Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 37
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Chem Phys ; 152(4): 044704, 2020 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-32007031

RESUMO

The coordination reactions of 4-Azidobenzoic Acid (ABA) molecules on different active surfaces are studied by scanning tunneling microscopy and density functional theory calculations. ABA molecules deposited on Ag(111)/Ag(100)/Cu(100) held at room temperature lead to the decomposition of azide groups and the release of a N2 molecule per ABA molecule. Two residual segments of ABA molecules can interact with one Ag/Cu adatom to form a coordination dimer through the N-Ag/Cu-N coordination bond on different substrates. Different orientations with different symmetries can result in different nanostructures based on the dimers. Interestingly, the residual segments of ABA molecules can generate four Cu adatoms as the coordination center on Cu(100) to form a novel coordination complex after annealing, which is the first report for trapping four adatoms as a coordination center. The number and the species of adatoms captured can be changed to alter coordination structures. It expounds that various regulatory effects of different substrates lead to the diversity of nanostructures dominated by coordination bonds.

2.
J Phys Condens Matter ; 32(3): 035808, 2020 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-31590161

RESUMO

Single-crystalline FeTe2 in marcasite phase with orthorhombic structure was prepared via chemical vapor transport. Cooling FeTe2 single crystals from room temperature down to [Formula: see text], multiple magnetic phase transitions were observed. Paramagnetic (PM) to antiferromagnetic (AFM) and then to ferromagnetic (FM) occurred at [Formula: see text] and [Formula: see text] for in-plane, [Formula: see text] and [Formula: see text] for out-of-plane, respectively. A strong uniaxial magnetic anisotropy was found due to FeTe6 octahedron distortion and structural modulation in FM region. The novel negative volume expansion (NVE) initiated in the vicinity of AFM to FM transition. An abrupt frequency shift of the most intense mode at [Formula: see text] and evolution of the Te-Te stretching mode near [Formula: see text], corresponding to the phase transition from AFM to FM were observed. The temperature-dependent resistance revealed an anomaly (semiconductor to metallic transition) around AFM-FM transition, which can easily be suppressed and move to high temperature by the applied magnetic field. The results from XRD, Raman and resistivity indicated that the structural parameters, vibration frequency and transport are sensitive to the phase transition from AFM to FM. The nature of direct band gap with [Formula: see text] was identified through UV-Vis-NIR spectrum of FeTe2 single crystals at room temperature.

3.
Opt Lett ; 44(19): 4678-4681, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31568415

RESUMO

Wide-range optical thermal sensing is achieved here based on the two-photon upconversion luminescence of the high-temperature (HT) cubic phase NaYF4:Yb, Er. In the range of room temperature to 973 K, the single-phase sample exhibits two bands of green and red emission with different dependences on the temperature. The CIE chromaticity diagram shows that the color point moves from deep red (0.6357, 0.3501) at room temperature to the yellow region (0.4379, 0.475) at 600 K and then to the green region (0.318, 0.669) at 973 K. It reveals that HT cubic phase NaYF4:Yb, Er is the promising ratiometric and colorimetric luminescent thermometer. The relative sensitivity decreases slightly up to 673 K and then increases with the increasing temperature. The lattice expansion of the HT cubic phase alters the crystal symmetry around the activator ion and further increases the green-to-red emission ratio.

4.
Materials (Basel) ; 12(20)2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31615085

RESUMO

Rigid polyurethane foam, foam concrete, and vacuum insulation board are common roofing insulation materials. Their weathering performance under long-term multi-field coupling determines the overall service life of the roof. The weathering properties of rigid polyurethane foam, foam concrete and vacuum insulation panels were studied under freeze thaw, humid-heat, dry-wet, high-low temperature, and multi-field coupling cycles, respectively. The heat transfer and construction process of roof panels was simulated base on upper loading and moisture transfer factors. The result indicates that the mass loss of the foam concrete and the rigid polyurethane foam in the weathering test was significant, which led to the gradual increase of thermal conductivity. Meanwhile, the thermal conductivity and mass loss of vacuum insulation panels did not change due to the lack of penetration under external pressure, therefore, it is necessary to construct composite thermal-insulation materials to alleviate the adverse effects of the service environment on a single material and realize the complementary advantages and disadvantages of the two materials. The results of the numerical simulations indicated that the roof structure must be waterproofed, and its weatherproof performance index should be the same as that of the thermal insulation material. Considering structural deformation, the overall heat transfer performance of the product was increased by around 5%.

