School of Materials, The University of Manchester, Grosvenor Street, Manchester M1 7HS, United Kingdom.
Langmuir. 2011 Dec 6;27(23):14438-49. doi: 10.1021/la202113j. Epub 2011 Nov 1.
We have investigated the self-assembly behavior of fluorenyl-9-methoxycarbonyl (Fmoc)-FG, Fmoc-GG, and Fmoc-GF and compared it to that of Fmoc-FF using potentiometry, fluorescence and infrared spectroscopy, transmission electron microscopy, wide-angle X-ray scattering, and oscillatory rheometry. Titration experiments revealed a substantially shifted apparent pK(a) transition for Fmoc-FG, Fmoc-GG, and Fmoc-GF. The apparent pK(a) values observed correlated with the hydrophobicity (log P) of the Fmoc-dipeptide molecules. Fmoc-GG and Fmoc-GF were found to self-assemble only in their protonated form (below their apparent pK(a)), while Fmoc-FG formed self-assembled structures above and below its apparent pK(a). Fmoc-GG and Fmoc-FG were found to form hydrogels below their apparent pK(a) transitions in agreement with the entangled fibers morphologies revealed by TEM. Unlike Fmoc-FF and Fmoc-GG, Fmoc-FG showed unusual gelation behavior as gels were found to form upon heating. Fmoc-GF formed precipitates instead of a hydrogel below its apparent pK(a) in agreement with the formation of micrometer scale sheetlike structures observed by TEM. The fact that all four Fmoc-dipeptides were found to self-assemble suggests that the main driving force behind the self-assembly process is a combination of the hydrophobic and π-π interactions of the fluorenyl moieties with a secondary role for hydrogen bonding of the peptidic components. The nature of the peptidic tail was found to have a pronounced effect on the type of self-assembled structure formed. This work indicates that the substitution of phenylalanine by glycine significantly impacts on the mode of assembly and illustrates the versatility of aromatic peptide amphiphiles in the formation of structurally diverse nanostructures.
我们研究了芴甲氧羰基-9-氟（Fmoc）-FG、Fmoc-GG 和 Fmoc-GF 的自组装行为，并通过电位滴定法、荧光光谱法和红外光谱法、透射电子显微镜、广角 X 射线散射和振荡流变学对其进行了比较。滴定实验表明 Fmoc-FG、Fmoc-GG 和 Fmoc-GF 的表观 pK(a) 转变发生了明显的偏移。观察到的表观 pK(a) 值与 Fmoc-二肽分子的疏水性（log P）相关。发现 Fmoc-GG 和 Fmoc-GF 仅在质子化形式（低于其表观 pK(a)）下自组装，而 Fmoc-FG 在其表观 pK(a) 以上和以下都形成自组装结构。Fmoc-GG 和 Fmoc-FG 在其表观 pK(a) 转变以下形成水凝胶，这与 TEM 揭示的缠结纤维形态一致。与 Fmoc-FF 和 Fmoc-GG 不同，Fmoc-FG 表现出异常的凝胶化行为，因为发现凝胶在加热时形成。Fmoc-GF 在其表观 pK(a) 以下形成沉淀物而不是水凝胶，这与 TEM 观察到的形成微米级片状结构一致。这四种 Fmoc-二肽都被发现能够自组装，这表明自组装过程的主要驱动力是芴基部分的疏水性和π-π相互作用与肽部分氢键的次要作用的结合。肽尾的性质对形成的自组装结构的类型有显著影响。这项工作表明，用甘氨酸取代苯丙氨酸会显著影响组装方式，并说明了芳香肽两亲物在形成结构多样的纳米结构方面的多功能性。
