G4-quartet·M(+) borate hydrogels.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Biomaterials

Background:

• Modulating supramolecular hydrogel properties is crucial for biomaterial and biomedical applications.
• Guanosine (G) is a key component in forming self-assembling structures.

Purpose of the Study:

• To investigate how countercations in borate salts influence the physical properties of guanosine-based hydrogels.
• To elucidate the structural basis for the observed property variations.

Main Methods:

• Rheology and Nuclear Magnetic Resonance (NMR) spectroscopy (1H NMR, 1H double-quantum solid-state MAS NMR) were used to assess hydrogel properties and structure.
• Powder X-ray Diffraction (XRD) and Small-Angle Neutron Scattering (SANS) provided insights into the supramolecular assembly.
• Thioflavin T fluorescence was employed to detect G4·M+ precursor structures.

Main Results:

• Guanosine combined with potassium borate formed a robust hydrogel (elastic moduli >10 kPa).
• The countercation (e.g., K+, Li+) significantly altered hydrogel strength, with K+ yielding the strongest system.
• Structural analysis indicated the formation of G4·M+ quartets stabilized by the cation, which stack into G4-nanowires.
• Additional salts (KCl, KNO3) enhanced hydrogel strength.
• Thioflavin T fluorescence correlated with the stability of G4·M+ structures and the gel point.

Conclusions:

• The choice of countercation is critical for tuning the mechanical properties of guanosine-borate hydrogels.
• The K+ cation stabilizes G4·M+ quartets, leading to stronger hydrogels suitable for advanced applications.
• Thioflavin T serves as a useful indicator for G4·M+ structures and gelation.