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Find video protocols related to scientific articles indexed in Pubmed.
Observing Grain Boundaries in CVD-Grown Monolayer Transition Metal Dichalcogenides.
ACS Nano
PUBLISHED: 10-25-2014
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Two-dimensional monolayer transition metal dichalcogenides (TMdCs), driven by graphene science, revisit optical and electronic properties, which are markedly different from bulk characteristics. These properties are easily modified due to accessibility of all the atoms viable to ambient gases, and therefore, there is no guarantee that impurities and defects such as vacancies, grain boundaries, and wrinkles behave as those of ideal bulk. On the other hand, this could be advantageous in engineering such defects. Here, we report a method of observing grain boundary distribution of monolayer TMdCs by a selective oxidation. This was implemented by exposing directly the TMdC layer grown on sapphire without transfer to ultraviolet light irradiation under moisture-rich conditions. The generated oxygen and hydroxyl radicals selectively functionalized defective grain boundaries in TMdCs to provoke morphological changes at the boundary, where the grain boundary distribution was observed by atomic force microscopy and scanning electron microscopy. This paves the way toward the investigation of transport properties engineered by defects and grain boundaries.
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Direct in situ observations of single Fe atom catalytic processes and anomalous diffusion at graphene edges.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 10-20-2014
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Single-atom catalysts are of great interest because of their high efficiency. In the case of chemically deposited sp(2) carbon, the implementation of a single transition metal atom for growth can provide crucial insight into the formation mechanisms of graphene and carbon nanotubes. This knowledge is particularly important if we are to overcome fabrication difficulties in these materials and fully take advantage of their distinct band structures and physical properties. In this work, we present atomically resolved transmission EM in situ investigations of single Fe atoms at graphene edges. Our in situ observations show individual iron atoms diffusing along an edge either removing or adding carbon atoms (viz., catalytic action). The experimental observations of the catalytic behavior of a single Fe atom are in excellent agreement with supporting theoretical studies. In addition, the kinetics of Fe atoms at graphene edges are shown to exhibit anomalous diffusion, which again, is in agreement with our theoretical investigations.
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Low Voltage Transmission Electron Microscopy of Graphene.
Small
PUBLISHED: 06-20-2014
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The initial isolation of graphene in 2004 spawned massive interest in this two-dimensional pure sp(2) carbon structure due to its incredible electrical, optical, mechanical, and thermal effects. This in turn led to the rapid development of various characterization tools for graphene. Examples include Raman spectroscopy and scanning tunneling microscopy. However, the one tool with the greatest prowess for characterizing and studying graphene is the transmission electron microscope. State-of-the-art (scanning) transmission electron microscopes enable one to image graphene with atomic resolution, and also to conduct various other characterizations simultaneously. The advent of aberration correctors was timely in that it allowed transmission electron microscopes to operate with reduced acceleration voltages, so that damage to graphene is avoided while still providing atomic resolution. In this comprehensive review, a brief introduction is provided to the technical aspects of transmission electron microscopes relevant to graphene. The reader is then introduced to different specimen preparation techniques for graphene. The different characterization approaches in both transmission electron microscopy and scanning transmission electron microscopy are then discussed, along with the different aspects of electron diffraction and electron energy loss spectroscopy. The use of graphene for other electron microscopy approaches such as in-situ investigations is also presented.
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A growth mechanism for free-standing vertical graphene.
Nano Lett.
PUBLISHED: 05-06-2014
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We propose a detailed mechanism for the growth of vertical graphene by plasma-enhanced vapor deposition. Different steps during growth including nucleation, growth, and completion of the free-standing two-dimensional structures are characterized and analyzed by transmission electron microscopy. The nucleation of vertical graphene growth is either from the buffer layer or from the surface of carbon onions. A continuum model based on the surface diffusion and moving boundary (mass flow) is developed to describe the intermediate states of the steps and the edges of graphene. The experimentally observed convergence tendency of the steps near the top edge can be explained by this model. We also observed the closure of the top edges that can possibly stop the growth. This two-dimensional vertical growth follows a self-nucleated, step-flow mode, explained for the first time.
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Free-standing single-atom-thick iron membranes suspended in graphene pores.
Science
PUBLISHED: 03-15-2014
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The excess of surface dangling bonds makes the formation of free-standing two-dimensional (2D) metals unstable and hence difficult to achieve. To date, only a few reports have demonstrated 2D metal formation over substrates. Here, we show a free-standing crystalline single-atom-thick layer of iron (Fe) using in situ low-voltage aberration-corrected transmission electron microscopy and supporting image simulations. First-principles calculations confirm enhanced magnetic properties for single-atom-thick 2D Fe membranes. This work could pave the way for new 2D structures to be formed in graphene membranes.
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Low-dimensional carboxylate-bridged Gd(III) complexes for magnetic refrigeration.
