Search

Dynamic chemistry utilizing both covalent and noncovalent bonds provides valid protocols in manipulating properties of self‐assemblies and functions. Here we employ dynamic chemistry to realize multiple‐route control over supramolecular chirality up to five states. N‐protected fluorinated phenylalanine in the carboxylate state self‐assembled into achiral nanoparticles ascribed to the amphiphilicity. Protonation promoted one‐dimensional growth into helices with shrunk hydrophilicity, which in the presence of disulfide pyridine undergo chirality inversion promoted by the hydrogen bonding‐directed coassembly. Further interacting with the water‐soluble reductant cleavages the disulfide bond to initiate the rearrangement of coassemblies with a chirality inversion as well. Finally, by tuning the pH environments, aromatic nucleophilic substitution reaction between reduced products and perfluorinated phenylalanine occurs, giving distinct chiral nanoarchitectures with emerged luminescence and circularly polarized luminescence. We thus realized a particular five‐state control by combining dynamic chemistry at one chiral compound, which greatly enriches the toolbox in fabricating responsive chiroptical materials. [ABSTRACT FROM AUTHOR]

Solvents influence the structure, aggregation and folding behaviors of solvatochromic compounds. Ultrasensitive solvent mediated chiroptical response is conducive to the fabrication of molecular platform for sensing and recognition, which however, remains great challenges in conceptual or applicable design. Here we report a cysteine‐based single benzene chromophore system that shows ultrasensitivity to solvents. Compared to the ratiometrically responsive systems, the chiroptical activities could be triggered or inverted depending on the substituents of chiral entities with an ultralow solvent volume fraction (<1 vol %). One drop of dipolar solvents shall significantly induce the emergence or inversion of chiroptical signals in bulky phases. Based on the experimental and computational studies, the ultrasensitivity is contributed to the intimate interplay between solvents and chiral compounds that anchors the specific chiral conformation. It illustrates that structurally simple organic compounds without aggregation or folding behaviors possess pronounced solvatochiroptical properties, which sheds light on the next‐generation of chiroptical sensors and switches. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) show particular properties compared to ionic liquids and other traditional organic solvents. Controlled synthesis of chiral materials in DESs is unprecedented due to the complex interplays between DESs and solutes. In this work, all bio‐derived chiral DESs were prepared using choline chloride or cyclodextrin as hydrogen bonding acceptors and natural chiral acids as donors, which performed as chiral matrices for the rational synthesis of chiroptical materials by taking advantage of the efficient chirality transfer between the DESs and solutes. In a very selective manner, building units with molecular pockets could facilitate strong binding affinity towards chiral acid components of DESs disregarding the presence of competitive hydrogen bonding acceptors. Chirality transfer from DESs to nanoassemblies leads to chirality amplification in the presence of minimal amounts of entrapped chiral acids, thanks to the spontaneous symmetry breaking of solutes during aggregation. This work utilizes chiral DESs to control supramolecular chirality, and illustrates the structural basis for the fabrication of DES‐based chiral materials. [ABSTRACT FROM AUTHOR]

Incorporation of giant molecular nanoparticles with atomic precision into chiral nanoassemblies facilitates the fabrication of functional ordered phases with supramolecular chirality, which remains mysterious. Reported here is the first example of polyhedral oligosilsesquioxane (POSS) derivatives that self‐assemble into well‐defined chiral nanoassemblies. POSSs were covalently conjugated to N‐terminal aromatic amino acids, which self‐assembled into nanohelices and twists with explicit handedness tuned by solvent polarity. Chiral nanoassemblies showed active chiroptical responses including Cotton effects and circularly polarized luminescence. The chiral systems can bind guest molecules by charge‐transfer interactions, whereby self‐assembled structures, chiroptical activities, and luminescent colors were further modulated. The unique coassembly systems were applied for instant information encryption and storage with multiple luminescent displays. This work offers a new protocol for the design of functional chiral materials of POSS by molecular self‐assembly. [ABSTRACT FROM AUTHOR]

