Impact of the inner solute structure on the electrostatic mean-field and strong-coupling regimes of macromolecular interactions

Abstract

The structural diversity of the solute molecules involved in biomolecular processes necessitates the characterization of the forces between charged macromolecules beyond the point-ion description. From the field theoretic partition function of an electrolyte confined between two anionic membranes, we derive a contact-value identity valid for general intramolecular solute structure and electrostatic coupling strength. In the electrostatic mean-field (MF) regime, the inner charge spread of the solute particles is shown to induce the twofold enhancement of the short-range Poisson-Boltzmann (PB)-level membrane repulsion, and a longer-range depletion attraction. Our contact theorem indicates that the twofold repulsion enhancement by solute size is equally present in the opposite strong-coupling (SC) regime of linear and spherical solute molecules. Upon the inclusion of the dielectric contrast between the electrolyte and the interacting membranes, the emerging polarization forces substantially amplify the solute specificity of the macromolecular interactions. Namely, the finite size of the solute particles composed of similar terminal charges such as putrescine molecules weaken the intermembrane repulsion. However, the extended structure of the solute molecules carrying opposite elementary charges such as ionized atoms and zwitterionic molecules enhance the membrane repulsion by several factors. We also show that these polarization forces can extend the range of the solute structure effects up to intermembrane distances exceeding the solute size by an order of magnitude. This radical alteration of the intermembrane interactions by the salt structure identifies the solute specificity as a key ingredient of the thermodynamic stability in colloidal systems.

References in corpus (10)

• Ions at the air-water interface: An end to one hundred year old mystery?
• Depletion potential in hard-sphere mixtures: theory and applications
• Beyond Poisson-Boltzmann: Fluctuations and Correlations
• Dipolar Poisson-Boltzmann Equation: Ions and Dipoles Close to Charged Surfaces
• Strong Coupling Electrostatics in the Presence of Dielectric Inhomogeneities
• Microscopic formulation of non-local electrostatics in polar liquids embedding polarizable ions
• Role of Multipoles in Counterion-Mediated Interactions between Charged Surfaces: Strong and Weak Coupling
• Electrostatic interactions mediated by polarizable counterions: weak and strong coupling limits
• The field theoretic derivation of the contact value theorem in planar geometries and its modification by the Casimir effect
• Explicit Solvent Effects on Macromolecular Interactions From a Solvent-Augmented Contact Value Theorem

Cited by in corpus (2)

• Systematic incorporation of the ionic hard-core size into the Debye-Huckel theory via the cumulant expansion of the Schwinger-Dyson equations
• Unified microscopic theory of equilibrium thermodynamics and ion association in aqueous and non-aqueous electrolytes with explicit hard-core size