Supramolecular helical columns from the self-assembly of chiral rods

Chiral-bridged rod molecules (CBRs) that consisted of bis(penta-p-phenylene) conjugated to an opened or closed chiral bridging group as a rigid segment and oligoether dendrons as flexible segments were synthesized and characterized. In the bulk state, both molecules self-assemble into a hexagonal columnar structure, as confirmed by X-ray scatterings and transmission electron microscopy (TEM) observations. Interestingly, these structures display opposite Cotton effects in the chromophore of the aromatic unit in spite of the same chirality (R,R) of the chiral bridging groups. The molecules were observed to self-assemble into cylindrical micellar aggregates in aqueous solution, as confirmed by light scattering and TEM investigations, and exhibit intense signals in the circular dichroism (CD) spectra, which are indicative of one-handed helical conformations. The CD spectra of each molecule showed opposite signals to each other, which were similar to those in the bulk. Notably, when the opened CBR was added to a solution of closed CBRs up to a certain concentration, the CD signal of the closed CBR was amplified. This implies that both molecules co-assemble into a one-handed helical structure because the opened chiral bridge is conformationally flexible, which is inverted to co-assemble with the closed CBR. These results demonstrate that small structural modifications of the chiral moiety can transfer the chiral information to a supramolecular assembly in the opposite way.     

Anion dependent self-assembly of "tetra-decker" and "triple-decker"luminescent Tb(III) salen complexes

The Schiff base complexes [Tb3L4(H2O)2]Cl and [Tb3L3(OAc)2Cl] both have unusual multi-decker architectures formed via intramolecular pi-pi interactions between phenylene units.     

DNA origami: a quantum leap for self-assembly of complex structures

The spatially controlled positioning of functional materials by self-assembly is one of the fundamental visions of nanotechnology. Major steps towards this goal have been achieved using DNA as a programmable building block. This tutorial review will focus on one of the most promising methods: DNA origami. The basic design principles, organization of a variety of functional materials and recent implementation of DNA robotics are discussed together with future challenges and opportunities.     

Three-dimensional self-assembly of metallic rods with submicron diameters using magnetic interactions

Metallic rods with submicron diameters that contain disklike ferromagnetic sections self-assemble into highly stable, hexagonally close-packed arrays of rods. The rods were fabricated by electrodeposition in porous alumina membranes and comprised alternating sections of gold and nickel. The thicknesses of the ferromagnetic nickel sections were approximately one-half the diameter of the rods (400 nm); this geometry orients the "easy" axis of magnetization perpendicular to the long axis of the rod. After magnetization of the rods with a rare-earth magnet, followed by sonication of the suspension, the rods spontaneously assembled into three-dimensional (3D) bundles that, on average, contained 15-30 rods. A macroscopic model of the rods suggests that the most stable orientation of the magnetic dipoles for rods in a defect-free, hexagonally close-packed arrangement is in concentric rings with the dipoles oriented head-to-tail. This configuration minimizes the energy of the bundle and does not generate a net dipole for the structure. This work provides a simple demonstration that magnetic interactions between ferromagnetic objects can direct and stabilize the formation of ordered, 3D structures by self-assembly.     

Perylenediimide-surfactant complexes: thermotropic liquid-crystalline materials via ionic self-assembly

In this communication we present the facile preparation and characterisation of thermotropic liquid-crystalline materials from the ionic self-assembly of a charged perylenediimide derivative and oppositely charged surfactants.     

Hierarchical self-assembly in polymeric complexes: towards functional materials

Combination of self-assembly at different length scales leads to structural hierarchies. It offers rich possibilities to construct nanostructured matter, nanoscale parts, and switching (responsive) properties based on the phase transitions of the self-assembled structures. Complexation of oligomeric amphiphiles to polymers using ionic interactions, coordination, or hydrogen bonding leads to polymeric comb-shaped supramolecules (complexes), which self-assemble at a length scale of a few nm. Self-assembly at an order of magnitude larger length scale is provided by block copolymers, and combination of the latter two concepts leads to structural hierarchies. They provide e.g. templates for mesoporous materials and nano-objects, and allow switching conductivity and switching optical properties. Structural hierarchies are also observed by complexing moderately monodisperse polymeric rods with amphiphiles. Finally, self-assembly at even a larger length scale upon using colloidal particles may be combined to the above structures, as encouraged by recent observations.     

