Localized Crystallization of Enantiomeric Organic Compounds on Chiral Micro‐patterns from Various Organic Solutions

The controlled crystallization of enantiomers of an organic compound (a cyclic phosphoric acid derivative) on templated micro‐patterned functionalised surfaces is demonstrated. Areas where a complementary chiral thiol has been located were effective heterogeneous nucleation centres when a solution of the compound is evaporated slowly. Various organic solvents were employed, which present a challenge with respect to other examples when water is used. The solvent and the crystallization method have an important influence on the crystal growth of these compounds. When chloroform was employed, well‐defined crystals grow away from the surface, whereas crystals grow in the plane from solutions in isopropanol. In both cases, nucleation is confined to the polar patterned regions of the surface, and for isopropanol growth is largely limited within the pattern, which shows the importance of surface chemistry for nucleation and growth. The apparent dependence on the enantiomer used in the latter case could imply stereo‐differentiation as a result of short‐range interactions (the templating monolayer is disordered, even at the nanometre scale). The size of the pattern of chiral monolayer also determines the outcome of the crystallization; 5 μm dots are most effective. Despite the low surface tension of the samples (relative to the high surface tension of water), differential solvation of the polar and hydrophobic layers of the solvents allows crystallization in the polar regions of the monolayer, therefore the polarity of the regions in which heterogeneous nucleation takes place is indeed very important. Despite the complex nature of the crystallization process, these results are an important step towards to the use of patterned surfaces for heterogeneous selective nucleation of enantiomers.     

Self‐Assembled Organic Microtubes from Amphiphilic Molecules

Getting the sizes sorted out : In recent years, there have been increasing numbers of reports about self‐assembled nano‐ or microtubular structures because of their potential uses in a variety of technical applications, which are largely determined by the tube sizes. This Focus Review highlights microsized self‐assembled organic tubular structures formed in aqueous solutions and organic solvents.

     

Dynamic Formation of Hybrid Peptidic Capsules by Chiral Self‐Sorting and Self‐Assembly

Owing to their versatility and biocompatibility, peptide‐based self‐assembled structures constitute valuable targets for complex functional designs. It is now shown that artificial capsules based on β‐barrel binding motifs can be obtained by means of dynamic covalent chemistry (DCC) and self‐assembly. Short peptides (up to tetrapeptides) are reversibly attached to resorcinarene scaffolds. Peptidic capsules are thus selectively formed in either a heterochiral or a homochiral way by simultaneous and spontaneous processes, involving chiral sorting, tautomerization, diastereoselective induction of inherent chirality, and chiral self‐assembly. Self‐assembly is shown to direct the regioselectivity of reversible chemical reactions. It is also responsible for shifting the tautomeric equilibrium for one of the homochiral capsules. Two different tautomers (keto‐enamine hemisphere and enol‐imine hemisphere) are observed in this capsule, allowing the structure to adapt for self‐assembly.     

Self‐Assembled Monolayer Formed by a Rhenium Complex Containing Hyperbranched Polymer

Summary: The synthesis of a hyperbranched polymer containing a rhenium bipyridine complex is reported. The polymer was synthesized from a monomer that contains two chlorotricarbonyl rhenium(I ) bipyridine moieties and a stilbazole ligand, and the polymer was formed by the coordination reaction in one single step. Gel permeation chromatography results showed that the resulting polymer had a strong interaction with the column packing material, which was reduced when the eluent was added with an electrolyte. Both atomic force microscopy and laser light scattering showed that the size of the polymer molecules was in the range between 25–30 nm. A monolayer of polymer molecules could form on a pretreated substrate by the self‐assembly process, which can serve as the building block for multilayer ultrathin film devices.

The metal‐containing hyperbranched polymer synthesized here.     

