Hydrophobic End‐Modulated Amino‐Acid‐Based Neutral Hydrogelators: Structure‐Specific Inclusion of Carbon Nanomaterials

Hydrophobic end‐modulated l ‐phenylalanine‐containing triethylene glycol monomethyl ether tagged neutral hydrogelators ( 1 – 4 ) are developed. Investigations determine the gelators’ structure‐dependent inclusion of carbon nanomaterials (CNMs) in the self‐assembled fibrillar network (SAFIN). The gelators ( 1 , 3 , and 4 ) can immobilize water and aqueous buffer (pH 3–7) with a minimum gelator concentration of 10–15 mg mL^?1. The hydrophobic parts of the gelators are varied from a long chain (C‐16) to an extended aromatic pyrenyl moiety, and their abilities to integrate 1 D and 2 D allotropes of carbon (i.e., single‐walled carbon nanotubes (SWNTs) and graphene oxide (GO), respectively) within the gel are investigated. Gelator 1 , containing a long alkyl chain (C‐16), can include SWNTs, whereas the pyrene‐containing 4 can include both SWNTs and GO. Gelator 3 fails to incorporate SWNTs or GO owing to its slow rate of gelation and possibly a mismatch between the aggregated structure and CNMs. The involvement of various forces in self‐aggregated gelation and physicochemical changes occurring through CNM inclusion are examined by spectroscopic and microscopic techniques. The distinctive pattern of self‐assembly of gelators 1 and 4 through J‐ and H‐type aggregation might facilitate the structure‐specific CNM inclusion. Inclusion of SWNTs/GO within the hydrogel matrix results in a reinforcement in mechanical stiffness of the composites compared with that of the native hydrogels.     

A Carbon Nanotube Confinement Strategy to Implement Homogeneous Asymmetric Catalysis in the Solid Phase

A readily recyclable asymmetric catalyst has been developed based on the self‐assembly of a homogeneous catalyst in a fibrous network of multiwalled carbon nanotubes (MWNTs). Dimerization of an amide‐based chiral ligand with a suitable spacer allows for the efficient formation of a heterogeneous catalyst by self‐assembly on addition of Er(OiPr)₃. The self‐assembly proceeds in the MWNT fibrous network and small clusters of assembled catalyst are confined in the MWNTs, producing an easily handled solid‐phase catalyst. The resulting MWNT‐confined catalyst exhibits a good catalytic performance in a catalytic asymmetric Mannich‐type reaction, which can be conducted in a repeated batch system and in a continuous‐flow platform.     

Self‐Assembly of Achiral Shape Amphiphiles into Multi‐Walled Nanotubes via Helicity‐Selective Nucleation and Growth

Soft nanotubes are normally constructed from chiral amphiphiles through helical self‐assembly. Yet, how to self‐assemble achiral molecules into nanotubes is still a challenge. Here, we report the nanotube construction with achiral shape amphiphiles through helical self‐assembly and also unravel the formation mechanisms. The amphiphiles have a dumbbell shape and are composed by covalently linking three achiral moieties together: two unlike clusters and an organic tether. The difference in polarity between the unlike clusters drives the amphiphiles to self‐assemble into single‐ and multi‐walled nanotubes as well as intermediates. Analysis of the key intermediates unravels the self‐assembly mechanism of helicity‐selective nucleation and growth. Meanwhile, direct visualization of the individual clusters in the ribbons displays a two‐dimensional deformed hexagonal lattice. Thus, we speculate that it is the lattice deformation that creates anisotropic tension along different directions of the ribbon which further results in the formation of helical ribbons towards nanotubes by amphiphiles.     

Loading of Vesicles into Soft Amphiphilic Nanotubes using Osmosis

The facile assembly of higher‐order nanoarchitectures from simple building blocks is demonstrated by the loading of vesicles into soft amphiphilic nanotubes using osmosis. The nanotubes are constructed from rigid interdigitated bilayers which are capped with vesicles comprising phospholipid‐based flexible bilayers. When a hyperosmotic gradient is applied to these vesicle‐capped nanotubes, the closed system loses water and the more flexible vesicle bilayer is pulled inwards. This leads to inclusion of vesicles inside the nanotubes without affecting the tube structure, showing controlled reorganization of the self‐assembled multicomponent system upon a simple osmotic stimulus.     