5.
Int J Biol Macromol ; 133: 1201-1209, 2019 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-30986466

RESUMO

A previously unknown, water-soluble polysaccharide, named DOTP-B, was isolated from the roots of the plant Dioscorea opposita Thunb, a well-known edible and medicinal plant in China. DOTP-B was found to be neutral in charge, with an average molecular weight of 5623 Da. Monosaccharide composition analysis by GC-MS revealed that DOTP-B was a hetero-polysaccharide consisting of glucose and galactose at a molar ratio of 14.6:1.0. Structural features of DOTP-B were investigated with a combination of chemical and instrumental methods, including complete acid hydrolysis, periodate oxidation, methylation, GC-MS, FTIR and several NMR spectra. Highly correlated results demonstrated that the main chain of DOTP-B consisted of →4)-α-d-glc(1 → residues, with about 6% internal →6)-ß-d-gal(1 → residues. The antioxidant activity of DOTP-B was also evaluated as the EC50 values against DPPH and PTIO radicals were 2.1 ±â€¯0.1 mg/mL and 1.6 ±â€¯0.1 mg/mL, respectively. Therefore, the polysaccharide DOTP-B could be possibly developed as a promising natural antioxidant for application in medical and food industries.


Assuntos
Antioxidantes/química , Antioxidantes/isolamento & purificação , Dioscorea/química , Polissacarídeos/química , Polissacarídeos/isolamento & purificação , Água/química , Sequência de Carboidratos , Monossacarídeos/análise , Raízes de Plantas/química , Solubilidade
6.
Langmuir ; 35(4): 870-874, 2019 01 29.
Artigo em Inglês | MEDLINE | ID: mdl-30589554

RESUMO

The self-assembly of two-dimensional chiral 1 H,5 H-benzo(1,2- d:4,5- d')bistriazole (H2bbta) on a Ag(110) surface was investigated by ultra-high-vacuum scanning tunneling microscopy. The gradual formation of ordered structures by H2bbta molecules with the same chirality recognizing each other was observed as the annealing temperature was increased from 300 to 333 K. When the sample was annealed at 355 K, the homochiral structures were converted to coexisting structures containing λ-H2bbta and δ-H2bbta in a ratio of 6:1. Density functional theory (DFT) calculations revealed that thermally driven and intermolecular interactions induced chiral self-recognition to form enantiomorphous H2bbta structures in which N-H···N hydrogen bonds and C-H···N hydrogen bonds are the main attractive forces.

7.
Nanotechnology ; 29(39): 395301, 2018 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-29989565

RESUMO

Assembling large organic molecules into predesigned structures for nanoscale devices is a long-standing challenge. Here, we present the atom-scale precise repositions of individual fullerene molecules and molecule transportation over the micrometer scale on a Si(111) surface via reproducible and reversible vertical manipulation by a scanning tunneling microscopy tip. A two-rod abacus consisting of ten fullerene molecules was used to perform arithmetic operations with double digits. This opens the door for the use of larger organic molecules displaying intrinsic characteristics as complex molecular devices with novel functions.

8.
Phys Chem Chem Phys ; 20(21): 14374-14383, 2018 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-29770413

RESUMO

Herein, pressure-induced phase transitions of RDX up to 50 GPa were systematically studied under different compression conditions. Precise phase transition points were obtained based on high-quality Raman spectra with small pressure intervals. This favors the correctness of the theoretical formula for detonation and the design of a precision weapon. The experimental results indicated that α-RDX immediately transformed to γ-RDX at 3.5 GPa due to hydrostatic conditions and possible interaction between the penetrating helium and RDX, with helium gas as the pressure-transmitting medium (PTM). Mapping of pressure distribution in samples demonstrates that the pressure gradient is generated in the chamber and independent of other PTMs. The gradient induced the first phase transition starts at 2.3 GPa and completed at 4.1 GPa. The larger pressure gradient promoted phase transition in advance under higher pressures. Experimental results supported that there existed two conformers of AAI and AAE for γ-RDX, as proposed by another group. δ-RDX was considered to only occur in a hydrostatic environment around 18 GPa using helium as the PTM. This study confirms that δ-RDX is independent of PTM and exists under non-hydrostatic conditions. Evidence for a new phase (ζ) was found at about 28 GPa. These 4 phases have also been verified via XRD under high pressures. In addition to this, another new phase (η) may exist above 38 GPa, and it needs to be further confirmed in the future. Moreover, all the phase transitions were reversible after the pressure was released, and original α-RDX was always obtained at ambient pressure.

