Organic Chemistry Institute and Graduate School of Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
Chemistry. 2011 Sep 5;17(37):10297-303. doi: 10.1002/chem.201100789. Epub 2011 Aug 1.
A competitive photoresponsive supramolecular system is formed in a dilute aqueous solution of three components: vesicles of amphiphilic α-cyclodextrin host 1a, divalent p-methylphenyl guest 2 or divalent p-methylbenzamide guest 3, and photoresponsive azobenzene monovalent guest 5. Guests 2 and 3 form weak inclusion complexes with 1a (K(a)≈10(2) M(-1)), whereas azobenzene guest 5 forms a strong inclusion complex (K(a)≈10(4) M(-1)), provided it is in the trans state. The aggregation and adhesion of vesicles of host 1a is mediated by guest 2 (or 3) due to the formation of multiple intervesicular noncovalent links, as confirmed by using isothermal titration calorimetry (ITC), optical density measurements at 600 nm (OD600), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM). The addition of excess monovalent guest trans-5 to vesicles of 1a aggregated by divalent guest 2 (or 3) causes the dispersion of vesicles of 1a because trans-5 displaces 2 (as well as 3) from the vesicle surface. Upon UV irradiation of a dilute ternary mixture of vesicles of 1a, guest 2 (or 3), and competitor trans-5, compound trans-5 isomerizes to cis-5, and renewed aggregation of vesicles of 1a by guest 2 (or 3) occurs because 2 (as well as 3) displaces cis-5 from the vesicle surface. Subsequent visible irradiation causes the redispersion of vesicles of 1a because cis-5 reisomerizes into trans-5, which again displaces guest 2 (or 3) from the vesicle surface. In this way, the competitive photoresponsive aggregation and dispersion of vesicles can be repeated for several cycles.
两亲性α-环糊精主体 1a 的囊泡、二价对甲基苯客体 2 或二价对甲基苯甲酰胺客体 3 以及光响应偶氮苯单价客体 5。客体 2 和 3 与 1a 形成弱包合络合物（K(a)≈10(2) M(-1)），而偶氮苯客体 5 形成强包合络合物（K(a)≈10(4) M(-1)），前提是它处于反式状态。由于形成多个囊泡间的非共价键连接，客体 2（或 3）介导了主体 1a 的囊泡的聚集和黏附，这一点通过使用等温滴定量热法（ITC）、600nm 处的光密度测量（OD600）、动态光散射（DLS）和低温透射电子显微镜（cryo-TEM）得到证实。向由二价客体 2（或 3）聚集的 1a 囊泡中加入过量的单价客体 trans-5 会导致 1a 囊泡的分散，因为 trans-5 从囊泡表面取代 2（以及 3）。当用紫外光辐照含有 1a 囊泡、客体 2（或 3）和竞争性 trans-5 的稀三元混合物时，化合物 trans-5 发生顺反异构化生成 cis-5，并且由于 2（以及 3）从囊泡表面取代 cis-5，重新发生 1a 囊泡的聚集。随后可见光照射导致 1a 囊泡的再分散，因为 cis-5 顺反异构化为 trans-5，这又使客体 2（或 3）从囊泡表面取代。通过这种方式，可以重复进行几个循环的竞争光响应囊泡的聚集和分散。
