H-aggregation of azobenzene-substituted amphiphiles in vesicular membranes
H-aggregation of azobenzene-substituted amphiphiles in vesicular membranes
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DOI：
10.1021/la0358724
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发表时间：
2004-02-17
期刊：
影响因子：
3.9
通讯作者：
Engberts, JBFN
中科院分区：
文献类型：
--
作者：
Kuiper, JM;Engberts, JBFN
研究了双尾含偶氮苯的磷酸两亲体在水囊状分散体和与1,2-二油基- n-甘油-3-磷酸胆碱（DOPC）混合囊状体系中的光化学开关。由于切换的难易程度取决于双层填料的强度，因此特别强调了在囊泡疏水核心中h聚集的发生。紫外-可见光谱法用于监测h -聚集，并显示了这一过程如何取决于离子强度和制备囊泡的方式。在含有5 mol %偶氮苯磷酸的混合DOPC囊泡中观察到两种类型的h聚集体：一种是在300 nm左右的a聚集体，另一种是在305-320 nm的λ (max)聚集体。λ (max)在300 nm处不能发生顺式光异构化，而λ (max)在305 ~ 320 nm处排列松散，可以进行光化学开关。以钙黄蛋白为荧光探针的渗漏实验检测了囊泡双层的渗透性，作为双层填充强度的另一种测量方法。只有在紫外光照射下，偶氮苯磷酸盐含量超过20 mol %的DOPC囊泡才会发生泄漏。我们认为，关于双层包装的详细信息对于微调囊泡膜的侧压力至关重要，最终目的是引导大电导的机械敏感蛋白通道的打开和关闭。
Photochemical switching has been studied of double-tailed phosphate amphiphiles containing azobenzene units in both tails in aqueous vesicular dispersions and in mixed vesicular systems with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Since the ease of switching depends on the strength of the bilayer packing, particular emphasis has been placed on the occurrence of H-aggregation in the hydrophobic core of the vesicles. UV-vis spectrometry was employed to monitor H-aggregation and showed how this process depends on the ionic strength and on the mode of preparation of the vesicles. Two types of H-aggregates were observed in mixed DOPC vesicles with 5 mol % of azobenzene phosphate: one with a at around 300 nm and one with lambda(max) at 305-320 nm. Those with lambda(max) at 300 nm could not be trans-cis photoisomerized, whereas those with lambda(max) at 305-320 nm are more loosely packed and can be photochemically switched. The permeability of the vesicular bilayers, as probed with leakage experiments using calcein as a fluorescent probe, was examined as another measure for the strength of bilayer packing. Leakage occurred only for DOPC vesicles containing more than 20 mol % of azobenzenephosphate, irradiated with UV light to induce trans-cis photoisomerization. We contend that detailed information on bilayer packing will be of crucial importance for fine-tuning the lateral pressure in vesicular membranes with the ultimate aim to steer the opening and closing of mechanosensitive protein channels of large conductance.