Surfactant‐Free Self‐Assembly of Nanocrystals into Ellipsoidal Architectures

A simple approach to control the self‐assembly of ZnS nanocrystals into well‐defined, uniform, three‐dimensional, micrometer‐scale, solid ellipsoidal structures with rattle‐type, multishelled, and hollow architectures is presented. There is no surfactant or small molecule to assist the self‐assembly of the nanocrystals. A possible mechanism of the controlled self‐assembly is proposed. The growth process can be divided into two stages: 1) the formation of ellipsoidal architectures via oriented aggregation, the growth kinetics of which is primarily attributed to the charge–charge, charge–dipole, and dipole–dipole interactions of preformed ZnS nanocrystals; and 2) Ostwald ripening, which results in multishelled, rattle‐type, and hollow structures. This self‐assembly concept is also applicable to other metal sulfides.     

Quadrangular Prism: A Unique Self‐Assembly from Amphiphilic Hyperbranched PMA‐b‐PAA

The novel hyperbranched poly(methyl acrylate)‐block‐poly(acrylic acid)s (HBPMA‐b‐PAAs) are successfully synthesized via single‐electron transfer‐living radical polymerization (SET‐LRP), followed with hydrolysis reaction. The copolymer solution could spontaneously form unimolecular micelles composed of the hydrophobic core (PMA) and the hydrophilic shell (PAA) in water. Results show that the size of spherical particles increases from 8.18 to 19.18 nm with increased pH from 3.0 to 12.0. Most interestingly, the unique regular quadrangular prisms with the large microstructure (5.70 μm in length, and 0.47 μm in width) are observed by the self‐assembly of unimolecular micelles when pH value is below 2. Such self‐assembly behavior of HBPMA‐b‐PAA in solution is significantly influenced by the pH cycle times and concentration, which show that increased polymer concentration favors aggregate growth.

     

Hydrophobic Self‐Assembly Affords Robust Noncovalent Polymer Isomers

In covalent polymerization, a single monomer can result in different polymer structures due to positional, geometric, or stereoisomerism. We demonstrate that strong hydrophobic interactions result in stable noncovalent polymer isomers that are based on the same covalent unit (amphiphilic perylene diimide). These isomers have different structures and electronic/photonic properties, and are stable in water, even upon prolonged heating at 100 °C. Such combination of covalent‐like stability together with structural/functional variation is unique for noncovalent polymers, substantially advancing their potential as functional materials.     

A Self‐Assembly Phase Diagram from Amphiphilic Perylene Diimides

Supramolecular forces govern self‐assembly and further determine the final morphologies of self‐assemblies. However, how they control the morphology remains hitherto largely unknown. In this paper, we have discovered that the self‐assembled nanostructures of rigid organic semiconductor chromophores can be finely controlled by the secondary forces by fine‐tuning the surrounding environments. In particular, we used water/methanol/hydrochloric acid to tune the environment and observed five different phases that resulted from versatile molecular self‐assemblies. The representative self‐assembled nanostructures were nanotapes, nanoparticles and their 1D assemblies, rigid microplates, soft nanoplates, and hollow nanospheres and their 1D assemblies, respectively. The specific nanostructure formation is governed by the water fraction, R_w, and the concentration of hydrochloric acid, [HCl]. For instance, nanotapes formed at low [HCl] and R_w values, whereas hollow nanospheres formed when either the HCl concentration is high, or the water fraction is low, or both. The significance of this paper is that it provides a useful phase diagram by using R_w and [HCl] as two variables. Such a self‐assembly phase diagram maps out the fine control that the secondary forces have on the self‐assembled morphology, and thus allows one to guide the formation toward a desired nanostructure self‐assembled from rigid organic semiconductor chromophores by simply adjusting the two key parameters of R_w and [HCl].     

Self‐Assembly of Pyridinium‐Functionalized Anthracenes: Molecular‐Skeleton‐Directed Formation of Microsheets and Microtubes

Two amphiphilic regioisomers, 9‐AP (1‐[11‐(9‐anthracenylmethoxy)‐11‐oxoundecyl]pyridinium bromide), and 2‐AP (1‐[11‐(2‐anthracenyl methoxy)‐11‐oxoundecyl]pyridinium bromide), were synthesized and their assembly behaviors were studied. Due to the anisotropic features of the anthracene structure, different substituted positions on the anthracene ring lead 9‐AP and 2‐AP to adapt “shaver” and “spatula”‐like molecular shapes, respectively, which consequently dictate the structure of their final assemblies. While “shaver”‐shaped 9‐AP assembled into microsheets, driven by π–π interactions, “spatula”‐shaped 2‐AP assembled into microtubular structures, promoted primarily by charge‐transfer interactions.     

Solid‐State Scrolls from Hierarchical Self‐Assembly of T‐Shaped Rod–Coil Molecules

On a roll : Attachment of flexible coils to the middle of a rigid rod generates T‐shaped rod–coil molecules that self‐assemble into layers that roll up to form filled cylindrical and hollow tubular scrolls, depending on the coil length, in the solid state (see picture); the rods are arranged parallel to the layer plane.

     

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.     

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.

