Showing papers by "Dong Wang published in 2011"

Oxygen-Aided Synthesis of Polycrystalline Graphene on Silicon Dioxide Substrates

Abstract: We report the metal-catalyst-free synthesis of high-quality polycrystalline graphene on dielectric substrates [silicon dioxide (SiO2) or quartz] using an oxygen-aided chemical vapor deposition (CVD) process The growth was carried out using a CVD system at atmospheric pressure After high-temperature activation of the growth substrates in air, high-quality polycrystalline graphene is subsequently grown on SiO2 by utilizing the oxygen-based nucleation sites The growth mechanism is analogous to that of growth for single-walled carbon nanotubes Graphene-modified SiO2 substrates can be directly used in transparent conducting films and field-effect devices The carrier mobilities are about 531 cm2 V–1 s–1 in air and 472 cm2 V–1 s–1 in N2, which are close to that of metal-catalyzed polycrystalline graphene The method avoids the need for either a metal catalyst or a complicated and skilled postgrowth transfer process and is compatible with current silicon processing techniques

Photo-induced phase transition from multilamellar vesicles to wormlike micelles

Abstract: A novel complex fluid system of tetradecyldimethylamine oxide (C14DMAO) mixed with para-coumaric acid (PCA) in water was investigated. The phase behavior was determined in detail; one observed sequentially the L1-phase (micelles), two-phase L1/Lα, Lα-phase (vesicles), and Lα/precipitates with increasing PCA concentration at constant concentration of C14DMAO. The samples in the regions of micelles and vesicles were characterized by rheological measurements and cryo-TEM observations. Fascinatingly, we found a phase transition from vesicles to wormlike micelles performed via UV-light irradiation. The properties and structures after UV-light irradiation were determined by rheological measurements and cryo-TEM observations to demonstrate the phase transition. To the best of our knowledge, this transition is rarely reported, which could provide a better understanding of the phase transition via light irradiation and find potential applications in drug delivery, biochemistry, and the oilfield industry.

Chiral Hierarchical Molecular Nanostructures on Two-Dimensional Surface by Controllable Trinary Self-Assembly

Abstract: The bottom-up fabrication of surface hierarchical nanostructures is of great importance for the development of molecular nanostructures for chiral molecular recognition and enantioselective catalysis Herein, we report the construction of a series of 2D chiral hierarchical structures by trinary molecular self-assembly with copper phthalocyanine (CuPc), 2,3,7,8,12,13-hexahexyloxy-truxenone (TrO23), and 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) A series of flower-like chiral hierarchical molecular architectures with increased generations are formed, and the details of these structures are investigated by high resolution scanning tunneling microscopy (STM) The flower-like hierarchical molecular architectures could be described by a unified configuration in which the lobe of each architecture is composed of a different number of triangular shape building units (TBUs) The off-axis edge-to-edge packing of TBUs confers the organizational chirality of the hierarchical assemblies On the other hand, the TBUs can tile the surface in a vertex-sharing configuration, resulting in the expansion of chiral unit cells, which thereby further modulate the periodicity of chiral voids in the multilevel hierarchical assemblies The formation of desired hierarchical structures could be controlled through tuning the molar ratio of each component in liquid phase The results are significant for the design and fabrication of multicomponent chiral hierarchical molecular nanostructures

Self-assembly fibrillar network gels of simple surfactants in organic solvents

Abstract: The self-assembled fibrillar network (SAFIN) organogels of a simple surfactant molecule, sodium laurate (C11H23COONa, SL), in organic solvents were investigated. The sol−gel transformation temperature depended on the SL concentration, the solvent, and the concentration of Na+ was evaluated. An important finding is that Na+ ions play an important role in forming organogels, which was regarded as the induction factor of gelation, but other cations, for instance, Li+, K+, Ca2+, and Mg2+, do not have this capability. The observations by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) proved that the organogels were network structures with fibers and ribbons by trapping a certain amount of organic solvent. High-resolution TEM (HR-TEM) images indicated that each of the fibers or ribbons was composed of cylindrical micelles. The X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra demonstrated that SL molecules in gels behave similarly to those in SL crystals. The ...

