Key Laboratory for Organic Electronics & Information Displays and Institute of Advanced Materials, Nanjing University of Posts & Telecommunications, Nanjing 210046, China.
Langmuir. 2010 Dec 21;26(24):19120-8. doi: 10.1021/la103394c. Epub 2010 Nov 29.
We reported here the synthesis and characterization of a novel water-soluble, meta-linked poly(phenylene ethynylene) (m-PPE-NEt(2)Me(+)) featuring quaternized side groups. We studied the solvent-induced self-assembly of m-PPE-NEt(2)Me(+) in MeOH/H(2)O solvent mixtures by using UV-vis absorption and fluorescence spectroscopies. The results showed that the polymer folded into a helical conformation and that the extent of helical folding increased with the volume % water in the solvent. This cationic polymer also exhibited unique pH-induced helix formation, which was attributed to the partial neutralization of quaternized side groups at high pH and the meta-links in the main chain of the polymer. Studies on the fluorescence quenching of m-PPE-NEt(2)Me(+) by anthraquinone-2,6-disulfonate (AQS) and Fe(CN)(6)(4-), two small-molecule anionic quenchers with different typical structures, revealed more efficient quenching of helical conformation by AQS than by Fe(CN)(6)(4-). We proposed that the two quenchers most likely interacted with the polymer helix in two different modes; that was, AQS featuring large planar aromatic ring could intercalate within adjacent π-stacked phenylene ethynylene units in the polymer helix, whereas Fe(CN)(6)(4-) mainly bound to the periphery of polymer helix through ion-pair formation. Finally, the results of FRET from the helical polymer to the fluorescein (C*)-labeled polyanions, ssDNA-C* (ssDNA: single-stranded DNA) and dsDNA-C* (dsDNA: double-stranded DNA) also suggested two different modes of interactions. As compared with the FRET to dsDNA-C*, the FRET to ssDNA-C* was slightly more efficient, which was believed to arise from the additional binding of ssDNA-C* with the polymer via intercalation of its exposed hydrophobic bases into the π stack of adjacent phenylene ethynylene units in the polymer helix.
我们在此报道了一种新型水溶性的、间位连接的聚（苯乙炔）（m-PPE-NEt(2)Me(+））的合成和表征，该聚合物具有季铵化的侧基。我们通过紫外-可见吸收光谱和荧光光谱研究了 m-PPE-NEt(2)Me(+)在 MeOH/H(2)O 溶剂混合物中的溶剂诱导自组装。结果表明，聚合物折叠成螺旋构象，并且螺旋折叠的程度随着溶剂中水的体积分数的增加而增加。这种阳离子聚合物还表现出独特的 pH 诱导螺旋形成，这归因于季铵化侧基在高 pH 下的部分中和以及聚合物主链中的间位连接。对 m-PPE-NEt(2)Me(+)与蒽醌-2,6-二磺酸盐（AQS）和铁氰化钾（Fe(CN)(6)(4-)）的荧光猝灭研究，这两种小分子阴离子猝灭剂具有不同的典型结构，结果表明 AQS 对螺旋构象的猝灭效率高于 Fe(CN)(6)(4-)。我们提出，这两种猝灭剂可能以两种不同的模式与聚合物螺旋相互作用；即，具有大平面芳香环的 AQS 可以嵌入聚合物螺旋中相邻的π堆叠苯乙炔单元之间，而 Fe(CN)(6)(4-)主要通过形成离子对与聚合物螺旋的外围结合。最后，从螺旋聚合物到荧光素（C*）标记的聚阴离子（ssDNA-C*（ssDNA：单链 DNA）和 dsDNA-C*（dsDNA：双链 DNA））的 FRET 结果也表明了两种不同的相互作用模式。与 FRET 到 dsDNA-C相比，FRET 到 ssDNA-C略为有效，这被认为是由于 ssDNA-C*通过其暴露的疏碱基插入聚合物螺旋中相邻苯乙炔单元的π堆积中与聚合物的额外结合所致。
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