Competition between Hydrophobic and Electrostatic Interactions determine pH-responsive Supramolecular Self-assembly

We present results from a molecular dynamics simulations study, inspired by experiments on pH-regulated self-assembly into filaments. Experiments are performed in aqueous media, with 1:1 binary mixture of amphiphilic peptide monomers having oppositely charged side chains. In neutral conditions, the monomers self-assemble into alternating copolymers. In acidic and basic conditions, selective screening of Coulombic interactions occurs. This leads to formation of homopolymers. Building on our model for homopolymers in implicit solvent¹, we introduce charges to mimic the two monomers. Our simulations reveal that the consideration of pH-dependent hydrophobic interactions is essential to observe pH-switch in polymerization. Further, assembly kinetics is analyzed, comparing simulations to experimental data which are obtained from circular dichroism spectroscopy. We relate both to appropriate growth models. While the nucleation and elongation are key mechanisms in simulations, fragmentation is important in experimental kinetics.

1. S. Chakraborty, C.M. Berac, B. Kemper, P. Besenius, T. Speck Macromolecules 52, 20, 7661-7667 (2019).