Photocontrol of the Catalytic Activity of aβ-Cyclodextrin Bearing Azobenzene and Histidine Moieties as a Pendant Group

An azobenzene group was linked to β-cyclodextrin via a histidine spacer (1) to produce a photoresponsive catalyst. The ester hydrolysis of p-nitrophenyl acetate, Boc-L-alanine-p-nitrophenyl ester and Boc-D-alanine-p-nitrophenyl ester was examined in the presence of trans-1 or cis-1. In the case of cis-1, the cyclodextrin cavity was used as the substrate binding site during imidazole-catalyzed ester hydrolysis. This was not possible in the case of trans-1 due to the inclusion of the trans-azobenzene moiety in the cyclodextrin cavity. Consequently, the catalytic mechanism switches in an on-off fashion on UV irradiation, associated with the conversion of the azobenzene moiety of 1 from trans to cis.