Study on the correlation between lateral diffusion effect and effective charge in neutral liposomes

Area of Science:

• Biophysics
• Physical Chemistry
• Materials Science

Background:

• Liposomes are crucial in drug delivery and biomembrane research.
• Understanding phospholipid behavior in liposomes is key to their application.
• Factors influencing liposome charge and membrane dynamics require detailed investigation.

Purpose of the Study:

• To investigate variables affecting the lateral diffusion coefficient (D(lat)) of dimyristoylphosphatidylcholine (DMPC).
• To determine the effective charge (Z(ef)) on liposomes under varying conditions.
• To correlate changes in D(lat) and Z(ef) with environmental factors like pH and salt concentration.

Main Methods:

• Dielectric relaxation time measurements to determine D(lat) of zwitterionic phospholipids.
• Microelectrophoretic mobility measurements using Henry and Coulomb equations to estimate Z(ef).
• Experiments conducted across different pH values, KBr concentrations, and phospholipid physical states (liquid-crystalline and gel phases).

Main Results:

• Liposome effective charge (Z(ef)) and lateral diffusion (D(lat)) were lower in the gel phase compared to the liquid-crystalline phase.
• A minor pH shift (approx. 0.5 units) induced significant variations in both Z(ef) and D(lat).
• A strong correlation was observed between Z(ef) and D(lat) across all tested conditions.

Conclusions:

• Ion adsorption, which dictates electrokinetic potential, also governs the lateral diffusion of dipolar phospholipids within the bilayer.
• The effective charge on the liposome's external surface is directly linked to the diffusion dynamics of its constituent phospholipids.
• Environmental factors like pH and ionic strength play a critical role in modulating liposome surface charge and membrane fluidity.