Oligopeptide‐Assisted Self‐Assembly of Oligothiophenes: Co‐Assembly and Chirality Transfer

The biomolecule‐assisted self‐assembly of semiconductive molecules has been developed recently for the formation of potential bio‐based functional materials. Oligopeptide‐assisted self‐assembly of oligothiophene through weak intermolecular interactions was investigated; specifically the self‐assembly and chirality‐transfer behavior of achiral oligothiophenes in the presence of an oligopeptide with a strong tendency to form β‐sheets. Two kinds of oligothiophenes without (QT) or with (QTDA) carboxylic groups were selected to explore the effect of the end functional group on self‐assembly and chirality transfer. In both cases, organogels were formed. However, the assembly behavior of QT was quite different from that of QTDA. It was found that QT formed an organogel with the oligopeptide and co‐assembled into chiral nanostructures. Conversely, although QTDA also formed a gel with the oligopeptide, it has a strong tendency to self‐assemble independently. However, during the formation of the xerogel, the chirality of the oligopeptide can also be transferred to the QTDA assemblies. Different assembly models were proposed to explain the assembly behavior.     

Self‐Assembly of Aggregation‐Induced‐Emission Molecules

The last decade has witnessed rapid developments in aggregation‐induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light‐emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self‐assembly behavior is very attractive because the formation of a well‐defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self‐assemble into well‐defined structures. To date, some strategies have been proposed to achieve the self‐assembly of AIEgens. Herein, we summarize the most recent approaches for the self‐assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.     

Sequence‐Dependent Self‐Assembly of Chiral Polyimides

Sequence‐defined chiral polyimides comprising identical asymmetric diamine monomers arranged in different directions along the main chain were designed and prepared. These new sequence‐defined polymers exhibit sequence‐dependent self‐assembly behaviors and responses to ibuprofen enantiomers, as revealed by their chiroptical spectra and gelation properties. For the first time, the self‐assembly of polymers and their interactions with guest molecules have been successfully controlled by means of the directional arrangement of the monomers in their polymer backbones.     

Flow‐Guided Assembly Processes

This Concept article focuses on capillary, hydrodynamics and electrokinetic flow‐guided assembly processes that can produce patterned or gradient functional surfaces either on solid surfaces or in deep micro‐ and nanoscale channels. This concept has the potential to produce low‐cost nanostructures, internal surface modifications, and devices in nanomedicine.     

Biocatalytic Self‐Assembly Cascades

The properties of supramolecular materials are dictated by both kinetic and thermodynamic aspects, providing opportunities to dynamically regulate morphology and function. Herein, we demonstrate time‐dependent regulation of supramolecular self‐assembly by connected, kinetically competing enzymatic reactions. Starting from Fmoc‐tyrosine phosphate and phenylalanine amide in the presence of an amidase and phosphatase, four distinct self‐assembling molecules may be formed which each give rise to distinct morphologies (spheres, fibers, tubes/tapes and sheets). By varying the sequence or ratio in which the enzymes are added to mixtures of precursors, these structures can be (transiently) accessed and interconverted. The approach provides insights into dynamic self‐assembly using competing pathways that may aid the design of soft nanostructures with tunable dynamic properties and life times.     

DNA‐Assisted Self‐Assembly of Pyrene Foldamers

Folding in the tides : Upon hybridization, pyrene molecules assemble through interstrand stacking interactions to form double‐stranded, helical structures. Structural organization of the pyrene molecules is an intrinsic property of the oligoaryl part and takes place independently of the sequence of the attached DNA. Pyrene helicity is most pronounced in a bi‐segmental chimera, in which a DNA stem is present only at one end of the pyrene section.

     

Amphiphilic Janus Gold Nanoparticles Prepared by Interface‐Directed Self‐Assembly: Synthesis and Self‐Assembly

