Controlled Helicity of the Rigid-Flexible Molecular Assembly Triggered by Water Addition: From Nanocrystal to Liquid Crystal Gel and Aqueous Nanofibers

Despite recent advances in synthetic nanometer-scale helical assembly, control of supramolecular chirality remains a challenge. Here, we describe the fine-tuning of the shape and morphology transitions of twisted and helical assembly from dumbbell-shaped rigid-flexible amphiphile triggered by concentration. The amphiphile <b>2</b> self-assembles into nonchiral 3D columnar crystals with alternative packing of aromatic segment in solid state. Remarkably, with the addition of water into the solid, the achiral crystal transforms into 2D hexagonally ordered liquid crystal gel with supramolecular chirality due to increased entropy of flexible coil in aqueous environment. Notably, the helical liquid crystal gel was observed to dissolve into optically active aqueous nanofibers caused by a conformational change of hydrophobic aromatic rods and enhanced hydro-volume of the ethylene oxide chains

Reversible, Short α‑Peptide Assembly for Controlled Capture and Selective Release of Enantiomers

Although significant progress has been achieved with short peptide nanostructures, the construction of switchable membrane assemblies remains a great challenge. Here we report short α-peptide assemblies that undergo thermo-reversible switching between assembly and disassembly states, triggered by the conformational change of laterally grafted short peptides from a folded α-helix to a random coil conformation. The α-helical peptide based on two oligoether dendron side groups forms flat disks, while the peptide helix based on three dendron side groups forms hollow vesicles. The vesicular membrane can spontaneously capture a racemic mixture through the self-formation of vesicular containers upon heating and enantio­selectively release the chiral guest molecule through preferential diffusion across the vesicular walls

Multivalent Nanofibers of a Controlled Length: Regulation of Bacterial Cell Agglutination

Control of the size and shape of molecular assemblies on the nanometer scale in aqueous solutions is very important for the regulation of biological functions. Among the well-defined supramolecular structures of organic amphiphiles, one-dimensional nanofibers have attracted much attention because of their potential applications in biocompatible materials. Although much progress has been made in the field of self-assembled nanofibers, the ability to control the fiber length remains limited. The approach for control of the fiber length presented herein overcomes this limitation through the coassembly of amphiphilic rod–coil molecules in which the crystallinity of the aromatic segment can be regulated by π–π stacking interactions. The introduction of carbohydrate segments into the fiber exterior endows the nanofibers with the ability to adhere to bacterial cells. Notably, the fiber length systematically regulates the agglutination and proliferation of bacterial cells exposed to these fibers

Guest-Driven Inflation of Self-Assembled Nanofibers through Hollow Channel Formation

The highlight of self-assembly is the reversibility of various types of noncovalent interactions which leads to construct smart nanostructures with switchable pores. Here, we report the spontaneous formation of inflatable nanofibers through the formation of hollow internal channels triggered by guest encapsulation. The molecules that form this unique nanofibers consist of a bent-shaped aromatic segment connected by a <i>m</i>-pyridine unit and a hydrophilic dendron at its apex. The aromatic segments self-assemble into paired dimers which stack on top of one another to form thin nanofibers with pyridine-functionalized aromatic cores. Notably, the nanofibers reversibly inflate into helical tubules through the formation of hollow cavities triggered by <i>p</i>-phenylphenol, a hydrogen-bonding guest. The reversible inflation of the nanofibers arises from the packing rearrangements in the aromatic cores from transoid dimers to cisoid macrocycles driven by the reversible hydrogen-bonding interactions between the pyridine units of the aromatic cores and the <i>p</i>-phenylphenol guest molecules

Directional Assembly of α‑Helical Peptides Induced by Cyclization

Effective stabilization of short peptide chains into a helical structure has been a challenge in the fields of chemistry and biology. Here we report a novel method for α-helix stabilization of short peptides through their confinement in a cyclic architecture. We synthesized block peptides based on a short peptide and a flexible linker as linear precursors. Subsequent cyclization of the peptide precursors resulted in a conformational change of the peptide unit from a random coil to an α-helix. The incorporation of hydrophobic residues into the peptide unit led to a facially amphiphilic conformation of the molecular cycle. The resulting amphiphilic peptide self-assembled into undulated nanofibers through the directional assembly of small oblate micelles

Self-Assembly of n‑Shaped Rod–Coil Molecules into Thermoresponsive Nanoassemblies: Construction of Reversible Helical Nanofibers in Aqueous Environment

Amphiphilic coil–rod–coil molecules <b>1</b>–<b>3</b>, consisting of an n-shaped rod building block and poly­(ethylene oxide) (PEO) with a degree of polymerization of 5 linked through a biphenyl unit as the coil segment, were synthesized. Molecule <b>1</b> self-assembles into lamellar and hexagonal perforated layer structures, in the crystalline and liquid crystalline phases, respectively. Remarkably, molecule <b>2</b> incorporating lateral methyl groups between the rod and coil segments spontaneously self-organizes into hexagonal perforated layer and oblique columnar structures. The additional incorporation of a lateral butyl group at the center of the rod segment of molecule <b>2</b> generates molecule <b>3</b>, which assumes an exclusively oblique columnar structure in the solid state. In aqueous solutions, molecule <b>1</b> self-assembles into fibrous aggregates, whereas molecules <b>2</b> and <b>3</b> exhibit a self-organizing capacity to form helical fibers. Additionally, circular dichroism (CD) experiments and atomic force microscope (AFM) measurements of molecule <b>3</b> highlight a switch of the helical sense to the opposite handedness, depending on the temperature of the aqueous solution

Supramolecular Switching between Flat Sheets and Helical Tubules Triggered by Coordination Interaction

Here we report the spontaneous formation of switchable sheets in aqueous solution, which is based on bent-shaped aromatic amphiphiles containing <i>m</i>-pyridine units at the terminals and a hydrophilic dendron at the apex. The aromatic segments self-assemble into flat sheets consisting of a zigzag conformation through π–π stacking interactions. Notably, the sheets reversibly transform into helical tubules at higher concentration and into discrete dimeric macrocycles at a lower concentration in response to Ag­(I) ions through reversible coordination interactions between the pyridine units of the aromatic segments and the Ag­(I) ions. While maintaining the coordination bonding interactions, the helical tubules reversibly transform into the dimeric macrocycles in response to the variation in concentration

Differential Self-Assembly Behaviors of Cyclic and Linear Peptides

Here we ask the fundamental questions about the effect of peptide topology on self-assembly. The study revealed that the self-assembling behaviors of cyclic and linear peptides are significantly different in several respects, in addition to sharing several similarities. Their clear differences included the morphological dissimilarities of the self-assembled nanostructures and their thermal stability. The similarities include their analogous critical aggregation concentration values and cytotoxicity profiles, which are in fact closely related. We believe that understanding topology-dependent self-assembly behavior of peptides is important for developing tailor-made self-assembled peptide nanostructures