Chem Asian J
PUBLISHED: 02-12-2014
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Four carboxylate-bridged Gd(III) complexes (1-4) with 1D/2D structures have been synthesized by using the hydrothermal reaction of Gd2O3 with various carboxylate ligands. Compounds 1 and 2 contained the same [2n] Gd(III)-OH ladders, but with different crystallographically independent Gd(III) ions, whilst the structures of compounds 3 and 4 were composed of [Gd4(?3-OH)2(piv)8(H2O)2](2+) units and 1D ladder Gd(III) chains, respectively. Antiferromagnetic interactions occurred in compounds 1-3, owing to their small Gd-O-Gd angles, whereas ferromagnetic coupling occurred in compound 4, in which the Gd-O-Gd angles were larger. These complexes exhibited a distinct magnetocaloric effect (MCE), which was affected by their different magnetic densities and exchange interactions. Among these compounds, complex 4 presented the largest MCE (-?S(m)(max)=43.6?J?kg(-1) K(-1)), the lowest M(w)/N(Gd) ratio (the highest magnetic density), and weak ferromagnetic coupling. Therefore, a lower M(w)/N(Gd) ratio and weaker exchange interactions (a smaller absolute value of ?) between Gd(III) ions resulted in a larger MCE for the Gd(III) complexes.
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Room temperature in situ growth of B/BOx nanowires and BOx nanotubes.
Nano Lett.
PUBLISHED: 01-29-2014
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Despite significant advances in the synthesis of nanostructures, our understanding of the growth mechanisms of nanowires and nanotubes grown from catalyst particles remains limited. In this study we demonstrate a straightforward route to grow coaxial amorphous B/BOx nanowires and BOx nanotubes using gold catalyst particles inside a transmission electron microscope at room temperature without the need of any specialized or expensive accessories. Exceedingly high growth rates (over 7 ?m/min) are found for the coaxial nanowires, and this is attributed to the highly efficient diffusion of B species along the surface of a nanowire by electrostatic repulsion. On the other hand the O species are shown to be relevant to activate the gold catalysts, and this can occur through volatile O species. The technique could be further developed to study the growth of other nanostructures and holds promise for the room temperature growth of nanostructures as a whole.
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Solitary plexiform neurofibroma of the stomach: a case report.
World J. Gastroenterol.
PUBLISHED: 01-14-2014
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Plexiform neurofibroma (PN) of the digestive tract is very rare and usually part of the generalized syndrome of neurofibromatosis type 1 (von Recklinghausen disease). Solitary PN of the stomach is extremely rare and has not been reported in the literatures. Here we present a case of solitary PN of the stomach, which was not associated with von Recklinghausen disease. A 38-year-old male presented abdominal pain and distention for 7 d. The patient underwent endoscopy of the upper gastrointestinal tract, which revealed a 3.5 cm protruding and cauliflower-shaped mass with a shallow 1 cm central ulcer in the greater curvature of the stomach. The lesion was removed by laparoscopic surgery. Histological examination demonstrated characteristic histological findings of spindle-shaped cells. Immunohistochemical analysis showed that the tumor cells were positive for S-100 protein, but negative for CD34, KI-67, CD117, and actin. Based on histological findings, gastrointestinal stromal tumor could be excluded, and thus the case was confirmed as PN. We described the clinical features, physical examination, endoscopic findings, and histopathological examination of this case.
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Mutation of the retinoblastoma tumor suppressor gene sensitizes cancers to mitotic inhibitor induced cell death.
Am J Cancer Res
PUBLISHED: 01-01-2014
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The retinoblastoma gene Rb is a prototype tumor suppressor, which encodes a protein that is inactivated in a broad range of human cancers through different mechanisms. Rb functions to regulate cell proliferation, differentiation, as well as cell death. Therefore, even though Rb inactivation promotes cancer development, this may also open up certain vulnerabilities of cancers that can potentially be targeted with drug intervention. Based on the assumption that cancers that have mutation, deletion, or rearrangement in the Rb locus represent strong loss of Rb function while cancers with WT Rb on average retain some Rb function, we searched Genomics of Drug Sensitivity in Cancer database to identify cancer drugs that are particularly effective to cancers with Rb genomic alterations. Three mitotic inhibitors were identified from this analysis. We further tested the effects of two mitotic inhibitors, Taxol and STLC, on prostate and breast cancer cells. We demonstrate that the Rb status affects cancer cell sensitivity to these mitotic drugs and that the sensitizing effects of Rb are mediated in part by its regulation of the cell cycle checkpoint protein Mad2. Since the mitotic inhibitors identified in our analysis inhibit mitosis through distinct targets, it is possible that the Rb functional status may serve as a general biomarker for cancer sensitivity to mitotic inhibitors. Because the Rb pathway is inactivated in a large number of human cancers, identification of agents that are particularly effective or ineffective based on the Rb status in cancers can potentially be used generally to matching patients with appropriate treatments to achieve better therapeutic outcome.