Self‐Assembled Ultralong Chiral Nanotubes and Tuning of Their Chirality Through the Mixing of Enantiomeric Components

Enantiomeric L ‐ or D ‐glutamic acid based lipids were designed and their self‐assembly was investigated. It was found that at a certain concentration, either L ‐ or D ‐enantiomeric derivatives could self‐assemble in absolute alcohol to form a white organogel, which was composed of ultralong nanotubes with an aspect ratio higher than 1000. Further investigations revealed that these nanotubes were in chiral forms. The chirality of the nanotubes was determined by that of the enantiomers employed. In addition, when D and L enantiomers were mixed in different ratios, the nanotube could be tuned consecutively from nanotubes with a helical seam to nanotwists, the chirality of which being determined by the excess enantiomer in the mixed systems. In the case of an equimolar mixture of the enantiomers, flat nanoplates instead of helical nanotubes or nanotwists were obtained. The FTIR vibrational data and XRD layer‐distance values showed a consecutive change as a function of the enantiomeric excess. It was further revealed that the slightly stronger interaction between D –L enantiomeric pairs than that between D –D or L –L pairs was responsible for the formation of the diverse self‐assembled nanostructures.     

Chiral Carbonaceous Nanotubes Containing Twisted Carbonaceous Nanoribbons,Prepared by the Carbonization of Chiral Organic Self‐Assemblies

Single‐handed helical silica nanotubes containing chiral organic self‐assemblies were prepared by using a supramolecular templating approach. After carbonization and the removal of the silica, single‐handed helical carbonaceous nanotubes that contained twisted carbonaceous nanoribbons were obtained. It is believed that the nanotubes formed as a result of the adsorption of low‐molecular‐weight gelators. The twisted nanoribbons were formed because of the carbonization of the organic self‐assemblies. The samples were characterized by using field‐emission scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Raman spectroscopy, and circular dichroism. For the samples carbonized at 900 °C for 3.0 h, a partially graphitized structure was identified. The circular dichroism (CD) spectra indicated that the twisted nanoribbons exhibited optical activity. The CD spectrum was simulated by using time‐dependent density functional theory. The results suggested that the CD signals originated from the chiral stacking of aromatic rings.     

Construction of Helical J‐Aggregates Self‐Assembled from a Thymidylic Acid Appended Anthracene Dye and DNA as a Template

Driven round the twist by DNA : One‐dimensional helical J‐aggregates are formed by the self‐assembly of thymidylic acid appended anthracene dye (shown in red and yellow) in the presence of complementary single‐stranded oligoadenylic acid (shown in green and blue) in an aqueous solution.

     

Self‐Assembly Studies of a Chiral Bisurea‐Based Superhydrogelator

A chiral bisurea‐based superhydrogelator that is capable of forming supramolecular hydrogels at concentrations as low as 0.2 mM is reported. This soft material has been characterized by thermal studies, rheology, X‐ray diffraction analysis, transmission electron microscopy (TEM), and by various spectroscopic techniques (electronic and vibrational circular dichroism and by FTIR and Raman spectroscopy). The expression of chirality on the molecular and supramolecular levels has been studied and a clear amplification of its chirality into the achiral analogue has been observed. Furthermore, thermal analysis showed that the hydrogelation of compound 1 has a high response to temperature, which corresponds to an enthalpy‐driven self‐assembly process. These particular thermal characteristics make these materials easy to handle for soft‐application technologies.     

A Self‐Assembled Superhydrophobic Electrospun Carbon–Silica Nanofiber Sponge for Selective Removal and Recovery of Oils and Organic Solvents

An oil spill needs timely cleanup before it spreads and poses serious environmental threat to the polluted area. This always requires the cleanup techniques to be efficient and cost‐effective. In this work, a lightweight and compressible sponge made of carbon–silica nanofibers is derived from electrospinning nanotechnology that is low‐cost, versatile, and readily scalable. The fabricated sponge has high porosity (>99 %) and displays ultra‐hydrophobicity and superoleophilicity, thus making it a suitable material as an oil adsorbent. Owing to its high porosity and low density, the sponge is capable of adsorbing oil up to 140 times its own weight with its sorption rate showing solution viscosity dependence. Furthermore, sponge regeneration and oil recovery are feasible by using either cyclic distillation or mechanical squeezing.     

