Effects of Lateral and Terminal Chains of X-Shaped Bolapolyphiles with Oligo(phenylene ethynylene) Cores on Self-Assembly Behaviour. Part 1: Transition between Amphiphilic and Polyphilic Self-Assembly in the Bulk

Highly branched bolapolyphilic liquid crystals with a cubic A15 network at the triangle-square transition

Rod-like bolapolyphiles with highly branched carbosilane-based side-chains self-assemble into several honeycomb structures if the oligo(p-phenylene ethynylene) core is polyfluorinated, whereas for the non-fluorinated series an A15 type cubic network of rod-bundles was observed instead, suggesting a brand new pathway for the transition between triangular and square honeycomb phases.

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.

Tetrahedral Liquid-Crystalline Networks: An A15-Like Frank-Kasper Phase Based on Rod-Packing

The Pm 3 ‾ n cubic and other low-symmetry Frank-Kasper phases are known to be formed by soft spheres, ranging from metals to block copolymer micelles and colloidal nanoparticles. Here, we report a series of X-shaped polyphiles composed of sticky rods and two non-symmetric branched side-chains, which self-assemble into the first example of a cubic liquid-crystalline phase representing a tetrahedral network of rods with a Pm 3 ‾ n lattice. It is the topological dual to the Weaire-Phelan foam, being the Voronoi tessellation of the A15 sphere packing, from which this network is obtained by Delaunay triangulation.

The rhombic honeycomb - a new mode of self-assembly in liquid crystalline soft matter

Rod-like liquid crystalline (LC) polyphilic compounds with a linear oligo(phenyleneethynylene) core, sticky glycerol groups at each end and two long alkyl side chains (C₂₀-C₃₂) at opposite sides form rhombic honeycombs with inner angles around 60/120°, occurring between triangular and square tiling patterns.

Emergence of uniform tilt and π-stacking in triangular liquid crystalline honeycombs

The synclinic tilted organization of specifically designed polyphilic oligo(p-phenylene ethynylene) rods in cylindrical shells around triangular prismatic cells on the <5 nm scale leads to a new kind of liquid crystalline honeycomb composed of helical shells with alternating helix sense. Core fluorination at the outer ring modifies the core-core interactions, thus resulting in triangular arrays with face-to-face π-stacking along the honeycomb.

Different Modes of Deformation of Soft Triangular Honeycombs at the Sub-5 nm Scale

Patterning on the sub-5 nm length scale is a contemporary challenge for further miniaturization of microelectronic circuits. Here, the first soft self-assembled triangular patterns are reported showing transitions between regular and two different kinds of isosceles (acute and obtuse angled) triangles on this length scale, formed by liquid crystalline honeycombs of polyphilic block molecules involving a fluorinated oligo(para-phenylene ethynylene) core. The type of formed triangular pattern depends on the degree and position of fluorination and on temperature. They are the first soft honeycombs combining tilted and nontilted organizations in a uniform nanostructure, where the tilted molecules in only one or two sides of the triangular prismatic cells dominate the shape and the size of the morphology.

A periodic dodecagonal supertiling by self-assembly of star-shaped molecules in the liquid crystalline state

Molecular tessellations are known in solid state systems and their formation is often induced or supported by a periodic surface lattice. Here we discover a complex tessellation on the 10 nm length scale, spontaneously formed in the highly dynamic liquid crystalline state. It is composed of overlapping dodecagonal supertiles combining prismatic cells with triangular and square cross sections. This complex honeycomb occurs between a triangular honeycomb at high and a square at low temperature, being opposite to the sequence expected for a thermal expansion of the side chains in the prismatic cells. Formation of the supertiles is supported by the segregation of alkyl chains with different length. The emergent behaviour of this complex soft matter structure is demonstrated, and intriguing connections between self-assembly on surfaces, in liquid crystals, and in block copolymers are drawn. Moreover, the tessellation represents a close approximant of the elusive columnar liquid quasicrystal with dodecagonal symmetry.

