Counterions release from electrostatic complexes of polyelectrolytes and proteins of opposite charge : a direct measurement

TL;DR

This study provides the first direct experimental measurement of counterion release in polyelectrolyte-protein complexes using Small Angle Neutron Scattering, revealing counterion expulsion from electrostatically balanced cores.

Contribution

It introduces a novel neutron scattering method to directly measure counterion release in polyelectrolyte-protein complexes, a process previously only inferred indirectly.

Findings

Counterions are expelled from the core regions of complexes.

Counterions, including Manning condensed ones, are released at electrostatic stoichiometry.

The spatial distribution of counterions within complexes was determined.

Abstract

Though often considered as one of the main driving process of the complexation of species of opposite charges, the release of counterions has never been experimentally directly measured on polyelectrolyte/proteins complexes. We present here the first structural determination of such a release by Small Angle Neutron Scattering in complexes made of lysozyme, a positively charged protein and of PSS, a negatively charged polyelectrolyte. Both components have the same neutron density length, so their scattering can be switched off simultaneously in an appropriate "matching" solvent; this enables determination of the spatial distribution of the single counterions within the complexes. The counterions (including the one subjected to Manning condensation) are expelled from the cores where the species are at electrostatic stoichiometry.