Jingcheng Hao

Evaporation‐Induced Ordered Honeycomb Structures of Gold Nanoparticles at the Air/Water Interface

The breath figure method was used to prepare dodecanethiol-capped gold nanoparticle macroporous structures with pore diameters from 1.7 to 3.5 mum on an air/water interface. A two-step procedure is proposed for the fabrication of these macroporous structures, by forming a surfactant monolayer on water, and drop-casting a gold nanoparticle dispersion in chloroform onto the surfactant monolayer. The self-assembled films are easily transferred from the water surface onto different substrates and were characterized by TEM, SEM, and AFM. Ordered honeycomb structures with different pore arrays (perforated monolayer films, hexagonal networks and alveoli-like porous films) were obtained. The change in morphology is concentration dependent, and deformed structures with elliptic honeycomb networks are also observed. In addition, honeycomb films using gold nanoparticles stabilized by a weakly bound ligand (dioctadecyldimethylammonium chloride) were formed by the same technique. These films have potential as substrates for surface-enhanced Raman spectroscopy.

Self-assembled vesicles prepared from amphiphilic cyclodextrins as drug carriers.

Controlled self-assembly of amphiphilic cyclodextrin is always a challenging topic in the field of supramolecular chemistry, since it provides the spontaneous generation of well-defined aggregation with functional host sites with great potential applications in drug-carrier systems. β-Cyclodextrin modified with an anthraquinone moiety (1) was successfully synthesized. In the aqueous solution, 1 was found able to self-assemble into vesicles, which was characterized in detail by TEM, SEM, EFM, and DLS. The formation mechanism of the vesicles was suggested based on the 2D ROESY and UV-vis results, and further verified by the MD simulation. Subsequently, the stimuli response property of the vesicles, including to Cu(2+) and H(+), was also studied. The vesicles can efficiently load Paclitaxel inside the membrane with functional macrocyclic cavities available, which can further carry small molecules, such as ferrocene. The vesicles loading with Paclitaxel have remarkable anticancer effects. This work will provide new strategy in drug-carrier systems and tumor treatment methods.

Reversible Heat-Set Organogel Based on Supramolecular Interactions of β-Cyclodextrin in N,N-Dimethylformamide

This paper describes the first reversible, heat-set organogel based on the supramolecular interactions of beta-cyclodextrin (beta-CD). The gel was prepared by interaction of diphenylamine (DPA) with beta-CD and lithium chloride in N,N-dimethylformamide (DMF). In this gel system, DPA could be gelated in DMF as the temperature increased and then dissolved again as the temperature decreased. In the microscopic structure of gel, beta-CDs play a key role in the formation of nanorods and microfibers. Some important features of the gel were observed. (1) The system is a multicomponent solution, in which each of the four components is required for the organogelation property. (2) The system is a reversible, thermo-responsive organogel composed of small organic molecules. When the temperature is lower than T(gel), the gel transforms back into a solution. The reversible thermo-transition was confirmed by differential scanning calorimetry (DSC). The gel system is responsive to the concentration of LiCl. No gel was formed without LiCl. The stimuli responses of the system with other salts such as KCl and NaCl were weaker than with LiCl. (4) The system is responsive to the addition of guest molecules. The structures and sizes of the guest molecules could influence the gel formation. Generally, T(gel) decreased by adding guest molecules in the gel system, but some guest molecules, whose structures are exactly fitted to the cavity of CDs, could prevent gel formation. This work may provide new avenues in delivery of functional molecules as well as design of intelligent materials and biomaterials.

Tunable Amphiphilicity and Multifunctional Applications of Ionic-Liquid-Modified Carbon Quantum Dots

During the past decade, increasing attention has been paid to photoluminescent nanocarbon materials, namely, carbon quantum dots (CQDs). It is gradually accepted that surface engineering plays a key role in regulating the properties and hence the applications of the CQDs. In this paper, we prepared highly charged CQDs through a one-pot pyrolysis with citric acid as carbon source and a room-temperature imidazolium-based ionic liquid as capping agent. The as-prepared CQDs exhibit high quantum yields up to 25.1% and are stable under various environments. In addition, the amphiphilicity of the CQDs can be facilely tuned by anion exchange, which leads to a spontaneous phase transfer between water and oil phase. The promising applications of the CQDs as ion sensors and fluorescent inks have been demonstrated. In both cases, these ionic-liquid-modified CQDs were found to possess novel characteristics and/or superior functions compared to existing ones.

