Ripple-like instability in the simulated gel phase of finite size phosphocholine bilayers

• Published in: Biochimica et biophysica acta. Biomembranes Vol. 1863; no. 11; p. 183714
• Main Authors: Walter, Vivien, Ruscher, Céline, Gola, Adrien, Marques, Carlos M., Benzerara, Olivier, Thalmann, Fabrice
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2021; Elsevier
• Subjects: Condensed Matter; Lipid bilayers; Molecular dynamics simulations; Phase transition; Physics; Soft Condensed Matter; Lipid bilayers; Molecular dynamics simulations; Phase transition
• ISSN: 0005-2736; 1879-2642
• DOI: 10.1016/j.bbamem.2021.183714

Atomistic molecular dynamics simulations have reached a degree of maturity that makes it possible to investigate the lipid polymorphism of model bilayers over a wide range of temperatures. However if both the fluid Lα and tilted gel Lβ′ states are routinely obtained, the Pβ′ ripple phase of phosphatidylcholine lipid bilayers is still unsatifactorily described. Performing simulations of lipid bilayers made of different numbers of DPPC (1,2-dipalmitoylphosphatidylcholine) molecules ranging from 32 to 512, we demonstrate that the tilted gel phase Lβ′ expected below the pretransition cannot be obtained for large systems (equal or larger than 94 DPPC molecules) through common simulations settings or temperature treatments. Large systems are instead found in a disordered gel phase which display configurations, topography and energies reminiscent from the ripple phase Pβ′ observed between the pretransition and the main melting transition. We show how the state of the bilayers below the melting transition can be controlled and depends on thermal history and conditions of preparations. A mechanism for the observed topographic instability is suggested. [Display omitted] •Atomistic simulations of DPPC bilayers display a low temperature bilayer corrugation.•This corrugated state is reminiscent of the ripple phase and depends on box geometry.•The difference between interfacial and projected areas can characterizes this state.•A simple model reproduces the competition between tilt, hydration and chain melting.