A Carbon Dioxide Bubble‐Induced Vortex Triggers Co‐Assembly of Nanotubes with Controlled Chirality

It is challenging to prepare co‐organized nanotube systems with controlled nanoscale chirality in an aqueous liquid flow field. Such systems are responsive to a bubbled external gas. A liquid vortex induced by bubbling carbon dioxide (CO₂) gas was used to stimulate the formation of nanotubes with controlled chirality; two kinds of achiral cationic building blocks were co‐assembled in aqueous solution. CO₂‐triggered nanotube formation occurs by formation of metastable intermediate structures (short helical ribbons and short tubules) and by transition from short tubules to long tubules in response to chirality matching self‐assembly. Interestingly, the chirality sign of these assemblies can be selected for by the circulation direction of the CO₂ bubble‐induced vortex during the co‐assembly process.     

Solvent‐Polarity‐Tuned Morphology and Inversion of Supramolecular Chirality in a Self‐Assembled Pyridylpyrazole‐Linked Glutamide Derivative: Nanofibers,Nanotwists, Nanotubes,and Microtubes

The self‐assembly of a low‐molecular‐weight organogelator into various hierarchical structures has been achieved for a pyridylpyrazole linked L ‐glutamide amphiphile in different solvents. Upon gel formation, supramolecular chirality was observed, which exhibited an obvious dependence on the polarity of the solvent. Positive supramolecular chirality was obtained in nonpolar solvents, whereas it was inverted into negative supramolecular chirality in polar solvents. Moreover, the gelator molecules self‐assembled into a diverse array of nanostructures over a wide scale range, from nanofibers to nanotubes and microtubes, depending on the solvent polarity. Such morphological changes could even occur for the xerogels in the solvent vapors. We found that the interactions between the pyridylpyrazole headgroups and the solvents could subtly change the stacking of the molecules and, hence, their self‐assembled nanostructures. This work exemplifies that organic solvents can significantly involve the gelation, as well as tune the structure and properties, of a gel.     

Precursor‐involved and Conversion Rate‐controlled Self‐assembly of a 'Super Gelator' in Thixotropic Hydrogels for Drug Delivery

Enzymatic hydrogelation is a totally different process to the heating‐cooling gelation process, in which the precursors of the gelators can be involved during the formation of self‐assembled structures. Using thixotropic hydrogels formed by a super gelator as our studied system, we demonstrated that the enzyme concentration/conversion rate of enzymatic reaction had a strong influence on the morphology of resulting self‐assembled nanostructures and the property of resulting hydrogels. The principle demonstrated in this study not only helps to understand and elucidate the phenomenon of self‐assembly triggered by enzymes in biological systems, but also offers a unique methodology to control the morphology of self‐assembled structures for specific applications such as controlled drug release.     

Poly(dimethylsiloxane)‐based polymer organogelators with L‐lysine derivatives as a organogelation‐causing segment

New poly(dimethylsiloxane)‐based polymer organogelators with L ‐lysine derivatives were synthesized on the basis of synthetically simple procedure, and their organogelation abilities were investigated. These polymer organogelators have a good organogelation ability and form organogels in many organic solvents. In the organogels, polymer gelators constructed a mesoporous structure with a pore size of about 1 μm formed by entanglement of the self‐assembled nanofibers. The L ‐lysine derivatives in the polymer gelators functioned as a gelation‐causing segment and the organogelation was induced by self‐assembly of the L ‐lysine segments through a hydrogen bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3817–3824, 2006     