Combinatorial self-assembly of DNA nanostructures

Here we report a modular design of self-assembly of DNA nanostructures in a combinatorial approach; a square with approximately 25 nm cavity dimension, a chair with approximately 80 nm in height and a line with approximately 100 nm in length are formed through combinations of four cross-shaped DNA tiles which are kept constant and six variable linker tiles.     

Lattice self-assembly of cyclodextrin complexes and beyond

While lipids form soft, fluidic membranes (soft assembly), proteins can readily assemble into rigid, crystalline structures such as viral capsids and bacterial compartments (lattice assembly). The key difference has to do with the driving forces, where the former is driven by the weak, directionless hydrophobic effect and the latter, by a combination of relatively strong, directional intermolecular interactions. In synthetic systems, the lipid assembly has been massively replicated but the protein assembly has been rarely rivaled. Herein, we briefly review these two kinds of assemblies with special emphasis on a recently reported lattice self-assembly system of cyclodextrin complexes. The complexes arrange themselves into an in-plane, rhombic lattice that develops into lamellar, tubular, and polygonal structures depending on concentration. We will then cover the formation mechanisms, driving forces, and an application of the tubes in particle encapsulation. We hope that this short review would draw people's attention to this emerging field of lattice self-assembly.     

Star-shaped hexa-peri-hexabenzocoronene "heptamer": synthesis and self-assembly

[structure: see text] A star-shaped hexa-peri-hexabenzocoronene "heptamer" was prepared, which showed a strong tendency to aggregate in solution and in the bulk states. Higher order was found in a high-temperature, columnar liquid crystalline phase due to the higher mobility of the molecules in comparison with the low-temperature solid. In addition, physical gel formation was observed due to the presence of covalent intercolumnar interactions.     

Thermal-induced dynamic self-assembly of adenine-grafted polyoxometalate complexes

A new kind of organic-inorganic hybrid complexes based on polyoxometalate were synthesized through symmetrically grafting two adeninyl groups onto Anderson-type MnMo(6) clusters and encapsulating the clusters by organic surfactants. The resultant complexes exhibited thermal-induced dynamic self-assembly behaviors which greatly depended on the ambient temperature and the chain length of cationic surfactants. With the encapsulation of a short surfactant tetrabutyl ammonium, the complex assembled into fibrous, rod-like, and tubular architectures respectively upon heating; while for the case of using a long surfactant dimethyldioctadecyl ammonium as counter ions, the assemblies of the complex transformed from fibers to spheres with the increased temperature. Moreover, the two types of transformations were both reversible during a cooling process. The related mechanism was investigated by combining multiple characterization methods including X-ray crystallography, XPS, FT-IR and temperature-dependent (1)H NMR, which indicated that such a thermal-induced morphological transformation resulted from a synergy effect of the variation of the multiple hydrogen bonds among the complexes and the rearrangement of the surfactants surrounding the MnMo(6) clusters. These results demonstrated a new concept that hydrogen bonds can be rationally employed as the driving force for the fabrication of polyoxometalate-based materials with smart responsive properties.     

pH dependent self-assembly of dimetallic lanthanide complexes

pH dependent self-association has been observed in a series of DO3A-derived lanthanide complexes bearing a carboxylate group that can act as a bridging ligand at high pH, switching on the luminescence from the lanthanide.     

