Institute of Chemistry and Center for Nanoscience and Nanotechnology and ‡Racah Institute of Physics, The Hebrew University of Jerusalem , Edmond J. Safra Campus, Givat Ram, Jerusalem, 9190401, Israel.
Langmuir. 2017 Jun 13;33(23):5636-5641. doi: 10.1021/acs.langmuir.7b00596. Epub 2017 May 26.
The interaction between multivalent ions and lipid membranes with saturated tails and dipolar (net neutral) headgroups can lead to adsorption of the ions onto the membrane. The ions charge the membranes and contribute to electrostatic repulsion between them, in a similar manner to membranes containing charged lipids. Using solution X-ray scattering and the osmotic stress method, we measured and modeled the pressure-distance curves between partially charged membranes containing mixtures of charged (1,2-dilauroyl-sn-glycero-3-phospho-l-serine, DLPS) and dipolar (1,2-dilauroyl-sn-glycero-3-phosphocholine, DLPC) lipids over a wide range of membrane charge densities. We then compared these pressure-distance curves with those of DLPC membranes in the presence of 10 mM CaCl. Our data and modeling show that when low osmotic stress is applied to the DLPC bilayers, the membrane charge density is equivalent to that of a charged membrane containing ca. 4 mol % DLPS and 96 mol % DLPC. As the osmotic stress increased, the charge density of the DLPC membrane decreased and resembled that of a membrane containing ca. 1 mol % DLPS. These data are consistent with desorption of the calcium ions from the DLPC membrane with increasing osmotic stress.
多价离子与具有饱和尾部和偶极（净中性）头基的脂质膜之间的相互作用可以导致离子吸附在膜上。这些离子使膜带电，并以类似于含有带电脂质的膜的方式，有助于它们之间的静电排斥。我们使用溶液 X 射线散射和渗透压方法，测量并模拟了在广泛的膜电荷密度范围内，含有混合带电（1,2-二月桂酰基-sn-甘油-3-磷酸-L-丝氨酸，DLPS）和偶极（1,2-二月桂酰基-sn-甘油-3-磷酸胆碱，DLPC）脂质的部分带电膜之间的压力-距离曲线。然后，我们将这些压力-距离曲线与存在 10 mM CaCl 的 DLPC 膜的压力-距离曲线进行了比较。我们的数据和模型表明，当对 DLPC 双层施加低渗透压时，膜的电荷密度相当于含有约 4 mol % DLPS 和 96 mol % DLPC 的带电膜的电荷密度。随着渗透压的增加，DLPC 膜的电荷密度降低，类似于含有约 1 mol % DLPS 的膜的电荷密度。这些数据与随着渗透压的增加，钙离子从 DLPC 膜上解吸的情况一致。
