Interplay of distinct modes of charge regulation on poly-acid ionization and conformation

TL;DR

This paper extends a theoretical model to study how proton binding and counterion condensation influence the charge and shape of poly-acid polymers, revealing non-monotonic behaviors driven by pH and salt levels.

Contribution

It introduces a modified theoretical framework to analyze the complex interplay of charge regulation modes on poly-acid ionization and conformation.

Findings

pH-induced non-monotonic transitions between polyelectrolyte behaviors

Salt concentration effects depend on charge regulation mode

Significant pKa shifts influenced by polymer flexibility

Abstract

We adapt the Edwards-Muthukumar theoretical framework for a single polymer chain to investigate the interplay between proton binding and counterion condensation for poly-acids. We find that changes to pH enable non-monotonic transitions between anti- and conventional polyelectrolyte behaviors. In the former, the net charge and the overall dimensions increase with increasing salt concentration, while the converse is true for conventional polyelectrolytes. The polymeric nature and local solvent polarization drive significant pKa shifts when compared to the values of reference monoacids. These pKa shifts are enhanced in semi-flexible chains.