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Magnetocaloric effect and slow magnetic relaxation in two only azido bridged ferromagnetic tetranuclear metal clusters.
Dalton Trans
PUBLISHED: 08-23-2013
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Two M(II) tetranuclear complexes bridged only by azido, Mn4(N3)(7.3)Cl(0.7)L4 (1) and Co4(N3)8L4 (2) in which the four M(II) ions are precisely coplanar bridged only by six azido anions, were obtained by using 4,5-diazafluoren-9-one (L) as a corner ligand. Magnetic studies indicate that ferromagnetic coupling was conducted by the azido anions between M(II) ions. At low temperature, 1 exhibits a large magnetocaloric effect and 2 shows field-induced multiple magnetic relaxations.
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An unprecedented decanuclear Gd(III) cluster for magnetic refrigeration.
Inorg Chem
PUBLISHED: 07-29-2013
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An unprecedented decanuclear Gd(III) cluster composed of the [Gd10(?3-OH)8](22+) core has been hydrothermally synthesized. Magnetic analyses indicate that this complex shows weak antiferromagnetic behavior with a relatively large magnetocaloric effect (-?S(m)(max) = 31.22 J kg(-1) K(-1)).
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Synthesis and ferrimagnetic properties of an unprecedented polynuclear cobalt complex composed of [Co24] macrocycles.
Chem. Commun. (Camb.)
PUBLISHED: 07-05-2013
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An unprecedented polynuclear cobalt complex with a [Co(24)] macrocycle in the presence of [Co(H(2)O)(6)](2+) has been prepared and characterized. In this complex, [Co(H(2)O)(6)](2+) not only acts as a counterion to balance the negative charge of the 2D layer, but may also serve as a template in the assembly of the [Co(24)] macrocyclic complex through hydrogen-bond interactions. Magnetic analyses indicate that the title compound shows homometallic ferrimagnetic behavior.
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A chiral 2p-3d heterometallic azido complex with 2,6-pyridinedicarboxylate as the co-ligand showing magnetic order.
Dalton Trans
PUBLISHED: 04-30-2013
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A new chiral 3D heterometallic coordination polymer [NaCo2(L)2(N3)·(MeOH)]? (1) (L = 2,6-pyridinedicarboxylate) was synthesized and characterized magnetically. Ferro- and antiferromagnetic interactions co-exist in 1, which results in a magnetic phase transition at the high temperature of 29 K.
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Tuning the structure and magnetism of heterometallic sodium(1+)-cobalt(2+) formate coordination polymers by varying the metal ratio and solvents.
Inorg Chem
PUBLISHED: 03-05-2013
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Three new heterometallic formate coordination polymers formulated as [Na2Co(HCOO)4]? (1), [NaCo(HCOO)3]? (2), and [Na2Co7(HCOO)16]? (3) were obtained by adjusting the solvent and ratio of the reactants. In 1, a (4,4) cobalt formate layer is formed and the sodium ions connect the layers to form a three-dimensional (3D) framework. In 2, each formate ligand binds two Co(2+) and two Na(+) ions with a syn,syn,anti,anti coordination mode to form a chrial network with 4,6-connected topology. 3 is a Na(+)-ion-linked 3D framework based on the cobalt formate layer, which has a 10-membered metal ring. Magnetic studies indicate the existence of ferromagnetic interactions between adjacent Co(2+) ions in 1, while dominating antiferromagnetic couplings in 2 and 3.
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Deregulated G1-S control and energy stress contribute to the synthetic-lethal interactions between inactivation of RB and TSC1 or TSC2.
J. Cell. Sci.
PUBLISHED: 02-27-2013
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Synthetic lethality is a potential strategy for cancer treatment by specifically promoting the death of cancer cells with particular defects such as the loss of the RB (RB1) tumor suppressor. We previously showed that inactivation of both RB and TSC2 induces synergistic apoptosis during the development of Drosophila melanogaster and in cancer cells. However, the in vivo mechanism of this synthetic-lethal interaction is not clear. Here, we show that synergistic cell death in tissues that have lost the RB and TSC orthologs rbf and dtsc1/gig, respectively, or overexpress Rheb and dE2F1, are correlated with synergistic defects in G1-S control, which causes cells to accumulate DNA damage. Coexpression of the G1-S inhibitor Dap, but not the G2-M inhibitor dWee1, decreases DNA damage and reduces cell death. In addition, we show that rbf and dtsc1 mutant cells are under energy stress, are sensitive to decreased energy levels and depend on the cellular energy stress-response pathway for survival. Decreasing mitochondrial ATP synthesis by inactivating cova or abrogating the energy-stress response by removing the metabolic regulator LKB1 both enhance the elimination of cells lacking either rbf or dtsc1. These observations, in conjunction with the finding that deregulation of TORC1 induces activation of JNK, indicate that multiple cellular stresses are induced and contribute to the synthetic-lethal interactions between RB and TSC1/TSC2 inactivation. The insights gained from this study suggest new approaches for targeting RB-deficient cancers.
