Temperature regulated supramolecular structures via modifying the balance of multiple non-covalent interactions

Abstract

Gelation of lithocholic acid (LCA) mixed with zwitterionic alkyldimethylamine oxide, (C_nDMAO, n = 10, 12, 14, 16, and 18), in water was detected. Hydrogels can only form at an appropriate hydrophilic–hydrophobic balance condition (n = 12, 14, and 16) with the highest gelation capability at n = 12. Microstructures of hydrogels were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) observations, indicating that the hydrogels are formed by helically intertwined fibrils. The formation of the hydrogel fibrils was suspected to be driven by a delicate balance of multiple non-covalent interactions including hydrogen bonding, electrostatic interaction, hydrophobic interaction, and the steric effect of LCA molecules. It is very interesting that temperature changes alone can induce a reversible transition between the helical fibrils and vesicle bilayers. The breakage or reconstruction of the hydrogen bonds produced by the temperature change determined the phase structure transition, i.e., the temperature change could modify the balance of the weak interactions for the formation of hydrogels. The observation of modification of supramolecular structures via temperature change may provide an efficient strategy for the phase structure transition and also may find potential applications in biosensors, shape memory, templating of functional molecular materials, etc.