Photoinduced Morphological Transformations of Soft Nanotubes

In water, synthetic amphiphiles composed of a photoresponsive azobenzene moiety and an oligoglycine hydrogen‐bonding moiety selectively self‐assembled into nanotubes with solid bilayer membranes. The nanotubes underwent morphological transformations induced by photoisomerization of the azobenzene moiety within the membranes, and the nature of the transformation depended on the number of glycine residues in the oligoglycine moiety (i.e., on the strength of intermolecular hydrogen bonding). Upon UV‐light irradiation of nanotubes prepared from amphiphiles with the diglycine residue, trans‐to‐cis isomerization induced a transformation from nanotubes (inner diameter (i.d.) 7 nm), several hundreds of nanometers to several tens of micrometers in length, to imperfect nanorings (i.d. 21–38 nm). The cis‐to‐trans isomerization induced by continuous visible‐light irradiation resulted in the stacking of the imperfect nanorings to form nanotubes with an i.d. of 25 nm and an average length of 310 nm, which were never formed by a self‐assembly process. Time‐lapse fluorescence microscopy enabled us to visualize the transformation of nanotubes with an i.d. of 20 nm (self‐assembled from amphiphiles with the monoglycine residue) to cylindrical nanofibers with an i.d. of 1 nm; shrinkage of the hollow cylinders started at the two open ends with simultaneous elongation in the direction of the long axis.     

Reversible Assembly and Disassembly of Receptor‐Decorated Gold Nanoparticles Controlled by Ion Recognition

The controlled assembly of randomly dispersed colloidal particles can provide access to materials with advanced optical and electronic properties while providing fundamental insights into self‐assembly processes in nature and nanotechnology. Typically, self‐assembled nanoparticles are prepared by exploiting electrostatic interactions, lithographic techniques, and covalently linked molecular scaffolds. This results in static morphologies that cannot be disassembled easily. On the other hand, having access to systems that can be assembled or disassembled in a controlled manner could allow for in‐depth understanding of the nanoparticles as well as rational control over the morphology and fundamental properties of the resulting constructs. If the changes in aggregation are induced by a specific external chemical stimulus, it could also permit the development of new chemosensors. Here we demonstrate the reversible assembly and disassembly of gold nanoparticles achieved by modulating the noncovalent interactions between surface‐bound calix[4]pyrroles and added bis‐imidazolium cations. We also demonstrate the use of these nanoparticles in the selective sensing of anions.     

Sonodynamic Therapeutic Effects of Sonosensitizers with Different Intracellular Distribution Delivered by Hollow Nanocapsules Exhibiting Cytosol Specific Release

Sonodynamic therapy (SDT) is a novel promising noninvasive therapy involving utilization of low‐intensity ultrasound and sonosensitizer, which can generate reactive oxygen species (ROS) by sonication. In SDT, a high therapeutic effect is achieved by intracellular delivery and accumulation at the target sites of sonosensitizer followed by oxidative damage of produced ROS by sonication. Here, pH‐ and redox‐responsive hollow nanocapsules are prepared through the introduction of disulfide cross‐linkages to self‐assembled polymer vesicles formed from polyamidoamine dendron‐poly(l‐ lysine) for the efficient delivery of sonosensitizer. As sonosensitizer, doxorubicin (DOX), an anticancer drug accumulating into cell nucleus, is selected. Also, the conjugate of DOX and triphenylphosphonium (TPP‐DOX) is synthesized as sonosensitizer with mitochondrial targeting ability. DOX and TPP‐DOX are delivered to nucleus and mitochondria by nanocapsules. Furthermore, DOX‐ or TPP‐DOX‐loaded nanocapsules exhibit in vitro sonodynamic therapeutic effect to HeLa cells with sonication, which might be through oxidative damage to nucleus and mitochondria.     

Spatially Controlled Supramolecular Polymerization of Peptide Nanotubes by Microfluidics

Despite the importance of spatially resolved self‐assembly for molecular machines, the spatial control of supramolecular polymerization with synthetic monomers had not been experimentally established. Now, a microfluidic‐regulated tandem process of supramolecular polymerization and droplet encapsulation is used to control the position of self‐assembled microfibrillar bundles of cyclic peptide nanotubes in water droplets. This method allows the precise preferential localization of fibers either at the interface or into the core of the droplets. UV absorbance, circular dichroism and fluorescence microscopy indicated that the microfluidic control of the stimuli (changes in pH or ionic strength) can be employed to adjust the packing degree and the spatial position of microfibrillar bundles of cyclic peptide nanotubes. Additionally, this spatially organized supramolecular polymerization of peptide nanotubes was applied in the assembly of highly ordered two‐dimensional droplet networks.     