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Slow magnetic relaxation in two new 1D/0D Dy(III) complexes with a sterically hindered carboxylate ligand.
Inorg Chem
PUBLISHED: 02-04-2013
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Two carboxylate-bridged Dy(III) complexes, [Dy(2)(piv)(5)(?(3)-OH)(H(2)O)](n) (1) and [Dy(2)(piv)(6)(phen)(2)] (2) (pivH = pivalic acid; phen = 1,10-phenanthroline), have been synthesized and structurally characterized. Complex 1 takes a one-dimensional (1D) chain structure based on [Dy(4)(?(3)-OH)(2)(piv)(8)(H(2)O)(2)](2+) units, while complex 2 is a dinuclear structure bridged by syn,syn-carboxylates. Magnetic investigation indicates weak ferromagnetic interaction between adjacent Dy(III) ions of the Dy(4) unit in 1 and weak intramolecular antiferromagnetic interaction between Dy(III) ions and/or depopulation of the Dy(III) excited-state Stark sublevels in 2. Alternating-current susceptibility measurements revealed frequency- and temperature-dependent out-of-phase signals under a zero direct-current field in 1, with typical slow magnetic relaxation behavior with an anisotropic barrier U ? 4.5 K, while 2 exhibits field-induced single-molecule-magnet behavior with ?E/k(B) = 28.43 K under a 2 kOe external field.
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Electrical breakdown of nanowires.
Nano Lett.
PUBLISHED: 10-14-2011
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Instantaneous electrical breakdown measurements of GaN and Ag nanowires are performed by an in situ transmission electron microscopy method. Our results directly reveal the mechanism that typical thermally heated semiconductor nanowires break at the midpoint, while metallic nanowires breakdown near the two ends due to the stress induced by electromigration. The different breakdown mechanisms for the nanowires are caused by the different thermal and electrical properties of the materials.
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Impact of Pb doping on the optical and electrical properties of ZnO nanowires.
J Nanosci Nanotechnol
PUBLISHED: 04-01-2011
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In this letter, effect of Pb-doping on the electrical and optical properties of the as grown ZnO nanowires (NWs) have been investigated. The microstructural investigations show that the Pb-dopant substituted into wurtzite ZnO nanowires without forming any secondary phase. The amount of contents and valence state of Pb ions has been investigated through energy dispersive spectroscopy and X-ray photospectroscopy. The doped nanowires show a remarkable reduction of 15.3 nm (127.4 meV) in the optical band gap, while an increase amount of deep-level defects transition in visible luminescence. Furthermore, the reduction in the band gap and the presence of deep-level defects induces strong effect in the electrical resistivity of doped NWs, which makes their potential for the fabrication of nanodevices. The possible growth mechanism is also briefly discussed.
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Electron microscopy and in situ testing of mechanical deformation of carbon nanotubes.
Micron
PUBLISHED: 02-24-2011
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In this paper, the electron diffraction technique to determine the helicity and atomic structure of carbon nanotubes is reviewed, as well as different mechanical test methods, tensile test, bending test, compression test and vibration test of carbon nanotubes by in situ electron microscopy are summarized while the relationship between mechanical properties and structures revealed by experiments is addressed. Except for these, the electric current and electron beam irradiation effect and some other novel electron microscopy experiments are also incorporated.
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Suppression of fatty acid synthase, differentiation and lipid accumulation in adipocytes by curcumin.
Mol. Cell. Biochem.
PUBLISHED: 01-09-2011
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Curcumin is a well-known component of the cook seasoning and traditional herb turmeric (Curcuma longa), which has been reported to prevent obesity. However, the mechanism still remains to be determined. In this study, curcumin is found to be an effective inhibitor of fatty acid synthase (FAS), and its effects on adipocytes are further evaluated. Curcumin shows both fast-binding and slow-binding inhibitions to FAS. Curcumin inhibits FAS with an IC?? value of 26.8 ?M, noncompetitively with respect to NADPH, and partially competitively against both substrates acetyl-CoA and malonyl-CoA. This suggests that the malonyl/acetyl transferase domain of FAS possibly is the main target of curcumin. The time-dependent inactivation shows that curcumin inactivates FAS with two-step irreversible inhibition, a specific reversible binding followed by an irreversible modification by curcumin. Like other classic FAS inhibitors, curcumin prevents the differentiation of 3T3-L1 cells, and thus represses lipid accumulation. In the meantime, curcumin decreases the expression of FAS, down-regulates the mRNA level of PPAR? and CD36 during adipocyte differentiation. Curcumin is reported here as a novel FAS inhibitor, and it suppresses adipocyte differentiation and lipid accumulation, which is associated with its inhibition of FAS. Hence, curcumin is considered to be having potential application in the prevention of obesity.
