Showing papers by "Dong Wang published in 2012"
TL;DR: The construction of well-ordered 2D covalent networks via the dehydration of di-borate aromatic molecules was successfully realized through introducing a small amount of water into a closed reaction system to regulate the chemical equilibrium.
182 citations
TL;DR: In this paper, HPLC analyses on saponin composition of processed notoginseng were conducted, which revealed that, during the steaming process, the five main ginsenosides (ginsenosides Rg(1), Rb-1, Rd, and Re, and notogsenoside R-1) decreased gradually and some other new saponins were formed.
67 citations
TL;DR: An in situ electrochemical scanning tunnelling microscopy (ECSTM) study of the surface morphology changes of a highly oriented pyrolytic graphite anode during initial lithium uptake in 1 M LiPF(6) dissolved in the solvents of ethylene carbonate plus dimethyl carbonate.
Abstract: Understanding the structure and formation dynamics of the solid electrolyte interphase (SEI) on the electrode/electrolyte interface is of great importance for lithium ion batteries, as the properties of the SEI remarkably affect the performances of lithium ion batteries such as power capabilities, cycling life, and safety issues. Herein, we report an in situ electrochemical scanning tunnelling microscopy (ECSTM) study of the surface morphology changes of a highly oriented pyrolytic graphite (HOPG) anode during initial lithium uptake in 1 M LiPF6 dissolved in the solvents of ethylene carbonate plus dimethyl carbonate. The exfoliation of the graphite originating from the step edge occurs when the potential is more negative than 1.5 V vs. Li+/Li. Within the range from 0.8 to 0.7 V vs. Li+/Li, the growth of clusters on the step edge, the decoration of the terrace with small island-like clusters, and the exfoliation of graphite layers take place on the surface simultaneously. The surface morphology change in the initial lithium uptake process can be recovered when the potential is switched back to 2.0 V. Control experiments indicate that the surface morphology change can be attributed to the electrochemical reduction of solvent molecules. The findings may lead to a better understanding of SEI formation on graphite anodes, optimized electrolyte systems for it, as well as the use of in situ ECSTM for interface studies in lithium ion batteries.
34 citations
TL;DR: One new flavan-3-ol dimer, talienbisflavan A (1), was isolated from green tea prepared from the leaves of C. taliensis collected from the east side of the Ai-Lao mountains, Yuanjiang county of Yunnan province, China.
Abstract: Camellia taliensis (W. W. Smith) Melchior, belonging to the genus Camellia sect. Thea (Theaceae), is an endemic species distributed from the west and southwest of Yunnan province, China, to the north of Myanmar. Known as a wild tea tree, its leaves have been used commonly for producing tea beverages by the local people of its growing area. One new flavan-3-ol dimer, talienbisflavan A (1), was isolated from green tea prepared from the leaves of C. taliensis collected from the east side of the Ai-Lao mountains, Yuanjiang county of Yunnan province, China. In addition, five hydrolyzable tannins (2-6), five flavonols and flavonol glycosides (9-13), three flavan-3-ols (14-16), nine simple phenolic compounds and glycosides (7, 8, and 17-23), and caffeine (24) were identified. Their structures were determined by detailed spectroscopic analysis. All of the isolated phenolic compounds were tested for their antioxidant activities by DPPH and ABTS(+) radical scavenging assays. The contents of its main chemical compositions were also compared with those collected from the Lincang area of Yunnan province by high-performance liquid chromatography analysis.
26 citations
TL;DR: The phase structural transition controlled via temperature and β-CD may find potential applications such as in actuators, shape memories, drug delivery systems, and drag-reducing fluids, etc.
