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Description
Dipalmitoylphosphatidylcholine (DPPC) is a phospholipid found in lung surfactant that exhibits three temperature-dependent structural phases: gel, ripple gel, and liquid-crystalline. These phases differ in lipid ordering and may respond differently to ionic conditions and external electrical stimulation.
To investigate these effects, DPPC bilayer systems were constructed using CHARMM-GUI at temperatures corresponding to each phase and compared under three conditions: no added ions, KCl, and electrical-field stimulation. Each system contained 150 lipids per leaflet and was simulated at 1 atm using GROMACS (version 2024.3). Simulations included energy minimization, equilibration, and 400 ns production runs, with the final 50 ns used for analysis.
Area-per-lipid, acyl-chain order parameters and bilayer thicknesses were calculated using the Molecular Dynamics Analysis (MDAnalysis) package in Python to evaluate membrane stability and lipid organization. The results for DPPC with no added ions showed an area per lipid of 0.528 nm² at 310 K and relatively high acyl-chain ordering, with order parameters of approximately 0.39 through the lipid tails. Bilayer thickness without added ions decreased from 4.41 nm at 298 K to 4.25 nm at 310 K and 3.99 nm at 325 K, indicating progressive temperature-dependent structural changes across the three membrane phases. This study compares how temperature-dependent membrane phases, KCl, and electrical-field stimulation influence DPPC bilayer structure, providing insight into how membrane state affects its response to ionic and electrical perturbations.