9.
ACS Omega ; 3(12): 18227-18233, 2018 Dec 31.
Artigo em Inglês | MEDLINE | ID: mdl-31458401

RESUMO

In situ Raman spectra of HoVO4 micro- and nanocrystals were obtained at high pressures up to 25.4 and 18.0 GPa at room temperature, respectively. The appearance of new peaks in the Raman spectra and the discontinuities of the Raman-mode shift provided powerful evidence for an irreversible zircon-to-scheelite structure transformation for HoVO4 microcrystals at 7.2 GPa and for HoVO4 nanocrystals at 8.7 GPa. The lattice contraction caused by the size effect was thought to be responsible for the different phase-transition pressures. Also, the higher stability of HoVO4 nanocrystals compared with the microcrystals was also confirmed using the Raman frequencies and pressure coefficients. The results of the phase transition of HoVO4 were compared with previously reported rare-earth orthovanadates, and the phase diagram of REVO4 with RE ionic radius at different pressures was presented.

10.
Sci Rep ; 7(1): 15114, 2017 11 08.
Artigo em Inglês | MEDLINE | ID: mdl-29118341

RESUMO

Serotonin transporter (SERT) is a classic target of drug discovery for neuropsychiatric and digestive disorders, and against those disorders, plants of Nardostachys genus have been valued for centuries in the systems of Traditional Chinese Medicine, Ayurvedic and Unani. Herein, chemical investigation on the roots and rhizomes of Nardostachys chinensis Batal. led to the isolation of forty sesquiterpenoids including six new aristolane-type sesquiterpenoids and six new nardosinane-type sesquiterprenoids. Their structures were elucidated by extensive spectroscopic methods, combined with analyses of circular dichroism and single-crystal X-ray diffraction data. To explore natural product scaffolds with SERT regulating activity, a high-content assay for measurement of SERT function in vitro was conducted to evaluate the SERT regulating properties of these isolates. In conclusion, eleven compounds could be potential natural product scaffolds for developing drug candidates targeting SERT. Among which, kanshone C of aristolane-type sesquiterpenoid inhibited SERT most strongly, while desoxo-nachinol A of nardosinane-type sesquiterpenoid instead enhanced SERT potently.


Assuntos
Nardostachys/química , Proteínas da Membrana Plasmática de Transporte de Serotonina/metabolismo , Inibidores de Captação de Serotonina/isolamento & purificação , Sesquiterpenos/isolamento & purificação , Produtos Biológicos/química , Produtos Biológicos/isolamento & purificação , Produtos Biológicos/farmacologia , Transporte Biológico/efeitos dos fármacos , Dicroísmo Circular , Cristalografia por Raios X , Estrutura Molecular , Raízes de Plantas/química , Rizoma/química , Inibidores de Captação de Serotonina/química , Inibidores de Captação de Serotonina/farmacologia , Sesquiterpenos/química , Sesquiterpenos/farmacologia
11.
Nat Nanotechnol ; 12(11): 1071-1076, 2017 11.
Artigo em Inglês | MEDLINE | ID: mdl-28920965

RESUMO

Building electronic components made of individual molecules is a promising strategy for the miniaturization and integration of electronic devices. However, the practical realization of molecular devices and circuits for signal transmission and processing at room temperature has proven challenging. Here, we present room-temperature intermolecular signal transfer and processing using SnCl2Pc molecules on a Cu(100) surface. The in-plane orientations of the molecules are effectively coupled via intermolecular interaction and serve as the information carrier. In the coupled molecular arrays, the signal can be transferred from one molecule to another in the in-plane direction along predesigned routes and processed to realize logical operations. These phenomena enable the use of molecules displaying intrinsic bistable states as complex molecular devices and circuits with novel functions.

12.
Neurochem Res ; 42(11): 3052-3060, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28819903

RESUMO

Amyloid plaques and neurofibrillary tangles are pathologic hallmarks of Alzheimer's disease (AD). Endoplasmic reticulum (ER) stress has been implicated in the loss of neurons in AD. The phosphatase and tensin homolog deleted on chromosome ten (PTEN) plays an important role in regulating neuronal survival processes. However, the direct effects of the PTEN on ER stress and apoptosis in AD have not been elucidated. In this study, we demonstrate that the expression of PTEN and ER stress related proteins, GRP78 and CHOP, increased in APP/PS1 transgenic AD mice compared with WT mice. A PTEN inhibitor, dipotassium bisperoxo-(5-hydroxypyridine-2-carboxyl)-oxovanadate (bpv) could decrease apoptosis, induce AKT phosphorylation and inhibit the ER stress response proteins in hippocampus in APP/PS1 transgenic AD model mice. Furthermore, treatment with the specific PI3K inhibitor, LY294002, significantly blocked the anti-apoptotic effects of bpv in AD mice. The expression in GRP78, CHOP and apoptosis levels by bpv was reversed after PI3K inhibitor treatment. Taken together, our results indicate that the neuroprotective role of bpv involves the suppression of ER stress via the activation of the PI3K/AKT signalling pathways in APP/PS1 transgenic AD model mice.


