Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 124
Filtrar
1.
Phys Chem Chem Phys ; 2020 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-32578603

RESUMO

The cooling-induced formation of a hydrate in aqueous NaCl solutions was probed using terahertz time-domain spectroscopy (THz-TDS). It was found that the NaCl hydrate formation is accompanied by the emergence of four new absorption peaks at 1.60, 2.43, 3.34 and 3.78 THz. Combining X-ray diffraction measurements with solid-state based density functional theory (DFT) calculations, we assign the observed terahertz absorption peaks to the vibrational modes of the formed NaCl·2H2O hydrate during cooling. This work shows that THz-TDS based analysis has great potential in studying ionic hydrates and the newly revealed collective vibrational modes could be sensitive indicators to achieve quantitative analysis in phase transitions and lattice dynamics.

2.
Mar Pollut Bull ; 154: 111039, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32174492

RESUMO

Heavy metals (HMs) in aquaculture-influenced sediments pose a threat to both aquatic ecosystems and human health via aquatic product intake. Based on a long-term (from 2011 to 2018) study, the concentrations of five HMs in oyster-cultured sediments in the Maowei Estuary, China, were ranked as follows: Pb (17.58 ± 10.82 mg/kg) > Cu (17.15 ± 8.61 mg/kg) > As (10.27 ± 5.24 mg/kg) > Cd (0.16 ± 0.14 mg/kg) > Hg (0.067 ± 0.033 mg/kg). These concentrations were all close to the guide values in China and those reported in other studies. However, through the Mann-Kendall test, Cu showed obvious increasing interannual trends, and according to ecological risk assessment, the sediments were highly contaminated with Cu and Hg. The health risks to local residents via oyster intake showed that both noncarcinogenic and carcinogenic risk did not exceed the safety criteria (THQ = 1, TCR = 10-6). The current study suggests that ecological and human health risks be integrated to control HMs in the Maowei Estuary.


Assuntos
Monitoramento Ambiental , Metais Pesados , Ostreidae , Poluentes Químicos da Água , Animais , China , Ecossistema , Estuários , Sedimentos Geológicos , Humanos , Medição de Risco
3.
Spectrochim Acta A Mol Biomol Spectrosc ; 225: 117509, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31606660

RESUMO

The low-frequency vibrational properties of D-, L- and DL-pyroglutamic acid (PGA) have been investigated with the terahertz time-domain spectroscopy (THz-TDS) from 0.5 to 4.5 THz. The enantiomers (D- and L-PGA) present similar absorption spectra, while the spectrum of racemate (DL-PGA) is obviously different. The temperature-dependent THz spectra of different PGA were recorded in the range of 293-83 K. The spectral changes during the cooling process suggest that D- and L-PGA undergo a structural phase transition, and no phase change of DL-PGA was found. The results indicate that THz spectroscopy is highly sensitive to the crystal structure of molecules. The density functional theory (DFT) calculations based on the crystal structures were performed to simulate the sample's THz spectra. It was demonstrated that the characteristic resonant absorption peaks of the enantiomeric and racemic PGA in the low-frequency THz region originate from the different vibrations, which corresponding to the specific structures and intermolecular interactions. The conformational diversity and fluctuation may help to understand the properties of PGA in biochemistry and functional material.

4.
Spectrochim Acta A Mol Biomol Spectrosc ; 225: 117476, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31470346

RESUMO

As the building blocks of proteins, amino acids serve vital metabolic functions in addition to protein synthesis and thus attract enormous interest. Here we reported the far-infrared optical properties of L-cysteine (Lcys) and its hydrochloride monohydrate (LCHM) characterized by terahertz time-domain spectroscopy. The Lcys and LCHM exhibit quite distinct characteristics in the terahertz region due to diverse collective vibrations of the molecules, which is further confirmed by the solid-state density functional theory (DFT) calculations. The presented studies indicate that the intermolecular hydrogen bonds play a critical role in the far-infrared terahertz response of Lcys and LCHM.