In situ STM evidence for the adsorption geometry of three N-heteroaromatic thiols on Au(111).

Abstract: The electrochemical behavior of three heteroaromatic thiols (MBs) (2-mercaptobenzimidazole (MBI), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzoxazole (MBO)) on a Au(111) surface has been investigated by electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry (CV) in 0.1 M HClO4 solution. All three thiols form oriented molecular cluster lines along the reconstruction line direction at 0.55 V. With the electrode potential shifting negatively, the molecules undergo a disordered–ordered structural transition. Molecularly resolved STM images show that all three molecules form striped adlayers in the desorption region on the Au(111) surface. The different heteroatoms in the heteroaromatic rings result in different electrochemical behavior of the MB self-assembled monolayers (SAMs). MBI, MBT, and MBO are proposed to interact with the substrate via the S–Au bonds from thiol group and the coordination interaction of N, S, and O with the substrate from the heteroaromatic ring, respectively...

Dammarane-type saponins from steamed leaves of Panax Notoginseng

Abstract: Four new dammarane-type triterpenoid saponins, namely notoginsenosides SFt1-SFt4 (1-4) were isolated from the steamed leaves of Panax notoginseng (Burk.) F. H. Chen (Araliaceae), together with 17 known saponins. Their structures were established on the basis of detailed spectroscopic analyses and acidic hydrolysis. The known ginsenosides Rk2 and Rh3 were obtained from P. notoginseng for the first time. All of these new saponins showed no in vitro cytotoxicity against five human cancer cell lines (HL-60, SMMC-7712, A-549, MCF-7, and SW480).

Saponin accumulation in the seedling root of Panax notoginseng

Abstract: Background: Panax notoginseng is an important Chinese medicinal plant. Dammarene-type triterpenoid saponins are main pharmacologically effective compounds in P. notoginseng. This study aims to investigate the formation and accumulation of saponins in P. notoginseng roots during germination and juvenile stage. Methods: P. notoginseng seeds were collected and stored in wet sand. After germination, the seedlings were transplanted into a soil nursery bed and cultivated for one year. During this period, samples were collected every month and the concentrations of ginsengnosides Rg1, Re, Rb1, Rd and notoginsengnoside R1 were determined by HPLC. Results: There was little saponin in the P. notoginseng seed. The chemical composition of seed was different from that of root. After germination, Rb1 ,R g1, Re, Rd and R1 appeared successively in the seedling root. And in the fivemonth-old root, all these five main saponins came into existence. The accumulation of saponins in P. notoginseng root was affected by seasons. Conclusion: The accumulation of saponins showed a time-dependent increase after germination of P. notoginseng.

Hydrogen bond partner reorganization in the coadsorption of a monodendron and pyridylethynyl derivatives.

Abstract: Hydrogen bonds with high selectivity and directionality are significant in harnessing molecules to form 2D supramolecular nanostructures. The competition and reorganization of hydrogen bond partners determine the ultimate molecular assembly and pattern in a 2D supramolecular system. In this study, multicomponent assemblies of a monodendron (5-benzyloxy-isophthalic acid derivative, BIC) and pyridylethynyl derivatives [1,4-bis(4-pyridylethynyl)-2,3-bis-dodecyloxy-benzene (PBPC12) and 1,4-bis(4-pyridylethynyl)-2,3-bis-octadecyloxy-benzene (PBPC18)] have been studied by scanning tunneling microscopy (STM) on a graphite surface. BIC molecules are able to associate with PBPC12 and PBPC18 molecules to induce the rearrangement of hydrogen bond partners and form coassembly structures. Interestingly, BIC acts as a template molecule in the coassembly process, and these multicomponent structures exhibit similar structural features to the assembly structures of BIC itself. The structural details of the coassembled str...

