Interactions between charged, uncharged, and zwitterionic bilayers containing phosphatidylglycerol

Area of Science:

• Biophysics
• Materials Science

Background:

• Phosphatidylglycerol bilayers are fundamental components of cell membranes.
• Understanding lipid bilayer interactions is crucial for drug delivery and biomaterial design.

Purpose of the Study:

• To determine the pressure-distance relationships for phosphatidylglycerol bilayers in charged and uncharged states.
• To elucidate the forces governing bilayer interactions, including hydration, electrostatic, and steric effects.

Main Methods:

• Lipid multilayers were subjected to osmotic pressures (0-2.7 x 10^9 dyn/cm^2) to control water removal.
• Lamellar x-ray diffraction and Fourier analysis were used to measure bilayer separations.
• Volta potential measurements in monolayers provided insights into bilayer surface potentials.

Main Results:

• Uncharged phosphatidylglycerol bilayers showed hydration pressure with decay lengths of 1.1 Å (low pH) and 1.5 Å (with stearylamine).
• Charged bilayers exhibited electrostatic repulsion (decay length 11 Å) at separations >10 Å.
• At separations <10 Å, charged bilayers displayed rapid pressure decay (<1 Å), attributed to hydration and steric hindrance.

Conclusions:

• The study differentiates pressure-distance behaviors of charged and uncharged phosphatidylglycerol bilayers.
• Hydration pressure dominates neutral bilayers, while charged bilayers show complex interactions involving electrostatic and steric forces.
• Findings contribute to the understanding of lipid-lipid interactions and membrane mechanics.