Abstract: A new ternary system of tetradecyldimethylamine oxide (C(14)DMAO)/4-phenylazo benzoic acid (AzoH)/H(2)O was first investigated, and it was found that the self-assembly can be regulated via temperature and β-cyclodextrin (β-CD) recognition. In the temperature regulated self-assembly, the self-assembled phase structural transition between wormlike micelles and multilamellar vesicles (onions) were determined by cryogenic-transmission electron microscopy (cryo-TEM) images and (2)H nuclear magnetic resonance ((2)H NMR) spectra. The phase structural transition temperatures (PSTT) controlled by changing the amount of AzoH were measured by differential scanning calorimetry analysis. The self-assembled phase structural transition mechanism was discussed. It is argued that the self-assembled phase structural transition is the synergetic balance among the hydrophilic headgroup, steric structures of the hydrophobic chain, and membrane charge. β-CD molecules were used as controlling hands to modulate the phase structural transition of self-assembly of the C(14)DMAO/AzoH/H(2)O system in solution via snatching C(14)DMAO molecules. The phase structural transitions from the threadlike micellar phase to the lamellar phase and from the lamellar phase to the vesicular phase can each be controlled because of the β-CD molecular recognition. The phase structural transitions were confirmed by cryo-TEM observations and (2)H NMR measurements. The rheological properties were also investigated to display the importance in the phase structural transition. It was found that the dye molecule, AzoH, is harder to enclose by β-CD than by C(14)DMAO because of the lower complex stability constant (i.e., K(C(14)DMAO@β-CD) ≫ K(AzoH@β-CD). Therefore, the phase structural transition is mainly controlled by the inclusion of C(14)DMAO into the hydrophobic cavity of β-CD molecules. The phase structural transition controlled via temperature and β-CD may find potential applications such as in actuators, shape memories, drug delivery systems, and drag-reducing fluids, etc.
20 citations
TL;DR: An efficient allylic amination of Morita-Baylis-Hillman acetates with simple aromatic amines provided good yields with excellent α-regioselectivity under the catalysis of Pd(2)(dba)(3)/ferrocene-type diphosphine ligand.
Abstract: An efficient allylic amination of Morita–Baylis–Hillman acetates with simple aromatic amines provided good yields with excellent α-regioselectivity (up to exclusive α-product) under the catalysis of Pd2(dba)3/ferrocene-type diphosphine ligand.
20 citations
TL;DR: Three new phenolic compounds, eucalmaidin F, (3S)‐5‐guaiacyl‐3‐hydroxypentanoic acid, and 8‐β‐C‐glucopyranosyl‐5,7‐dihydroxy‐2‐isobutylchromone (3), were isolated from the branches of E. maideni and evaluated for their cytotoxicities against five human cancer cell lines.
Abstract: Three new phenolic compounds, eucalmaidin F (1), (3S)-5-guaiacyl-3-hydroxypentanoic acid (2), and 8-beta-C-glucopyranosyl-5,7-dihydroxy-2-isobutylchromone (3), were isolated from the branches of E. maideni, together with 30 known compounds, including four phenylpropanoids, three lignans, four phloroglucinol glucosides, five dihydroflavonoids, seven simple phenolic compounds, six terpenoids, and glycerol. The new structures were established by spectroscopic studies (MS, and 1D- and 2D-NMR), chemical degradation, and modified Mosher's method. Compounds 3, guaiacylglycerol, 3-hydroxy-1-(4-hydroxyphenyl)propan-1-one, caffeic acid, (2E)-3-(4-hydroxyphenyl)prop-2-enoic acid, (7'S,8R,8'R)-lyoniresinol, (+)-lyoresinol 3a-O-a-L-rhamnopyranoside, garcimangosone, phlorocetophenone 2'-glucopyranoside, (+)-taxifolin 3a-O-a-L-rhamnopyranoside, (+)-aromadendrin, (+)-taxifolin, resveratrol, piceatannol, 3,4,5-trihydroxyphenol. Tachiaside, gallic acid, macrocapals A und G, and oleuropeic acid were evaluated for their cytotoxicities against five human cancer cell lines. Resveratrol, piceatannol, gallic acid, and macrocapal G exhibited moderate inhibitory effects on human myeloid heukemia HL-60 cell, with IC50 values of 22.05, 22.05, 7.75, and 31.93 mu M, respectively; and only macrocapal G showed inhibitory effect on hepatocellular carcinoma SMMC-7721 cell, with an IC50 value of 26.75 mu M.
18 citations
TL;DR: The results demonstrated that the all-carbon electrode structure was effective for charge separation and a sensitive and stable photocurrent signal could be produced in such a device.