5.
ACS Appl Mater Interfaces ; 12(2): 2566-2571, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31854183

RESUMO

PbSe colloidal quantum dots (CQDs) are widely used in solar cells because of their tunable band gap, solution processability, and efficient multiple exciton generation effect. The most efficient PbSe CQD solar cells use high-temperature-processed ZnO as the electron transport layer (ETL), limiting their applications in flexible photovoltaics. Currently, low-temperature solution-processed SnO2 has been demonstrated as an efficient ETL for high-efficient PbS CQD and perovskite solar cells because of less parasitic light absorption and higher electron mobility. Herein, we introduce low-temperature solution-processed SnO2 as ETL for PbSe CQD solar cells, and fabricate the PbSe CQD absorber layer with a one-step spin-coating method. The champion device with the structure of FTO (SnO2:F)/SnO2/PbSe-PbI2/PbS-EDT (1,2-ethanedithiol)/Au achieves a high open-circuit voltage of 577.1 mV, a short-circuit current density of 24.87 mA cm-2, a fill factor of 67%, and an impressive power conversion efficiency of 9.67%. Our results pave the way for the development of low-temperature flexible PbSe CQD solar cells.

6.
Chem Commun (Camb) ; 55(100): 15141-15144, 2019 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-31789329

RESUMO

The terahertz dynamics of water nanodroplets confined in phospholipid reverse micelles have been developed as a probe to explore the interactions of metal ions with lipid membrane interfaces. The terahertz absorption coefficients of reverse micelles vary greatly with different Cu2+ concentrations and with different headgroups. The results proved that the metal ion effects on water dynamics near a membrane surface can be detected via terahertz spectroscopy, thus providing a novel tool for investigating ion-lipid interactions.


Assuntos
Micelas , Fosfolipídeos/química , Cobre/química , Íons/química , Nanoestruturas/química , Fosfatidilgliceróis/química , Espectroscopia Terahertz
7.
J Phys Chem Lett ; 10(24): 7665-7671, 2019 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-31769296

RESUMO

0D-2D mixed-dimensional hybrid structures, which combine tunable optical properties of 0D quantum dots (QDs) and high transport mobilities of 2D layered materials, have shown great potential in optoelectronic applications. Understanding charge transfer dynamics at the 0D-2D interface is essential but still lacking. Here, using PbS QD/WSe2 system, by simply controlling PbS QD size, we show a tunable hole transfer (HT) rate by more than 4 orders of magnitude (from ∼1 ns to <100 fs) and, interestingly, transition from the weak to strong coupling regime due to quantum confinement effect. In contrast to reported layer-dependent energy transfer dynamics, we observe a robust HT rate against WSe2 layer number, which can be ascribed to a subtle change of WSe2 valence band structure with layer number. Our results are important to not only fundamental understanding of charge transfer behavior at nanoscale low-dimensional interface but also help design next-generation mixed-dimensional optoelectronic devices.

8.
Opt Express ; 27(19): 26459-26470, 2019 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-31674527

RESUMO

Herein, we demonstrate one of the highest terahertz group delay of 42.4 ps achieved experimentally at 0.23 THz, on a flexible planar metamaterial. The unit cell of metasurface is made up of a textured closed cavity and another experimentally concentric metallic arc. By tuning the central angle of the metallic arc, its intrinsic dipolar mode is in destructive interference with the spoof localized surface plasmon (SLSP) on textured closed cavity, which results in a plasmon-induced transparency phenomenon. The measured transmittances of as-fabricated samples using terahertz-time domain spectroscopy validate numerical results using extended coupled Lorentz oscillator model. It is found that the coupling coefficient and damping ratio of SLSP relies on the radius of the ring structure of textured closed cavity. As a consequence, the slow light maximum values become manoeuverable in strength at certain frequencies of induced transparency windows. To the best of our knowledge, our experimental result is currently the highest value demonstrated so far within metasurface at terahertz band.