New Dammarane‐Type Saponins from the Rhizomes of Panax japonicus

Abstract: Phytochemical investigation of the rhizomes of Panax japonicus C. A. Meyer (Araliaceae) resulted in the isolation of two new dammarane-type triterpenoid saponins, yesanchinoside R1 (1) and yesanchinoside R2 (2), together with one new natural product, 6'''-O-acetylginsenoside Re (3). In addition, 25 known compounds, including 23 triterpenoid saponins, 426, beta-sitosterol 3-O-beta-D-glucopyranoside (27), and ecdysterone (28), were also identified. The known saponins 12, 15, and 1822 were reported for the first time from the title plant. Their structures were elucidated on the basis of detailed spectroscopic analyses, including 1D- and 2D-NMR techniques, as well as acidic hydrolysis.

Shape-persistent two-component 2 D networks with atomic-size tunability

Abstract: Over the past few years, two-dimensional (2D) nanoporous networks have attracted great interest as templates for the precise localization and confinement of guest building blocks, such as functional molecules or clusters on the solid surfaces. Herein, a series of two-component molecular networks with a 3-fold symmetry are constructed on graphite using a truxenone derivative and trimesic acid homologues with carboxylic-acid-terminated alkyl chains. The hydrogen-bonding partner-recognition-induced 2D crystallization of alkyl chains makes the flexible alkyl chains act as rigid spacers in the networks to continuously tune the pore size with an accuracy of one carbon atom per step. The two-component networks were found to accommodate and regulate the distribution and aggregation of guest molecules, such as COR and CuPc. This procedure provides a new pathway for the design and fabrication of molecular nanostructures on solid surfaces.

Mild and Efficient Iodine-Catalyzed Direct Substitution of Hydroxy Group of Alcohols with C- and N-Nucleophiles

Abstract: The iodine-catalyzed direct substitution of hydroxy group of allylic, propargylic and other alcohols with various C- and N-nucleophiles, such as (II), (VII) and (IX), respectively, is described.

2D Hexagonal Tilings Based on Triangular and Hexagonal Structural Units in the Self-Assembly of Thiacalix[4]arene Tetrasulfonate on an Au(111) Surface

Abstract: The formation of several molecular 2D tilings with long-range periodicity, including the Kagome network, distorted Kagome network, and snub trihexagonal tiling from the adsorption and assembly of thiacalix[4]arene tetrasulfonate (TCAS) at the 0.1 M HClO(4)/Au(111) interface has been investigated by electrochemical scanning tunneling microscopy (STM). The internal structures of the tilings have been disclosed by high-resolution STM images. The basic structural motifs, namely, the tiles of these tilings are similar, including triangular units and hexagonal units. Due to the different arrangement of the molecules within the triangular units, tiles with different configurations are formed, which further result in the polymorphism of the 2D tiling. This result is of significance for understanding the formation of 2D tiling as well as the design and construction of molecular self-assembled nanostructures.

Scanning Tunneling Microscopy Investigation of Copper Phthalocyanine and Truxenone Derivative Binary Superstructures on Graphite

Abstract: The binary self-assembly of copper phthalocyanine (CuPc) and 2,3,7,8,12,13-hexahexyloxy-truxenone (TrO23) at the solid/liquid interface of highly oriented pyrolytic graphite (HOPG) was investigated by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Pseduohexagonal and linear patterned superstructures of CuPc are obtained by co-adsorbing with TrO23. High-resolution STM images reveal the structural details of the arrangement of TrO23 and CuPc in the binary assembly structures. The molecular ratio between CuPc and TrO23 in the adlayer can be modulated by the CuPc concentration in liquid phase. The electronic properties of CuPc and TrO23 in the co-adsorbed self-assembly are investigated by STS. The results presented here are helpful to the design and fabrication of multi-component functional molecular nanostructures.

Disorder–Order Transformation of Trithiocyanuric Acid Adlayer on a Au(111) Surface Induced by Electrode Potential

Abstract: Self-assembled monolayers (SAMs) of trithiocyanuric acid (TTCA) on Au(111) surfaces are investigated by scanning tunneling microscopy (STM), cyclic voltammetry, and density functional theory calculation (DFT). The SAM exhibits a wormlike disordered structure from 1.0 V to 260 mV vs RHE (reversible hydrogen electrode). At 260 mV, an irreversible disorder–order phase transformation occurs and results in an ordered striped phase. High resolution STM images and DFT calculations suggest that TTCA molecules are parallel to each other within the stripes, which prompts the π–π stacking interactions between the molecules. Each molecule adsorbs vertically on the substrate via two S atoms and one heterocyclic N atom anchoring on the surface at the bridge sites and the top site, respectively. This adsorption geometry promises the SAM with good stability (binding energy 3.27 eV) and free reactive S terminals. The high stability and free S terminals of the TTCA SAM makes it a promising scaffold for applications in mole...

