Approach toward Artificial Enzyme Models Using Water-soluble Cyclophanes with Hyrophobic Cavities

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Studies aiming at application of cyclophanes having diphenylmethane units to artificial enzyme models in aqueous solutions and at membrane surfaces were carried out, and the following results were obtained.1. Catalytic cyclophanes in which an imidazolyl or thiol group as a catalytic functional group was introduced to a cyclophane macrocycle having diphenylmethane units were synthesized, and their abilities to accelerate ester docomposition were compared in aqueous solution (pH 8.65). Although 3.8-fold acceleration was observed for a cyclophane having an imidazolyl group, control experiments with addition of a nonreactive guest or 4-methyl-imidazole without a cyclophane ring showed that the acceleration by the imidazolyl cyclophane was not due to the reaction with a guest included in the cyclophane cavity. These results manifested the necessity of the design of catalytic cylophanes in which the catalytic group is located in close proximity to the reactive site of the included guest.2. An optically active, anionic cyclophane having a C_2-symmetrical structure with two OH groups was synthesized as a new type of chiral hydrophobic cavity that is capable of introducing catalytic functional groups. This cyclophane showed strong complexation to cationic aromatic guests (K_3-10^3M^<-1>) in aqueous solution (pD12.8).3. A series of lipophilic cyclophanes having long alkyl chains were synthesized to achieve molecular recognition at a membrane surface, evaluated as guest-induced changes in membrane potential by using PVC-supported liquid membrane systems. A cyclophane having a definite charged group on one side and a lipophilic alkyl chain on the other side of the benzene rings gave greatest potential changes, indicating an important principle for designing interfacial receptors.