A G₄·K⁺ Hydrogel Stabilized by an Anion

Supramolecular hydrogels derived from natural products have promising applications in diagnostics, drug delivery, and tissue engineering. We studied the formation of a long-lived hydrogel made by mixing guanosine (G, <b>1</b>) with 0.5 equiv of KB­(OH)₄. This ratio of borate anion to ligand is crucial for gelation as it links two molecules of <b>1</b>, which facilitates cation-templated assembly of G₄·K⁺ quartets. The guanosine–borate (GB) hydrogel, which was characterized by cryogenic transmission electron microscopy and circular dichroism and ¹¹B magic-angle-spinning NMR spectroscopy, is stable in water that contains physiologically relevant concentrations of K⁺. Furthermore, non-covalent interactions, such as electrostatics, π-stacking, and hydrogen bonding, enable the incorporation of a cationic dye and nucleosides into the GB hydrogel