A gel state from densely packed multilamellar vesicles in the crystalline state

A salt-free, cationic and anionic (cat-anionic) fluoro/hydrocarbon surfactant system comprised of tetradecyldimethylaminoxide (C14DMAO) and perfluorolauric acid (PFLA) shows novel phase behavior and structure. A classic micelle phase (L1), an L1/Lα two-phase, a birefringent Lα-phase, an L1/P two-phase, a birefringent gel-phase, and another L1/P two-phase are observed in the system. Solutions of 100 mmol L−1 L1 and birefringent Lα and gel phases, at PFLA mole fractions XPFLA = 0.10, 0. 25, and 0.85, respectively, were further characterized. The gel phase is an elastic, network aqueous gel, and made from close-packed multilamellar vesicles. The atomic force microscopy (AFM) images indicated that the aqueous gel is formed from densely packed vesicles. Small-angle X-ray scattering was used to demonstrate the microstructure of the gel-phase. DSC measurements were used to determine the temperature-dependent transitions of fluorinated alkyl chains of PFLA, the results of which indicate that the fluorocarbon chains are in the crystalline state at room temperature. This is the first example of a network aqueous gel formed from closely-packed vesicles in a salt-free cat-anionic surfactant mixture.

Self-Assembled Aggregates Originated from the Balance of Hydrogen-Bonding, Electrostatic, and Hydrophobic Interactions

Rich phase behavior was observed in salt-free cationic and anionic (catanionic) mixtures of a double-tailed surfactant, di(2-ethylhexyl)phosphoric acid (abbreviated as DEHPA), and tetradecyldimethylamine oxide (C(14)DMAO) in water. At a fixed C(14)DMAO concentration, phase transition from L(1) phase to L(α) phase occurs with increasing amounts of DEHPA. Moreover, in the L(α) phase, with the increase in DEHPA concentration, a gradual transition process from vesicle phase (L(αv)) to stacked lamellar phase (L(αl)) was determined by cryo- and FF-TEM observations combining with (2)H NMR measurements. The rheological data show that the viscosity increases with DEHPA amounts for L(αv) phase samples because of the increase in vesicle density. At a certain molar ratio of DEHPA to C(14)DMAO, i.e., 80:250, the samples are with the highest viscoelasticity, indicating the existence of densely packed vesicles. While for L(αl) phase samples, with increasing DEHPA amount, a decrease of bilayer curvature was induced, leading to a decrease of viscosity obviously. Compared with general catanionic surfactant mxitures, in addition to the electrostatic interaction of ion pairs, the transition of the microstructures is also ascribed to the formation of the hydrogen bonding (-N(+)-O-H···O-N-) between C(14)DMAO molecules and protonated C(14)DMAOH(+), which induces the growth of aggregates and the decrease of aggregate curvatures.

Ionic liquid tunes microemulsion curvature.

Middle-phase microemulsions formed from cationic dioctadecyldimethylammonium chloride (DODMAC), anionic sodium dodecylsulfate (SDS), n-butanol, and n-heptane were studied. An ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), was employed as the electrolyte in the aqueous media instead of inorganic salts usually used in microemulsion formulation. Studies have been carried out as a function of the concentrations of [bmim][BF4], n-butanol, total surfactant (cDODMAC+SDS), and temperature on the phase behavior and the ultralow interfacial tensions in which the anionic component is present in excess in the catanionic film. Ultralow interfacial tension measurements confirmed the formation of middle-phase microemulsions and the necessary conditions for stabilizing middle-phase microemulsions. Electrical conductivity, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) experiments were also performed, indicating that the typical heptane domain size has an average radius of 360 A and the ionic liquid induces softening of the charged catanionic film. Most interestingly, the IL concentration (cIL) is shown to act as an effective interfacial curvature-control parameter, representing a new approach to tuning the formulation of microemulsions and emulsions. The results expand the potential uses of ILs but also point to the design of new ILs that may achieve superefficient control over interfacial and self-assembly systems.