In the solid state, amino acids (alanine and phenylglycine) with appended pyrene segments self‐assembled into α‐helix‐like structures by asymmetrical H‐bonds between carboxylic acid and amide segments, further inducing supramolecular tilted chirality of the achiral pyrenes. These structures bind melamine and electron‐deficient units through H‐bond and charge‐transfer interactions, respectively. Charge‐transfer interactions enhance the dissymmetry g‐factor of absorption (gabs; up to 1.4×10−2) with an extended Cotton effect active region (from 250 to 600 nm). Incorporating melamine inverts the handedness of circularly polarized luminescence and boosts the dissymmetry g‐factor (glum). Melamine also induces macroscopic chirality at the nanoscale, whereby the 2D lamellar structures are transformed into 1D helices at the nanoscale, leading to giant tubular structures at the microscale. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we developed a strategy to fabricate self‐assembled aggregates encapsulating graphene from direct exfoliation of graphite. Naphthalene‐anhydride‐appended glutamic acid (NG) and pyrene‐appended glutamic acid (PG) were utilized to exfoliate graphite to generate few‐layer graphene in basic aqueous media. Acidification‐triggered self‐assembly of PG could encapsulate graphene sheets to give graphene@microsheet hybrids. Melamine (Mm) was introduced to induce the morphological transformation of PG from microsheets to twisted fibers with columnar packing. In the presence of graphene, this transformation allowed the fabrication of twisted‐fiber‐encapsulated graphene (graphene@twist fiber). Tricomponent hybrids were also built up via in situ preparation of gold nanoparticles (AuNPs) on the negatively charged surface of few‐layer graphene during the self‐assembly process. This study presents an approach to construct directly exfoliated graphene‐based hybrids through self‐assembly. [ABSTRACT FROM AUTHOR]

Self-assembly of N-fluorenyl-9-methoxycarbonyl glutamic acid (Fmoc-Glu) in water generates metastable single-wall nanotubes. These nanotubes entangle and bundle together to form unstable gels that shrink with time and finally result in lamellar crystalline precipitates. Melamine (Mm) was employed as a supramolecular modifier and stabilizer to improve the stability of the nanotubes. Mm interacts with the carboxyl-rich surfaces of the nanotubes via H-bonds and static electronic forces to diminish the high affinity of individual nanotubes and facilitate Fmoc-Glu supergelation (critical gelation concentration <0.1 wt %). Although the basic process of nanotube formation is not disturbed, Mm inverts the supramolecular helicity of nanotubes from P to M. [ABSTRACT FROM AUTHOR]

Ethyl benzoate was found to complex with cyclodextrins in formation of vesicles for the first time. These vesicles were characterized by transmission electron microscopy and dynamic light scattering. The complex stoichiometry, the stability constant and conformations of ethyl benzoate · cyclodextrins in aqueous solution were investigated by ultraviolet and nuclear magnetic resonance analyses. The vesicle system was prepared without complicated synthesis. This kind of vesicles prepared by cyclodextrin inclusion complexes could be applied in many fields. [ABSTRACT FROM PUBLISHER]

Multi-responsive cyclodextrin vesicles (CDVs) self-assembled by 'supramolecular bola-amphiphiles', consisting of a guest (N,N'-bis(ferrocenylmethylene)-diaminohexane, 1) and a host (γ-hydroxybutyric-β-cyclodextrin, γ-HB-β-CD), were prepared and investigated for the first time. The morphologies and sizes of these novel vesicles in water were observed by transmission electron microscopy (TEM), scanning electron microscopy and dynamic light scattering. The effects of the host-guest ratio, the concentration and the solvent composition are also discussed. The host-guest interactions, complex stoichiometry and structures of 1·γ-HB-β-CD in water were investigated by cyclic voltammetry, UV and NMR spectroscopy. According to the complex stoichiometry, TEM observations and Chem3D estimation, the 'supramolecular bola-amphiphiles', made from 1·γ-HB-β-CD and assumed for the first time, formed the membranes of the CDVs. The CDV system was responsive to an oxidising agent, which is the first report on redox-responsive systems in this field. The CDVs are also responsive to pH and the presence of metal ions, such that they disassemble upon addition of acetic acid or Cu2+ ions, providing possible routes to drug delivery systems. [ABSTRACT FROM AUTHOR]

Just as biological behaviors that can be tuned by salt ions, salt-containing soft materials are of great importance in various fields. Here we report a supramolecular cyclodextrin gel, of which properties including gelation behavior, fiber size, thermal stability as well as mechanical strength could be well tailored by inorganic salts. The concentrations, types of alkali salts were tested and had a profound impact on the gel properties. The formation/collapse behaviors and variations of gel fiber size were characterized through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and optical microscopy (OM). Infrared spectroscopy (IR), differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) revealed the mechanism of molecular arrangement and provided insight into the outstanding salt effects. This might have potential applications in designing novel smart materials and provide a new course of constructing multi-morphological gels by salts. [ABSTRACT FROM AUTHOR]