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One pot synthesis of heterometallic 3d-3d azide coordination architectures: effect of the single-ion anisotropy.
Inorg Chem
PUBLISHED: 11-16-2010
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Five new isomorphic three-dimensional (3D) heterometallic 3d-3d azide complexes, [CuNi(1-x)Co(x)(N(3))(2)(isonic)(2)](?) (x = 0 for 1, x = 0.3 for 2, x = 0.5 for 3, x = 0.6 for 4, and x = 1 for 5), were obtained by assembling Cu(II), M(II) (Ni(II) and Co(II)), azide, and pyridyl carboxylate in hydrothermal condition. The 3D structure can be described as end on (EO) azide and syn,syn carboxylates mixed bridged alternate Cu-M chains linked by the pyridyl groups. Dominant ferromagnetic interactions were observed between the Cu(II) and M(II) ions in the chains. At low temperature diverse magnetic phenomena were presented in those complexes. As the Ni(II) ions were replaced by Co(II) ions with large anisotropy, the magnetism of the complexes change gradually from metamagnet to single-chain magnet (SCM)-like behaviors.
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Synthesis, structure and magnetic properties of two new azido-Co(II) coordination architectures: from ferromagnetic coupling to single-chain-magnets.
Dalton Trans
PUBLISHED: 10-25-2010
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Two new azido-Co(II) complexes with pyrazine carboxylato ligands, [Co(N(3))(L)·H(2)O](n) (L = pyrazine-2-carboxylato) (1) and [CoNa(N(3))(2)(L)](n) (2), have been obtained by carefully tuning the Co(II):N(3)(-) ratio. Here we present the structural and magnetic characterization of these new species. Modulation of the coordination environment of Co(II) leads to a variation of the magnetic properties of the obtained compounds. Complex 1 exhibits ferromagnetically coupled [Co(2)] units that form the rungs of the ladder with a nearly negligible coupling between these units, while complex 2 is a 2D arrangement of 1D Co(II) single-chain magnets.
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Mass transportation mechanism in electric-biased carbon nanotubes.
Nano Lett.
PUBLISHED: 10-21-2010
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The mass transportation mechanism in electric-biased carbon nanotubes (CNTs) is investigated experimentally. Except for the widely accepted electromigration mechanism, we find out the thermal effect can also induce the mass transportation in the form of thermomigration or thermal evaporation. Moreover, the convincing in situ transmission electron microscope experiment results show the thermal gradient force overrides the electromigration force in most conditions, according to specific parameters of the CNTs and "cargos". A full analysis on the thermal gradient force and electromigration force imposed on the cargos is given, thus our experimental results are well explained and understood.
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Chiral magnetic metal-organic frameworks of Mn(II) with achiral tetrazolate-based ligands by spontaneous resolution.
Chem. Commun. (Camb.)
PUBLISHED: 10-19-2010
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The enantiomers of complex 1 (1a and 1b) have been obtained by spontaneous resolution upon crystallization in the absence of a chiral source. The enantiomeric nature of 1a and 1b was confirmed by circular dichroism (CD) spectra and theoretical investigation.
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Magnetic behavior control in niccolite structural metal formate frameworks [NH2(CH3)2][Fe(III)M(II)(HCOO)6] (M = Fe, Mn, and Co) by varying the divalent metal ions.
Inorg Chem
PUBLISHED: 10-11-2010
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By changing template cation but introducing trivalent iron ions in the known niccolite structural metal formate frameworks, three complexes formulated [NH(2)(CH(3))(2)][Fe(III)M(II)(HCOO)(6)] (M = Fe for 1, Mn for 2, and Co for 3) were synthesized and magnetically characterized. The variation in the compositions of the complexes leads to three different complexes: mixed-valent complex 1, heterometallic but with the same spin state complex 2, and heterometallic heterospin complex 3. The magnetic behaviors are closely related to the divalent metal ions used. Complex 1 exhibits negative magnetization assigned as Ne?el N-Type ferrimagnet, with an asymmetric magnetization reversal in the hysteresis loop, and complex 2 is an antiferromagnet with small spin canting (?(canting) ? 0.06° and T(canting) = 35 K), while complex 3 is a ferrimagnet with T(N) = 32 K.
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Ginsenoside Rh2 induces apoptosis and paraptosis-like cell death in colorectal cancer cells through activation of p53.
Cancer Lett.
