Effect of charge regulation on the screening properties of zwitterionic macroion solutions

Precisely controlling the surface charge of zwitterionic macromolecules is crucial for tailoring their properties and optimizing them for specific applications. Here, we present a generalized calculation scheme for determining the screening length in solutions containing zwitterionic macroions, where the charge of the macroion is controlled by the electrolyte solution. This scheme bypasses the need to solve the Poisson Boltzmann equation by expressing the inverse screening parameter in terms of the derivative of pressure with respect to chemical potential. The scheme reveals that the screening length has two components: one related to the Debye length with effective charges, and another stemming from the macroion surface dissociation equilibrium, which exhibits a screening resonance behavior. Furthermore, we find that the nonuniform surface charge distribution induced by pH responsive charge regulation strongly affects the screening behavior. The charge regulation properties of macroions, even in dilute solutions, are a key factor in the screening of electrostatic interactions, offering insights into complex biological and nanomaterial systems.