All-small-molecule dynamic covalent gels with antibacterial activity by boronate-tannic acid gelation

Reversible boronate-catechol linkage was widely used to construct two-dimensional coatings and three-dimensional nanostructures or hydrogels. The construction of these functional materials usually requires the pre-synthesis of macromolecular building blocks, and direct gelation between natural polyphenols and small molecule boronic acids is yet to be investigated. In this study, we fabricated a family of all-small-molecule dynamic covalent gels consisting of tannic acid and boronic acids. Transparent and thixotropic gels were formed by boronate affinity towards catechol groups abundant on natural polyphenols. The gels showed multi-responsiveness, such as acid-, base-, reduction- and oxidant-sensitive depending on the used boronic acid building blocks. The chemistry for gel formation and stimuli-responsiveness was characterized by 11B NMR spectroscopy. The multi-stimuli responsiveness, green processing and facile modular design make the boronic acid-tannic acid gels promising candidates for the development of smart soft materials.