Abstract: In this work, we described a facile route for the fabrication of free-standing single-walled carbon nanotubes (SWCNT)–CdSe quantum dots (QDs) hybrid ultrathin films and investigated their optoelectronic conversion properties. A free-standing SWCNT film with thickness of ∼36 nm was firstly prepared via vacuum filtration. The film was then immersed into the pre-synthesized oleic acid-capped CdSe QDs (average diameter of 3.5 nm) solution, where CdSe QDs anchored spontaneously onto the surface of SWCNT film to produce SWCNT–CdSe QDs hybrid film. By using pure SWCNT films in different thicknesses as bottom and top electrodes, a flexible all-carbon electrode optoelectronic conversion device with sandwich structure of SWCNT film (thickness of ∼200 nm)/SWCNT–CdSe QDs hybrid film (thickness of ∼36 nm)/SWCNT film (thickness of ∼36 nm) was constructed to generate optoelectronic conversion under illumination of solar-simulated light. Our results demonstrated that the all-carbon electrode structure was effective for charge separation and a sensitive and stable photocurrent signal could be produced in such a device. In addition, our SWCNT–CdSe QDs hybrid film exhibited high flexibility and durability. No clear change in the resistance of the film was detected under bending in various bending angles.
14 citations
TL;DR: In this article, the adsorption and electrochemical behaviors of 2,5-dihydroxybenzoic acid (DHB) at the electrochemical interface of Au(111) electrode and 0.1 M aqueous perchloric acid solution have been studied by cyclic voltammetry and in situ electrochemical scanning tunneling microscopy.
Abstract: Adsorption and electrochemical behaviors of 2,5-dihydroxybenzoic acid (DHB) at the electrochemical interface of Au(111) electrode and 0.1 M aqueous perchloric acid solution have been studied by cyclic voltammetry and in situ electrochemical scanning tunneling microscopy. Under modulation of the substrate potential, three distinct phases labeled as I, II, and III are observed. DHB molecules take the flat-lying configuration and form the herringbone structure in phase I, which exists at lower potential range. DHB molecules take upstanding configuration and form short-range ordered phase II at higher potential range. A transitional phase consisted of alternately arranged flat-lying and upstanding DHB molecules is disclosed at intermediate potential. The potential induced structural transition can be ascribed to the deprotonation process of carboxylic group and redox reaction of hydroquinone moiety. The present study provides important experiment evidence for understanding the adsorption, redox, and structura...
13 citations
TL;DR: Block copolymer nanolithography has been extended to the nanopatterning of organic functionalities on pyrolyzed photoresist carbon films (PPFs) via diazonium chemistry, using PS-b-P4VP as the template.
10 citations
TL;DR: In this article, the selfassemblies of three barbituric acid compounds on highly oriented pyrolytical graphite surface were investigated using scanning tunneling microscopy, and they formed chiral structures with grouping of three molecular pairs as a unit motif.
Abstract: The self-assemblies of three barbituric acid compounds on highly oriented pyrolytical graphite surface were investigated using scanning tunneling microscopy. On graphite surface, 5-(4-N-hexadecylaminobenzylidene))-2,4,6-(1H,3H)-pyrimidinetrione (BA I) pairs together with head–head styles and forms chiral structure with grouping of three molecular pairs as a unit motif. 5-(4-(N,N-Dihexadecylaminobenzylidene))-2,4,6-(1H,3H)-pyrimidinetrione (BA II) also appears as head–head molecular pairs but with slight displacement between each other. The small shift destroys the symmetry of molecular pairs and introduces chirality to the molecular pairs and in turn the formation of chiral domains. In this dense packing arrangement, only one hexadecyl chain of BA II lies on graphite surface, whereas the other one hangs in air. 5-(4-(N-Methyl-N-hexadecylamin obenzylidene))-(1,3-diethyl)-2-thioxodihydro-4,6-pyrimidinedione (BA III) organized into similar structure to BA II. Single molecular lines of BA III could be found i...
