Catalytic Functions of Paracyclophanes Based on Molecular Recognition

Summary

A cubic cyclophane surrounded by six faces, each being constructed with the [3.3.3.3]paracyclophane ring, acted as a polycationic host in acidic aqueous media and exhibited pH-dependent guest-binding behavior. Hydrophobicity of its internal cavity was markedly enhanced as medium pH was raised. The cubic cyclophane exercised the size-sensitive molecular discrimination that originates from restricted and rigid geometry of its hydrophobic cavity and perfectly protected an incorporated guest from oxygen attack. An octopus cyclophane, constructed with the [3.3.3.3]paracyclophane skeleton and eight hydrocarbon chains, provided a cavity that is deep and hydrophobic enough to incorporate hydrophobic guests of various bulkiness through an induced-fit mechanism. Unique biphasic guest-binding behavior was observed for an octopus cyclophane having L-aspartate residues as connector units interposed between the macrocyclic skeleton and the alkyl branches. An artificial holoenzyme system, composed of a hydrophobic vitamin B₁₂ and the octopus cyclophane, could simulate catalytic functions of methylmalonyl-CoA mutase and glutamate mutase in the presence of vanadium trichloride under aerobic irradiation conditions.