Assembly and Reassembly of Polyelectrolyte Complex Formed by Poly(ethylene glycol)-block-poly(glutamate sodium) and S5R4 Peptide

The structure and stability of polyelectrolyte complex are controlled not only by electrostatic interaction but also by hydrogen bonding and hydrophobic interaction if they are present. The complexes formed by such multiple interactions should exhibit different responses to the environmental changes, such as ionic strength and pH. In this work, we designed a positively charged peptide S5R4, which can interact with poly(ethylene glycol)-block-poly(glutamate sodium) (PEG114-PGlu64) via electrostatic interaction, hydrogen bonding, and hydrophobic interaction. In deionized water at pH 7.1, the complexes formed by PEG114-PGlu64 and S5R4 assemble into wormlike micelles, spheres, and even hierarchical "wool balls", depending on mixing ratio. However, a distinct dissociation–reassembly process is observed when 30 mM NaCl is added to screen the electrostatic interaction. The spheres transform into loose clusters after reassembly. This process is caused by the switch of driving force from electrostatic interaction to hydrogen bonding. Similarly, when the driving force is switched from electrostatic interaction to hydrophobic interaction by increasing solution pH to above 8.7, the original structure quickly dissociates and reassembles into dense aggregates. The rich structures formed by polyelectrolyte complexes and their drastic and sensitive responses to environmental changes are helpful to understand the working mechanism of biomolecules regulated by pH or ion strength.