Reversible supramolecular assembly in water
Enzymes, chains of amino acids, are ubiquitous in nature and facilitate catalysis through reversible interactions with other molecules. The interactions are largely guided by the complex 3D architectures of the enzymes. These are a result of bending and folding and non-covalent bonding among individual moieties of the chains. Supramolecular polymers are similar to enzymes, capable of self-organisation dictated by secondary non-covalent bonding interactions that determine novel functionalities. However, until now, supramolecular chemistry was limited by a lack of synthetic systems that show reversible aggregation in water. By incorporating novel water-soluble molecules with photosensitive binding affinities, EU-funded scientists working on the PHOTOTRAP project overcame this barrier. The building blocks consisted of the macrocyclic barrel-shaped host molecule cucurbit[8]uril (CB[8]). CB[8] is capable of simultaneously accommodating two organic guest molecules and azobenzene-compound was selected as one of the guest molecules. Despite azobenzene’s potential as a photosensitive material, most previous studies used neutral versions that have relatively low water solubility. Unique to PHOTOTRAP, scientists employed cationic (charged) azobenzene-containing molecules with both excellent water solubility and high binding association. The groundbreaking demonstration of light-induced reversible CB[8] complexation/decomplexation in water paved the way to preparation of micelles and investigation of their use in drug delivery. PHOTOTRAP methodologies and materials have significantly advanced the field of polymer chemistry. Outcomes have demonstrated the immense potential of using supramolecular compounds in aqueous media for creating targeted drug delivery and smart self-healing materials.
