Induced Order and Reciprocal Disorder in DPPC/DOPC Asymmetric Membranes.

Asymmetric bilayers demonstrate unique structural and dynamic properties compared to symmetric membranes. We investigated asymmetric bilayers constructed with dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) at 300 K using atomistic molecular dynamics simulations. The bilayers exhibited domain interdigitation, with DOPC lipids penetrating the DPPC leaflet. Alongside this, the DOPC lipids exhibited an increased order, indicating order induction in asymmetric bilayers. Interestingly, the DPPC leaflet—normally characterized by a higher degree of order—showed a reduction in order when paired with DOPC, suggesting reciprocal disorder induction across the bilayer interface. To further probe the mechanism of induced order and disorder, the DOPC bilayers were artificially compressed up to 25 atm, reducing their area per lipid by ~10% and thereby increasing their order parameter before constructing the asymmetric bilayer. Asymmetric bilayers composed of compressed DOPC and non-compressed DPPC leaflets displayed reduced interdigitation while maintaining elevated DOPC order. These results highlight how artificially tuning order by compression modulates interdigitation and reveal a coupled mechanism of order–disorder induction between the two leaflets in asymmetric membranes.