Hydrogen bond directed molecular recognition in water in a strapped-porphyrin-cyclodextrin assembly

Abstract

A water soluble, phenanthroline-strapped zinc porphyrin bearing four arylsulfonate groups formed a stable host–guest complex with two per-[Formula: see text]-methylated [Formula: see text]-cyclodextrin cavities. In the host–guest assembly, the zinc porphyrin was capable of binding imidazole within the cavity between the zinc(II) ion and the phenanthroline strap in an aqueous medium. The formation of a hydrogen bond between the imidazole NH and the nitrogen atoms of the phenanthroline was an essential element of the binding event, as shown by comparative binding studies with a non-strapped tetrasulfonated zinc porphyrin and with [Formula: see text]-methylimidazole. This hydrogen bonding in an aqueous medium was possible due to the protected hydrophobic environment created by the cyclodextrins around the phenanthroline strap. This type of binding event may provide a biomimetic approach to study water soluble heme protein models.