BIOPHYSICAL THEORY AND MODELING |
Comparing Experimental and Simulated Pressure-Area Isotherms for DPPC
Susan L Duncan 1 and Ronald G Larson 1*
1 University of Michigan
* To whom correspondence should be addressed. E-mail: rlarson{at}umich.edu.
Submitted on June 5, 2007
Revised on July 26, 2007
Accepted on 3 December 2007
 |
Abstract |
|---|
Although pressure-area isotherms are commonly measured for lipid monolayers, it is not always appreciated how much they can vary depending on experimental factors. Here, we compare experimental and simulated pressure-area isotherms for DPPC (dipalmitoylphosphatidylcholine) at temperatures ranging between 293.15K and 323.15K, and explore and possible factors influencing the shape and position of the isotherms. Molecular dynamics simulations of DPPC monolayers using both a coarse grained (CG) and an atomistic model yield results that are in rough agreement with some of the experimental isotherms, but with a steeper slope in the liquid-condensed (LC) region than seen experimentally and shifted to larger areas. The CG lipid model of Marrink et al. gives predictions that are very close to those of atomistic simulations, while greatly improving computational efficiency. There is much more variation among experimental isotherms than between isotherms obtained from CG simulations and from the most refined simulation available. Both atomistic and CG simulations yield LC and liquid-expanded (LE) phase area compressibility moduli that are significantly larger than those typically measured experimentally, but compare well with some experimental values obtained under rapid compression.
Key Words:
coarse grained, dipalmitoyl lecithin, dipalmitoylphosphatidylcholine, liquid-condensed, liquid-expanded, phase transition
