Understanding Thermal Phases in Atomic Detail by All-Atom Molecular-Dynamics Simulation of a Phospholipid Bilayer

Importance of Hydrophilic Groups on Modulating the Structural, Mechanical, and Interfacial Properties of Bilayers: A Comparative Molecular Dynamics Study of Phosphatidylcholine and Ion Pair Amphiphile Membranes

An ion pair amphiphile (IPA), a molecular complex composed of two oppositely charged amphiphiles, is a phospholipid mimic which differs from a phospholipid only in the hydrophilic compositions. Here, we utilized molecular dynamics (MD) simulations to compare the bilayer systems composed of phosphatidylcholines (PC) and alkyltrimethylammonium-alkylsulfate IPAs with various alkyl chain lengths. The membrane properties for both liquid-disordered (Ld) and gel (S) phase bilayers were examined via running simulations above and below the main transition temperatures. The electrostatic attraction between the IPA hydrophilic groups leads to a more ordered molecular packing within both S and Ld phase IPA membranes, as revealed by the molecular area, deuterium order parameter, and gauche conformation analyses. Furthermore, IPA bilayers possess a higher area compressibility modulus, molecular tilt modulus, and effective bending rigidity than PC systems. The variation of hydrophilic groups of IPA also leads to fewer hydrogen bonds on the membrane surface and smaller electrostatic potentials for the biomimetic bilayer. The non-covalently linked head groups of IPA further decouple alkyl tilting and surface water retention. The combined results reveal the importance of hydrophilic groups of amphiphiles on modulating the membrane properties, which also provides insights for designs of biomimetic membranes.

Monitoring drug–lipid membrane interactions via a molecular rotor probe

A label-free sensing method based on membrane viscosity changes to study the interactions between small drug molecules and lipid bilayers.

Molecular Simulation of the DPPE Lipid Bilayer Gel Phase: Coupling between Molecular Packing Order and Tail Tilt Angle

The structural properties and thermal stability of dipalmitoylphosphatidylethanolamine (DPPE) in the ordered gel phase have been studied by molecular dynamics simulation using two force fields: the Berger united-atom model and the CHARMM C36 atomistic model. As is widely known, structural features are sensitive to the initial preparation of the gel phase structure, as some degrees of freedom are slow to equilibrate on the simulation time scale of hundreds of nanoseconds. In particular, we find that the degree of alignment of the lipids' glycerol backbones, which join the two hydrocarbon tails of each molecule, strongly affects the tilt angle of the tails in the resulting structures. Disorder in the backbone correlates with lower tilt angles: bilayer configurations initiated with aligned backbones produced tilt angles near 21° and 29° for the Berger and C36 force fields, respectively, while structures initiated with randomized backbone orientations showed average tilt angles of 7° and 18°, in closer agreement with the untilted structure observed experimentally. The transition temperature for the Berger force field gel bilayer has been determined by monitoring changes in width of gel phase stripe domains as a function of temperature and is 12 ± 5 K lower than the experimental value.