PUBLISHED: 06-17-2010
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Ginsenosides are the main bioactive components in American ginseng, a commonly used herb. In this study, we showed that the ginsenoside Rh2 exhibited significantly more potent cell death activity than the ginsenoside Rg3 in HCT116 and SW480 colorectal cancer cells. Cell death induced by Rh2 is mediated in part by the caspase-dependent apoptosis and in part by the caspase-independent paraptosis, a type of cell death that is characterized by the accumulation of cytoplasmic vacuoles. Treatment of cells with Rh2 activated the p53 pathway and significantly increased the levels of the pro-apoptotic regulator, Bax, while decreasing the levels of anti-apoptosis regulator Bcl-2. Removal of p53 significantly blocked Rh2-induced cell death as well as vacuole formation, suggesting that both types of cell death induced by Rh2 are mediated by p53 activity. Furthermore, we show that Rh2 increased ROS levels and activated the NF-?B survival pathway. Blockage of ROS by NAC or catalase inhibited the activation of NF-?B signaling and enhanced Rh2-induced cell death, suggesting that the anti-cancer effect of Rh2 can be enhanced by antioxidants.
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Three-dimensional porous metal-organic frameworks exhibiting metamagnetic behaviors: synthesis, structure, adsorption, and magnetic properties.
Inorg Chem
PUBLISHED: 04-07-2010
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Two isomorphous 3D porous metamagnets, {[M(6)(N(3))(12)L(6)].(H(2)O)(13)}(infinity) (M = Ni(II), 1; Co(II), 2), have been constructed from 2-(1,3,4-thiadiazol-2-ylthio)acetic acid (HL), with azido as the auxiliary ligand. Single-crystal X-ray analysis indicates that the complexes possess hexagonal channels with dimensions of about 8.3 A x 8.3 A along the c axis and void space of about 25% per cell volume. Hydrogen adsorption measurements at 740 Torr and 77 K reveal that hydrogen uptakes of 0.68 and 0.83 wt % were observed in 1 and 2, respectively, with BET surface areas of 309 and 328 m(2)/g. Magnetic measurement reveals that both of them exhibit global metamagnetic behaviors resulted from strong intrachain ferromagnetic couplings and weak interchain antiferromagnetic interactions, with critical fields of 22 kOe and 6 kOe for 1 and 2, respectively.
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New manganese(II) azido coordination polymers with nicotinic/isonicotinic acids as coligands: synthesis, structure, and magnetic properties.
Inorg Chem
PUBLISHED: 03-25-2010
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The reactions of Mn(II) ions with azido ligands in the presence of nicotinic/isonicotinic acids gave two manganese(II) azido coordination polymers, [Mn(3)(L(1))(2)(N(3))(4)](n).nH(2)O (1) and [Mn(2)(L(2))(N(3))(3)](n) (2), where L(1) = nicotinate and L(2) = isonicotinate, with different topological structures. Complex 1 consists of 2D azido-Mn(II) planes, which is further linked by L(1) to form a 3D framework with unprecedented 3,6-connected 4-nodal net topology, and complex 2 presents an unprecedented 3,4,6-connected 6-nodal 3D azido-Mn(II) structure with L(2) as the coligand. Magnetic susceptibility measurements reveal dominant antiferromagnetic coupling existing in 1 and 2. Complex 1 is a spin-competitive system and enters into a weak ferromagnetic-to-magnetic phase transition at the critical temperature of 6 K due to spin canting. Complex 2 is an antiferromagnet and exhibits field-induced spin-flop behavior.
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New 3D coordination polymers constructed from pillared metal-formate Kagomé layers exhibiting spin canting only in the nickel(II) complex.
Inorg Chem
PUBLISHED: 12-02-2009
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Sparked by the strategy of pillared-layer MOFs, three formate coordination polymers, {[Ni(2)(HCO(2))(3)(L)(2)](NO(3)).2H(2)O}(infinity) (1), {[Co(2)(HCO(2))(3)(L)(2)](HCO(2)).2H(2)O}(infinity) (2), and {[Cu(2)(HCO(2))(3)(L)(2)](HCO(2)).2H(2)O}(infinity) (3), have been synthesized by employing the rodlike ligand 4,4-bis(imidazol-1-yl)biphenyl (L) as the pillar. Structural analysis indicates that the title complexes 1-3 are isostructural compounds, which possess metal-formate 2D layers perpendicularly pillared by the ligand L to afford a 3D open framework. This is an interesting example of a Kagome lattice based on the formate mediator. Moreover, the formate anion of this 2D Kagome layer exhibits various bridging modes: anti-anti, syn-anti, and 3.21 modes. Their magnetic measurements reveals that only complex 1 presents the spin canting phenomenon, while its isostructural Co(II) and Cu(II) complexes are simply paramagnets with antiferromagnetic coupling.
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One-dimensional metal-azido complex constructed by a double EO azido bridged trinuclear nickel(II) unit: synthesis, structure and magnetic properties.
Dalton Trans
PUBLISHED: 11-05-2009
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The hydrothermal reaction of Ni(NO(3))(2).6H(2)O, NaN(3) phenanthroline and nicotinic acid yielded a one-dimensional (1D) complex, [Ni(1.5)(N(3))(2)(phen)(nic)](n) (1) (phen = phenanthroline, nic = nicotinate), which is a new example of the named orbital countercomplementarity-like complex. In 1, the nicotinate shows mu(3)-nic-N,O,O coordination mode, and the azide groups adopt mu(1,1) bridging mode linking Ni(II) ions to form a rare trinuclear Ni(II) unit bridged by a double mu(1,1) azido.