Two-dimensional self-assembly of linear molecular rods at the liquid/solid interface

We report on the synthesis and scanning tunneling microscopy (STM) studies of a series of linear molecular rods (1-5) comprising different numbers and/or spatial arrangements of perfluorinated benzene and benzene subunits interlinked with diacetylenes in the para position and decorated with or without terminal dodecyl chains. The molecules organize themselves into well-ordered 2D crystal structures at the liquid/solid interface through intermolecular and molecule-substrate interactions. Whereas the molecules substituted by dodecyl chains form the lamellar structures with alternating rigid core rows and alkyl chain rows, the unsubstituted ones change the orientation of the rigid backbones with respect to the lamellar axis. The molecular arrangement is not influenced by fluoro substituents on any phenyl ring of the backbone, which suggests that the interactions between the π-conjugated backbones are dominated by close packing rather than by the dipole moments of the rods or fluorine-based intermolecular interactions.     

Parallel molecular computations of pairwise exclusive-or (XOR) using DNA "string tile" self-assembly

Self-assembling DNA nanostructures are an efficient means of executing parallel molecular computations. However, previous experimental demonstrations of computations by DNA tile self-assembly only allowed for one set of distinct input to be processed at a time. Here, we report the multibit, parallel computation of pairwise exclusive-or (XOR) using DNA "string tile" self-assembly. A set of DNA tiles encoding the truth table for the XOR logical operation was constructed. Parallel tile self-assembly and ligation led to the formation of reporter DNA strands which encoded both the input and the output of the computations. These reporter strands provided a molecular look-up table containing all possible pairwise XOR calculations up to a certain input size. The computation was readout by sequencing the cloned reporter strands. This is the first experimental demonstration of a parallel computation by DNA tile self-assembly in which a large number of distinct input were simultaneously processed.     

Chelating DTPA amphiphiles: ion-tunable self-assembly structures and gadolinium complexes

A series of chelating amphiphiles and their gadolinium (Gd(iii)) metal complexes have been synthesized and studied with respect to their neat and lyotropic liquid crystalline phase behavior. These amphiphiles have the ability to form ion-tunable self-assembly nanostructures and their associated Gd(III) complexes have potential as magnetic resonance imaging (MRI) contrast enhancement agents. The amphiphiles are composed of diethylenetriaminepentaacetic acid (DTPA) chelates conjugated to one or two oleyl chain(s) (DTPA-MO and DTPA-BO), or isoprenoid-type chain(s) of phytanyl (DTPA-MP and DTPA-BP). The thermal phase behavior of the neat amphiphiles was examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cross polarizing optical microscopy (POM). Self-assembly of neat amphiphiles and their associated Gd complexes, as well as their lyotropic phase behavior in water and sodium acetate solutions of different ionic strengths, were examined by POM and small and wide angle X-ray scattering (SWAXS). All neat amphiphiles exhibited lamellar structures. The non-complexed amphiphiles showed a variety of lyotropic phases depending on the number and nature of the hydrophobic chain in addition to the ionic state of the hydration. Upon hydration with increased Na-acetate concentration and the subtle changes in the effective headgroup size, the interfacial curvature of the amphiphile increased, altering the lyotropic liquid crystalline structures towards higher order mesophases such as the gyroid (Ia3d) bicontinuous cubic phase. The chelation of Gd with the DTPA amphiphiles resulted in lamellar crystalline structures for all the neat amphiphiles. Upon hydration with water, the Gd-complexed mono-conjugates formed micellar or vesicular self-assemblies, whilst the bis-conjugates transformed only partially into lyotropic liquid crystalline mesophases.     

有机阳离子-无机多阴离子复合物:高分子体系中的组装及其自组装

有机阳离子包覆多金属氧簇无机多阴离子形成的具有确定化学组成、两亲性核壳结构超分子复合物,具有易于调控和集成有机和无机组分结构与功能的特性.以此类复合物为预组装体的自组装和高分子功能杂化材料展现了一类具有多方面构筑超分子组装体的新型构筑基元体系.如何实现预组装体复合物在结构稳定、具有良好加工性基材中的组装和功能化成为这一领域的重要研究内容.本文系统地总结了基于此类超分子复合物的高分子纳米复合材料和溶液中组装方面的研究进展与发展趋势.