Micrometer‐Sized Hexagonal Tubes Self‐Assembled by a Cyclic Peptide in a Liquid Crystal

Abstract

Self-assembly of cyclic peptides is an attractive strategy for making hollow tubular structures. [1][2][3][4] Stacking of ring-shaped molecules of flat conformation can be stabilized by intermolecular hydrogen bonds formed between the amide groups. Cyclic peptides of rationally designed chemical structures can form nanotubes of different internal diameters and structures, which may find applications in biology and materials sciences. [2,5,6] Generally, the self-assembly process occurs in solution, is often triggered by a change in solubility of the peptide in organic solvents, and results in crystals organized by nanotubes. Herein, we report on the observation of selfassembled structures of a cyclic peptide in a nematic liquid crystal (LC). Hexagonal hollow tubes that have diameters in the order of micrometers and reaching several millimetres in length were observed. Strong experimental evidence suggests the occurrence of a hierarchical and self-similar-structured self-assembly of the cyclic peptide. That is, individual molecules of hexagonal conformation stack up into hexagonal nanotubes, which then self-organize into larger aggregates with the same appearance. Each molecule provides both intra-and intertube H bonding that ensure the molecular stacking within and the packing of nanotubes. To the best of our knowledge, this is the first work exploring the use of liquid crystals for the self-assembly of cyclic peptides, and the results show the surprising impact of the liquid crystalline medium.Previous work showed that the lipophilic macrolactam cyclo-(NHCH 2 CH=CHCH 2 CO) 3 (E olefin) is soluble in ethanol and can be crystallized by diffusion of diethyl ether.[4] The crystal structure determined by X-ray crystallography shows the stacking of macrocycles, which have a

Self‐Assembly of Hexagonal Peptide Microtubes and Their Optical Waveguiding

“…In some sense, such hierarchical and ordered organization of substructures mimics biological systems. A distinctive tubular structure (e.g., rectangular or hexagonal structures) may provide exceptional optical, electrical, and mechanical properties that are not achievable in a circular tube 5, 6. In this work, hexagonal peptide microtubes were controllably obtained upon solvent thermal annealing.…”

“…The key to the formation of hexagonal hollow microtubes may be the relatively slow growth process allowing for the kinetic regulation. The slow growth leads to the confined organization of nanotubes into arrays, which undergo kinetic regulation and ultimately form hexa­gonal structures that are likely as a consequence of self‐similar‐structured growth 6, 15. As shown in Figure , the molecular packing occurs hexagonally.…”

Stretchable conducting gold films prepared with composite MWNT/PDMS substrates

“…This has been observed for peptide solutions. 30 However, the most significant result of the present paper is the electro-mechanical response of the gold-coated composites during tensile testing. The main effect of MWMT addition is to reduce the electrical resistance under load and to produce a more stable and reproducible electrical behaviour.…”

Macrocycles as Precursors for Organic Nanotubes

“…In a very recent publication, Dory and co-workers have also explored how the self-assembly of cyclic peptides can be influenced by the presence of a liquid crystalline medium (LC), a fluid presenting a molecular order [31]. The selfassembly of the macrolactam 9 is triggered by cooling very slowly a mixture of 9 (0.5-2.0% w/w) and LC below the nematic-isotropic transition temperature (115ºC) of the LC.…”