Micelle-assisted fabrication of gel-like PEDOT microspheres: in situ observation of the growth process

Abstract: Novel gel-like poly(ethylene dioxythiophene) (PEDOT) microspheres were fabricated via micelle-mediated polymerization from room temperature ionic liquids (RTILs). The microspheres consist of PEDOT chains as three-dimensional solid networks and a large volume of EDOT as liquid medium span them. Due to synergistic effect of micelles and RTILs, the polymerization rate of PEDOT in the system is slowed down greatly. Gel-like PEDOT microspheres spontaneously grew from several tens of nanometers to centimeter scale and the whole process lasted for several days. Thus, the growth of the microspheres is tracked in situ. The microspheres could release and adsorb EDOT reversibly under certain conditions, indicating a gel-like behavior.

Surface-confined conformers and coassembly-induced conformer resolution.

Abstract: Stereoisomerism is a fundamental chemistry issue and has been intensively investigated because of its importance in organic chemistry, biology, and pharmacology. Molecules with freely rotatable single bonds have many interconvertable conformers. Herein, we report the surface-adsorption-induced conformer resolution by employing azobenzene-3,3-dicarboxylic acid (ADA-33) as a model compound. Two linear assembly phases composed of trans conformers on a highly oriented pyrolytic graphite (HOPG) surface are observed by scanning tunneling microscopy. With the codeposition with 1-octanoic acid (OA), only one trans conformer of ADA-33 can be recognized by OA to form a two-component assembly with alternately arranged ADA-33 and OA stripes, which can be attributed to the epitaxial assembly of ADA-33 and OA on the HOPG surface, and weak hydrogen bonding exists between conformer I and OA molecules. The results are of significance with respect to the discrimination and resolution of conformers on a solid surface and pr...

Characterizing Temporal Structure of the Relativistic Electron Bunch

Abstract: Using proper beam energy chirp and the undulator detuning effect, we propose a modified optical replica synthesizer scheme to characterize the temporal structure of a relativistic electron bunch, which predicts a 100-fs temporal resolution in numerical simulation. The proof of principle experiment demonstrates a peak current of 9 A and a slice energy spread of about 0.5 keV for the uncompressed electron beam of the Shanghai Deep UV Free Electron Laser Facility.

tert-Butyl 3-benzyl-3-[(E)-2-benzyl-idene-3-oxocyclo-pent-yl]-2-oxoindoline-1-carboxyl-ate.

Abstract: In the title compound, C32H31NO4, the dihedral angles between the indoline ring and the two phenyl rings are 48.11 (9) and 66.55 (9)°. The mol­ecular conformation is stabilized by a weak intramolecular π–π stacking inter­action [centroid–centroid distance = 3.6377 (7) A]. The crystal structure is stabilized by inter­molecular C—H⋯O hydrogen bonds, which form chains along the b axis.

10-Phenyl-6b,7,8,9,9a,10-hexa-hydro-6H-cyclo-penta-[4,5]pyrano[3,2-c]chromen-6,9-dione.

Abstract: In the title compound, C21H16O4, the dihedral angle between the phenyl ring and the 2H-chromene ring system is 59.8 (2)°. The crystal packing is stabilized by weak π–π stacking inter­actions [centroid–centroid distances = 3.667 (2) A] and inter­molecular C—H⋯O hydrogen-bonding inter­actions.

Mild and Efficient Iodine-Catalyzed Direct Substitution of Hydroxy Group of Alcohols with C- and N-Nucleophiles.

Abstract: The iodine-catalyzed direct substitution of hydroxy group of allylic, propargylic and other alcohols with various C- and N-nucleophiles, such as (II), (VII) and (IX), respectively, is described.