Unbinding Transition Induced by Osmotic Pressure in Relation to Unilamellar Vesicle Formation

TL;DR

This study investigates how osmotic pressure influences vesicle formation in a DOPC/water/NaI system, revealing that osmotic pressure induces an unbinding transition leading to unilamellar vesicle formation.

Contribution

It demonstrates that osmotic pressure causes an unbinding transition during hydration, promoting unilamellar vesicle formation, supported by experimental and free-energy calculations.

Findings

Multi-lamellar vesicles form without NaI

Unilamellar vesicles form with sufficient NaI

Osmotic pressure induces an unbinding transition

Abstract

Small-angle X-ray scattering and phase-contrast microscopy experiments were performed to investigate the effect of the osmotic pressure on vesicle formation in a dioleoylphosphatidylcholine (DOPC)/water/NaI system. Multi-lamellar vesicles were formed when a pure lipid film was hydrated with an aqueous solution of NaI. On the other hand, uni-lamellar vesicles (ULVs) were formed when a lipid film mixed with an enough amount of NaI was hydrated. To confirm the effect of the osmotic pressure due to NaI, a free-energy calculation was performed. This result showed that the osmotic pressure induced an unbinding transition on the hydration process, which resulted in ULV formation.