Previous MD simulations of six phosphocholine (PC) lipid bilayers demonstrated the accuracy of the CHARMM36 force field (C36FF) for PC bilayer simulation at varied temperatures (BBA-Biomembranes, 1838 (2014): 2520-2529). In this work, we further examine the accuracy of C36FF over a wide temperature range for a broader range of lipid types such as various head groups (phosphatidic acid (PA), PC, phosphoethanolamine (PE), phosphoglycerol (PG), and phosphoserine (PS)), and tails (saturated, mono-, mixed- and poly-unsaturated acyl chains with varied chain lengths). The structural properties (surface area per lipid (SA/lip), overall bilayer thickness, hydrophobic thickness, headgroup-to-headgroup thickness, deuterium order parameter (SCD), and spin-lattice relaxation time (T1)) obtained from simulations agree well with nearly all available experimental data. Our analyses indicate that PS lipids have the most inter-lipid hydrogen bonds, while PG lipids have the most intra-lipid hydrogen bonds, which play the main role in their low SA/lip in PS lipids and low thicknesses in PG lipids, respectively. PS, PE, and PA lipids have the largest contact clusters with on average 5-8 lipids per cluster, while PC and PG have clusters of 4 lipids based on a cutoff distance of 6.5Å. PS lipids have much slower lipid wobble (i.e., higher correlation time) than other head groups at a given temperature as the hydrogen bonded network significantly reduces a lipid's mobility, and the rate of lipid wobble increases dramatically as temperature increases. These in-depth analyses facilitate further understanding of lipid bilayers at the atomic level.
Keywords: Force field accuracy; Lipid wobble; Molecular dynamics; Structural property.
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