Hexagonal Lyotropic Liquid Crystal from Simple "Abiotic" Foldamers

Molecular Sensing and Manipulation of Protein Oligomerization in Membrane Nanotubes with Bolaamphiphilic Foldamers

Adaptive and reversible self-assembly of supramolecular protein structures is a fundamental characteristic of dynamic living matter. However, the quantitative detection and assessment of the emergence of mesoscale protein complexes from small and dynamic oligomeric precursors remains highly challenging. Here, we present a novel approach utilizing a short membrane nanotube (sNT) pulled from a planar membrane reservoir as nanotemplates for molecular reconstruction, manipulation, and sensing of protein oligomerization and self-assembly at the mesoscale. The sNT reports changes in membrane shape and rigidity caused by membrane-bound proteins as variations of the ionic conductivity of the sNT lumen. To confine oligomerization to the sNT, we have designed and synthesized rigid oligoamide foldamer tapes (ROFTs). Charged ROFTs incorporate into the planar and sNT membranes, mediate protein binding to the membranes, and, driven by the luminal electric field, shuttle the bound proteins between the sNT and planar membranes. Using Annexin-V (AnV) as a prototype, we show that the sNT detects AnV oligomers shuttled into the nanotube by ROFTs. Accumulation of AnV on the sNT induces its self-assembly into a curved lattice, restricting the sNT geometry and inhibiting the material uptake from the reservoir during the sNT extension, leading to the sNT fission. By comparing the spontaneous and ROFT-mediated entry of AnV into the sNT, we reveal how intricate membrane curvature sensing by small AnV oligomers controls the lattice self-assembly. These results establish sNT-ROFT as a powerful tool for molecular reconstruction and functional analyses of protein oligomerization and self-assembly, with broad application to various membrane processes.

Self-assembly of chiral foldamers with alternating hydrophilic and hydrophobic side chains into acid-sensitive and solvent-exchangeable vesicular particles

It is difficult for the same molecule to self-assemble into stable vesicular particles in water and aliphatic hydrocarbon (oil), respectively. Here we demonstrated that chiral oligo(methylene-p-phenyleneethynylene)s with alternating hydrophilic and hydrophobic side chains were able to self-assemble into vesicular particles independent of solvent polarity. These particles were well dispersed in aliphatic hydrocarbon, alcohol or water for at least one month at room temperature, and readily transferred from organic to aqueous phases via dialysis. They displayed a noticeable response to the acidity of the aqueous phase, and could be used as simple cargos for loading hydrophilic or hydrophobic molecules in aqueous cores, which were different from loading in polymersomes. The vesicular particles loaded with hydrophobic paclitaxel exhibited comparable anti-HeLa cell activity to free paclitaxel in vitro.

Self-assembly of chiral oligo(methylene-p-phenylene-ethynylene)s into vesicle-like particles independent of hydrophobicity/hydrophilicity of side chains and solvents

It is difficult for the same molecule to form vesicular assemblies in water and alipatic hydrocarbon (oil), respectively. Here, we report that chiral oligo(methylene-p-phenyleneethynylene)s bearing hydrophobic or hydrophilic side chains can take extended conformations to self-assemble into vesicle-like particles in a hydrophobic or hydrophilic solvent system. The self-assembly processes are highly independent of molecular design and chemical environments. Based on the analyses of TEM, UV, CD and PXRD data, it is plausible to expect that the vesicular membranes could be stabilized together by π-π stacking interactions between foldamer backbones and collective van der Waals interactions between side chains.

Hexagonal Lyotropic Liquid Crystal from Simple "Abiotic" Foldamers

The motivation of foldamer chemistry is to identify novel building blocks that have the potential to imitate natural species. Peptides and peptide mimetics can form stable helical conformations and further self-assemble into diverse aggregates in water, where it is difficult to isolate a single helix. In contrast, most "abiotic" foldamers may fold into helical structures in solution, but are difficult to assemble into tertiary ones. It remains a challenge to obtain "abiotic" species similar to peptides. In this paper, a novel foldamer scaffold, in which p-phenyleneethynylene units are linked by chiral carbon atoms, was designed and prepared. In very dilute solutions, these oligomers were random coils. The hexamer and octamers could form a hexagonal lyotropic liquid crystal (LC) in CH2Cl2 when the concentrations reached the critical values. The microscopic observations indicated that they could assemble into the nanofibers in the LC. Interestingly, after some LC phases were diluted at room temperature, the nanofibers could be preserved. The good stabilities of the assemblies are possibly attributed to a more compact backbone and more rigid side chains.