Aldolase Cascade Facilitated by Self‐Assembled Nanotubes from Short Peptide Amphiphiles

Early evolution benefited from a complex network of reactions involving multiple C?C bond forming and breaking events that were critical for primitive metabolism. Nature gradually chose highly evolved and complex enzymes such as lyases to efficiently facilitate C?C bond formation and cleavage with remarkable substrate selectivity. Reported here is a lipidated short peptide which accesses a homogenous nanotubular morphology to efficiently catalyze C?C bond cleavage and formation. This system shows morphology‐dependent catalytic rates, suggesting the formation of a binding pocket and registered enhancements in the presence of the hydrogen‐bond donor tyrosine, which is exploited by extant aldolases. These assemblies showed excellent substrate selectivity and templated the formation of a specific adduct from a pool of possible adducts. The ability to catalyze metabolically relevant cascade transformations suggests the importance of such systems in early evolution.     

Nanostructured Micelle Nanotubes Self‐Assembled from Dinucleobase Monomers in Water

Despite the central importance of aqueous amphiphile assemblies in science and industry, the size and shape of these nano‐objects is often difficult to control with accuracy owing to the non‐directional nature of the hydrophobic interactions that sustain them. Here, using a bioinspired strategy that consists of programming an amphiphile with shielded directional Watson–Crick hydrogen‐bonding functions, its self‐assembly in water was guided toward a novel family of chiral micelle nanotubes with partially filled lipophilic pores of about 2 nm in diameter. Moreover, these tailored nanotubes are successfully demonstrated to extract and host molecules that are complementary in size and chemical affinity.     

Self‐Assembly of Pyridinium‐Tailored Anthracene Amphiphiles into Supramolecular Hydrogels

The mixing of a polyacid cross‐linker with a pyridinium‐functionalized anthracene amphiphile afforded a supramolecular hydrogel through a self‐assembly process that was primarily driven by π‐stacking and electrostatic interactions.     

Cluster‐Based Self‐Assembly Route toward MoO3 Single‐Walled Nanotubes

MoO₃ has a unique rigid double‐layer structure, which makes it a real challenge to prepare nanotubular structures. The controlled synthesis of MoO₃ single‐walled nanotubes (SWNTs) is achieved through a cluster‐based self‐assembly route on the dodecanethiol/water interface. Various factors are studied at length, including precursor type, reaction time, temperature, pH value, and their influence on the morphology of products. The concept of “self‐assembly—from simple clusters to nanostructures” is proposed here based on preliminary results from the synthesis of MoO₃ SWNTs, which provides a new aspect for traditional synthetic chemistry of nanomaterials and polyoxometalates.     

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.     

Nonionic Dendritic and Carbohydrate Based Amphiphiles: Self‐Assembly and Transport Behavior

Herein, a new series of non‐ionic dendritic and carbohydrate based amphiphiles is synthesized employing biocompatible starting materials and studied for supramolecular aggregate formation in aqueous solution. The dendritic amphiphiles 12 and 13 possessing poly(glycerol) [G2.0] as hydrophilic unit and C‐10 and C‐18 hydrophobic alkyl chains, respectively, exhibit low critical aggregation concentration (CAC) in the order of 10⁻⁵m and hydrodynamic diameters in the 8–10 nm range and supplemented by cryogenic transmission electron microscopy. Ultraviolet‐visible (UV‐Vis) and fluorescence spectroscopy suggests the effective solubilization of hydrophobic guests by the self‐assembled architectures, with the nanotransporters 12 and 13 possessing the highest encapsulation efficiency of 80.74 and 98.03% for curcumin. Efficient uptake of encapsulated curcumin in adenocarcinomic human alveolar basal epithelial (A549) cells is observed by confocal laser scanning microscopy. Amphiphiles 12 and 13 are non‐cytotoxic at the concentrations studied, however, curcumin encapsulated samples efficiently reduce the viability of A549 cells in vitro. Experimental studies indicate the ability of amphiphile 13 to encapsulate 1‐anilinonaphthalene‐8‐sulfonic acid (ANS) and curcumin with binding constant of 1.16 × 105⁵m ⁻¹ and 1.43 × 10⁶m ⁻¹, respectively. Overall, our findings demonstrate the potential of these dendritic amphiphiles for the development of prospective nanocarriers for the solubilization of hydrophobic drugs.     

