基于Boc-D-丙氨酸的手性聚合物纳米颗粒的聚集诱导发光

Aggregation Induced Emission of Chiral Polymer Nanoparticles Based on Boc-D-Alanine

研究氨基酸对聚合物手性和聚集诱导发光(AIE)性能的影响,利用自由基聚合制备了一种侧链含有联苯和Boc-D-丙氨酸的聚甲基丙烯酸酯.圆二色光谱(CD)结果表明该聚合物具有手性,并在四氢呋喃/水混合溶剂中表现出AIE特性.透射电镜结果表明这种聚合物在混合溶剂中形成了聚集体.同时,该聚合物还可以对盐酸和氢氧化钠溶液产生响应.该手性AIE聚合物纳米颗粒在生物成像和荧光探针等众多领域具有潜在的应用.

In order to study the effect of amino acids on the chirality and aggregation induced emission (AIE) feature of polymers, polymethacrylate containing both biphenyl and Boc-D-alanine was synthesized using free radical polymerization. Biphenyl, a simplest AIE moiety, was introduced into the side chains as a spacer connecting the main chains and the side chains themselves. The molecular weight of the obtained polymer were determined to be 8.7×104 by gel permeation chromatography. The circular dichroism (CD) spectrum of the prepared polymer displayed a significantly positive peak around 270 nm, implying that a torsion conformation was formed in the polymer. FT-IR spectra proved that hydrogen bonds were formed between the side chains, which played important roles in the stabilizing of the chirality of the polymer. Importantly, the fluorescence intensity of such polymer in 90% tetraphydrofuran (THF)/water mixture is 5.7 times higher than that in pure THF, indicating an obvious AIE phenomenon. Transmission electron microscopy (TEM) images further revealed that such polymer could self-assemble into aggregates of nanoparticles in THF/water mixtures. These results suggest that the AIE property can be mainly attributed to the restriction of the intramolecular rotation of biphenyl in aggregates. More importantly, such polymer could respond to the variation of pH adjusted by HCl and NaOH: the fluorescence intensity increased with the addition of NaOH, but decreased with the addition of HCl. It is likely that such a pH-responsive behavior results from the change of solubility of the polymer in acid base solutions. Such polymer nanoparticles with the AIE-property and the chirality have a promising potential for various practical applications, such as bio-imaging, chemical sensor, and so on.