, better
coordination of the ion.
Tricyclic molecules have a more spherical shape, eg:
N1(CCOCCN23)CCOCCN(CCOCC2)CCOCCN(CCOCC3)CCOCC1