Introducing Chirality into Nonionic Dendritic Amphiphiles and Studying Their Supramolecular Assembly

Chiral head groups have been introduced into water‐soluble hydroxyl‐terminated nonionic amphiphiles and the impact of the head group stereochemistry on the supramolecular ultrastructures has been studied. Enantiomeric isomers were compared with the achiral meso form and the racemic mixture by means of cryogenic transmission electron microscopy and circular dichroism spectroscopy. Structurally, all amphiphiles are composed of the first‐generation hydrophilic polyglycerol head group coupled to a single hydrophobic hexadecyl chain through an amide linkage and diaromatic spacer. The enantiomers aggregate to form twisted ribbons with uniform handedness, whereas the meso stereoisomer and racemic mixture produce elongated assemblies, namely, tubules and platelets, but without a chiral ultrastructure. Simulations on the molecular packing geometries of the stereoisomers indicate different preferential assembly routes that explain the individual supramolecular aggregation behavior.     

Functionalization of Multi‐Walled Carbon Nanotubes by Electrografting of Polyacrylonitrile

Summary: Multi‐walled carbon nanotubes (MWNTs) have been successfully modified with polyacrylonitrile (PAN) by a cathodic electrochemical process. The surface‐modified MWNTs afforded are then dispersible in good solvents for PAN, such as N,N‐dimethylformamide (DMF). Collected from a dilute dispersion, these MWNTs are essentially disentangled, as confirmed by transmission electron microscopy (TEM) analysis. From the differential scanning calorimetry (DSC) traces for polyacrylonitrile and polyacrylonitrile‐grafted MWNTs, the maximum grafting ratio is estimated at 0.28.

Electrochemical grafting of polyacrylonitriles onto the surface of multi‐walled carbon nanotubes.     

Sonophysically‐Exfoliated Individual Multi‐Walled Carbon Nanotubes in Water Solution

We report the sonophysically‐exfoliated methods access to the preparation of homogeneous‐free multi‐walled carbon nanotubes (MWCNTs) in water solution. Highly stable, uniform, individual MWCNTs are entirely performed through sodium dodecylsulfate surfactants by means of a tip sinicator. HRTEM images show that the crystalline finger walls of individual CNTs are apparently observed. Raman spectrum of MWCNTs shows that the so‐called G'‐band, associated with metallic electronic structure, was significantly observed at 2644 cm^?1 with full‐width at half‐maximum of 262 cm^?1, indicating that the sonication physical methods do not alter their electric properties. Owing to its easy‐to‐use procedure and low cost of implementation, this approach could lead to the commercial viability of the large‐scale MWCNTs processing.     

The Effect of Hydrophile Topology in RAFT‐Mediated Polymerization‐Induced Self‐Assembly

Polymerization‐induced self‐assembly (PISA) was employed to compare the self‐assembly of different amphiphilic block copolymers. They were obtained by emulsion polymerization of styrene in water using hydrophilic poly(N‐acryloylmorpholine) (PNAM)‐based macromolecular RAFT agents with different structures. An average of three poly (ethylene glycol acrylate) (PEGA) units were introduced either at the beginning, statistically, or at the end of a PNAM backbone, resulting in formation of nanometric vesicles and spheres from the two former macroRAFT architectures, and large vesicles from the latter. Compared to the spheres obtained with a pure PNAM macroRAFT agent, composite macroRAFT architectures promoted a dramatic morphological change. The change was induced by the presence of PEGA hydrophilic side‐chains close to the hydrophobic polystyrene segment.     

Aqueous Ring‐Opening Polymerization‐Induced Self‐Assembly (ROPISA) of N‐Carboxyanhydrides

Reported here is the first aqueous ring‐opening polymerization (ROP) of N‐carboxyanhydrides (NCAs) using α‐amino‐poly(ethylene oxide) as a macroinitiator to protect the NCA monomers from hydrolysis through spontaneous in situ self‐assembly (ISA). This ROPISA process affords well‐defined amphiphilic diblock copolymers that simultaneously form original needle‐like nanoparticles.     

End‐to‐End Self‐Assembly of Semiconductor Nanorods in Water by Using an Amphiphilic Surface Design

One‐dimensional (1D) self‐assemblies of nanocrystals are of interest because of their vectorial and polymer‐like dynamic properties. Herein, we report a simple method to prepare elongated assemblies of semiconductor nanorods (NRs) through end‐to‐end self‐assembly. Short‐chained water‐soluble thiols were employed as surface ligands for CdSe NRs having a wurtzite crystal structure. The site‐specific capping of NRs with these ligands rendered the surface of the NRs amphiphilic. The amphiphilic CdSe NRs self‐assembled to form elongated wires by end‐to‐end attachment driven by the hydrophobic effect operating between uncapped NR ends. The end‐to‐end assembly technique was further applied to CdS NRs and CdSe tetrapods (TPs) with a wurtzite structure.     

