Kinetically stable complexes of alkali cations with calixspherands: an evaluation of shielding

A novel route to calixspherands which provide ligands in quantities suited for practical use reveals that an enhancement in the kinetic stability of the complexes accompanies improved protection of the cavity against solvent molecules. The maximum kinetic stabilities are evident for Na+, K+ and Rb+ complexes of 3. Stability is high for in vivo application in apolar and polar solvents. Decomplexation of the complexed reaction is the rate-limiting state in the exchange mechanism.