Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan, 250100, China.
Soft Matter. 2017 Sep 27;13(37):6490-6498. doi: 10.1039/c7sm01528c.
A novel photo-responsive anionic surfactant with a dimethylamino-substituted azobenzene located at the end of the hydrophobic chain, 6-(4-dimethylaminoazobenzene-4'-oxy)hexanoate sodium (DAH), has been designed. Through the host-guest interaction in aqueous solution, the trans-DAH could be spontaneously included by using two native α-cyclodextrin (α-CD) molecules. The formed hydrophilic inclusion complex (DAH@2α-CD), however, could act as a gelator to induce the formation of a supramolecular hydrogel, which is driven mainly by hydrogen bonds between neighboring α-CDs and also between the carboxylate in DAH and water. Compared with common hydrogels that consist of networks with fibres or discrete polymer chains, the hydrogel formed by DAH@2α-CD was composed of periodic lamellar structures possessing good shear-thinning behavior and much swollen water layers. The more interesting point for such a hydrogel was its visible-light responsibility for gel-sol reversible phase transition. This originated from the introduction of an electron-donating group (dimethylamino) to azobenzene, which noticeably red-shifted the responsive wavelength for its trans-to-cis isomerization. It was also worth noting that the host-guest interaction between azobenzene in DAH and α-CD significantly improved the photo-transition efficiency from trans to cis forms of azobenzene, which played a critical role in the visible-light responsibility of the hydrogel. This unique visible-light-responsive behavior combined with the inherent thermo-responsive property from α-CD should make the prepared hydrogel find more potential applications in biomedical systems.
设计了一种新型光响应阴离子表面活性剂，其疏水链末端带有二甲氨基取代的偶氮苯，即 6-（4-二甲氨基偶氮苯-4'-氧基）己酸钠（DAH）。通过在水溶液中的主体-客体相互作用，反式 DAH 可以自发地被两个天然的α-环糊精（α-CD）分子包合。形成的亲水性包合物（DAH@2α-CD），然而，可以作为凝胶剂诱导超分子水凝胶的形成，该水凝胶主要是由相邻的α-CDs 之间以及 DAH 中的羧酸盐与水之间的氢键驱动的。与由纤维或离散聚合物链组成的网络的普通水凝胶相比，由 DAH@2α-CD 形成的水凝胶由具有良好的剪切稀化行为和更多溶胀水层的周期性层状结构组成。这种水凝胶更有趣的一点是其对可见光的响应能力，可实现凝胶-溶胶的可逆相转变。这源于在偶氮苯中引入供电子基团（二甲氨基），明显红移了其反式到顺式异构化的响应波长。值得注意的是，DAH 中的偶氮苯与α-CD 之间的主体-客体相互作用显著提高了偶氮苯从反式到顺式形式的光转变效率，这在水凝胶的可见光响应中起着关键作用。这种独特的可见光响应行为与α-CD 固有的热响应特性相结合，应该使制备的水凝胶在生物医学系统中找到更多潜在的应用。
