Hierarchically Ordered Self‐Assembly of Amphiphilic Bifullerenes

A series of novel functionalised dumbbell‐shaped bifullerenes in which two [5.0] pentakis‐adducts of C₆₀ are covalently connected by cyclic bismalonates were synthesised. These dimeric compounds, carrying various combinations of hydrophilic and hydrophobic addends, self‐assemble in aqueous solution towards supramolecular architectures of different structural complexity as observed by cryogenic transmission electron microscopy (cryo‐TEM). The detailed analysis of the image data revealed an unprecedented hierarchical aggregation behaviour. Whereas completely hydrophilic substituted bifullerenes formed profoundly monodisperse populations of small oligomeric elementary micelles consisting of only three or four bifullerene molecules in a supposedly bent conformation, their amphiphilic equivalents underwent a hierarchical two‐step assembly process towards larger spherical and even rod‐like structures. The data suggest that the hierarchical assembly process is driven by hydrophobic interactions of preformed tetrameric elementary micelles.     

Hierarchical Analysis of Self‐Assembled PEGylated Hexaphenylalanine Photoluminescent Nanostructures

Despite the growing literature about diphenylalanine‐based peptide materials, it still remains a challenge to delineate the theoretical insight into peptide nanostructure formation and the structural features that could permit materials with enhanced properties to be engineered. Herein, we report the synthesis of a novel peptide building block composed of six phenylalanine residues and eight PEG units, PEG₈‐F6. This aromatic peptide self‐assembles in water in stable and well‐ordered nanostructures with optoelectronic properties. A variety of techniques, such as fluorescence, FTIR, CD, DLS, SEM, SAXS, and WAXS allowed us to correlate the photoluminescence properties of the self‐assembled nanostructures with the structural organization of the peptide building block at the micro‐ and nanoscale. Finally, a model of hexaphenylalanine in aqueous solution by molecular dynamics simulations is presented to suggest structural and energetic factors controlling the formation of nanostructures.     

Self‐Assembled Vesicles with Functionalized Membranes

Biological membranes play a key role for the function of living organisms. Thus, many artificial systems have been designed to mimic natural cell membranes and their functions. A useful concept for the preparation of functional membranes is the embedding of synthetic amphiphiles into vesicular bilayers. The dynamic nature of such noncovalent assemblies allows the rapid and simple development of bio‐inspired responsive nanomaterials, which find applications in molecular recognition, sensing or catalysis. However, the complexity that can be achieved in artificial functionalized membranes is still rather limited and the control of their dynamic properties and the analysis of membrane structures down to the molecular level remain challenging.     

Local Probe Oxidation of Self‐Assembled Monolayers: Templates for the Assembly of Functional Nanostructures

Surfaces with purposes : The electroinitiated patterning of self‐assembled monolayers enables the fabrication of a variety of complex nanostructures (see picture). The possibilities offered by the introduction of chemical selectivity through the local generation of chemically active groups and subsequent derivatization are reviewed, with a focus on progress in this area of research over the last four years.

     

Oligomeric Hydrogels Self‐Assembled from Reduction‐Controlled Condensation

Polymer hydrogels and small‐molecule‐based (SMB) supramolecular hydrogels have been widely explored. But oligomeric hydrogels have remained a challenge because synthetic difficulties of the oligomers and control of their amphiphilicities. Reported herein is the rational design of two precursors Cys(SEt)‐Lys‐CBT ( 1 ) and (Cys‐Lys‐CBT)₂ ( 2 ) (CBT=2‐cyano‐6‐aminobenzothiazole) and the use of a biocompatible condensation to prepare oligomeric hydrogels. Glutathione reduction of 1 or 2 yields the same gelator Cys‐Lys‐CBT ( 3 ) which condenses with each other to yield amphiphilic cyclic oligomers. The oligomers instantly self‐assemble into nanofibers and form oligomeric hydrogels with similar mechanic properties. Chemical analyses indicated that the major condensation product in both two hydrogels is a cyclic dimer. Considering its biocompatibility, optimal mechanical strength, and biodegradability, we believe that our oligomeric hydrogel might be useful for long‐term drug delivery in the future.     

Self‐Assembled Cage‐Like Protein Structures

Proteins and protein‐based assemblies represent the most structurally and functionally diverse molecules found in nature. Protein cages, viruses and bacterial microcompartments are highly organized structures that are composed primarily of protein building blocks and play important roles in molecular ion storage, nucleic acid packaging and catalysis. The outer and inner surface of protein cages can be modified, either chemically or genetically, and the internal cavity can be used to template, store and arrange molecular cargo within a defined space. Owing to their structural, morphological, chemical and thermal diversity, protein cages have been investigated extensively for applications in nanotechnology, nanomedicine and materials science. Here we provide a concise overview of the most common icosahedral viral and nonviral assemblies, their role in nature, and why they are highly attractive scaffolds for the encapsulation of functional materials.     

