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Hierarchical self-assembly of di-, tri- and tetraphenylalanine peptides capped with two fluorenyl functionalities: from polymorphs to dendrites

机译:具有两个芴基官能团的二 - ,三 - 和四苯丙氨酸肽的分级自组装:从多晶型到树枝状晶体

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摘要

Homopeptides with 2, 3 and 4 phenylalanine (Phe) residues and capped with fluorenylmethoxycarbonyl and fluorenylmethyl esters at the N-terminus and C-terminus, respectively, have been synthesized to examine their self-assembly capabilities. Depending on the conditions, the di-and triphenylalanine derivatives self-organize into a wide variety of stable polymorphic structures, which have been characterized: stacked braids, doughnut-like shapes, bundled arrays of nanotubes, corkscrew-like shapes and spherulitic microstructures. These highly aromatic Phe-based peptides also form incipient branched dendritic microstructures, even though they are highly unstable, making their manipulation very difficult. Conversely, the tetraphenylalanine derivative spontaneously self-assembles into stable dendritic microarchitectures made of branches growing from nucleated primary frameworks. The fractal dimension of these microstructures is similar to 1.70, which provides evidence for self-similarity and two-dimensional diffusion controlled growth. DFT calculations at the M06L/6-31G(d) level have been carried out on model beta-sheets since this is the most elementary building block of Phe-based peptide polymorphs. The results indicate that the antiparallel beta-sheet is more stable than the parallel one, with the difference between them growing with the number of Phe residues. Thus, the cooperative effects associated with the antiparallel disposition become more favorable when the number of Phe residues increases from 2 to 4, while those of the parallel disposition remained practically constant.
机译:合成了具有2、3和4个苯丙氨酸(Phe)残基并分别在N端和C端分别用芴基甲氧基羰基和芴基甲基酯封端的同肽,以检查其自组装能力。根据条件的不同,二苯丙氨酸和三苯丙氨酸衍生物会自组织成各种稳定的多晶型结构,其特征是:堆叠的编织物,甜甜圈状,纳米管束状排列,开瓶器状和球形微结构。这些高度芳香族的基于Phe的肽也形成了初始的分支树状微结构,即使它们非常不稳定,也使其很难操作。相反,四苯丙氨酸衍生物自发地自组装成稳定的树枝状微结构,该树枝状微结构由从有核一级骨架生长的分支组成。这些微结构的分形维数接近1.70,这为自相似和二维扩散控制生长提供了证据。在M06L / 6-31G(d)级别上的DFT计算已在模型beta-sheets上进行,因为这是基于Phe的肽多晶型物的最基本组成部分。结果表明,反平行β-折叠比平行β-折叠更稳定,并且它们之间的差异随着Phe残基的数量而增加。因此,当Phe残基的数目从2增加到4时,与反平行布置有关的协同作用变得更有利,而平行布置的那些实际上保持恒定。

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