Mixed DPPC/POPC Monolayers: All-atom Molecular Dynamics Simulations and Langmuir Monolayer Experiments

Area of Science:

• Biophysics
• Materials Science
• Surface Chemistry

Background:

• Lipid monolayers, particularly mixtures of saturated and unsaturated lipids, are fundamental to biological systems, such as lung surfactant.
• Investigating these systems at physiological temperatures provides insights into their functional relevance.

Purpose of the Study:

• To investigate the consequences of saturated-unsaturated lipid mixtures in monolayers under varying surface pressures.
• To compare the behavior of a binary lipid mixture with its individual components.

Main Methods:

• Utilized all-atom molecular dynamics simulations and Langmuir trough experiments.
• Analyzed atomistic-level alterations in monolayer molecular properties during lateral compression.
• Examined changes in lipid chain ordering, orientation, and hydration.

Main Results:

• The presence of unsaturated 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) moderated the phase transition and reduced the coexistence region in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/POPC mixtures.
• Simulations predicted nanoscale lipid de-mixing and transient DPPC cluster formation.
• Observed vertical lipid sorting, with DPPC moving towards the water phase upon compression.

Conclusions:

• Monolayer compression induces significant conformational changes and lateral inhomogeneities in lipid films.
• These findings are relevant to the dynamic and non-homogeneous nature of lipid interfacial systems in biological contexts.