Peptide amphiphiles (PAs) are highly tunable molecules that were recently found to exhibit aggregation-induced emission (AIE) when they self-assemble into nanofibers. Here, we leverage decades of molecular design and self-assembly study of PAs to strategically tune their molecular motion within nanofibers to enhance AIE, making them a highly useful platform for applications such as sensing, bioimaging, or materials property characterization. Since AIE increases when aggregated molecules are rigidly and closely packed, we altered the four most closely packed amino acids nearest to the hydrophobic core by varying the order and composition of glycine, alanine, and valine pairs. Of the six PA designs studied, C₁₆VVAAK₂ had the highest quantum yield at 0.17, which is a more than 10-fold increase from other PA designs including the very similar C₁₆AAVVK₂, highlighting the importance of precise amino acid placement to anchor rigidity closest to the core. We also altered temperature to increase AIE. C₁₆VVAAK₂ exhibited an additional 4-fold increase in maximum fluorescence intensity when the temperature was raised from 5 to 65 °C. As the temperature increased, the secondary structure transitioned from β-sheet to random coil, indicating that further packing an already aligned molecular system makes it even more readily able to transfer energy between the electron-rich amides. This work both unveils a highly fluorescent AIE PA system design and sheds insights into the molecular orientation and packing design traits that can significantly enhance AIE in self-assembling systems.

中文翻译：

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调节分子运动增强肽两亲纳米纤维的固有荧光

肽两亲物（PA）是高度可调的分子，最近发现它们在自组装成纳米纤维时表现出聚集诱导发射（AIE）。在这里，我们利用数十年的 PA 分子设计和自组装研究来战略性地调整纳米纤维内的分子运动，以增强 AIE，使其成为传感、生物成像或材料特性表征等应用的非常有用的平台。由于当聚集的分子刚性且紧密堆积时，AIE 会增加，因此我们通过改变甘氨酸、丙氨酸和缬氨酸对的顺序和组成来改变最接近疏水核心的四个最紧密堆积的氨基酸。在研究的六种 PA 设计中，C ₁₆ VVAAK _{2 的量子产率最高，为 0.17，比其他 PA 设计（包括非常相似的 C 16} AAVVK _{2 ）}提高了 10 倍以上，这凸显了精确氨基酸布局对最接近核心的锚固刚性。我们还改变了温度以提高 AIE。当温度从 5 °C 升至 65 °C 时，C ₁₆ VVAAK _{2 的}最大荧光强度增加了 4 倍。随着温度升高，二级结构从β-折叠转变为无规卷曲，这表明进一步堆积已经排列好的分子系统使其更容易在富电子酰胺之间转移能量。这项工作不仅揭示了高荧光 AIE PA 系统设计，还深入了解了分子取向和包装设计特征，这些特征可以显着增强自组装系统中的 AIE。