A simple electrostatic model applicable to biomolecular recognition

TL;DR

This paper presents an exact analytical electrostatic model for biomolecular recognition, revealing how a dielectric screening layer influences charge interactions, with implications for understanding biomolecular binding forces.

Contribution

It introduces a simple, exact electrostatic model with a variable dielectric layer, demonstrating asymmetric screening effects relevant to biomolecular recognition.

Findings

Screening layer lowers energy for identical charges.

Thick screening layer reduces energy for opposite charges.

Asymmetric screening increases repulsive forces between same-sign charges.

Abstract

An exact, analytic solution for a simple electrostatic model applicable to biomolecular recognition is presented. In the model, a layer of high dielectric constant material (representative of the solvent, water) whose thickness may vary separates two regions of low dielectric constant material (representative of proteins, DNA, RNA, or similar materials), in each of which is embedded a point charge. For identical charges, the presence of the screening layer always lowers the energy compared to the case of point charges in an infinite medium of low dielectric constant. Somewhat surprisingly, the presence of a sufficiently thick screening layer also lowers the energy compared to the case of point charges in an infinite medium of high dielectric constant. For charges of opposite sign, the screening layer always lowers the energy compared to the case of point charges in an infinite medium of either high or low dielectric constant. The behavior of the energy leads to a substantially increased repulsive force between charges of the same sign. The repulsive force between charges of opposite signs is weaker than in an infinite medium of low dielectric constant material but stronger than in an infinite medium of high dielectric constant material. The presence of this behavior, which we name asymmetric screening, in the simple system presented here confirms the generality of the behavior that was established in a more complicated system of an arbitrary number of charged dielectric spheres in an infinite solvent.