Synthesis and assembly of gold nanoparticle-doped polymer solid foam films at the liquid/liquid interface and their catalytic properties.

Gold nanoparticle-doped poly(2-vinylpyridine) (P2VP) microcapsules and foam films were synthesized and assembled at the P2VP chloroform solution/HAuCl(4) aqueous solution interface at 25 °C. It was found that Au nanoparticles with the average diameter of 2.1 nm were homogeneously embedded in and adsorbed on the walls of the capsules and foams, the nanoparticles were composed of Au(0) and Au(III) with the molar ratio of about 75/25, and the mass percent of Au elements was measured to be 19.65%. The formation of the nanostructures was attributed to the self-assembly of P2VP at the liquid/liquid interface, the simultaneous reduction of AuCl(4)(-) ions by a small amount of ethanol in the chloroform and adsorption of AuCl(4)(-) ions. After irradiated by UV-light for 1h, the average diameter of the nanoparticles was found to be 2.2 nm, and the AuCl(4)(-) ions were transformed to Au(0) completely. The catalytic performance of these composite nanostructures were evaluated by using the reduction of 4-nitrophenol (4-NP) by potassium borohydride in aqueous solutions. The catalytic activity was very high in the first cycle, decreased rapidly and slightly in the second and third cycles, respectively, due to the aggregation of some nanoparticles, and stabilized after the third cycle.

Transfection efficiency of DNA enhanced by association with salt-free catanionic vesicles.

The interaction of DNA with salt-free tetradecyltrimethylammonium hydroxide and lauric acid lamellar vesicles with positive charges was investigated to probe potential applications of vesicles in DNA transfection. The aggregation morphology of the vesicles changes greatly with the addition of DNA due to the dissociation of anionic surfactants, as indicated by (1)H nuclear magnetic resonance, and the expelled surfactant molecules self-assemble into micelles at high concentrations of DNA. Salt-free cationic and anionic (catanionic) vesicles have a much higher binding saturation point with DNA at R = 2.3 (the ratio of DNA to the excess positive charge in vesicles) than formerly reported salt-containing systems, implying high transfection efficiency. DNA retains its native stretched state during the interaction process. This very interesting result shows that catanionic vesicles could help transport undisturbed and extended DNA molecules into the target cells, which is of great importance in gene delivery, nanomedicine field, and controlling the formation of certain morphological aggregates.

Transition from Vesicle Phase to Lamellar Phase in Salt-Free Catanionic Surfactant Solution

A salt-free cationic and anionic (catanionic) surfactant system was formed by mixing a double-tailed di-(2-ethylhexyl) phosphoric acid (DEHPA, commercial name P204), which is an excellent extractant of rare earth metal ions, with a single-tailed cationic trimethyltetradecylammonium hydroxide (TTAOH) in water. With the mole ratio (r) of DEHPA to TTAOH varying from 0.9 to 1, the phase transition occurred from a densely stacked vesicle phase (Lalphav) to a lamellar phase (Lalphal). Macroscopic properties, such as polarization and rheology, were measured and changed greatly during the course of the phase transition. When r was 0.96 or 0.98, the steady state shear curves exhibited two yield stress values, indicating the coexistence of the Lalphav phase and the Lalphal phase. The Lalphal phase formed in the salt-free and zero-charged system (r=1.0) is defective and undulating, which was confirmed by cryogenic transmission electron microscopy (cryo-TEM). The deuterium nuclear magnetic resonance spectra (2H NMR) showed that a single peak (singlet) split into two symmetric peaks (doublet) gradually, indicating the phase transition from the Lalphav phase to the Lalphal phase. Correspondingly, phosphorus nuclear magnetic resonance spectra (31P NMR) presented changes in both the chemical shift and the peak width, indicating that these two types of bilayer structures are of different anisotropy degrees and different viscosities. When the Lalphal phase is subjected to a certain shear force, it can be reversed to a Lalphav phase again, which was proved by rheological, 2H NMR, and 31P NMR measurements. Furthermore, a theoretical consideration about the formation of the defective and undulating Lalphal phase was taken into account from a viewpoint of energy.