Asymmetric charge distributions in planar bilayer systems

Area of Science:

• Physical Chemistry
• Biophysics
• Electrochemistry

Background:

• The distribution of charged lipid molecules within bilayers is crucial for membrane function.
• Understanding transbilayer potential requires knowledge of ion interactions at the membrane interface.

Purpose of the Study:

• To investigate the equilibrium distribution of charged lipids in bilayer membranes.
• To determine if ionic strength and valency differences in bathing solutions induce asymmetry.
• To quantify the resulting transbilayer potential.

Main Methods:

• Application of irreversible thermodynamics principles.
• Utilizing the Gouy-Chapman theory of the electrical double layer.
• Numerical calculations based on specific ionic concentrations and lipid compositions.

Main Results:

• Equilibrium distribution of charged lipids is asymmetric under conditions of equal ionic strength but differing ion valencies.
• A specific example showed a 1.46 ratio of charged lipids and an 18 mV transbilayer potential.
• Comprehensive numerical results are provided, illustrating various scenarios.

Conclusions:

• Ion valency, not just ionic strength, dictates charged lipid distribution asymmetry.
• This asymmetry is a direct cause of measurable transbilayer potentials.
• The findings have implications for membrane electrostatics and function.