In-Situ Exploration of Phytic Acid-Mediated Supramolecular Self-Assembly and Gelation

Molecular gels emerge as a promising type of material owing to their high tunability for versatile applications. However, there are still gaps in our mechanistic understanding of the molecular assembly and its consequent physicochemical properties. Additionally, most of the methods for hydrogel characterization require pretreatment, which makes it difficult to verify the exact fibril structures of the hydrogels and the intermolecular interactions involved. Herein, we employed Raman spectroscopy, a technique frequently used to verify intermolecular forces, to revisit the dynamic molecular self-assembly of guanosine monophosphate in the acidic milieu. In addition to the confirmed presence of G-quadruplexes in the hydrogel, a previously unidentified peak was discovered in the low wavenumber region (∼96-110 cm^-1), potentially referring to the lattice packing of G-tetrads. The phytic acid (PA)-mediated formation of G-quadruplex-based hydrogels consisted of a bifibre-bundle structure, resulting in higher mechanical strength. Furthermore, we found that monitoring the P-OH stretching mode (850-860 cm^-1) and the water-associated hydrogen bonding in the high wavenumber region (>2000 cm^-1) revealed that, at low PA concentrations, PA molecules mainly act as cross-linkers between G-quadruplex fibrils. When the concentration increases, the aggregation of excess PA may form clusters to support the gel void, providing extra mechanical strength. This study establishes a methodology to noninvasively resolve the supramolecular hydrogel self-assembly.