9.
ACS Appl Mater Interfaces ; 11(51): 48551-48555, 2019 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-31782302

RESUMO

The photophysics of charge-transfer and recombination mechanisms in a heterojunction structure of CdSe/CdS/Au quantum dots (QDs) are studied by temperature-dependent steady-state photoluminescence (PL) and time-resolved PL (TRPL). We manipulate the charge transfer from core to shell surface by varying the tunneling barrier height resulting from temperature variation and the barrier width resulting from shell thickness variation. The charge-transfer process, which can be described by a tunneling transmission model, is manifested by two competitive recombination processes, an intrinsic exciton emission and a trap emission in the near-infrared (NIR) range. Our study establishes the photophysics foundation for the core/shell/metal application in photocatalyst and optoelectronics.

10.
Elife ; 82019 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-31571584

RESUMO

Free heme is cytotoxic as exemplified by hemolytic diseases and genetic deficiencies in heme recycling and detoxifying pathways. Thus, intracellular accumulation of heme has not been observed in mammalian cells to date. Here we show that mice deficient for the heme transporter SLC48A1 (also known as HRG1) accumulate over ten-fold excess heme in reticuloendothelial macrophage lysosomes that are 10 to 100 times larger than normal. Macrophages tolerate these high concentrations of heme by crystallizing them into hemozoin, which heretofore has only been found in blood-feeding organisms. SLC48A1 deficiency results in impaired erythroid maturation and an inability to systemically respond to iron deficiency. Complete heme tolerance requires a fully-operational heme degradation pathway as haplo insufficiency of HMOX1 combined with SLC48A1 inactivation causes perinatal lethality demonstrating synthetic lethal interactions between heme transport and degradation. Our studies establish the formation of hemozoin by mammals as a previously unsuspected heme tolerance pathway.


Assuntos
Heme/toxicidade , Hemeproteínas/metabolismo , Macrófagos/metabolismo , Animais , Heme Oxigenase-1/metabolismo , Hemeproteínas/deficiência , Proteínas de Membrana/metabolismo , Camundongos
11.
Chin J Nat Med ; 17(9): 672-681, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31526502

RESUMO

Evidence continues to grow on potential health risks associated with Ginkgo biloba and its constituents. While biflavonoid is a subclass of the flavonoid family in Ginkgo biloba with a plenty of pharmacological properties, the potential toxicological effects of biflavonoids remains largely unknown. Thus, the aim of this study was to investigate the in vitro and in vivo toxicological effects of the biflavonoids from Ginkgo biloba (i.e., amentoflavone, sciadopitysin, ginkgetin, isoginkgetin, and bilobetin). In the in vitro cytotoxicity test, the five biflavonoids all reduced cell viability in a dose-dependent manner in human renal tubular epithelial cells (HK-2) and human normal hepatocytes (L-02), indicating they might have potential liver and kidney toxicity. In the in vivo experiments, after intragastrical administration of these biflavonoids at 20 mg·kg-1·d-1 for 7 days, serum biochemical analysis and histopathological examinations were performed. The activity of alkaline phosphatase was significantly increased after all the biflavonoid administrations and widespread hydropic degeneration of hepatocytes was observed in ginkgetin or bilobetin-treated mice. Moreover, the five biflavonoids all induced acute kidney injury in treated mice and the main pathological lesions were confirmed to the tubule, glomeruli, and interstitium injuries. As the in vitro and in vivo results suggested that these biflavonoids may be more toxic to the kidney than the liver, we further detected the mechanism of biflavonoids-induced nephrotoxicity. The increased TUNEL-positive cells were detected in kidney tissues of biflavonoids-treated mice, accompanied by elevated expression of proapoptotic protein BAX and unchanged levels of antiapoptotic protein BCL-2, indicating apoptosis was involved in biflavonoids-induced nephrotoxicity. Taken together, our results suggested that the five biflavonoids from Ginkgo biloba may have potential hepatic and renal toxicity and more attentions should be paid to ensure Ginkgo biloba preparations safety.


