Multicomponent hydrogels from enantiomeric amino acid derivatives: helical nanofibers, handedness and self-sorting
Multicomponent hydrogels from enantiomeric amino acid derivatives: helical nanofibers, handedness and self-sorting
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DOI：
10.1039/c1sm05907f
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发表时间：
2011-01-01
期刊：
影响因子：
3.4
通讯作者：
Banerjee, Arindam
中科院分区：
文献类型：
--
作者：
Adhikari, Bimalendu;Nanda, Jayanta;Banerjee, Arindam
在这项研究中，手性螺旋纳米纤维是由合适的、共组装的、两个相反电荷的氨基酸基双组分水凝胶得到的。N-末端保护氨基酸Fmoc-(L/D)Glu(Fmoc：N-荧基-9-甲氧基甲酰基，Glu：谷氨酸)和(L/D)赖氨酸(赖氨酸：赖氨酸)的等摩尔混合物可以共同组装形成水凝胶。用圆二色谱(CD)、原子力显微镜(AFM)、透射电子显微镜(TEM)、X-射线粉末衍射、荧光光谱和流变学研究对这些水凝胶进行了表征。圆二色谱和原子力显微镜研究已被广泛用于研究从不同水凝胶体系获得的纤维的手性/非手性。两个L异构体的等摩尔混合物{Fmoc-(L)Glu+(L)Lys}在组装状态下导致了左旋螺旋纳米纤维的独占形成，而两个D-异构体的等摩尔混合物{Fmoc-(D)Glu+(D)Lys}产生了右旋螺旋纳米纤维。从{Fmoc-(L)Glu+(L)Lys}体系得到的凝胶的CD研究正好是从{Fmoc-(D)Glu+(D)Lys}体系凝胶获得的CD信号的镜像。这些结果表明，分子手性正在转化为超分子螺旋性，而这些纤维的手性取决于两组分混合体系中相应的分子手性。通过使用对映体构建块，可以逆转螺旋纤维的利手性。四个组分的外消旋和等摩尔混合物[{Fmoc-(L)Glu+(L)Lys}+{Fmoc-(D)Glu+(D)Lys}]也可以形成水凝胶。有趣的是，在这种外消旋混合物中，观察到了几乎等量的左旋和右旋螺旋纳米纤维的自我分选。Fmoc-(L)-谷氨酸和L-鸟氨酸/L-精氨酸的等摩尔混合物也产生具有左旋螺旋纤维的水凝胶。此外，在Ca~(2+)/Mg~(2+)离子存在下，从双组分水凝胶{Fmoc-(L)Glu+(L)Lys}体系中观察到了直纤维。这表明在合适的条件下得到了直的纳米纤维，酸碱相互作用是形成纳米级螺旋纤维的原因。
In this study, chiral helical nanofibers have been obtained from suitable, co-assembling, two oppositely charged amino acid based two component hydrogels. An equimolar mixture of an N-terminally protected amino acid Fmoc-(L/D)Glu (Fmoc: N-fluorenyl-9-methoxycarbonyl, Glu: glutamic acid) and (L/D)Lys (Lys: lysine) can co-assemble to form hydrogels. These hydrogels have been characterised using circular dichroism (CD), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray powder diffraction, fluorescence spectroscopic and rheological studies. CD and AFM studies have been extensively used to examine the chiral/achiral nature of fibers obtained from different hydrogel systems. The equimolar mixture of two L-isomers, {Fmoc-(L)Glu + (L)Lys} in the assembled state, leads to the exclusive formation of left-handed helical nanofibers, whereas an equimolar mixture of two D-isomers, {Fmoc-(D) Glu + (D) Lys}, gives rise to right-handed helical nanofibers. The CD study of the gel obtained from the {Fmoc-(L) Glu + (L) Lys} system is exactly the mirror image of the CD signal obtained from the gel of the {Fmoc-(D) Glu + (D) Lys} system. These results suggest that the molecular chirality is being translated into the supramolecular helicity and the handedness of these fibers depends on the corresponding molecular chirality in the mixture of the two component system. Reversing the handedness of helical fibers is possible by using enantiomeric building blocks. Co-assembly of racemic and equimolar mixtures of all four components, i.e., [{Fmoc-(L)Glu + (L)Lys} + {Fmoc-(D)Glu + (D)Lys}] can also form hydrogels. Interestingly, in this racemic mixture self-sorting has been observed with the presence of almost equal amount of left-and right-handed helical nanofibers. The equimolar mixture of Fmoc-(L) Glu and L-ornithine/L-arginine also produces hydrogel with left-handed helical fibers. Moreover, the straight fiber has been observed from the two component hydrogel {Fmoc-(L)Glu + (L)Lys} system in the presence of Ca2+/Mg2+ ions. This indicates the straight nanofibers are obtained under suitable conditions and acid-base interaction is responsible for making the helical fibers at the nanoscale.