Self‐Assembly of DNA–Oligo(p‐phenylene‐ethynylene) Hybrid Amphiphiles into Surface‐Engineered Vesicles with Enhanced Emission

Surface‐addressable nanostructures of linearly π‐conjugated molecules play a crucial role in the emerging field of nanoelectronics. Herein, by using DNA as the hydrophilic segment, we demonstrate a solid‐phase “click” chemistry approach for the synthesis of a series of DNA–chromophore hybrid amphiphiles and report their reversible self‐assembly into surface‐engineered vesicles with enhanced emission. DNA‐directed surface addressability of the vesicles was demonstrated through the integration of gold nanoparticles onto the surface of the vesicles by sequence‐specific DNA hybridization. This system could be converted to a supramolecular light‐harvesting antenna by integrating suitable FRET acceptors onto the surface of the nanostructures. The general nature of the synthesis, surface addressability, and biocompatibility of the resulting nanostructures offer great promises for nanoelectronics, energy, and biomedical applications.     

Facile Synthesis and Enhanced Nonlinear Optical Properties of Porphyrin‐Functionalized Multi‐Walled Carbon Nanotubes

Two multi‐walled carbon nanotube (MWCNT)‐based nanohybrids, MWCNT–ZnTPP and MWCNT–TPP (TPP=5‐[4‐{2‐(4‐formylphenoxy)‐ ethyloxy}phenyl]‐10,15,20‐triphenylporphyrin, ZnTPP=5‐[4‐{(4‐formylphenyl)ethynyl}phenyl]‐10,15,20‐triphenylporphinatozinc(II)), were prepared directly from pristine MWCNTs through 1,3‐dipolar cycloaddition reactions. Covalent attachment of the porphyrins to the surfaces of the MWCNTs was confirmed by Fourier transform infrared spectroscopy, ultraviolet/visible absorption, fluorescence, Raman, and X‐ray photoelectron spectroscopy, elemental analysis, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin moieties to the surface of the MWCNTs significantly improves the solubility and ease of processing of these MWCNT–porphyrin composite materials. Z‐scan studies reveal that these MWCNT–porphyrin nanohybrids exhibit enhanced nonlinear optical properties under both nanosecond and picosecond laser pulses at λ=532 nm in comparison with free MWCNTs and the free porphyrin chromophores, whereas superior optical limiting performance was displayed by MWCNT–porphyrin composite materials rather than MWCNTs/ZnTPP and MWCNTs/TPP blends, which is consistent with a remarkable accumulation effect as a result of the covalent linkage between the porphyrin and the MWCNTs.     

Selective and Scalable Chemical Removal of Thin Single‐Walled Carbon Nanotubes from their Mixtures with Double‐Walled Carbon Nanotubes

Double‐walled carbon nanotubes (DWCNTs) are materials in high demand due to their superior properties. However, it is very challenging to prepare DWCNTs samples of high purity. In particular, the removal of single‐walled carbon nanotubes (SWCNTs) contaminants is a major problem. Here, a procedure for a selective removal of thin‐diameter SWCNTs from their mixtures with DWCNTs by lithium vapor treatment is investigated. The results are evaluated by Raman spectroscopy and in situ Raman spectroelectrochemistry. It is shown that the amount of SWCNTs was reduced by about 35 % after lithium vapor treatment of the studied SWCNTs–DWCNTs mixture.     

Directed Assembly of Multi-Walled Nanotubes and Nanoribbons of Amino Acid Amphiphiles Using a Layer-by-Layer Approach

Monodisperse unilamellar nanotubes (NTs) and nanoribbons (NRs) were transformed to multilamellar NRs and NTs in a well-defined fashion. This was done by using a step-wise approach in which self-assembled cationic amino acid amphiphile (AAA) formed the initial NTs or NRs, and added polyanion produced an intermediate coating. Successive addition of cationic AAA formed a covering AAA layer, and by repeating this layer-by-layer (LBL) procedure, multi-walled nanotubes (mwNTs) and nanoribbons were formed. This process was structurally investigated by combining small-angle neutron scattering (SANS) and cryogenic-transmission electron microscopy (cryo-TEM), confirming the multilamellar structure and the precise layer spacing. In this way the controlled formation of multi-walled suprastructures was demonstrated in a simple and reproducible fashion, which allowed to control the charge on the surface of these 1D aggregates. This pathway to 1D colloidal materials is interesting for applications in life science and creating well-defined building blocks in nanotechnology.