TL;DR: Molecular templates are effective for inducing the formation of functional organic molecular structures on solid surfaces Various surface nanopatterns as molecular templates were developed by self-assembly and molecular engineering as mentioned in this paper.
Abstract: Molecular templates are effective for inducing the formation of functional organic molecular structures on solid surfaces Various surface nanopatterns as molecular templates were developed by self-assembly and molecular engineering These molecular templates were used and led to the formation of ordered assembly of alien species into designed two-dimensional matrices targeting at future applications Both molecular template and so-fabricated nanopatterned assembly were clearly observed by scanning tunneling microscopy (STM) This paper summarizes some recent results on molecular templates for controlling and ordering organic molecules on solid surfaces mainly from our group Several typical molecular templates and the consequent nanofabrication of ordered assemblies are described, including template design and fabrication, molecule ordering and patterning with the template as well as the possible application of these systems
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TL;DR: In this article, a polarization control experiment by utilizing a pair of crossed undulators has been proposed for the Shanghai deep ultraviolet free electron laser test facility, and the physical design study and the preparation status of the experiment are presented in the paper.
Abstract: A polarization control experiment by utilizing a pair of crossed undulators has been proposed for the Shanghai deep ultraviolet free electron laser test facility. Numerical simulations indicate that, with the electromagnetic phaseshifter located between the two crossed planar undulators, fully coherent radiation with 100 nJ order pulse energy, 5 picoseconds pulse length and circular polarization degree above 90% could be generated. The physical design study and the preparation status of the experiment are presented in the paper.
TL;DR: The co-adsorption structures of 4-nitroaniline (4-NA) and polycyclic aromatic molecules, such as pyrene and perylene, on Au(111) surface have been investigated by cyclic voltammetry (CV) and electrochemical scanning tunneling microscopy (ECSTM) as discussed by the authors.
TL;DR: In this paper, the evolution of grain boundary phases during high temperature creep has been systematically investigated in a directionally solidified Ni-base superalloy, and the phase transformation between M23(C,B)6 and M5BB3 is thought to correlate strongly with the strain rate of different creep stages.
Abstract: The evolution of grain boundary phases during high temperature creep has been systematically investigated in a directionally solidified Ni-base superalloy. At the primary creep stage, precipitation of nanosize M5BB3 boride from γ matrix and phase transformation from M23(C,B)6 borocarbide to M5B3B boride occur at grain boundaries. At the steady-state creep stage, precipitation of blocky M23(C,B)6 borocarbide and coarsening of M23(C,B)6 with the dissolution of M5BB3 boride occur at grain boundaries. At the tertiary creep stage, precipitation of M5B3B boride from γ matrix or phase transformation from M23(C,B)6 borocarbide to M5BB3 boride occur again at grain boundaries. The precipitation of M5B3B is due to diffusion of B atoms promoted by applied tensile stress during high temperature creep, and the phase transformation between M23(C,B)6 and M5BB3 is thought to correlate strongly with the strain rate of different creep stages.
01 Jan 2012
TL;DR: In this article, the potential-induced structural transition and reaction at the solid/liquid interface with atomic and molecular resolution was investigated using high-resolution STM images, where the ability to control the adlayer structure is important for modulating the structure and function of the electrode surfaces.
Abstract: The reaction and adsorption of organic molecules at electrode-electrolyte interfaces have been intensively studied to understand the fundamental pro cesses at the electrochemical interface. Electrochemical scanning tunneling microscopy (ECSTM) has been recognized as a powerful tool to investigate potential-induced structural transition and reaction at the solid/liquid interface with atomic and molecular resolution. This review article presents some recent progress in ECSTM application for exploring potential-dependent chemical reactions and phase transitions. Details of the molecular adsorption structure and structural transition controlled by electrode potential are revealed by high resolution STM images. The ability to control the adlayer structure is important for modulating the structure and function of the electrode surfaces.
TL;DR: In this paper, an efficient one-pot synthesis of the title compounds is proposed without additional catalysts, and the synthesis is shown to be possible in a single-stage manner. But it requires a large number of synthesized compounds.
Abstract: An efficient one-pot synthesis of the title compounds is possible without additional catalyst.