“…valinomycin, for recognition of metal cations (Hughes, 1987). There are however a variety of other macrocyclic natural products, such as the bisbenzyliso-quinoline family of alkaloids (Glasby, 1975), other macrocyclic alkaloids (Lewis, 1994), macrocyclic bis(bibenzy1s) (Kesed and Nbgrtidi, 1995) and some antibiotics, e.g. rifamycins (Riva and Silvestri, 1972), which possess suitable structural characteristics to function as host molecules.…”