Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
The Fritz Haber Center, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 9190401, Israel.
Langmuir. 2020 Sep 15;36(36):10715-10724. doi: 10.1021/acs.langmuir.0c01511. Epub 2020 Sep 1.
The interaction between lipid membranes and ions is associated with a range of key physiological processes. Most earlier studies have focused on the interaction of lipids with cations, while the specific effects of the anions have been largely overlooked. Owing to dissolved atmospheric carbon dioxide, bicarbonate is an important ubiquitous anion in aqueous media. In this paper, we report on the effect of bicarbonate anions on the interactions between dipolar lipid membranes in the presence of previously adsorbed calcium cations. Using a combination of solution X-ray scattering, osmotic stress, and molecular dynamics simulations, we followed the interactions between 1,2-didodecanoyl--glycero-3-phosphocholine (DLPC) lipid membranes that were dialyzed against CaCl solutions in the presence and absence of bicarbonate anions. Calcium cations adsorbed onto DLPC membranes, charge them, and lead to their swelling. In the presence of bicarbonate anions, however, the calcium cations can tightly couple one dipolar DLPC membrane to the other and form a highly condensed and dehydrated lamellar phase with a repeat distance of 3.45 ± 0.02 nm. Similar tight condensation and dehydration has only been observed between charged membranes in the presence of multivalent counterions. Bridging between bilayers by calcium bicarbonate complexes induced this arrangement. Furthermore, in this condensed phase, lipid molecules and adsorbed ions were arranged in a two-dimensional oblique lattice.
脂质膜与离子的相互作用与一系列关键的生理过程有关。大多数早期的研究都集中在脂质与阳离子的相互作用上，而阴离子的具体影响在很大程度上被忽视了。由于溶解在大气中的二氧化碳，碳酸氢根是水介质中一种重要的普遍存在的阴离子。在本文中，我们报告了碳酸氢根阴离子对先前吸附的钙离子存在下二酰基甘油磷酸胆碱（DLPC）脂质膜之间相互作用的影响。我们使用溶液 X 射线散射、渗透压和分子动力学模拟的组合，研究了在存在和不存在碳酸氢根阴离子的情况下，DLPC 脂质膜在 CaCl2 溶液中透析时的相互作用。钙离子吸附在 DLPC 膜上，使它们带电，并导致它们膨胀。然而，在碳酸氢根阴离子的存在下，钙离子可以将一个偶极 DLPC 膜紧密地耦合到另一个膜上，并形成一个高度浓缩和脱水的层状相，其重复距离为 3.45±0.02nm。只有在存在多价抗衡离子的情况下，带电荷的膜之间才会观察到类似的紧密凝聚和脱水。由钙碳酸氢盐复合物在双层之间形成的桥接导致了这种排列。此外，在这个浓缩相中，脂质分子和吸附离子被排列在二维斜晶格中。
