The Effect of Divalent Ions on the Structure of Bilayers in the Dimyristoylphosphatidylcholine Vesicles

Abstract

Abstract: We have studied changes in the structural parameters of 1,2-dimyristoyl-sn-3-phosphocholine (DMPC) unilamellar vesicles at a concentration series 0–30 mM of divalent metal cations Ca2+, Mg2+, and Co2+ by means of small-angle neutron scattering (SANS). The membrane structural parameters (thickness and area per lipid) were obtained at different concentrations of cations in the gel and fluid phases of membrane. Both Ca2+ and Mg2+ ions at the concentrations of 0–1 mM increase the membrane thickness by 1.9 Å and 2.9 Å in the fluid and gel phase, respectively. In the concentration range of 1–30 mM, either a weak tendency to a thickness decrease of ~ 1 Å is observed, or the thickness does not change at all. In the case of Co2+ ions, all changes are extremely weak. We advocate a model of electrostatic interactions for these systems that encompasses the formation of ion bridges between lipid headgroups. Using the Langmuir adsorption isotherm we estimate the fraction of Ca2+ ions bound to the DMPC membrane. The developed model is of an interest to the future studies of membrane interactions with various charged peptides, such as those from the amyloid-β family.