Poly(ester amide)s with pendant azobenzenes: multi-responsive self-immolative moieties for modulating polymer assemblies
Poly(ester amide)s with pendant azobenzenes: multi-responsive self-immolative moieties for modulating polymer assemblies
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DOI：
10.1039/c5py01824b
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发表时间：
2016-03
影响因子：
4.6
通讯作者：
Andrew D. Wong;Alexander L. Prinzen;E. Gillies
中科院分区：
文献类型：
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作者：
Andrew D. Wong;Alexander L. Prinzen;E. Gillies
偶氮苯是众所周知的，他们的反-顺式光异构化，但它最近被证明，偶氮苯衍生物也可以进行还原，引发1，6-消除和引发解聚的自分解聚合物。在这里，我们探索的优化偶氮苯作为还原敏感的部分，并将其纳入功能材料。合成了一系列具有吸电子基团的偶氮苯化合物，并测定了它们被肼还原的速率。出乎意料的是，2-Cl取代基比其他电负性或空间要求高的取代基增加了还原速率。接下来，合成了一种新的含有2-Cl-偶氮苯的二酯单体，并将其引入到聚（酯酰胺）（PEA）骨架中，然后用PEO官能化，得到两亲性多响应材料。然后利用偶氮苯的光敏感性和还原敏感性，在水中对聚合物纳米组装体产生可逆和不可逆的变化。通过紫外-可见光谱、动态光散射和荧光光谱研究了它们对光和/或肼的响应。交替照射紫外光和可见光导致可逆的反-顺异构化，这改变了胶束核心的极性，而不破坏组件。肼还原导致尼罗红从胶束核心中释放，而DLS仍然检测到残留的组装体，可能是由于存在剩余的疏水物。紫外线和肼的组合导致尼罗红的释放和组装件的分解。这些结果表明，偶氮苯对光和还原刺激的固有响应性可以提供聚合物组装体，其通过单个多响应单元以独特和协同的方式响应一种或多种刺激。
Azobenzenes are well-known for their trans–cis photoisomerization, but it was recently demonstrated that azobenzene derivatives could also undergo reduction to trigger a 1,6-elimination and initiate depolymerization of a self-immolative polymer. Herein we explore the optimization of azobenzenes as reduction-sensitive moieties, and their incorporation into functional materials. A library of azobenzenes with electron-withdrawing groups was synthesized, and their rates of reduction by hydrazine were determined. Unexpectedly, a 2-Cl substituent increased the rate of reduction more than other electronegative or sterically-demanding substituents. Next, a new diester monomer containing the 2-Cl-azobenzene was synthesized and incorporated into a poly(ester amide) (PEA) backbone, which was then functionalized with PEO to afford an amphiphilic multi-responsive material. The photo- and reduction-sensitivity of the azobenzenes was then exploited to produce reversible and irreversible changes to the polymer nanoassemblies in water. Their responsiveness to light and/or hydrazine was studied by ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS), and fluorescence spectroscopy of encapsulated nile red. Alternating irradiation with UV and visible light resulted in reversible trans–cis isomerization, which changed the polarity of the micelle core without disrupting the assemblies. Reduction by hydrazine resulted in the release of nile red from the micelle core, while residual assemblies were still detected by DLS, likely due to the presence of remaining hydrophobes. A combination of UV light and hydrazine resulted in the release of nile red and breakdown of the assemblies. These results suggest that the intrinsic responsiveness of azobenzene to both light and reductive stimuli can provide polymer assemblies that respond to one or more stimuli in unique and synergistic ways through a single multi-responsive unit.