Materials with Janus structures are attractive for wide applications in materials science. Although extensive efforts in the synthesis of Janus particles have been reported, the synthesis of sub‐10 nm Janus nanoparticles is still challenging. Herein, the synthesis of Janus gold nanoparticles (AuNPs) based on interface‐directed self‐assembly is reported. Polystyrene (PS) colloidal particles with AuNPs on the surface were prepared by interface‐directed self‐assembly, and the colloidal particles were used as templates for the synthesis of Janus AuNPs. To prepare colloidal particles, thiol‐terminated polystyrene (PS‐SH) was dissolved in toluene and citrate‐stabilized AuNPs were dispersed in aqueous solution. Upon mixing the two solutions, PS‐SH chains were grafted to the surface of AuNPs and amphiphilic AuNPs were formed at the liquid–liquid interface. PS colloidal particles decorated with AuNPs on the surfaces were prepared by adding the emulsion to excess methanol. On the surface, AuNPs were partially embedded in the colloidal particles. The outer regions of the AuNPs were exposed to the solution and were functionalized through the grafting of atom‐transfer radical polymerization (ATRP) initiator. Poly[2‐(dimethamino)ethyl methacrylate] (PDMAEMA) on AuNPs were prepared by surface‐initiated ATRP. After centrifugation and dissolving the colloidal particles in tetrahydrofuran (THF), Janus AuNPs with PS and PDMAEMA on two hemispheres were obtained. In acidic pH, Janus AuNPs are amphiphilic and are able to emulsify oil droplets in water; in basic pH, the Janus AuNPs are hydrophobic. In mixtures of THF/methanol at a volume ratio of 1:5, the Janus AuNPs self‐assemble into bilayer structures with collapsed PS in the interiors and solvated PDMAEMA at the exteriors of the structures.     

Self‐Assembly of Amphiphilic Nanocrystals

Amphiphilic hybrid materials are formed from polymer‐coated semiconductor nanoparticles that simulate a surfactant‐like response (see picture). The strength and density of the surface coating are the key assembling forces driving a transition from single particles to cylindrical or vesicular superstructures.

     

Self‐Assembly of Tetraphenylalanine Peptides

Three different tetraphenylalanine (FFFF) based peptides that differ at the N‐ and C‐termini have been synthesized by using standard procedures to study their ability to form different nanoassemblies under a variety of conditions. The FFFF peptide assembles into nanotubes that show more structural imperfections at the surface than those formed by the diphenylalanine (FF) peptide under the same conditions. Periodic DFT calculations (M06L functional) were used to propose a model that consists of three FFFF molecules defining a ring through head‐to‐tail NH₃⁺???^?OOC interactions, which in turn stack to produce deformed channels with internal diameters between 12 and 16 Å. Depending on the experimental conditions used for the peptide incubation, N‐fluorenylmethoxycarbonyl (Fmoc) protected FFFF self‐assembles into a variety of polymorphs: ultra‐thin nanoplates, fibrils, and star‐like submicrometric aggregates. DFT calculations indicate that Fmoc‐FFFF prefers a parallel rather than an antiparallel β‐sheet assembly. Finally, coexisting multiple assemblies (up to three) were observed for Fmoc‐FFFF‐OBzl (OBzl = benzyl ester), which incorporates aromatic protecting groups at the two peptide terminals. This unusual and noticeable feature is attributed to the fact that the assemblies obtained by combining the Fmoc and OBzl groups contained in the peptide are isoenergetic.     

Frame‐Guided Assembly of Amphiphiles

Frame‐guided assembly, a recently discovered strategy for amphiphilic assembly, is discussed as a strategy for constructing vesicle assemblies with programmed geometries and dimensions under identical surrounding conditions. The strategy is inspired by the cytoskeletal‐membrane protein–lipid bilayer structure and shows great potential in the understanding and controlling of the amphiphilic assembly process. Both the principles and basic requirements are discussed, along with recently reported examples. The prospects and potential investigations of frame‐guided assembly are also proposed.     

Self‐Assembly of Aniline Oligomers

A great number of nano/microscaled morphologies have recently been prepared during the oxidation of aniline. At the early stage of oxidation, aniline oligomers are obtained, often in spectacular morphologies depending on reaction conditions. Herein, the flower‐like hierarchical architectures assembled from aniline oligomers by a template‐free method are reported. Their formation process is ascribed to the self‐assembly of oligoanilines through non‐covalent interactions, such as hydrogen bonding, hydrophobic forces, and π–π stacking. The model of directional growth is offered to explain the formation of petal‐like objects and, subsequently, flowers. In order to investigate the chemical structure of the oligomers, a series of characterizations have been carried out, such as matrix‐assisted laser desorption ionization, time‐of‐flight mass spectrometry, gas chromatography coupled with mass spectrometry analysis, X‐ray diffraction, and UV/Vis, Fourier‐transform infrared, and Raman spectroscopies. Based on the results of characterization methods, a formation mechanism for aniline oligomers and their self‐assembly is proposed.     

