Peptide nanostructures compose a new class of materials that have gained attention due to their interesting properties. Among them, nanotubes of diphenylalanine (FF) and its analogues have been one of the most studied structures in the last few years. Their importance originates from the need to better understand the formation of β-amyloid fibrils which are associated with Alzheimer's disease. In this work, the FF self-assembly process was probed using time-resolved Raman microscopy. The changes in the Raman spectra are followed over time after injecting water into a FF-film until micro/nanotubes (MNTs) are formed. Specific features of the Raman spectra clearly suggest that FF-molecules after water injection form an intermediate species before forming FF-MNTs. The broad Raman bands observed for the intermediate species suggest the presence of very heterogeneous structures based on FF. The FF-MNTs appear almost instantaneously (detected via the rise of the typical Raman bands of FF-MNTs at 761, 1249 and 1426 cm⁻¹) after the intermediate structures are formed. This delayed formation of FF-MNTs supports a nucleation process. The formation via nucleation of FF-MNTs is further corroborated by a simulation of the Raman spectra based on a 2-step kinetic model and the respective vibrational Raman modes are identified using Density Functional Theory vibrational calculations. Our results indicate that the driving force for the FF-MNT patterning process is the electric dipole re-orientation originating from the FF dipeptide unit connectivity over time.

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二苯丙氨酸微/纳米管形成自组装机理的两步动力学模型

肽纳米结构构成了一类新的材料，由于其有趣的性能而受到关注。其中，二苯丙氨酸（FF）及其类似物的纳米管已成为最近几年研究最多的结构之一。它们的重要性源于需要更好地了解与阿尔茨海默氏病相关的β-淀粉样蛋白原纤维的形成。在这项工作中，使用时间分辨拉曼显微镜探测了FF自组装过程。将水注入FF膜后，随着时间的推移，拉曼光谱的变化会不断变化，直到形成微型/纳米管（MNT）。拉曼光谱的特定特征清楚地表明，注水后的FF分子在形成FF-MNT之前形成中间物种。观察到的中间物种的宽拉曼谱带表明存在基于FF的非常异质的结构。FF-MNT几乎瞬间出现（检测到在形成中间结构之后，通过在761、1249和1426 cm ^-1处FF-MNTs的典型拉曼带的上升）。FF-MNT的这种延迟形成支持成核过程。通过基于两步动力学模型的拉曼光谱模拟进一步证实了通过FF-MNT的成核形成，并使用密度泛函理论振动计算确定了相应的振动拉曼模式。我们的结果表明，FF-MNT构图过程的驱动力是电偶极子重新定向，其随着时间的变化而源自FF二肽单元的连接性。