Solubilization of phospholipids by chaotropic ion solutions

Area of Science:

• Biochemistry and Biophysics
• Lipid Self-Assembly
• Chaotropic Agent Effects

Background:

• Phosphatidylcholine (PC) is a key component of biological membranes.
• Chaotropic agents are known to disrupt the structure of water and biomolecules.
• Understanding lipid solubilization is crucial for membrane biophysics and drug delivery.

Purpose of the Study:

• To investigate the solubilization of phosphatidylcholine (PC) by concentrated neutral chaotropic anions.
• To characterize the structure and dynamics of the resulting lipid aggregates.
• To elucidate the mechanism of lipid phase destabilization and micelle formation.

Main Methods:

• Solubilization assays using sodium trichloroacetate and sodium tribromoacetate.
• Gel exclusion chromatography to determine micelle size.
• 31P Nuclear Magnetic Resonance (NMR) spectroscopy for molecular dynamics.
• Differential Scanning Calorimetry (DSC) to assess phase transition properties.
• Surface tension measurements to confirm micelle formation.

Main Results:

• Egg yolk PC solubilized in 2-3 M Na-trichloroacetate and 1.5-2 M Na-tribromoacetate.
• Formed optically clear solutions of micelles (approx. 100 lipid molecules) with rapid, isotropic motion.
• Dipalmitoyl-PC's phase transition temperature and enthalpy were significantly reduced in 3 M Na-trichloroacetate.
• Trichloroacetate bound to PC liposomes with an affinity constant of ~1 M-1, promoting lamellar to micellar phase transition.

Conclusions:

• Highly chaotropic anions, particularly trichloroacetate and tribromoacetate, effectively solubilize phosphatidylcholine into micelles.
• Anion binding and intercalation destabilize the lamellar lipid phase, favoring micelle formation.
• The chaotropic effect likely reduces the energetic cost of forming micelles with high curvature.