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

Efficient Synthesis and Astonishing Supramolecular Architectures of Several Symmetric Macrolactams

“…[c] Structure described in ref. [46]. (EtOH/Et 2 O and EtOAc) produced crystals with similar 3D arrangements of C 1 symmetric molecules ( Figure 3).…”

“…[45] The unconjugated trimer 3 yielded long hexagonal hollow nanotubes when it was dissolved into some liquid crystals at high temperature, then allowed to slowly cool down. [46] New crystallization conditions were applied to rings 2 and 3 in order to study possible polymorphism and to improve the structural precision for 3. Indeed the length of the double bounds previously found for 3 were rather short at 1.28 and even 1.22 .…”

“…[33][34][35][36] We have been particularly interested in synthesizing tubes through controlled stacking of sufficiently rigid ring units 1-4; each unit consisted of a macrolactam [37][38][39][40][41][42][43][44] of C n symmetry (n = 2, 3, 4, Figure 1). [45,46] Owing to the vast potential of such compounds we looked for expedient and efficient syntheses. We also tried to scrutinize the relationships between structure of macrocycles and how they assemble to supramolecular objects.…”

Thermal and Textural Properties of Organogels Developed by Candelilla Wax in Safflower Oil

“…The shape and size of microcrystalline structures vary with the chemical characteristics of the gelator molecule (i.e., fatty acid, sterols, phospholipids, n-alkanes) [10,11,14], but also might be affected by annealing. Although annealing has been extensively studied in starches [20], hydrogels [21], and liquid crystals [22], there is no agreement in the molecular mechanism involved during this process. Nevertheless, it is generally accepted that after molecules attain a three-dimensional organization, an appropriate combination of time and temperature results in additional ordering of the three-dimensional molecular structure (i.e., annealing or perfection of the crystalline regions) and/or ordering of amorphous regions.…”

Conducting Organic–Metallic Composite Submicrometer Rods Based on Ionic Liquids

“…Figure 3 A shows the randomly oriented rods of composite materials. Organic molecules of hexagonal conformation are known to stack upon one another to form nanorods; furthermore, these nanorods can self‐organize into larger aggregates with similar appearance 14. In the current case, we believe that the pyridinium cations complexed to gold( III )/chloride/[BF 4 ] − ions stack upon one another and assemble in rodlike macrostructures.…”