Assuntos
Biflavonoides/toxicidade , Ginkgo biloba/química , Rim/efeitos dos fármacos , Fígado/efeitos dos fármacos , Animais , Apoptose/efeitos dos fármacos , Biflavonoides/química , Biomarcadores/sangue , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Feminino , Hepatócitos/efeitos dos fármacos , Hepatócitos/metabolismo , Hepatócitos/patologia , Humanos , Rim/metabolismo , Rim/patologia , Fígado/metabolismo , Fígado/patologia , Camundongos Endogâmicos BALB C , Proteína X Associada a bcl-2/metabolismo
12.
ACS Nano ; 13(8): 9028-9037, 2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31408313

RESUMO

As an emerging two-dimensional semiconductor, Bi2O2Se has recently attracted broad interests in optoelectronic devices for its superior mobility and ambient stability, whereas the diminished photoresponse near its inherent indirect bandgap (0.8 eV or λ = 1550 nm) severely restricted its application in the broad infrared spectra. Here, we report the Bi2O2Se nanosheets based hybrid photodetector for short wavelength infrared detection up to 2 µm via PbSe colloidal quantum dots (CQDs) sensitization. The type II interfacial band offset between PbSe and Bi2O2Se not only enhanced the device responsivity compared to bare Bi2O2Se but also sped up the response time to ∼4 ms, which was ∼300 times faster than PbSe CQDs. It was further demonstrated that the photocurrent in such a zero-dimensional-two-dimensional hybrid photodetector could be efficiently tailored from a photoconductive to photogate dominated response under external field effects, thereby rendering a sensitive infrared response >103 A/W at 2 µm. The excellent performance up to 2 µm highlights the potential of field-effect modulated Bi2O2Se-based hybrid photodetectors in pursuing highly sensitive and broadband photodetection.

13.
Mar Pollut Bull ; 146: 945-954, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31426242

RESUMO

This study uses multivariate statistics to analyze hydrochemical spatial-temporal variations in the Maowei Sea of Beibu Gulf, South China Sea and evaluates its susceptibility to nutrient enrichment by a risk model. The seasonal variations of sea surface temperature (T), salinity (S), pH, dissolved oxygen (DO), chemical oxygen demand, transparency, total suspended particulate (TSP), petroleum hydrocarbons (PHCs), NO2-, and SiO32- were mainly driven by the meteorological factors (precipitation and air temperature), while NO3-, NH4+, and PO43- content were more likely related to the point-source factors. The spatial and seasonal variations of T, DO, TSP, PHCs, and SiO32- might also be affected by sea-source factors such as thermal water discharge from adjacent parts of the Beibu Gulf. The sea's susceptibility to nutrient enrichment was moderate, and is mainly affected by precipitation, temperature, and high irradiation. The results present the complexity of natural and anthropogenic influences on a small subtropic estuary.


Assuntos
Monitoramento Ambiental , Estuários , Eutrofização , Água do Mar/química , Poluentes Químicos da Água/análise , China , Monitoramento Ambiental/métodos , Humanos , Medição de Risco , Estações do Ano , Tempo (Meteorologia)
15.
Adv Mater ; 31(33): e1900593, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31222874

RESUMO

Low-cost solution-processed lead chalcogenide colloidal quantum dots (CQDs) have garnered great attention in photovoltaic (PV) applications. In particular, lead selenide (PbSe) CQDs are regarded as attractive active absorbers in solar cells due to their high multiple-exciton generation and large exciton Bohr radius. However, their low air stability and occurrence of traps/defects during film formation restrict their further development. Air-stable PbSe CQDs are first synthesized through a cation exchange technique, followed by a solution-phase ligand exchange approach, and finally absorber films are prepared using a one-step spin-coating method. The best PV device fabricated using PbSe CQD inks exhibits a reproducible power conversion efficiency of 10.68%, 16% higher than the previous efficiency record (9.2%). Moreover, the device displays remarkably 40-day storage and 8 h illuminating stability. This novel strategy could provide an alternative route toward the use of PbSe CQDs in low-cost and high-performance infrared optoelectronic devices, such as infrared photodetectors and multijunction solar cells.

