Calculations of the electrostatic potential adjacent to model phospholipid bilayers

Area of Science:

• Biophysics
• Electrochemistry
• Physical Chemistry

Background:

• Phospholipid bilayers are fundamental to cell membranes.
• Understanding electrostatic potentials at interfaces is crucial for membrane function.
• Previous models often simplify lipid charge distribution and bilayer surface complexity.

Purpose of the Study:

• To calculate electrostatic potentials adjacent to model phospholipid bilayers with varying acidic lipid content.
• To compare theoretical predictions with simulation results under different lipid compositions.
• To assess the impact of simplified bilayer features on electrostatic potential calculations.

Main Methods:

• Nonlinear Poisson-Boltzmann equation used for electrostatic potential calculations.
• Model bilayers composed of zwitterionic (phosphatidylcholine) and acidic (phosphatidylserine/phosphatidylglycerol) lipids.
• Simulations conducted in a 0.1 M monovalent salt aqueous phase (relative permittivity, εr = 80).

Main Results:

• At <11% acidic lipid, equipotential surfaces (-25 mV) formed discrete domes over charged lipids, deviating from Debye-Hückel theory.
• At >25% acidic lipid, equipotential profiles (-25 mV) became flat, agreeing with Gouy-Chapman theory.
• At 100% acidic lipid, all equipotential surfaces matched Gouy-Chapman predictions.
• Factors like distributed partial charges, ion-exclusion zones, and surface roughness had minor effects on aqueous phase potentials.

Conclusions:

• The distribution of acidic lipids significantly alters electrostatic potentials at bilayer interfaces.
• Gouy-Chapman theory accurately predicts potentials for bilayers with high acidic lipid content.
• Simplified models can effectively capture the essential electrostatic behavior of complex lipid bilayers.