Synchronization of Two Assembly Processes To Build Responsive DNA Nanostructures

Herein, we report a strategy for the synchronization of two self‐assembly processes to assemble stimulus‐responsive DNA nanostructures under isothermal conditions. We hypothesized that two independent assembly processes, when brought into proximity in space, could be synchronized and would exhibit positive synergy. To demonstrate this strategy, we assembled a ladderlike DNA nanostructure and a ringlike DNA nanostructure through two hybridization chain reactions (HCRs) and an HCR in combination with T‐junction cohesion, respectively. Such proximity‐induced synchronization adds a new element to the tool box of DNA nanotechnology. We believe that it will be a useful approach for the assembly of complex and responsive nanostructures.     

Steric‐Structure‐Dependent Gel Formation,Hierarchical Structures,Rheological Behavior,and Surface Wettability

A series of bicholesteryl‐based gelators with different central linker atoms C, N, and O (abbreviated to GC , GN , and GO , respectively) have been designed and synthesized. The self‐assembly processes of these gelators were investigated by using gelation tests, field‐emission scanning electron microscopy, field‐emission transmission electron microscopy, UV/Vis absorption, IR spectroscopy, X‐ray diffraction, rheology, and contact‐angle experiments. The gelation ability, self‐assembly morphology, rheological, and surface‐wettability properties of these gelators strongly depend on the central linker atom of the gelator molecule. Specifically, GC and GN can form gels in three different solvents, whereas GO can only form a gel in N,N‐dimethylformamide (DMF). Morphologies from nanofibers and nanosheets to nanospheres and nanotubes can be obtained with different central atoms. Gels of GC , GN , and GO formed in the same solvent (DMF) have different tolerances to external forces. All xerogels gave a hydrophobic surface with contact angles that ranged from 121 to 152°. Quantum‐chemical calculations indicate that the GC , GN , and GO molecules have very different steric structures. The results demonstrate that the central linker atom can efficiently modulate the molecular steric structure and thus regulate the supramolecular self‐assembly process and properties of gelators.     

Supramolecular Self‐Assembly of Polymer‐Functionalized Carbon Nanotubes on Surfaces

Summary: Supramolecular self‐assembly of poly(methyl methacrylate)‐grafted multiwalled carbon nanotubes (MWNT‐g‐PMMA) was reported herein. The MWNT‐g‐PMMA (85 wt.‐% PMMA) dispersed in tetrahydrofuran could self‐assemble into suprastructures on surfaces such as gold, mica, silicon, quartz, or carbon films. With decreasing concentration of the MWNT‐g‐PMMA from 3 to 0.1 mg · mL⁻¹, the assembled structures changed from cellular and basketwork‐like forms to multilayer cellular networks and individual needles. SEM, AFM, and TEM measurements confirmed the morphology of the assembled suprastructures, and revealed the assembly mechanism. Phase separation during evaporation of the solvent drives the MWNT‐g‐PMMA nanohybrids to assemble and form the suprastructures, and the rigid MWNTs stabilize the structures.

SEM images of self‐assembled suprastructures of basketwork (a), cellular network (b), and needles (c) from the THF solution of the PMMA‐grafted MWNTs on gold surface.     

Synthesis and Supramolecular Self‐Assembly of Coil‐Rod‐Coil Molecules: The Relationship between Self‐Assembled Nanostructures and Molecular Structures

Herein, the relationship between the supramolecularly self‐assembled nanostructures and the chemical structures of coil‐rod‐coil molecules is discussed. A series of nonamphiphilic coil‐rod‐coil molecules with different alkyl chains, central mesogenic groups, and chemical linkers were designed and synthesized. The solvent‐mediated supramolecular self‐assembling of these coil‐rod‐coil molecules resulted in rolled‐up nanotubes, nanofibers, submicron sized belts, needle‐like microcrystals, and amorphous structures. The self‐assembling behaviors of these coil‐rod‐coil molecules have been systematically investigated to reveal the relationship between the supramolecularly self‐assembled nanostructures and their chemical structures. With respect to the formation of rolled‐up nanotubes by self‐assembly of coil‐rod‐coil molecules, we have systematically investigated the following three influencing structural factors: 1) the alkyl chain length; 2) the central mesogenic group; (3) the linker type. These studies disclosed the key structural features of coil‐rod‐coil molecules for the formation of rolled‐up nanotubes.     