     

Cover Picture: Solid‐State Scrolls from Hierarchical Self‐Assembly of T‐Shaped Rod–Coil Molecules (Angew. Chem. Int. Ed. 9/2009)

Solid scrolls are reversibly formed by self‐assembly of rod‐shaped molecules with laterally attached coil units, in contrast to the layered structures formed from self‐assembly of planar molecules. As described by M. Lee and co‐workers in their Communication on page 1664 ff., the core structure of the scrolls, which are either filled cylinders or hollow tubes, can be controlled by variation of the length of the coil unit. The cover picture shows aligned tubular scrolls displaying well‐defined in‐plane ordering of the rod segments.

     

Synthesis of Aromatic Macrocyclic Amphiphiles and their Self‐Assembling Behavior in Aqueous Solution

A triblock amphiphilic macrocycle consisting of a macrocyclic aromatic segment, a hydrophilic oligo(ethylene oxide) branch, and a hydrophobic alkyl dendron is successfully synthesized and characterized. The resulting cyclic amphiphile is observed to self‐assemble into hollow double‐layered capsules in aqueous solution, as confirmed by dynamic light scattering and cryogenic transmission electron microscopy investigations. The capsules are able to encapsulate hydrophobic guest molecules through aromatic interactions with high stability.

     

Carbonic Anhydrase‐Mimetic Bolaamphiphile Self‐Assembly for CO2 Hydration and Sequestration

A biomimetic catalyst was prepared through the self‐assembly of a bolaamphiphilic molecule with histidine moieties for the sequestration of carbon dioxide. The histidyl bolaamphiphilic molecule bis(N‐α‐amidohistidine)‐1,7‐heptane dicarboxylate has been synthesized and self‐assembled to produce analogues of the active sites of carbonic anhydrase (CA) after association with Zn²⁺ ions. Spectroscopic analysis demonstrated the coordination of the Zn²⁺ ions with histidine imidazole moieties, which is the core conformation of CA active sites. The Zn‐associated self‐assembly worked as a CA‐mimetic catalyst that shows catalytic activity for CO₂ hydration. Evaluation of the kinetics of using para‐nitrophenylacetate revealed that the kinetic parameters of the CA‐mimetic catalyst were maximized at the optimal Zn concentration and that excess Zn ions resulted in deteriorated catalytic activity. The performance of the CA‐mimetic catalyst was enhanced by changing the pH value and temperature of the reaction, which implies that the hydrolysis of the substrate is the rate‐determining step. The catalyst‐assisted sequestration of CO₂ was demonstrated by CaCO₃ precipitation upon the addition of Ca²⁺ ions. This study offers an easy way to prepare enzyme analogues for CO₂ sequestration through the self‐assembly of bolaamphiphile molecules with designer biochemical moieties.     

Polyglycidol Based Amphiphilic Double‐Comb Copolymers and Their Self‐Association in Aqueous Solution

Herein, we report synthesis and self‐association properties of amphiphilic double‐comb polymers with polyglycidol backbones. First, a bifunctional polyglycidol precursor is synthesized via monomer activated anionic polymerization. Next, two efficient and orthogonal polymer analogous reactions are carried out for grafting hydrophilic oligoethylene glycol side chains and hydrophobic linear aliphatic side‐chains. The polymers are analyzed by means of NMR, GPC, and DSC. From the DSC analysis of the bulk samples it is evident that aliphatic side chains segregate from the polar backbone and thus crystallize. Furthermore, in aqueous media the double‐comb polymers spontaneously self‐assemble to form a multilayer structure. The present results pave a way to tailor and design amphiphilic polymers based on glycidols. Major advantages are spontaneous self‐assembly in water and the possibility to form onion polymersomes relevant to encapsulation.

     

Dendronized Triangular Oligo(phenylene ethynylene) Amphiphiles: Nanofibrillar Self‐Assembly and Dye Encapsulation

Triangular‐shaped oligo(phenylene ethynylene) amphiphiles 1 a and 1 b decorated in their periphery with two‐ and four‐branched hydrophilic triethyleneglycol dendron wedges, have been synthesized and their self‐assembling properties in solution and onto surfaces investigated. The steric demand produced by the dendritic substituents induces a face‐to‐face rotated π stacking of the aromatic moieties. Studies on the concentration and temperature dependence confirm this mechanism and provide binding constants of 1.2×10⁵ and 1.7×10⁵ M ^?1 in acetonitrile for 1 a and 1 b , respectively. Dynamic and static light scattering measurements complement the study of the self‐assembly in solution and demonstrate the formation of rod‐like supramolecular structures in aqueous solution. The nanofibers formed in solution can be efficiently transferred onto surfaces. Thus, TEM images reveal the presence of strands of various thickness, with the most common being several micrometers long and with diameters of around 70 nm. Some of these nanofibers present folded edges that are indicative of their ribbon‐like nature. Interestingly, compound 1 b can also form thick filaments with a rope‐like appearance, which points to a chiral arrangement of the fibers. AFM images under highly diluted conditions also reveal long fibers with height profiles that fit well with the molecular dimensions calculated for both amphiphiles. Finally, we have demonstrated the intercalation of the hydrophobic dye Disperse Orange 3 within the filaments and its subsequent release upon increasing the temperature.