Abstract:
Moderate chain-length mismatch in saturated lipid mixtures provides a
useful model for understanding how structural perturbations influence
membrane behavior. Here, all-atom molecular dynamics simulations were
used to investigate DPPC/DLPC bilayers across compositions at 50 °C,
focusing on the coupled evolution of structure, dynamics, and hydration.
Increasing DLPC content leads to a systematic increase in area per lipid and
a reduction in bilayer thickness, indicating weakened packing within the
hydrophobic core. These structural changes are accompanied by enhanced
interleaflet coupling and decreased acyl-chain ordering. The lateral diffusion
behavior is composition-dependent: DLPC mobility increases steadily with
concentration, whereas DPPC exhibits a non-monotonic trend, reflecting
competing effects of increased free volume and heterogeneous packing. Mean
squared displacement analysis in log–log representation reveals persistent
subdiffusive dynamics for both lipid species, with diffusion exponents α ≈
0.30–0.35 across all compositions. This indicates that lipid motion remains
governed by transient confinement and spatial heterogeneity, even as overall
mobility increases. In parallel, water density profiles show enhanced
penetration of water into the bilayer interior with increasing DLPC fraction,
driven by packing defects and increased free volume rather than pore
formation. These results demonstrate that moderate chain-length mismatch
induces a coupled structural and dynamical response that governs
membrane transport properties