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3D Mn(II) coordination polymer with alternating azide/azide/formate/formate bridged chains: synthesis, structure and magnetic properties.
Dalton Trans
PUBLISHED: 10-28-2009
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A new 3D Mn(II) coordination polymer, [Mn(2)(HCO(2))(L)(2)(N(3)) x MeOH](infinity) (1) (L = nicotinate N-oxide), was synthesized by a solvothermal reaction and characterized magnetically. Complex 1 is a typical antiferromagnet with alternating azide/azide/formate/formate bridges, exhibiting a new -J(1)J(1)J(2)J(2)- coupling sequence. This is the first complex to contain an azide, formate and another type of carboxylate ligand.
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Single-crystal-to-single-crystal transformation in unusual three-dimensional manganese(II) frameworks exhibiting unprecedented topology and homospin ferrimagnet.
Inorg Chem
PUBLISHED: 06-24-2009
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A new three-dimensional Mn(II) complex, [Mn(3)(HCO(2))(2)(L)(2)(OCH(3))(2)], 1 (L = nicotinate N-oxide), was synthesized by solvothermal reaction and magnetically characterized. Complex 1 exhibits an unprecedented 3,6-connected 5-nodal net topology with Schlafli notation {4(2);6}4{4(3)}2{4(6);6(6);8(3);10}2{4(8);6(6);8} and was assigned as a homospin ferrimagnet. Interestingly, when 1 was placed in air for ca. one month, the methoxy anions in 1 were gradually exchanged by hydroxyl anions and 1 underwent a single-crystal-to-single-crystal structural transition to a new but similar complex, [Mn(3)(HCO(2))(2)(L)(2)(OH)(2)] x 4 H(2)O, 2. The anion exchange and water molecules filling the channels of 2 affect the magnetic behavior at low temperature compared to that of 1.
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Tuning the structure and magnetism of azido-mediated Cu(II) systems by coligand modifications.
Inorg Chem
PUBLISHED: 02-14-2009
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Through the use of a series of structurally related benzoates bearing different substituents as coligands, three new azido-copper compounds, [Cu(benzoate)(N(3))](n) (1), [Cu(2-methyl-benzoate)(N(3))](n) (2), and [Cu(1-naphthoate)(N(3))](n) (3), have been successfully obtained and structurally and magnetically characterized. Single-crystal structure analyses indicated that the uncoordinating substituents in the benzoates greatly affect the structure of the complexes. Complex 1 displays isolated ferromagnetic chains with the largest Cu-N-Cu angle in known carboxylate/end-on-azido mixed-bridged copper systems, while complexes 2 and 3 were 2D coordination polymers, containing mu-(1,1,3,3) and mu-(1,1,3) bridging azides and exhibiting new azido-copper networks with (4(4)) and (4.8(2)) topologies, respectively. Furthermore, 2 was a chiral complex obtained through spontaneous resolution. In the low-temperature range, both 2 and 3 showed spontaneous magnetization with characteristics of soft ferromagnetic magnetism with phase transition temperatures of 13 and 10 K, respectively.
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Novel lanthanide-azido complexes: hydrothermal syntheses, structures and magnetic properties.
Dalton Trans
PUBLISHED: 02-13-2009
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Three new 1D lanthanide-azido complexes, [Ln(2)(N(3))(isonic)(2)-(OH)(3)(Hisonic)(H(2)O)](n) (Ln = Gd(III), Eu(III) and Sm(III)), were synthesized by hydrothermal reaction and their magnetic properties were studied.
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Antiaging effect of Cordyceps sinensis extract.
Phytother Res
PUBLISHED: 02-12-2009
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This experiment studied the effect of Cordyceps sinensis extract (CSE) on mice aged by d-galactose and castrated rats to analyse its antiaging effect. Water maze and step-down type avoidance tests were used to examine the effect of CSE on learning and memory. CSE shortened escape latency, prolonged step-down latency and decreased the number of errors in mice aged by d-galactose. The effect of CSE on the sexual function of castrated rats was evaluated by measuring the penis erection latency, mount latency and ejaculation latency. CSE appeared to shorten penis erection latency and mount latency in castrated rats. The study also measured the effect of CSE on the activity of age-related enzymes. The results showed that CSE improved the activity of superoxide dismutase, glutathione peroxidase and catalase and lowered the level of lipid peroxidation and monoamine oxidase activity in the aged mice. The study demonstrated that CSE can improve the brain function and antioxidative enzyme activity in mice with d-galactose-induced senescence and promote sexual function in castrated rats. All of these findings suggest that CSE has an antiaging effect.
