pH-Induced cucurbit[7]uril hydrogels: Understanding microenvironment of the aggregates through excited state reactivity of dibenzyl ketones

The supramolecular chemistry of cucurbituril aggregates arising from peripheral interactions to form hydrogels is a relatively new and less explored aspect of the cavitand family. The hydrogels formed by cucurbit[7]uril (CB7) in aqueous media is understood to consist of CB7 networks linked through C-H center dot center dot center dot O interactions with readily manipulable material and mechanical properties, and is envisioned to contain high application potential. Therefore, understanding the microenvironmental properties of this newly emerging CB-based hydrogels is important. In this reported study we present our understanding about the microenvironmental characteristics of the CB7 hydrogels inferred from (a) the modified photoreactivity of non-C2-symmetric dibenzyl ketones (DBK) encapsulated within the hydrogels, and (b) NMR diffusion experiments. Reaction selectivity in DBK photochemistry offered insight regarding the structural integrity and effects of pH, temperature, and concentration on the aggregates, while the diffusion studies were useful in developing a qualitative idea about the equilibrium dynamics of the CB7 aggregates that constitute the hydrogels. (C) 2016 Elsevier B.V. All rights reserved.