Search

A multiresponsivehydrogel material consisting of a commercialcationic surfactant and an azobenzene derivative functionalized withfour carboxylic acid groups was constructed. The achiral azobenzenemolecule as a gelator produces chirality at the supramolecular levelin the presence of H+. The acid-induced gelation and morphologychange of supramolecular gels were investigated in detail by cryogenictransmission electron microscopy (cryo-TEM), rheological measurements,circular dichroism (CD), and 1H NMR spectra. Based on theresults, a mechanism of the intermolecular H-bond-directed gelationand supramolecular chirality was proposed. Other than the pH sensitivity,the microstructure and the chirality of the hydrogel demonstrate reversibleswitching behavior in response to photoirradiation, on account ofthe photoisomerization of the azobenzene derivative. Accordingly,a chiroptical switch comprising four different states in responseto pH and light stimuli is strategically constructed. Not only doesthe present system provide a good opportunity for investigating thegelation-induced supramolecular chirality by symmetry breaking totallybased on achiral molecules, but it also proposes a new strategy tobuild multiresponsive supramolecular switches as particularly attractivefor the future development of functional materials. [ABSTRACT FROM AUTHOR]

Cationic magnetic Gemini surfactants (mag-G-surfs), [C 14 H 29 (CH 3 ) 2 N(CH 2 ) 2 N(CH 3 ) 2 C 14 H 29 ] 2+ ·2[XCl 3 Br] - (14-2-14·2X, X = Ce, Gd, or Ho), efficiently induce the aggregation of glutathione-protected Au nanoclusters (NCs) (GSH-Au NCs). These magnetic luminescent aggregates not only possess aggregation-induced emission (AIE) behavior but also display aggregation-induced magnetic enhancement. In particular, 14-2-14·2Ce and 14-2-14·2Gd have a better effect on boosting the luminescence intensity, quantum yield (QY), and luminescence lifetime (τ). The luminescent aggregates of GSH-Au NCs triggered by 14-2-14·2Gd or 14-2-14·2Ho exhibit more favorable paramagnetic behavior. Other Au NCs containing a Au(I)-thiolate complex shell also exhibit the obvious AIE phenomenon after introducing 14-2-14·2Gd, demonstrating the luminescence enhancement effect of mag-G-surfs. The luminescent aggregate 14-2-14·2Ce@GSH-Au NCs can serve as a "light up" fluorometric probe to detect cysteine selectively with the detection limit (DL) of 36 μM, and the magnetic luminescent aggregate 14-2-14·2Gd@GSH-Au NCs has the potential to be a novel contrast agent in T 1 -weighted magnetic resonance (MR) imaging due to its satisfactory contrasting ability.

Developing nontoxic artificial carriers for stimuli-responsive capture, transport, and delivery of biomolecules is of immense scientific interest. Herein, for the first time, we synthesize a double-tailed cationic surfactant, (C 16 H 33 ) 2 (CH 3 ) 2 N + [FeCl 3 Br] - , which possesses magnetic properties [magnetic surfactants (Mag-Surfs)]. The time-dependent formation of virus-shaped hybrid mixed assemblies of polyoxometalates (POMs) {Mo 72 Fe 30 }/Mag-Surf with hollow-shell structures is followed. These structures serve well as robust high-surface-area shuttles, which can be manipulated with applied magnetic fields. By using cationic Mag-Surfs, the anionic POMs and DNA can be complexed in these ternary mixtures. These virus-shaped complexes act as nanoanchors and nanomotors, which can be utilized for binding, anchoring, and delivery of biomolecules, such as DNA. It is found that they have a good absorption capacity for DNA and myoglobin over 24 h, after application of a magnetic field. The realization of magnetic virus-shaped {Mo 72 Fe 30 }/Mag-Surf spheres may open possibilities for designing other functional nanoparticles, allowing effective control over the delivery/separation of biomolecules.