Assuntos
Doença de Alzheimer/metabolismo , Apoptose/fisiologia , Estresse do Retículo Endoplasmático/fisiologia , PTEN Fosfo-Hidrolase/metabolismo , Fosfatidilinositol 3-Quinases/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Doença de Alzheimer/genética , Animais , Apoptose/efeitos dos fármacos , Cromonas/farmacologia , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Masculino , Camundongos , Camundongos Transgênicos , Morfolinas/farmacologia , PTEN Fosfo-Hidrolase/antagonistas & inibidores , Proteínas Proto-Oncogênicas c-akt/antagonistas & inibidores , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia
13.
Chem Commun (Camb) ; 53(65): 9151-9154, 2017 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-28765848

RESUMO

We present for the first time an adjacent dehydrogenative homocoupling and cyclodehydrogenation reaction of mesityl groups to form a synthetic nanoribbon on Cu(110). Submolecular resolution scanning tunneling microscopy (STM) observations and density functional theory (DFT) calculations confirm the formation of an ethylene (-CH[double bond, length as m-dash]CH-) unit or an aromatic six-membered ring group.

14.
Bioorg Med Chem Lett ; 27(4): 875-879, 2017 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-28094186

RESUMO

Nardonaphthalenones A and B (1-2), one new apo-α-carotenone (3) and four new monoterpenoids (4, 8-9 and 11), along with six known compounds (5-7, 10, 12-13) were isolated from the dried roots and rhizomes of Nardostachys chinensis Batal. Their structures were elucidated by analysis of the spectroscopic data including NMR, HRESIMS and circular dichroism data. Furthermore, the serotonin transporter (SERT)-regulating activities of these isolates were evaluated, among them compound 3 showed the strongest enhancement activity while compound 12 showed a moderate inhibition activity on SERT.


Assuntos
Monoterpenos/química , Naftalenos/química , Nardostachys/química , Expressão Gênica/efeitos dos fármacos , Células HEK293 , Humanos , Espectroscopia de Ressonância Magnética , Conformação Molecular , Monoterpenos/isolamento & purificação , Monoterpenos/farmacologia , Naftalenos/isolamento & purificação , Naftalenos/farmacologia , Nardostachys/metabolismo , Raízes de Plantas/química , Raízes de Plantas/metabolismo , Rizoma/química , Rizoma/metabolismo , Proteínas da Membrana Plasmática de Transporte de Serotonina/química , Proteínas da Membrana Plasmática de Transporte de Serotonina/genética , Proteínas da Membrana Plasmática de Transporte de Serotonina/metabolismo
15.
Angew Chem Int Ed Engl ; 55(34): 9872-6, 2016 08 16.
Artigo em Inglês | MEDLINE | ID: mdl-27385550

RESUMO

Purely organic materials with room-temperature phosphorescence (RTP) are currently under intense investigation because of their potential applications in sensing, imaging, and displaying. Inspired by certain organometallic systems, where ligand-localized phosphorescence ((3) π-π*) is mediated by ligand-to-metal or metal-to-ligand charge transfer (CT) states, we now show that donor-to-acceptor CT states from the same organic molecule can also mediate π-localized RTP. In the model system of N-substituted naphthalimides (NNIs), the relatively large energy gap between the NNI-localized (1) π-π* and (3) π-π* states of the aromatic ring can be bridged by intramolecular CT states when the NNI is chemically modified with an electron donor. These NNI-based RTP materials can be easily conjugated to both synthetic and natural macromolecules, which can be used for RTP microscopy.

16.
Yao Xue Xue Bao ; 51(1): 100-4, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27405169

RESUMO

A new caffeate compound, (E)-erythro-syringylglyceryl caffeate (1), was isolated from the roots and rhizomes of Nardostachys chinensis Batal., together with nine known phenolic compounds, including (+)-licarin A (2), naringenin 4', 7-dimethyl ether (3), pinoresinol-4-O-ß-D-glucoside (4), caraphenol A (5), Z-miyabenol C (6), protocatechuic acid (7), caffeic acid (8), gallic acid (9) and vanillic acid (10). Their chemical structures were elucidated on the basis of spectroscopic data and physicochemical properties. Furthermore, this is the first report of compounds 2, 5 and 6 from Nardostachys genus.