Atomic‐Level Elucidation of the Initial Stages of Self‐Assembled Monolayer Metallization and Nanoparticle Formation

The development of high‐performance molecular electronics and nanotech applications requires deep understanding of atomic level structural, electronic, and magnetic properties of electrode/molecular interfaces. Recent electrochemical experiments on self‐assembled monolayers (SAMs) have identified highly practical means to generate nanoparticles and metal monolayers suspended above substrate surfaces through SAM metallizations. A rational basis why this process is even possible is not yet well‐understood. To clarify the initial stages of interface formation during SAM metallization, we used first‐principles spin‐polarized density functional theory (DFT) calculations to study Pd diffusion on top of 4‐mercaptopyridine (4MP) SAMs on Au(111). After distinguishing potential‐energy surfaces (PESs) for different spin configurations for transition metal atoms on the SAM, we find adatom diffusion is not possible over the clean 4MP–SAM surface. Pre‐adsorption of transition‐metal atoms, however, facilitates atomic diffusion that appears to explain multiple reports on experimentally observed island and monolayer formation on top of SAMs. Furthermore, these diffusions most likely occur by moving across low‐lying and intersecting PESs of different spin states, opening the possibility of magnetic control over these systems. Vertical diffusion processes were also investigated, and the electrolyte was found to play a key role in preventing metal permeation through the SAM to the substrate.     

Self‐Assembled Fluorescent Organic Nanoparticles for Live‐Cell Imaging

Fluorescent, cell‐permeable, organic nanoparticles based on self‐assembled π‐conjugated oligomers with high absorption cross‐sections and high quantum yields have been developed. The nanoparticles are generated with a tuneable density of amino groups for charge‐mediated cellular uptake by a straightforward self‐assembly protocol, which allows for control over size and toxicity. The results show that a single amino group per ten oligomers is sufficient to achieve cellular uptake. The non‐toxic nanoparticles are suitable for both one‐ and two‐photon cellular imaging and flow cytometry, and undergo very efficient cellular uptake.     

Fabrication of a Metal Particle Array Based on a Self‐Assembled Template from a Two‐Armed Polymer

A two‐armed polymer with a crown ether core self‐assembles to produce macroporous films with pores perpendicularly reaching through the film down to the substrate. A possible assembling mechanism is discussed. The pore size can be conveniently adjusted by changing the solution concentration. These through‐hole macroporous films provide a template for fabricating an array of Cu nanoparticle aggregates.

     

Utilization of Evaporation during the Crystallization Process: Self‐Templation of Organic Parallelogrammatic Pipes

Analogues of 4‐dodecyloxy‐2‐trifluoromethylbenzamide ( 12FH2 ) consisting of a hydrophobic alkyl chain, a trifluoromethylated aromatic ring, and a self‐complementary hydrogen‐bonding amido group were synthesized, and the structural effect of each component on the formation of parallelogrammatic pipes was investigated. Differential scanning calorimetry and powder XRD analyses revealed that all‐trans L and gauche‐rich S polymorphic forms appeared for the analogues with more than eight carbon atoms in the alkyl chain, that is, the polymorphism originates in the conformation of the alkyl groups and hydrogen‐bonding patterns of the benzamide group. Also, the trifluoromethyl substituent is crucial in that it provides an appropriate molecular balance between the benzamide and alkyl groups. Scanning electron microscopy and powder XRD analyses of solids obtained by a drying‐mediated assembly process revealed that production of the L polymorph by polymorphic transition from the S polymorph resulted in evolution of a three‐dimensional structure when the alkyl group has more than 12 carbon atoms. Among the series of compounds, 12FH2 and 4‐tetradecyloxy‐2‐trifluoromethylbenzamide ( 14FH2 ) formed parallelogrammatic pipes with micrometer dimensions. An atomic force microscopy study of 12FH2 suggested that a single pipe may be composed of platelike crystallites of L polymorph. From a mercury‐intrusion porosimetry study, it was determined that macroporous materials with average pore diameters of about 40 μm and porosity of about 80 % were obtained. The previously proposed self‐templation mechanism by polymorphic transition from S to L polymorph was further discussed in view of polymorphism and the crystallization rate. An appropriate molecular balance between the benzamide and alkyl groups is necessary to induce a proper polymorphic transition for the development of a three‐dimensional hollow structure in the evaporation process.