Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Graduate School Materials Science in Mainz, Staudingerweg 9, 55128 Mainz, Germany.
Sci Adv. 2018 Mar 28;4(3):eaap7415. doi: 10.1126/sciadv.aap7415. eCollection 2018 Mar.
The electrical charge of biological membranes and thus the resulting alignment of water molecules in response to this charge are important factors affecting membrane rigidity, transport, and reactivity. We tune the surface charge density by varying lipid composition and investigate the charge-induced alignment of water molecules using surface-specific vibrational spectroscopy and molecular dynamics simulations. At low charge densities, the alignment of water increases proportionally to the charge. However, already at moderate, physiologically relevant charge densities, water alignment starts to saturate despite the increase in the nominal surface charge. The saturation occurs in both the Stern layer, directly at the surface, and in the diffuse layer, yet for distinctly different reasons. Our results show that the soft nature of the lipid interface allows for a marked reduction of the surface potential at high surface charge density via both interfacial molecular rearrangement and permeation of monovalent ions into the interface.
生物膜的电荷以及由此产生的水分子对这种电荷的排列，是影响膜刚性、传输和反应性的重要因素。我们通过改变脂质组成来调节表面电荷密度，并使用表面特异性振动光谱和分子动力学模拟研究电荷诱导的水分子排列。在低电荷密度下，水的排列与电荷成正比增加。然而，即使在名义表面电荷增加的情况下，在中等、生理相关的电荷密度下，水的排列就开始饱和。这种饱和发生在 Stern 层（直接在表面）和扩散层中，但原因明显不同。我们的结果表明，脂质界面的柔软性质允许通过界面分子重排和单价离子渗透到界面中来显著降低高表面电荷密度下的表面电势。
