Hsu Lorraine, Cvetanovich Gregory L, Stupp Samuel I
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
J Am Chem Soc. 2008 Mar 26;130(12):3892-9. doi: 10.1021/ja076553s. Epub 2008 Mar 4.
The coupling of electronic and biological functionality through self-assembly is an interesting target in supramolecular chemistry. We report here on a set of diacetylene-derivatized peptide amphiphiles (PAs) that react to form conjugated polydiacetylene backbones following self-assembly into cylindrical nanofibers. The polymerization reaction yields highly conjugated backbones when the peptidic segment of the PAs has a linear, as opposed to a branched, architecture. Given the topotactic nature of the polymerization, these results suggest that a high degree of internal order exists in the supramolecular nanofibers formed by the linear PA. On the basis of microscopy, the formation of a polydiacetylene backbone to covalently connect the beta-sheets that help form the fibers does not disrupt the fiber shape. Interestingly, we observe the appearance of a polydiacetylene (PDA) circular dichroism band at 547 nm in linear PA nanofibers suggesting the conjugated backbone in the core of the nanostructures is twisted. We believe this CD signal is due to chiral induction by the beta-sheets, which are normally twisted in helical fashion. Heating and cooling shows simultaneous changes in beta-sheet and conjugated backbone structure, indicating they are both correlated. At the same time, poor polymerization in nanofibers formed by branched PAs indicates that less internal order exists in these nanostructures and, as expected, then a circular dichroism signal is not observed for the conjugated backbone. The general variety of materials investigated here has the obvious potential to couple electronic properties and in vitro bioactivity. Furthermore, the polymerization of monomers in peptide amphiphile assemblies by a rigid conjugated backbone also leads to mechanical robustness and insolubility, two properties that may be important for the patterning of these materials at the cellular scale.
通过自组装实现电子功能与生物功能的耦合是超分子化学中一个有趣的目标。我们在此报告了一组二乙炔衍生化的肽两亲分子（PAs），它们在自组装成圆柱形纳米纤维后会发生反应形成共轭聚二乙炔主链。当PAs的肽段具有线性而非支化结构时，聚合反应会产生高度共轭的主链。鉴于聚合反应的拓扑规整性，这些结果表明由线性PA形成的超分子纳米纤维中存在高度的内部有序性。基于显微镜观察，形成共价连接有助于形成纤维的β-折叠片层的聚二乙炔主链不会破坏纤维形状。有趣的是，我们在线性PA纳米纤维中观察到在547 nm处出现聚二乙炔（PDA）圆二色性带，这表明纳米结构核心中的共轭主链发生了扭曲。我们认为这种CD信号是由于β-折叠片层的手性诱导，β-折叠片层通常以螺旋方式扭曲。加热和冷却显示β-折叠片层和共轭主链结构同时发生变化，表明它们是相关的。同时，由支化PA形成的纳米纤维中聚合效果不佳，这表明这些纳米结构中的内部有序性较低，正如预期的那样，共轭主链未观察到圆二色性信号。这里研究的各种材料显然具有耦合电子性质和体外生物活性的潜力。此外，通过刚性共轭主链在肽两亲分子组装体中进行单体聚合还会导致机械稳定性和不溶性，这两个性质对于在细胞尺度上对这些材料进行图案化可能很重要。