Bacillus-shaped bilayer vesicles of nanoscale size are very rare structures of stable surfactant self-assembly, because they are both thermodynamically and electrostatically unfavorable in solution. It is evidently demonstrated that appropriately aqueous mixtures of single-tailed cationic and anionic (catanionic) surfactants can produce rigidly bacillus-shaped bilayer vesicles with both flat parts and bent edges. The crucial requirement for forming bacillus-shaped bilayer vesicles is the use of cationic surfactants with relatively hydrophobic [FeCl 3 Br] - as counterions. [FeCl 3 Br] - can strongly associate with cationic surfactants to partition into the hydrophobic bilayer of bacillus-shaped bilayer vesicles, significantly increasing the edge energy of cationic surfactants to make them distribute in the low curvature part of bilayers. This causes the formation of bacillus-shaped bilayer vesicles, but not completely bent spherical vesicles, in the case of cationic surfactant excess. The specificity of hydrophobic counterions, [FeCl 3 Br] - , could also make the catanionic mixtures do not precipitate at the stoichiometric point. This new self-assembly on catanionic systems is culminated in the discovery of beautifully structured colloidal objects which are of practical use for molecular templating and controlled drug or DNA release.

Precise control of phase structure transition for the synthesis of multi-dimensional soft materials is a fascinating target in amphiphilic molecule self-assembly. Here, we demonstrate a spontaneous formation of a closely packed lamellar phase consisting of uni- and multi-lamellar vesicles through the incorporation of a small amount of an extractant, di(2-ethylhexyl)phosphoric acid (DEHPA), into the highly swollen, planar lamellar phase of a non-ionic tetraethylene glycol monododecyl ether (C12EO4) surfactant in water. It is figured out that the introduction of negative membrane charges results in the electrostatic repulsion among the lamellae, which suppresses the Helfrich undulation and induces a phase structure transition from planar lamellae to closely packed vesicles. Our results provide important insight into amphiphilic molecule self-assembly, where additives and pH can satisfy the opportunities for the precise tuning of the lamellar structures, which makes a way for the development of lamellar soft materials.

For the first time, a new fabrication method for manipulating the ferromagnetic property of molecular magnets by forming wormlike micelles in magnetic-ionic-liquid (mag-IL) complexes is reported. The ferromagnetism of the mag-IL complexes was enhanced 4-fold because of the formation of wormlike micelles, presenting new evidence for the essence of magnetism generation at a molecular level. Characteristics such as morphology and magnetic properties of the wormlike micelle gel were investigated in detail by cryogenic transmission electron microscopy (Cryo-TEM), rheological measurements, circular dichroism (CD), FT-IR spectra, and the superconducting quantum interference device method (SQUID). An explanation of ferromagnetism elevation from the view of the molecular (ionic) distribution is also given. For the changes of magnetic properties (ferromagnetism elevation) in the wormlike micelle systems, the ability of CTAFe in magnetizing AzoNa4 (or AzoH4) can be ascribed to an interplay of the magnetic [FeCl3Br](-) ions both in the Stern layer and in the cores of the wormlike micelles. Formation of colloidal aggregates, i.e., wormlike micelles, provides a new strategy to tune the magnetic properties of novel molecular magnets.

We report a chiral gel of vesicles and disklike micelles that originated from achiral molecules. The supramolecular chirality was obtained via regulating pH, in which a sol-gel-sol transition in a colloidal system consisting of a gelator, 4,4-di(2,3-dicarboxylphenoxyl)azobenzene (AzoNa4), and a zwitterionic surfactant, tetradecyldimethylamine oxide (C14DMAO), happened. The supramolecular chirality was related to the state of aggregation, i.e., only the condensed gels show chiral sense and sols are chiral-silent. The coexistence of vesicles and disklike micelles was captured for the first time in supramolecular chiral hydrogels by cryo- and freeze-fracture transmission electron microscopy (cryo- and FF-TEM) observations. Ascribed to the photoisomerization of the azobenzene units, upon alternative UV/visible light irradiation, the gel chirality can be switched reversibly with the macroscopic changes between vesicles/disks and wormlike micelles. A pH- and light-dual-responsive chiroptical switch can be constructed, which may require understanding the regulating membrane permeability and reagent release of structural transformation through photoisomerization and also require understanding the origin of gelation-induced supramolecular chirality completely based on achiral molecules.