PCage: Fluorescent Molecular Temples for Binding Sugars in Water

Abstract

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 carbohydratebased 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.

Cycloalkyl Groups as Building Blocks of Artificial Carbohydrate Receptors: Studies with Macrocycles Bearing Flexible Side-Arms

“…The carbohydrate is embedded between two benzene rings, thus forming CH∙∙∙π interactions with these central aromatic moieties of the two receptor molecules (for examples of other macrocyclic carbohydrate receptors, see refs. [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 12 , 65 , 66 , 67 , 68 ]). All-equatorially substituted sugars, such as β -glucopyranosides, are particularly well suited to participate in the formation of the 1:1 complexes, therefore octyl β -D-glucopyranoside ( βGlc ) was chosen as the model substrate in these studies.…”

“…[ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]; for recent reports on binding studies, see refs. [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]). On the one hand, such model systems help to better understand the phenomena of biological carbohydrate-mediated processes, and on the other hand, X-ray structural analyses of the protein-carbohydrate complexes [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ] serve as a source of ideas for the design of the biomimetic systems.…”

When Molecules Meet in Water‐Recent Contributions of Supramolecular Chemistry to the Understanding of Molecular Recognition Processes in Water

“…Interestingly, NH donors may not be required in such “temple” receptors to achieve carbohydrate recognition in water according to results obtained by Stoddart and co‐workers. [203] They introduced receptor 56 (Figure 20 ), consisting of two parallel pyrene units as “roof” and “floor” that can engage in CH‐π interactions with the axially oriented protons of carbohydrate rings. Polarized pyridinium CH bonds are available for hydrogen bonding interactions, while the xylylene moieties ensure the proper distance between the pyrene units.…”

“…[202] Interestingly, NH donors may not be required in such "temple" receptors to achieve carbohydrate recognition in water according to results obtained by Stoddart and coworkers. [203] They introduced receptor 56 (Figure 20), consisting of two parallel pyrene units as "roof" and "floor" that can engage in CH-π interactions with the axially oriented protons of carbohydrate rings. Polarized pyridinium CH bonds are available for hydrogen bonding interactions, while the xylylene moieties ensure the proper distance between the pyrene units.…”

Alkoxy-Substituted Quadrupolar Fluorescent Dyes

“…Extended bipyridinium-based cyclophanes − (Ex n Box 4+ ) and their π-conjugated analogues − have been investigated extensively by us in the past. We consider box-like fluorescent tetracationic cyclophanes to be good candidates for biological imaging because of the excellent water solubility of their chloride salts and low cytotoxicity profiles based on our own previous investigations − carried out on tetra- and octacationic fluorescent cyclophanes, cages, , and catenanes. − …”