# From self-assembly to controlled release: synthesis and properties of dynamic imine-based Gemini surfactants for curcumin delivery

## TL;DR

This paper introduces new pH-responsive Gemini surfactants that can self-assemble and effectively deliver curcumin.

## Contribution

The synthesis of novel pH-responsive Gemini surfactants with tunable imine linkers and chain lengths is presented.

## Key findings

- Gemini surfactants with specific chain lengths reduced water surface tension to 28.88 mN·m−1.
- Self-assembled structures like vesicles and worm-like micelles were observed using Cryo-TEM and rheology.
- The surfactants showed excellent curcumin encapsulation and pH-controlled release.

## Abstract

Surfactants based on dynamic covalent bonds have attracted great interest in the past few decades due to the coexistence of covalent and non-covalent bonds. As a novel structure of surfactants, Gemini surfactants exhibit excellent surface activity and aggregation behavior. This work synthesized dicot quaternary ammonium salts containing aldehyde precursors, which can self-bind with primary amines of different chain lengths in water to undergo Schiff base reactions and generate pH responsive dynamic surfactants. Different linking groups and hydrophobic chain lengths were used to synthesize Gemini surfactants. The micelle aggregation behavior and surface activity of Gemini surfactants were systematically studied through surface tension, fluorescent probes, and conductivity. Particularly, the Gemini surfactant with 6 carbon atoms between amphiphilic groups and 10 carbon atoms in hydrophobic tail chain change the surface tension of water to 28.88mN·m−1 with a critical micelle concentration of 0.117 mmol·L−1.Products with different chain lengths and linking groups exhibit different micelle aggregation characteristics. Dynamic light scattering, rheology, and cryogenic transmission electron microscopy were used to study their high concentration aggregation behavior and the self-assembled vesicles and worm-like micelles of Gemini surfactants were revealed finally. The ability of micelles to encapsulate and release curcumin was studied by UV-visible spectroscopy and fluorescence spectroscopy, and it was found that they have excellent encapsulation ability for curcumin. Different from micelles, the aggregation behavior of Gemini surfactants changed with the concentration of them in aqueous solution increased.

•Synthesis of a series of novel pH-responsive Gemini surfactants with tunable imine linkers and chain lengths.•The surfactants exhibit excellent surface-active properties.•The self-assembly of Gemini surfactants in aqueous solution was discovered through rheological and Cryo-TEM.•The pH-responsiveness of the Gemini surfactants was demonstrated and applied to control the release of curcumin.

Synthesis of a series of novel pH-responsive Gemini surfactants with tunable imine linkers and chain lengths.

The surfactants exhibit excellent surface-active properties.

The self-assembly of Gemini surfactants in aqueous solution was discovered through rheological and Cryo-TEM.

The pH-responsiveness of the Gemini surfactants was demonstrated and applied to control the release of curcumin.