Self-Assembly Mechanism for a Naphthalene-Dipeptide Leading to Hydrogelation
Self-Assembly Mechanism for a Naphthalene-Dipeptide Leading to Hydrogelation
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DOI：
10.1021/la903694a
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发表时间：
2010-04-06
期刊：
影响因子：
3.9
通讯作者：
Adams, Dave J.
中科院分区：
文献类型：
--
作者：
Chen, Lin;Morris, Kyle;Adams, Dave J.
适当官能化的二肽已被证明是有效的水凝胶。水凝胶剂的设计和水凝胶化发生的机理目前都不是很清楚。在这里，我们利用葡萄糖酸-三角洲-内酯的水解为葡萄糖酸作为一种方法来调节萘-丙氨酰-丙氨酸溶液中的pH值，从而允许特定的目标最终的pH值。此外，该方法还允许对组装过程进行表征。我们证明，当电荷从二肽的C末端移除时，组装就开始了。电荷的去除允许分子的侧向组装，导致pi-pi堆积(如CD所示)和β片层的形成(如IR和X-射线纤维衍射所示)。这会导致纤维状结构的形成。电子显微镜观察发现，纤维最初形成较细，保留长度较低。然后发生横向联合，使纤维束具有更高的持续期长度。这导致最初较弱的水凝胶随着时间的推移而变得更强。无论GDL的加入量如何，水凝胶的最终机械性能都非常相似；相反，获得最终凝胶所需的时间取决于GDL的浓度。然而，在应变下观察到网络之间的差异，这意味着组装的动力学确实提供了不同的最终材料的性质。总体而言，这项研究提供了导致水凝胶的组装过程的详细了解。
Suitably functionalized dipeptides have been shown to be effective hydrogelators. The design of the hydrogelators and the mechanism by which hydrogelation occurs are both currently not well understood. Here, we have utilized the hydrolysis of glucono-delta-lactone to gluconic acid as a means of adjusting the pH in a naphthalene-alanylvaline solution allowing the specific targeting of the final pH. In addition, this method allows the assembly process to be characterized. We show that assembly begins as charge is removed from the C-terminus of the dipeptide. The removal of charge allows lateral assembly of the molecules leading to pi-pi stacking (shown by CD) and beta-sheet formation (as shown by IR and X-ray fiber diffraction). This leads to the formation of fibrous structures. Electron microscopy reveals that thin fibers form initially, with low persistence length. Lateral association then occurs to give bundles of fibers with higher persistence length. This results in the initially weak hydrogel becoming stronger with time. The final mechanical properties of the hydrogels are very similar irrespective of the amount of GdL added; rather, the time taken to achieving the final gel is determined by the GdL concentration. However, differences are observed between the networks under strain, implying that the kinetics of assembly do impart different final materials' properties. Overall, this study provides detailed understanding of the assembly process that leads to hydrogelation.