Effect of pH on the Binding of Sodium, Lysine, and Arginine Counterions to L-Undecyl Leucinate Micelles
Effect of pH on the Binding of Sodium, Lysine, and Arginine Counterions to L-Undecyl Leucinate Micelles
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DOI：
10.1007/s11743-016-1875-y
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发表时间：
2016-11-01
影响因子：
1.6
通讯作者：
Morris, Kevin F.
中科院分区：
文献类型：
--
作者：
Lewis, Corbin;Hughes, Burgoyne H.;Morris, Kevin F.
采用核磁共振、动态光散射和荧光光谱技术研究了氨基酸基表面活性剂十一烯基亮氨酸形成胶束与溶液pH的关系。核磁共振和动态光散射表明，50 mM的十乙烯基亮氨酸和50 mM的NaHCO3溶液中含有直径约为20的胶束，胶束半径和与胶束相关的表面活性剂分子的摩尔分数随溶液pH变化很小。在pH 7.0 ~ 11.5范围内，研究了氨基酸精氨酸和赖氨酸与阴离子胶束的结合。在pH为9.0时，与胶束结合的精氨酸阳离子摩尔分数约为0.4。当pH值高于9.0时，精氨酸反离子变为两性离子，结合后的精氨酸分子摩尔分数在pH值为11时稳定下降至0.1以下。当精氨酸与胶束分离时，胶束半径从14减小到10。赖氨酸也有类似的行为；然而，当赖氨酸从胶束表面解离时，胶束半径几乎没有变化。二维核磁共振实验表明，在pH 9.0以下，l-精氨酸主要通过其侧链胺与胶团表面垂直结合，而l-赖氨酸则通过其两个胺官能团与胶团表面平行结合。最后，用核磁共振波谱法研究了表面活性剂头团上酰胺质子与溶剂交换的速率。在仅含表面活性剂单体的溶液中，交换反应速度较快，而当表面活性剂为胶束形式且头团酰胺质子与溶剂接触较少时，交换反应速度较慢。
Micelle formation by the amino acid-based surfactant undecylenyl l-leucine was investigated as a function of solution pH with NMR, dynamic light scattering, and fluorescence spectroscopy. NMR and dynamic light scattering showed that 50 mM undecylenyl l-leucine and 50 mM NaHCO3 solutions contained micelles approximately 20 in diameter and that micelle radius and the mole fraction of surfactant molecules associated with micelles changed very little with solution pH. The binding of the amino acids arginine and lysine to the anionic micelles was also investigated from pH 7.0 to 11.5. Below pH 9.0, the mole fraction of arginine cations bound to the micelles was approximately 0.4. Above pH 9.0, the arginine counterions became zwitterionic, and the mole fraction of bound arginine molecules decreased steadily to less than 0.1 at pH 11. When arginine dissociated from the micelles, their radii decreased from 14 to 10 . Similar behavior was observed with lysine; however, when lysine dissociated from the micelle surface, little change in micelle radius was observed. Two-dimensional NMR experiments suggested that below pH 9.0, l-arginine bound perpendicular to the micelle surface primarily though its side chain amine while l-lysine bound parallel to the surface through both of its amine functional groups. Finally, the rate at which the amide protons on the surfactant headgoup exchanged with solvent was investigated with NMR spectroscopy. The exchange reaction was faster in solutions containing only surfactant monomers and slower when the surfactants were in micellar form and the headgoup amide protons were less exposed to solvent.