Controlling the Miscibility of X-Shaped Bolapolyphiles in Lipid Membranes by Varying the Chemical Structure and Size of the Polyphile Polar Headgroup

Bolaamphiphiles are well-known naturally occurring structures that can increase the thermal and mechanical stability of the phospholipid membrane by incorporation in a transmembrane manner. Modifications of bolaamphiphiles to introduce particular structural elements such as a conjugated aromatic backbone and lateral side chains in the hydrophobic region lead to bolapolyphiles (BPs). We investigated the ability of BPs to form lyotropic phases in water. The BPs had an identical backbone and side chains, but different headgroup structures, leading to different abilities to act as hydrogen bond donors and acceptors. BPs with hydrophilic headgroups capable of acting as hydrogen bond donors as well as acceptors did not form lyotropic phases and were insoluble in water, independent of whether the polar groups were small or large. The extended lipophilic core structure and the multiple intermolecular hydrogen bonds between the headgroups prevented the formation of well-hydrated lyotropic aggregates. A BP with two large hydrophilic headgroups of several ethylene oxide moieties terminated by methyl groups formed sheet- and vesicle-like aggregates in water. These headgroups act only as hydrogen bond acceptors and cannot form hydrogen bonds in the absence of water. The miscibility of BPs with vesicles of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) in water and the resulting aggregate structures were also investigated. For BPs with headgroups acting as donors and acceptors of hydrogen bonds, macroscopic phase separation occurred in the mixed membranes, and two different membrane domains, a DPPC-rich one containing only little polyphile and a BP-rich one containing varying amounts of lipid, were formed. For headgroups without the ability to act as hydrogen bond donors, small BP aggregates were formed that were homogeneously distributed over the membrane. The lateral organization of BPs in lipid membranes can thus be controlled by the nature of the BP headgroup.

Construction of Supramolecular Nanostructures from V-Shaped Amphiphilic Rod-Coil Molecules Incorporating Phenazine Units

A series of bent-shaped molecules, consisting of dibenzo[a,c]phenazine and phenyl groups connected together as a rod segment, and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 6 as the coil segment, were synthesized. The self-assembling behavior of these molecules by differential scanning calorimetry (DSC), thermal optical polarized microscopy (POM), small-angle X-ray scattering spectroscopy (SAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM), revealed that carboxyl or butoxy carbonyl groups at the 11 position of dibenzo[a,c]phenazine noticeably influence self-organization of molecules into supramolecular aggregates in bulk and aqueous solutions. Molecules 1 and 2 with chiral or non-chiral PEO coil chains and the carboxyl group at the rod segments self-organize into a hexagonal perforated lamellar structure and a hexagonal columnar structure in the solid state. In aqueous solution, molecules 1 and 2 self-assemble into diverse lengths of nanofibers, whereas molecules 3 and 4 with butoxy carbonyl groups exhibit a self-organizing capacity to form diverse sizes of spherical aggregates.

Effects of Lateral and Terminal Chains of X-Shaped Bolapolyphiles with Oligo(phenylene ethynylene) Cores on Self-Assembly Behavior. Part 2: Domain Formation by Self-Assembly in Lipid Bilayer Membranes

Supramolecular self-assembly of membrane constituents within a phospholipid bilayer creates complex functional platforms in biological cells that operate in intracellular signaling, trafficking and membrane remodeling. Synthetic polyphilic compounds of macromolecular or small size can be incorporated into artificial phospholipid bilayers. Featuring three or four moieties of different philicities, they reach beyond ordinary amphiphilicity and open up avenues to new functions and interaction concepts. Here, we have incorporated a series of X-shaped bolapolyphiles into DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) bilayers of giant unilamellar vesicles. The bolapolyphiles consist of a rod-like oligo(phenylene ethynylene) (OPE) core, hydrophilic glycerol-based headgroups with or without oligo(ethylene oxide) expansions at both ends and two lateral alkyl chains attached near the center of the OPE core. In the absence of DPPC and water, the compounds showed thermotropic liquid-crystalline behavior with a transition between polyphilic and amphiphilic assembly (see part 1 in this issue). In DPPC membranes, various trends in the domain morphologies were observed upon structure variations, which entailed branched alkyl chains of various sizes, alkyl chain semiperfluorination and size expansion of the headgroups. Observed effects on domain morphology are interpreted in the context of the bulk behavior (part 1) and of a model that was previously developed based on spectroscopic and physicochemical data.