Cell‐Mediated Assembly of Phototherapeutics

Light‐activatable drugs offer the promise of controlled release with exquisite temporal and spatial resolution. However, light‐sensitive prodrugs are typically converted to their active forms using short‐wavelength irradiation, which displays poor tissue penetrance. We report herein erythrocyte‐mediated assembly of long‐wavelength‐sensitive phototherapeutics. The activating wavelength of the constructs is readily preassigned by using fluorophores with the desired excitation wavelength λ_ex. Drug release from the erythrocyte carrier was confirmed by standard analytical tools and by the expected biological consequences of the liberated drugs in cell culture: methotrexate, binding to intracellular dihydrofolate reductase; colchicine, inhibition of microtubule polymerization; dexamethasone, induced nuclear migration of the glucocorticoid receptor.     

Self‐Assembly of Bolaamphiphilic Molecules

The current buzzword in science and technology is self‐assembly and molecular self‐assembly is one of the most prominent fields as far as research in chemical and biological sciences is concerned. Generally, self‐assembly of molecules occurs through weak non‐covalent interactions like hydrogen bonding, π–π stacking, hydrophobic effects, etc. Inspired by many natural systems consisting of self‐assembled structures, scientists have been trying to understand their formation and mimic such processes in the laboratory to create functional “smart” materials, which respond to temperature, light, pH, electromagnetic field, mechanical stress, and/or chemical stimuli. These responses are usually manifested as remarkable changes from the molecular (e. g., conformational state, hierarchical order) to the macroscopic level (e. g., shape, surface properties). Many molecules such as peptides, viruses, and surfactants are known to self‐assemble into different structures. Among them, glycolipids are the new entries in the area of molecules that are being investigated for their self‐assembly characteristics. Among the different classes of glycolipids like rhamnolipids and trehalose lipids, owing to their biological preparations and their structural novelty, sophorolipids (SLs) are evoking greater interest among researchers. Sophorolipids are a class of asymmetric bolas bearing COOH groups at one end and sophorose (dimeric glucose linked by an unusual β(1→2) linkage). The extreme membrane stability of Archaea, attributed to the membrane‐spanning bolas (tetraether glycolipids), has inspired chemists to unravel the molecular designs that underpin the self‐assembly of bolaamphiphilic molecules. Apart from these self‐assembled structures, bolaamphiphiles find applications in many fields such as drug delivery, membrane mimicking, siRNA therapies, etc. The first part of this Personal Account presents some possible self‐assembled structures of bolaamphiphiles and their mechanism of formation. The later part covers our work on one of the typical bolaamphiphiles known as sophorolipids.     

Proton‐Coupled Self‐Assembly of a Porphyrin‐Naphthalenediimide Dyad

The construction of an n–p heterojunction through the self‐assembly of a dyad based on tetraphenylporphyrin (TPP) and 1,4,5,8‐naphthalenedimide (NDI) ( 1 ) is described. Proton transfer from the lysine head group of 1 to the porphyrin ring occurs concomitantly with self‐assembly into 1D nanorods in CHCl₃. TEM and AFM studies showed that the nanorods are formed by the lateral and vertical fusion of multilameller vesicles into networks and hollow ribbons, respectively. These intermediate structures transitioned to nanorods over the course of 4–6 days. Time‐resolved spectroscopy revealed that photoinduced charge separation occurs with rate constants that depend on the nature of the aggregation.     

Harnessing Thin‐Film Continuous‐Flow Assembly Lines

Inspired by nature's ability to construct complex molecules through sequential synthetic transformations, an assembly line synthesis of α‐aminophosphonates has been developed. In this approach, simple starting materials are continuously fed through a thin‐film reactor where the intermediates accrue molecular complexity as they progress through the flow system. Flow chemistry allows rapid multistep transformations to occur via reaction compartmentalization, an approach not amenable to using conventional flasks. Thin film processing can also access facile in situ solvent exchange to drive reaction efficiency, and through this method, α‐aminophosphonate synthesis requires only 443 s residence time to produce 3.22 g h^?1. Assembly‐line synthesis allows unprecedented reaction flexibility and processing efficiency.     

Flow‐Enabled Self‐Assembly of Large‐Scale Aligned Nanowires

One‐dimensional nanowires enable the realization of optical and electronic nanodevices that may find applications in energy conversion and storage systems. Herein, large‐scale aligned DNA nanowires were crafted by flow‐enabled self‐assembly (FESA). The highly oriented and continuous DNA nanowires were then capitalized on either as a template to form metallic nanowires by exposing DNA nanowires that had been preloaded with metal salts to an oxygen plasma or as a scaffold to direct the positioning and alignment of metal nanoparticles and nanorods. The FESA strategy is simple and easy to implement and thus a promising new method for the low‐cost synthesis of large‐scale one‐dimensional nanostructures for nanodevices.