Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, United States.
Langmuir. 2012 May 29;28(21):8165-73. doi: 10.1021/la301090t. Epub 2012 May 14.
A macrocyclic and a linear trimer of a facially amphiphilic cholate building block were labeled with a fluorescent dansyl group. The environmentally sensitive fluorophore enabled the aggregation of the two oligocholates in lipid membranes to be studied by fluorescence spectroscopy. Concentration-dependent emission wavelength and intensity revealed a higher concentration of water for the cyclic compound. Both compounds were shown by the red-edge excitation shift (REES) to be located near the membrane/water interface at low concentrations, but the cyclic trimer was better able to migrate into the hydrophobic core of the membrane than the linear trimer. Fluorescent quenching by a water-soluble (NaI) and a lipid-soluble (TEMPO) quencher indicated that the cyclic trimer penetrated into the hydrophobic region of the membrane more readily than the linear trimer, which preferred to stay close to the membrane surface. The fluorescent data corroborated with the previous leakage assays that suggested the stacking of the macrocyclic cholate trimer into transmembrane nanopores, driven by the strong associative interactions of water molecules inside the macrocycles in a nonpolar environment.
一种具有两亲性的胆酸盐构筑块的大环和线性三聚体被荧光丹磺酰基标记。环境敏感的荧光团能够通过荧光光谱研究两种低聚物在脂质膜中的聚集。浓度依赖性的发射波长和强度表明环状化合物具有更高的水浓度。通过红边激发位移（REES）显示，两种化合物在低浓度时都位于靠近膜/水界面的位置，但环状三聚体比线性三聚体更能够迁移到膜的疏水区。通过水溶性（NaI）和脂溶性（TEMPO）淬灭剂的荧光猝灭表明，环状三聚体比线性三聚体更容易穿透膜的疏水区，而线性三聚体则更倾向于靠近膜表面。荧光数据与之前的泄漏实验结果一致，表明在非极性环境中，大环胆酸盐三聚体通过分子内水分子的强烈缔合相互作用堆叠成跨膜纳米孔。
