Kralj Slavko, Bellotto Ottavia, Parisi Evelina, Garcia Ana M, Iglesias Daniel, Semeraro Sabrina, Deganutti Caterina, D'Andrea Paola, Vargiu Attilio V, Geremia Silvano, De Zorzi Rita, Marchesan Silvia
Chemical and Pharmaceutical Sciences Department, University of Trieste, Via Giorgieri 1, 34127 Trieste, Italy.
Materials Synthesis Department, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
ACS Nano. 2020 Dec 22;14(12):16951-16961. doi: 10.1021/acsnano.0c06041. Epub 2020 Nov 11.
Diphenylalanine is an amyloidogenic building block that can form a versatile array of supramolecular materials. Its shortcomings, however, include the uncontrolled hierarchical assembly into microtubes of heterogeneous size distribution and well-known cytotoxicity. This study rationalized heterochirality as a successful strategy to address both of these pitfalls and it provided an unprotected heterochiral dipeptide that self-organized into a homogeneous and optically clear hydrogel with excellent ability to sustain fibroblast cell proliferation and viability. Substitution of one l-amino acid with its d-enantiomer preserved the ability of the dipeptide to self-organize into nanotubes, as shown by single-crystal XRD analysis, whereby the pattern of electrostatic and hydrogen bonding interactions of the backbone was unaltered. The effect of heterochirality was manifested in subtle changes in the positioning of the aromatic side chains, which resulted in weaker intermolecular interactions between nanotubes. As a result, d-Phe-l-Phe self-organized into homogeneous nanofibrils with a diameter of 4 nm, corresponding to two layers of peptides around a water channel, and yielded a transparent hydrogel. In contrast with homochiral Phe-Phe stereoisomer, it formed stable hydrogels thermoreversibly. d-Phe-l-Phe displayed no amyloid toxicity in cell cultures with fibroblast cells proliferating in high numbers and viability on this biomaterial, marking it as a preferred substrate over tissue-culture plastic. Halogenation also enabled the tailoring of d-Phe-l-Phe self-organization. Fluorination allowed analogous supramolecular packing as confirmed by XRD, thus nanotube formation, and gave intermediate levels of bundling. In contrast, iodination was the most effective strategy to augment the stability of the resulting hydrogel, although at the expense of optical transparency and biocompatibility. Interestingly, iodine presence hindered the supramolecular packing into nanotubes, resulting instead into amphipathic layers of stacked peptides without the occurrence of halogen bonding. By unravelling fine details to control these materials at the meso- and macro-scale, this study significantly advanced our understanding of these systems.
二苯基丙氨酸是一种可形成多种超分子材料的淀粉样生成结构单元。然而，其缺点包括在组装成尺寸分布不均一的微管时缺乏可控的层级结构以及众所周知的细胞毒性。本研究提出将异手性作为解决这两个问题的成功策略，并提供了一种未受保护的异手性二肽，该二肽可自组装成均匀且光学透明的水凝胶，具有出色的维持成纤维细胞增殖和活力的能力。用其d - 对映体取代一个l - 氨基酸保留了二肽自组装成纳米管的能力，单晶X射线衍射分析表明，主链的静电和氢键相互作用模式未改变。异手性的影响表现为芳族侧链位置的细微变化，这导致纳米管之间的分子间相互作用较弱。结果，d - Phe - l - Phe自组装成直径为4 nm的均匀纳米纤维，相当于围绕水通道的两层肽，并形成了透明水凝胶。与同手性的Phe - Phe立体异构体相比，它能热可逆地形成稳定的水凝胶。在成纤维细胞大量增殖且在此生物材料上具有活力的细胞培养中，d - Phe - l - Phe未显示出淀粉样毒性，这表明它是比组织培养塑料更优的底物。卤化还能够对d - Phe - l - Phe的自组装进行调控。如XRD所证实，氟化允许类似的超分子堆积，从而形成纳米管，并产生中等程度的聚集。相比之下，碘化是增强所得水凝胶稳定性的最有效策略，尽管以牺牲光学透明度和生物相容性为代价。有趣的是，碘的存在阻碍了超分子堆积成纳米管，反而形成了堆叠肽的两亲层，且未发生卤键作用。通过揭示在中观和宏观尺度上控制这些材料的精细细节，本研究显著推进了我们对这些体系的理解。
