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Configurational entropies of lipids in pure and mixed bilayers from atomic-level and coarse-grained molecular dynamics simulations.

Authors
  • Baron, Riccardo1
  • de Vries, Alex H
  • Hünenberger, Philippe H
  • van Gunsteren, Wilfred F
  • 1 Laboratorium für Physikalische Chemie, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland. , (Switzerland)
Type
Published Article
Journal
The Journal of Physical Chemistry B
Publisher
American Chemical Society
Publication Date
Aug 10, 2006
Volume
110
Issue
31
Pages
15602–15614
Identifiers
PMID: 16884285
Source
Medline
License
Unknown

Abstract

Single-chain and single-fragment configurational entropies of lipid tails in hydrated lipid bilayers are evaluated from molecular dynamics simulations using the quasi-harmonic approximation. The entropy distribution along individual acyl tails is obtained and compared to that of corresponding hydrocarbon chains in the liquid phase. We consider pure dipalmitoylphosphatidylcholine and mixed dioleoylphosphatidylcholine/dioleoylphosphatidylethanolamine bilayers. The systems are modeled at different levels of spatial resolution: In an atomic-level (AL) model all (heavy) atoms are explicitly simulated; in a coarse-grained (CG) model particles (beads) representing groups of covalently bound atoms are used, which map approximately four non-hydrogen atoms to one interaction site. Single-chain and single-fragment entropies and correlations between the motions of (single) acyl chains are compared. A good correspondence is found between the flexibility of the AL and CG models. The loss in configurational entropy due to the reduction in the number of degrees of freedom upon coarse-graining of the model is estimated. The CG model shows about 4 times faster convergence of the chain entropies than the more detailed AL model. Corrections to the quasi-harmonic entropy estimates were found to be small for the CG model. For the AL model, the correction due to mode anharmonicities is small, but the correction due to pairwise (supralinear) mode correlations is sizable.

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