Assuntos
Ácidos Cafeicos/isolamento & purificação , Nardostachys/química , Ácidos Cafeicos/química , Flavanonas/química , Flavanonas/isolamento & purificação , Furanos/química , Furanos/isolamento & purificação , Glucosídeos/química , Glucosídeos/isolamento & purificação , Hidroxibenzoatos/química , Hidroxibenzoatos/isolamento & purificação , Lignanas/química , Lignanas/isolamento & purificação , Raízes de Plantas/química , Rizoma/química , Ácido Vanílico/química , Ácido Vanílico/isolamento & purificação
17.
Chem Commun (Camb) ; 52(54): 8420-3, 2016 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-27302478

RESUMO

One-dimensional π-conjugated polymer chains with variable lengths have been synthesized successfully via thermal polymerization reaction on the Au(111) surface. Such polymer chains form parallel arrays along specific directions according to the initial assembly orientations of the close-packed Br-BTTN precursors.

18.
Chemistry ; 21(37): 12978-83, 2015 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-26216335

RESUMO

Cyclotrimerization-induced chiral supramolecular structures of 4-ethynyltriphenylamine (ETPA) have been synthesized on the Au(111) surface through alkyne-based reactions. Whereas the ETPA molecules adsorbed on the Au(111) surface remain inert and form a close-packed self-assembled structure at room temperature, the combination of scanning tunneling microscopy observations and theoretical calculations unambiguously reveal that the ETPA molecules cyclotrimerize to form new trimer-like species-1,3,5-tris[4-(diphenylamino)phenyl]benzene (TPAPB)-after annealing at 323 K. Further annealing drives these cyclotrimerized TPAPB molecules to form chiral hexagonal supramolecular structures with an extraordinary self-healing ability.

19.
Sci Rep ; 5: 9279, 2015 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-25797217

RESUMO

Effective optical constants of Ag thin films are precisely determined with effective thickness simultaneously by using an ellipsometry iterated with transmittance method. Unlike the bulk optical constants in Palik's database the effective optical constants of ultrathin Ag films are found to strongly depend on the thickness. According to the optical data two branches of thickness dispersion of surface plasmon energy are derived and agreed with theoretical predication. The thickness dispersion of bulk plasmon is also observed. The influence of substrate on surface plasmon is verified for the first time by using ellipsometry. The thickness dependent effective energy loss function is thus obtained based on this optical method for Ag ultrathin films. This method is also applicable to other ultrathin films and can be used to establish an effective optical database for ultrathin films.

20.
Int J Mol Med ; 35(1): 263-70, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25384498

RESUMO

Accumulating evidence suggests that anti-inflammatory agents and antioxidants have neuroprotective properties and may be beneficial in the treatment of neurodevelopental disorders, such as autism. In the present study, the possible neuroprotective properties of sulindac, a non-steroidal anti-inflammatory drug (NSAID), were investigated in vitro using cultured cortical neurons with valproic acid (VPA)-induced neurotoxicity, as well as in vivo through the behavioral analysis of rats prenatally exposed to VPA as a model of autism. VPA induced 4-hydroxynonenal (4-HNE) expression, reactive oxygen species (ROS) generation and decreased cell viability in primary cultured cortical neurons established from timed-pregnant (embryonic day 18) Wistar rat pups. However, co-incubation of the neurons with VPA and sulindac reduced oxidative stress and increased cell viability. The rats were administered an intraperitoneal injection with one of the following: VPA, sulindac, VPA and sulindac, or physiological saline, and their offspring were subjected to the open field test. During the test trials, repetitive/stereotypic-like movements for each rat were recorded and analyzed. The results revealed that treatment with both sulindac and VPA reduced the VPA-induced repetitive/stereotypic-like activity and the sulindac and VPA-treated animals responded better in the open field test compared to the VPA-treated animals. The results from the present study demonstrate that the antioxidant properties of sulindac may prove to be beneficial in the treatment of autism, suggesting that the upregulation of the Wnt/ß-catenin signaling pathway disrupts oxidative homeostasis and facilitates susceptibility to autism.


Assuntos
Transtornos dos Movimentos/etiologia , Transtornos dos Movimentos/metabolismo , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Estresse Oxidativo/efeitos dos fármacos , Sulindaco/farmacologia , Ácido Valproico/efeitos adversos , Animais , Células Cultivadas , Modelos Animais de Doenças , Feminino , Quinase 3 da Glicogênio Sintase/metabolismo , Glicogênio Sintase Quinase 3 beta , Exposição Materna , Gravidez , Efeitos Tardios da Exposição Pré-Natal , Ratos , Ratos Wistar , beta Catenina/metabolismo
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA