Cu²⁺-Induced Gelation of Guanosine: Supramolecular Transition From G₂·(Cu²⁺)₂ to G₄·Cu⁺ Assemblies in Gel

Guanosine (G) self-assembles into metal-stabilized architectures such as G-quartets (G₄·Mⁿ⁺) with metal ions, including Na⁺, K⁺, Rb⁺ and Cu⁺, and G-dimers G₂·(Mⁿ⁺)₂ with Ag⁺. Here, we show that Cu²⁺ forms a stable G₂·(Cu²⁺)₂ dimer-based gel at elevated temperatures. This gel exhibits self-healing and time-dependent syneresis behavior. In situ reduction of Cu²⁺ to Cu⁺ by ascorbic acid converts the G₂·(Cu²⁺)₂ dimeric gel to a G₄·Cu⁺ G-quadruplex gel, enabling a redox-controlled gel-to-gel transformation. The G₂·(Cu²⁺)₂ gel is mechanically stronger but dilution-sensitive, whereas the G₄·Cu⁺ gel is weaker yet more dilution-tolerant. These results establish copper oxidation states as determinants of G-based assembly and demonstrate a redox-triggered route to adaptive, stimuli-responsive soft materials.