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Calculating the bulk modulus for a lipid bilayer with nonequilibrium molecular dynamics simulation.
Gary Ayton1, Alexander M Smondyrev, Scott G Bardenhagen
1Department of Chemistry and Henry Eyring Center for Theoretical Chemistry, University of Utah, Salt Lake City, Utah, 84112 USA.
Biophysical Journal
|February 28, 2002
Summary
Nonequilibrium molecular dynamics simulations reveal differing bulk moduli for lipid bilayers during expansion versus contraction. This study explains the molecular origins of this pressure response difference in dimyristoylphosphatidylcholine bilayers.
Area of Science:
- Computational biophysics
- Materials science of lipid bilayers
Background:
- Lipid bilayers are complex systems exhibiting long time-scale conformational changes.
- Accurate calculation of material properties like bulk modulus is crucial for understanding bilayer behavior.
Purpose of the Study:
- To develop and apply a methodology using nonequilibrium molecular dynamics (NEMD) to calculate the bulk modulus of a dimyristoylphosphatidylcholine (DMPC) bilayer.
- To investigate the molecular origins of pressure response differences during bilayer expansion and contraction.
- To reconcile simulation findings with experimental osmotic stress data.
Main Methods:
- Utilized nonequilibrium molecular dynamics (NEMD) computer simulations.
- Developed a novel NEMD methodology for complex, long time-scale systems.
- Analyzed molecular-level pressure responses to explain observed mechanical properties.
Main Results:
- Calculated the bulk modulus for a DMPC bilayer using NEMD.
- Observed that the bulk modulus upon expansion from a zero stress state agrees with experimental estimates.
- Found a larger bulk modulus upon contraction from a zero stress state compared to expansion.
- Identified molecular-level mechanisms responsible for the observed pressure response asymmetry.
Conclusions:
- The NEMD methodology is effective for calculating material properties in complex, dynamic systems.
- The asymmetry in bulk modulus during compression and expansion is explained by molecular interactions.
- The study addresses an apparent contradiction with previous osmotic stress experiments, providing a more comprehensive understanding of lipid bilayer mechanics.