Inversion of Supramolecular Chirality by Sonication-Induced Organogelation

Abstract

Natural helical structures have inspired the formation of well-ordered peptide-based chiral nanostructures in vitro. These structures have drawn much attention owing to their diverse applications in the area of asymmetric catalysts, chiral photonic materials, and nanoplasmonics. The self-assembly of two enantiomeric fluorinated aromatic dipeptides into ordered chiral fibrillar nanostructures upon sonication is described. These fibrils form organogels. Our results clearly indicate that fluorine-fluorine interactions play an important role in self-assembly. Circular dichroism analysis revealed that both peptides (peptides 1 and 2), containing two fluorines, depicted opposite cotton effects in their monomeric form compared with their aggregated form. This shows that supramolecular chirality inversion took place during the stimuli-responsive self-aggregation process. Conversely, peptide 3, containing one fluorine, did not exhibit chirality inversion in sonication-induced organogelation. Therefore, our results clearly indicate that fluorination plays an important role in the organogelation process of these aromatic dipeptides. Our findings may have broad implications regarding the design of chiral nanostructures for possible applications such as chiroptical switches, asymmetric catalysis, and chiral recognitions.

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“…However, in few solvents (aromatic solvent and long-chain aliphatic alcohol) viscous precipitation were observed. Later, we noticed that sonication 27,30,[32][33][34][35] is an interesting stimulus to induce gelation in this system.…”

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“…Beyond the intramolecular and intermolecular factors, there are also various external stimuli that can modulate supramolecular chirality, such as heat, pH, light, sonication, and solvents, and provide abundant references for dynamic tuning . Feringa et al.…”

“…Beyondt he intramolecular and intermolecular factors, there are also various external stimuli that can modulate supramolecular chirality,s uch as heat, [30] pH, [31] light, [32] sonication, [33] and solvents, [34] and provide abundant references for dynamic tuning. [35] Feringa et al reported reversible chirality control by using UV and visible light in as elf-assembling molecular system based on ad ithienylethene photochromic unit functionalized with (R)-1-phenylethylamine-derived amides, in which molecular and supramolecular chirality could communicate.…”

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