Directed Self‐Assembly of DNA Tiles into Complex Nanocages

Tile‐based self‐assembly is a powerful method in DNA nanotechnology and has produced a wide range of well‐defined nanostructures. But the resulting structures are relatively simple. Increasing the structural complexity and the scope of the accessible structures is an outstanding challenge in molecular self‐assembly. A strategy to partially address this problem by introducing flexibility into assembling DNA tiles and employing directing agents to control the self‐assembly process is presented. To demonstrate this strategy, a range of DNA nanocages have been rationally designed and constructed. Many of them can not be assembled otherwise. All of the resulting structures have been thoroughly characterized by gel electrophoresis and cryogenic electron microscopy. This strategy greatly expands the scope of accessible DNA nanostructures and would facilitate technological applications such as nanoguest encapsulation, drug delivery, and nanoparticle organization.     

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.

     

Self‐Assembled Discrete Molecules for Sensing Nitroaromatics

Efficient sensing of trace amount nitroaromatic (NAC) explosives has become a major research focus in recent time due to concerns over national security as well as their role as environment pollutants. NO₂‐containing electron‐deficient aromatic compounds, such as picric acid (PA), trinitrotoluene (TNT), and dinitrotoluene (DNT), are the common constituents of many commercially available chemical explosives. In this article, we have summarized our recent developments on the rational design of electron‐rich self‐assembled discrete molecular sensors and their efficacy in sensing nitroaromatics both in solution as well as in vapor phase. Several π‐electron‐rich fluorescent metallacycles (squares, rectangles, and tweezers/pincers) and metallacages (trigonal and tetragonal prisms) have been synthesized by means of metal–ligand coordination‐bonding interactions, with enough internal space to accommodate electron‐deficient nitroaromatics at the molecular level by multiple supramolecular interactions. Such interactions subsequently result in the detectable fluorescence quenching of sensors even in the presence of trace quantities of nitroaromatics. The fascinating sensing characteristics of molecular architectures discussed in this article may enable future development of improved sensors for nitroaromatic explosives.     

A Case Study of the Likes and Dislikes of DNA and RNA in Self‐Assembly

Programmed self‐assembly of nucleic acids (DNA and RNA) is an active research area as it promises a general approach for nanoconstruction. Whereas DNA self‐assembly has been extensively studied, RNA self‐assembly lags much behind. One strategy to boost RNA self‐assembly is to adapt the methods of DNA self‐assembly for RNA self‐assembly because of the chemical and structural similarities of DNA and RNA. However, these two types of molecules are still significantly different. To enable the rational design of RNA self‐assembly, a thorough examination of their likes and dislikes in programmed self‐assembly is needed. The current work begins to address this task. It was found that similar, two‐stranded motifs of RNA and DNA lead to similar, but clearly different nanostructures.     

pH‐Switchable Self‐Assembled Materials

Self‐assembled materials, which are able to respond to external stimuli, have been extensively studied over the last decades. A particularly exciting stimulus for a wide range of biomedical applications is the pH value of aqueous solutions, since deprotonation‐protonation events are crucial for structural and functional properties of biopolymers. In living cells and tissues, intra‐ and extracellular pH values are stringently regulated, but can deviate from pH neutral as observed for example in tumorous, inflammatory sites, in endocytic pathways, and specific cellular compartments. By using a pH‐switch as a stimulus, it is thereby possible to address specific targets in order to cause a programmed response of the supramolecular material. This strategy has not only been successfully applied in fundamental research but also in clinical studies. In this feature article, current strategies that have been used in order to design materials with pH‐responsive properties are illustrated. This discussion only addresses selected examples from the last four years, the self‐assembly of polymer‐based building blocks, assemblies emerging from small molecules including surfactants or derived from biological macromolecules, and finally the controlled self‐assembly of oligopeptides.

     

Hierarchical Nanoporous Structures by Self‐Assembled Hybrid Materials Based on Block Copolymers

Hierarchical nanoporous structures are fabricated by adsorption of micelles of diblock copolymer‐templated Au‐nanoparticles onto a hydrophilic solid substrate. Gold nanoparticles are prepared using micelles (19 nm) of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) as nanoreactors. Deposition of thin films of the micellar solution, modified with a non‐selective solvent (THF), on hydrophilic surfaces leads to the formation of hierarchical nanoporous morphologies. The thin films exhibit two different pore diameters and a total pore density of 15 × 10⁸ holes per cm². The structure was analyzed in terms of topography and chemical composition using AFM, TEM and XPS measurements. The PS‐b‐P4VP template was subsequently removed by oxygen plasma etching, to leave behind metallic nanopores that mimic the original thin film morphology.

     

Decrypting the TEM images for deciphering the microstructural code of complex oxides

The knowledge of the structure of the real solids is required for achieving the desired architectures in the research of new materials and/or optimizing the relationships between structure and properties. Understanding complex oxides needs accurate characterization at different length scales and the combined application of all solid-state techniques. Deciphering the relationships between all this information provides codes that allow the identification of the different structural levels, their roles and the way they interact. These step-by-step routes are illustrated through two basic mechanisms of solid-state chemistry: to determine the building units of one complex oxide in order to predict the existence of other arrangements on the one hand and to correlate complex ordering phenomena, such as those involving charges, orbitals and spins of manganese atoms in perovskite-type manganites on the other hand.