ABSTRACT
The ideal macrocyclic carrier would thus exhibit large binding constants (K), hopefully high selectivity coefficients, and rapid binding dynamics. The basic idea behind a switching scheme involves the presence of at least two distinct molecular states with widely different cation-binding properties. Based on the chemical process involved in the switching scheme, four general types of mechanisms have been identified. These are proton ionization or ph control, photochemical control, thermal control and redox control. Thermal control as a switching mode has also been proposed and studied by S. Shinkai et al. The use of redox processes to change the cation-binding and transport ability of macrocyclic compounds has been relatively widely explored. The most convenient technique to measure the cation-binding enhancement is cyclic voltammetry. Interestingly, cyclic voltammetric studies of compound (28) did not provide conclusive evidence of electron-transfer switching enhancement as for the previously discussed lariat ether cases nor as detected by electron spin resonance (ESR) spectroscopy.
