A Molecular Chaperone for G4-Quartet Hydrogels

Thioflavin T (ThT) functions as a molecular chaperone for gelation of water by guanosine and lithium borate. Substoichiometric ThT (1 mol % relative to hydrogelator) results in faster hydrogelation as monitored by ¹H NMR and visual comparison. Vial-inversion tests and rheology show that ThT increases the stiffness of the Li⁺ guanosine-borate (GB) hydrogel. In addition, the dye promotes relatively rapid and complete repair of a Li⁺ GB hydrogel destroyed by shearing. We used rheology to show that other planar aromatics, some cationic and one neutral dye (methylene violet), also stiffened the Li⁺ GB hydrogel. Data from powder X-ray diffraction, UV, and circular dichroism spectroscopy and ThT fluorescence indicate that G4 quartets are formed by the Li⁺ GB system. We observed a species in solution by ¹H NMR that was intermediate in size between monomeric gelator and NMR-invisible hydrogel. The concentration of this intermediate decreased much faster when ThT was present in solution, again showing that the dye can accelerate hydrogel formation. We propose that ThT functions as a molecular chaperone by end stacking on terminal G4-quartets and promoting the assembly of these smaller fragments into longer G4-based structures that can then provide more cross-linking sites needed for hydrogelation.