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The role of order-disorder transitions in the quest for molecular multiferroics: structural and magnetic neutron studies of a mixed valence iron(II)-iron(III) formate framework.
J. Am. Chem. Soc.
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Neutron diffraction studies have been carried out to shed light on the unprecedented order-disorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)-iron(III) formate framework compound [NH(2)(CH(3))(2)](n)[Fe(III)Fe(II)(HCOO)(6)](n). The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order-disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [Fe(III)Fe(II)(HCOO)(6)](n) framework. In the low-temperature phase, a change in space group from P31c to R3c occurs, involving a tripling of the c-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different Fe(II) and Fe(III) magnetic moments.
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A unique substituted Co(II)-formate coordination framework exhibits weak ferromagnetic single-chain-magnet like behavior.
Chem. Commun. (Camb.)
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A magnetic isolated chain-based substituted cobalt-formate framework was obtained with isonicotine as a spacer. In the chain, canted antiferromagnetic interactions exist in between the Co(II) ions, and slow magnetic relaxation is detected at low temperature. For the block effects of the isonicotine ligands, the complex could be considered as a peculiar example of a weak ferromagnetic single-chain-magnet.
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Electron-beam-induced elastic-plastic transition in Si nanowires.
Nano Lett.
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It is generally accepted that silicon nanowires (Si NWs) exhibit linear elastic behavior until fracture without any appreciable plastic deformation. However, the plasticity of Si NWs can be triggered under low strain rate inside the transmission electron microscope (TEM). In this report, two in situ TEM experiments were conducted to investigate the electron-beam (e-beam) effect on the plasticity of Si NWs. An e-beam illuminating with a low current intensity would result in the bond re-forming processes, achieving the plastic deformation with a bent strain over 40% in Si NWs near the room temperature. In addition, an effective method was proposed to shape the Si NWs, where an e-beam-induced elastic-plastic (E-P) transition took place.
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Two azido-bridged cobalt(II) coordination polymers with nicotinate co-ligand: synthesis, structures and magnetic properties.
Dalton Trans
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By utilizing nicotinic acid as a co-ligand, two new azido-bridged cobalt(II) complexes with the formulae [Co(2)(N(3))(nic)(2)Cl(H(2)O)](n) (1) and [Co(N(3))(nic)](n) (2) (nic = nicotinate) have been synthesized under solvothermal condition and structurally characterized. Complex 1 exhibits a rare three-dimensional (3D) Kagomé topology with [Co4] units as connecting nodes. Complex 2 is also a 3D structure which contains 1D Co(II)-?-1,1-azido chains as rod-shaped SBUs. Magnetic data analysis shows that ferromagnetic coupling intra-[Co4]-cluster and antiferromagnetic interaction inter-[Co4]-cluster exists in complex 1, while complex 2 exhibits metamagnetism with a critical field of 5.5 kOe.
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catena-Poly[[(1,10-phenanthroline)cobalt(II)]-di-?-azido].
Acta Crystallogr Sect E Struct Rep Online
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In the crystal structure of the binuclear title complex, [Co(N(3))(2)(C(12)H(8)N(2))](n), each Co(II) cation is coordinated by two N atoms from one chelating 1,10-phenanthroline ligand and four azide ligands in a slightly distorted octa-hedral coordination. The two Co(II) cations of the binuclear complex are related by an inversion centre and are bridged by two symmetry-related azide ligands in both ?(1,1) and ?(1,3) modes. The ?(1,3) bridging mode gives rise to an infinite one-dimensional chain along the a axis, whereas the ?(1,1) bridging mode is responsible for the formation of the binuclear Co(II) complex.
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One pot synthesis of heterometallic 3d-3d azido architectures: assembling strategy and magnetic properties.
Dalton Trans
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The Cu(II) ions usually have different coordinated geometry to other 3d ions, especially Ni(II) and Co(II) ions, in azido-carboxylate mixed ligand systems. That provides a potential way to synthesize rare heterometallic 3d-3d azido complexes with peculiar magnetic properties. Assembling Cu(II), M(II) (M = Ni and Co), azido and nicotinic acid in hydrothermal condition, two novel isomorphic 3D heterometallic 3d-3d azido complexes, [CuM(N(3))(2)(nicotinate)(2)](?) (M = Ni(II) for 1 and Co(II) for 2) were obtained. The structure of the complexes can be described as EO azido and syn,syn carboxylate mixed bridged spin sequence chains (-1/2-J(1)-1-J(2)-1/2- for 1 and -1/2-J(1)-3/2-J(2)-1/2- for 2) linked by the pyridyl groups. Dominant ferromagnetic interactions were observed between the Cu(II) and M(II) ions in the chains despite the largest M-N-M angle of about 129° in the 3d metal azido-carboxylate mixed coordinated systems and weak antiferromagnetic interactions between the chains. At low temperature, a spin-flop phase transition was present in the Co(II) involved complex 2.
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