p‐Quaterphenylene as an Aggregation‐Induced Emission Fluorogen in Supramolecular Organogels and Fluorescent Sensors

Two dumbbell‐shaped organogelators with a p ‐quaterphenylene core were synthesized, and their self‐assembly properties were investigated. These low‐molecular‐weight gelators could form self‐supporting gels in many apolar organic solvents with an H‐type aggregation form through a synergic effect of π–π stacking, intermolecular translation‐related hydrogen bonding, and van der Waals forces. In comparison to the p ‐terphenylene‐cored gelator, the extended π‐conjugated segment improved the gelation efficiency significantly with enhanced gelation rate. Additionally, these p ‐quaterphenylene‐centered gelators exhibited strong fluorescence emission induced by aggregation, which not only provided an in situ method to optically monitor the gelation process, but also endowed these self‐assemblies with substantial applications in sensing explosives.     

Switch from intra- to intermolecular H-bonds by ultrasound: induced gelation and distinct nanoscale morphologies

During cooling of the ( R)-N-Fmoc-Octylglycine (Fmoc-OG)/cyclohexane solution, gelation is observed exclusively when ultrasound is used as an external stimulus, while deposit is obtained without sonication. The xerogel consists of entangled fibrous network made by interconnected nanofibers, while the deposit comprises large numbers of unbranched nanowires. It is found that the Fmoc-OG molecules form bilayer structures in both the deposit and the gel. However, the ratio ( R) between the Fmoc-OG molecules in a stable intramolecular H-bonding conformation and those in a metastable intermolecular H-bonding conformation can be tuned by the ultrasound, R (deposit) > R (gel). The increased population of the intermolecular H-bonding Fmoc-OG molecules induced by the ultrasonication facilitates to the interconnection of nanofibers for the formation of the fibrous network, and therefore gelation. The alteration in the morphologies and properties of the obtained nanomaterials induced by the ultrasound wave demonstrates a potential method for smart controlling of the functions of nanomaterials from the molecular level.     

Emulsion‐Assisted Polymerization‐Induced Hierarchical Self‐Assembly of Giant Sea Urchin‐like Aggregates on a Large Scale

Hierarchical solution self‐assembly has become an important biomimetic method to prepare highly complex and multifunctional supramolecular structures. However, despite great progress, it is still highly challenging to prepare hierarchical self‐assemblies on a large scale because the self‐assembly processes are generally performed at high dilution. Now, an emulsion‐assisted polymerization‐induced self‐assembly (EAPISA) method with the advantages of in situ self‐assembly, scalable preparation, and facile functionalization was used to prepare hierarchical multiscale sea urchin‐like aggregates (SUAs). The obtained SUAs from amphiphilic alternating copolymers have a micrometer‐sized rattan ball‐like capsule (RBC) acting as the hollow core body and radiating nanotubes tens of micrometers in length as the hollow spines. They can capture model proteins effectively at an ultra‐low concentration (ca. 10 nm ) after functionalization with amino groups through click copolymerization.     

Salt Responsive Morphologies of ssDNA‐Based Triblock Polyelectrolytes in Semi‐Dilute Regime: Effect of Volume Fractions and Polyelectrolyte Length

A comprehensive study is reported on the effect of salt concentration, polyelectrolyte block length, and polymer concentration on the morphology and structural properties of nanoaggregates self‐assembled from BAB single‐strand DNA (ssDNA) triblock polynucleotides in which A represents polyelectrolyte blocks and B represents hydrophobic neutral blocks. A morphological phase diagram above the gelation point is developed as a function of solvent ionic strength and polyelectrolyte block length utilizing an implicit solvent ionic strength method for dissipative particle dynamics simulations. As the solvent ionic strength increases, the self‐assembled DNA network structures shrinks considerably, leading to a morphological transition from a micellar network to worm‐like or hamburger‐shape aggregates. This study provides insight into the network morphology and its changes by calculating the aggregation number, number of hydrophobic cores, and percentage of bridge chains in the network. The simulation results are corroborated through cryogenic transmission electron microscopy on the example of the self‐assembly of ssDNA triblocks.