The dipole potential of lipid bilayers is an underexplored yet critical property that influences numerous membrane-associated biophysical processes. It arises from the alignment of water and lipid dipolar groups, and does not depend on the presence of charged lipids or external electric fields. In this study, we used the voltage-sensitive fluorophore Di8-ANEPPS to measure the dipole potential of a wide variety of phosphatidylcholine (PC) lipids with different chain structure and backbone chemistry. Confirming previous studies, we find that fully saturated lipids have consistently larger dipole potential than unsaturated and branched-chain lipids, which in turn have larger potential than ether-linked lipids. Remarkably, the lowest dipole potentials were found for sphingomyelins and plasmalogen-PC. The trends reported by Di8 were in excellent agreement with dipole potential values calculated from all-atom molecular dynamics simulations using the CHARMM36 force field. The addition of cholesterol increased the dipole potential to different extents for different species, a result that was also replicated in MD simulations. We further measured ternary mixtures consisting of high- and low-melting species plus cholesterol at compositions corresponding to liquid-disordered (Ld) and liquid-ordered (Lo) phases. Consistent with the results from single-component bilayers, the dipole potential contrast between Lo and Ld was lowest for mixtures of sphingomyelins and unsaturated lipids. A strong correlation was found between the dipole potential contrast of Ld and Lo phases and the miscibility transition temperature of corresponding phase-separated mixtures measured with FRET. Overall, this work establishes a foundation for quantitative and comparative studies of dipole potential across diverse membrane compositions, thus paving the way for deeper understanding of the role of electrostatics in lateral lipid organization.
Sarker et al. (2026) studied this question.