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A novel supramolecular hydrogel was designed and constructed by molecular self-assembly of a cationic gemini surfactant, 1,3-bis(N,N-dimethyl-N-cetylammonium)-2-propylacrylate dibromide (AGC16), and an anionic aromatic compound, trisodium 1,3,6-naphthalenetrisulfonate (NTS). Owing to its unique structure, the hydrogel (abbreviated as AGC16/NTS) has the potential to be used as a multifunctional drug delivery system. The structure and properties of AGC16/NTS were characterized by rheological measurements, differential scanning calorimetry, variable-temperature 1H nuclear magnetic resonance, ultraviolet-visible spectroscopy, variable-temperature fluorescence emission spectroscopy, cryogenic scanning electron microscopy, transmission electron microscopy and X-ray diffraction methods. The rheological and DSC analysis results revealed that the gel AGC16/NTS was formed below 57 °C. It was found from UV-vis, fluorescence and 1H NMR spectroscopy characterization that aromatic π-π stacking and hydrophobic forces were indispensable to the formation of AGC16/NTS. The Cryo-SEM and TEM observation results indicated that gelators AGC16 and NTS self-assembled into one-dimensional fibers which further tightly intertwined to form a three-dimensional network structure. Based on the spectroscopic data and X-ray diffraction measurement results, a self-assembly model was proposed, helping to further understand the molecular self-assembly mechanism of AGC16/NTS. It was also found that the electrostatic force, hydrophobic force and π-π interaction were the three main driving forces for the gelation. The multiple non-covalent interactions between AGC16 and NTS endowed the hydrogel with excellent performance when the hydrogel was used as a carrier for drug delivery, due to multiple micro-domains within the same gel system. We further investigated the encapsulation and releasing properties of the hydrogel, using the hydrophobic model drug curcumin (Cur) and the model drug naproxen sodium (Npx) with aromatic ring structure. The fluorescence spectroscopy analysis confirmed that Npx was carried through aromatic π-π stacking and the 1H NMR measurement result revealed that Cur was encapsulated within the hydrophobic cavities of AGC16/NTS through hydrophobic interaction. Moreover, the drug release study results showed a sustained release of drugs from the hydrogel, indicating good application prospects in exploring new multifunctional drug delivery systems.

An efficient method was developed to encapsulate water insoluble organic particles of Sudan red III (SR) in aqueous suspensions by using a polymerizable cationic gemini surfactant, 1,3-bis(N,N-dimethyl-N-cetylammonium)-2-(propylacrylate dibromide) (AGC16). The AGC16 coated SR microcapsules (AGC16@SR) were prepared by absorption of AGC16 on the surface of SR, followed by in situ homopolymerization (PAGC16). Several measurements, including transmission and scanning electron microscopy, isothermal titration calorimetry, zeta potential, electron paramagnetic resonance and small angle X-ray scattering, were performed to determine the adsorption amount of AGC16, and the layer structures and the molecular assembly mechanism in the AGC16@SR and PAGC16@SR systems, respectively. For comparison purposes, the polymerizable cationic surfactant with one head group and a single alkyl chain, acryloyloxyethyl-N,N-dimethyl-N-cetylammonium bromide (referred to as ASC16), as well as the systems of ASC16@SR and PASC16@SR were also investigated in parallel. It was found that AGC16 molecules and their aggregates were simultaneously assembled into a shell layer, in which the saturated adsorption amount of AGC16 on SR is less than 1/2 that of ASC16, but the assembly layer of AGC16 is more hydrophobic with greater packing tightness compared with that of ASC16. It was also revealed that after in situ homopolymerization, the microcapsule shell becomes more compact. In the case of PAGC16@SR, the layers show higher surface roughness and irregularity compared with that of PASC16@SR. Moreover, the sustained release behavior of SR was also evaluated. The results revealed that PAGC16@SR performed well for SR controlled release, which was sorted by release performance as the following sequence: PAGC16@SR > AGC16@SR > PASC16@SR > ASC16@SR. Thus, the polymerizable cationic gemini surfactant holds substantial potential to be developed as an ideal candidate of soft matter to construct efficient controllable release systems.