Binder Hans, Zschörnig Olaf
Department of Medicine, Institute of Medical Physics and Biophysics, University of Leipzig, Liebigstr. 27, Leipzig, Germany.
Chem Phys Lipids. 2002 May;115(1-2):39-61. doi: 10.1016/s0009-3084(02)00005-1.
To characterize the specificity of ion binding to phospholipids in terms of headgroup structure, hydration and lyotropic phase behavior we studied 1-palmitoyl-2-oleoyl-phosphatidylcholine as a function of relative humidity (RH) at 25 degrees C in the presence and absence of Li+, Na+, K+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Zn2+ and Cu2+ ions by means of infrared (IR) spectroscopy. All divalent cations and Li+ shift the gel-to-liquid crystalline phase transition towards bigger RH values indicating stabilization of the gel state. The observed shift correlates in a linearly fashion with the electrostatic solvation free energy for most of the ions in water that in turn, is inversely related to the ionic radius. This interesting result was interpreted in terms of the excess chemical potential of mixing of hydrated ions and lipids. Calcium, zinc and partially lithium, cause a positive deviation from the linear relationship. IR spectral analysis shows that the carbonyl groups become more accessible to the water in the presence of Mg2+, Ca2+, Sr2+ and Ba2+ probably because of their involvement into the hydration shell of the ions. In contrast, Be2+, Zn2+ and Cu2+ dehydrate the carbonyl groups at small and medium RH. The ability of the lipid to take up water is distinctly reduced in the presence of Zn2+ and, partially, of Cu2+ meaning that the headgroups have become less hydrophilic. The binding mode of Be2+ to lipid headgroups involves hydrolyzed water. Polarized IR spectra show that complex formation of the phosphate groups with divalent ions gives rise to conformational changes and immobilization of the headgroups. The results are discussed in terms of the lyotropic Hofmeister series and of fusogenic activity of the ionic species.
为了从头部基团结构、水合作用和溶致相行为方面表征离子与磷脂结合的特异性，我们在25℃下，通过红外（IR）光谱研究了1-棕榈酰-2-油酰磷脂酰胆碱在有和没有Li⁺、Na⁺、K⁺、Be²⁺、Mg²⁺、Ca²⁺、Sr²⁺、Ba²⁺、Zn²⁺和Cu²⁺离子存在时，作为相对湿度（RH）的函数。所有二价阳离子和Li⁺都将凝胶-液晶相转变移向更高的RH值，表明凝胶态得到稳定。观察到的转变与大多数水中离子的静电溶剂化自由能呈线性相关，而静电溶剂化自由能又与离子半径成反比。这个有趣的结果是根据水合离子和脂质混合的过量化学势来解释的。钙、锌以及部分锂导致与线性关系出现正偏差。红外光谱分析表明，在Mg²⁺、Ca²⁺、Sr²⁺和Ba²⁺存在时，羰基对水变得更易接近，这可能是因为它们参与了离子的水合壳层。相反，在中低RH下，Be²⁺、Zn²⁺和Cu²⁺使羰基脱水。在Zn²⁺以及部分Cu²⁺存在时，脂质吸收水的能力明显降低，这意味着头部基团的亲水性降低。Be²⁺与脂质头部基团的结合模式涉及水解水。偏振红外光谱表明，磷酸基团与二价离子的络合会引起头部基团的构象变化和固定。根据溶致霍夫迈斯特序列和离子种类的融合活性对结果进行了讨论。
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