PCage: Fluorescent Molecular Temples for Binding Sugars in Water

The development of synthetic receptors that recognize carbohydrates in water with high selectivity and specificity is challenging on account of their structural complexity and strong hydrophilicity. Here, we report on the design and synthesis of two pyrene-based, temple-shaped receptors for the recognition of a range of common sugars in water. These receptors rely on the use of two parallel pyrene panels, which serve as roofs and floors, capable of forming multiple [C-H···π] interactions with the axially oriented C-H bonds on glycopyranosyl rings in the carbohydrate-based substrates. In addition, eight polarized pyridinium C-H bonds, projecting from the roofs and floors of the temple receptors toward the binding cavities, form [C-H···O] hydrogen bonds, with the equatorially oriented OH groups on the sugars located inside the hydrophobic cavities. Four para-xylylene pillars play a crucial role in controlling the distance between the roof and floor. These temple receptors are highly selective for the binding of glucose and its derivatives. Furthermore, they show enhanced fluorescence upon binding with glucose in water, a property which is useful for glucose-sensing in aqueous solution.