On the Structural and Dynamical Properties of DOPC Reverse Micelles

Area of Science:

• Physical Chemistry
• Soft Matter Physics
• Computational Biophysics

Background:

• Phospholipid reverse micelles are crucial self-assembled nanostructures in various chemical and biological systems.
• Understanding their structure-property relationships is key to applications in drug delivery and nanotechnology.
• Previous studies on synthetic surfactants provide a basis for investigating natural lipid systems.

Purpose of the Study:

• To investigate the structure and dynamics of 1,2-dioleoyl-sn-phosphatidylcholine (DOPC) reverse micelles in benzene using molecular dynamics.
• To determine the aggregation number of DOPC reverse micelles and correlate it with experimental data.
• To elucidate the influence of micelle size and water content on internal water dynamics and head group hydration.

Main Methods:

• All-atom unconstrained molecular dynamics simulations were performed for DOPC reverse micelles of varying sizes (W₀ = 1 to 16) in benzene.
• Aggregation numbers were calculated to match experimental light-scattering measurements of micelle diameter.
• Analysis included structural characterization (layered vs. non-layered), head group hydration, and water molecule dynamics (reorientation).

Main Results:

• Simulated reverse micelles were generally spherical, with larger micelles (W₀ > 4) showing a distinct layered structure (water core, head groups, tails).
• Smaller micelles (W₀ ≤ 4) displayed less defined structures, with partially hydrated head groups often found within the water core.
• Water molecule dynamics slowed considerably with decreasing micelle size, and were notably slower in DOPC micelles compared to AOT/Igepal micelles at equivalent W₀, attributed to smaller water pools and stronger water-head group interactions.

Conclusions:

• DOPC reverse micelle structure is size-dependent, transitioning from disordered to layered arrangements as size increases.
• Water dynamics are significantly hindered in smaller DOPC reverse micelles, impacting their behavior and interactions.
• The findings provide insights into the fundamental properties of phospholipid self-assembly and water confinement in nanoscale environments.