Sovago Maria, Wurpel George W H, Smits Marc, Müller Michiel, Bonn Mischa
FOM Institute for Atomic and Molecular Physics (AMOLF), Kruislaan 407, 1098 SJ, Amsterdam, The Netherlands.
J Am Chem Soc. 2007 Sep 12;129(36):11079-84. doi: 10.1021/ja071189i. Epub 2007 Aug 16.
The effect of sodium and calcium ions on zwitterionic and anionic phospholipids monolayers is investigated using vibrational sum-frequency generation in conjunction with surface pressure measurements and fluorescence microscopy. Sodium ions only subtly affect the monolayer structure, while the effect of calcium is large and depends strongly on the surface pressure. At low surface pressures (approximately 5 mN/m), the presence on Ca2+ results in the unexpected appearance of ordered domains. For pressures between approximately 5 and approximately 25 mN/m, Ca2+ ions induce disorder in the monolayer. For pressures exceeding 25 mN/m, calcium cations expand the monolayer, while simultaneously ordering the lipid chains. Interestingly, effects are similar for both zwitterionic lipids and negatively charged lipids. In both vibrational sum-frequency generation and surface tension measurements, the molecular signature of the association of Ca2+ with the lipids is evident from Ca2+-induced changes in the signals corresponding to area changes of 4 A2/lipid-precisely the surface area of a Ca2+ ion, with evidence for a change in lipid Ca2+ complexation at high pressures.
利用振动和频产生技术结合表面压力测量和荧光显微镜，研究了钠离子和钙离子对两性离子和阴离子磷脂单层的影响。钠离子仅对单层结构有细微影响，而钙离子的影响较大且强烈依赖于表面压力。在低表面压力（约5 mN/m）下，Ca2+的存在导致有序域意外出现。对于约5至约25 mN/m之间的压力，Ca2+离子会在单层中诱导无序。对于超过25 mN/m的压力，钙阳离子会使单层扩展，同时使脂质链有序排列。有趣的是，两性离子脂质和带负电荷的脂质的效应相似。在振动和频产生测量以及表面张力测量中，Ca2+与脂质结合的分子特征从Ca2+诱导的对应于4 Å2/脂质面积变化的信号变化中明显可见——这正是Ca2+离子的表面积，并且有证据表明在高压下脂质与Ca2+的络合发生了变化。