16.
Small ; 15(28): e1901606, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31140743

RESUMO

Strong near-surface electromagnetic field formed by collective oscillation of electrons on Cu nanostructure a shows a strong dependence on geometry, offering a promising approach to boost the light absorption of ZnO photoactive layers with enhanced plasmon scattering. Here, a facile way to fabricate UV photodetectors with tunable configuration of the self-assembled Cu nanostructures on ZnO thin films is reported. The incident lights are effectively confined in ZnO photoactive layers with the existence of the uplayer Cu nanostructures, and the interdiffusion of Cu atoms during fabrication of the Cu nanostructures can improve the carrier transfer in ZnO thin films. The optical properties of the hybrid architectures are successfully tailored over a control of the geometric evolution of the Cu nanostructures, resulting in significantly enhanced photocurrent and responsivity of 2.26 mA and 234 A W-1 under a UV light illumination of 0.62 mW cm-2 at 10 V, respectively. The photodetectors also exhibit excellent reproducibility, stability, and UV-visible rejection ratio (R370 nm /R500 nm ) of ≈370, offering an approach of high-performance UV photodetectors for practical applications.

17.
Adv Sci (Weinh) ; 6(9): 1802202, 2019 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-31065525

RESUMO

The growth of nanocrystals has widely been researched recently through an in situ high-resolution transmission electron microscopy technique, which reveals the process of morphological and structural evolutions. For nanocrystals, the underlying growth modes are mostly determined by growth environment and crystal morphology. Here, the direct growth process of the PbSe nanocrystals via controlling the temperature is clearly observed. The results show that the PbSe nanocrystals start growth following oriented attachment growth mode, and then change to growth with grain boundary migration at moderate temperature as the heat activated nanocrystals gather together with decreased degree of freedom for crystal rotation. During the grain boundary migration, the smaller nanocrystals are inclined to be assimilated by larger ones through interfacial atom reconfigurations, which are observed to take place through strain mediated atom migration. The growth mode changes in different growth states with a hybrid growth mode of oriented attachment and grain boundary migration during the whole growth process.

18.
Sci Rep ; 9(1): 6205, 2019 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-30996226

RESUMO

A terahertz (THz) electromagnetically-induced transparency (EIT) phenomenon is observed from two types of self-complementary meta-molecules (MMs) based on rectangular shaped electric split-ring resonators (eSRR) on Croatian checkerboard. Each MM contains a couple of identical size eSRRs and a couple of structural inversed eSRRs twisted π/2 in checkerboard pattern. In the first type of MM (type-I), the gap is in the middle line of eSRR. In the second type of MM (type-II), the gap is on the two arms of eSRR. Both types of MMs exhibit EIT effect. A maximum 20 ps group delay is observed at the transparency window of 0.63 THz in type-I MM; while a maximum 6.0 ps group delay is observed at the transparent window of 0.60 THz in type-II MM. The distribution of surface currents and electrical energy reveals that only CeSRR contribute to the transparency window as well as the side-modes in type-I MM, where the current leakage via contact point contributes to the low-frequency side-mode, and the coupled local inductive-capacitive (LC) oscillation in CeSRRs contributes to the high-frequency side-mode. In type-II MM, however, the localized dipolar oscillator of CeSRR contributes to the low-frequency side-mode; while the hybridization of dipole oscillation on eSRR and LC resonance on CeSRR contributes to the high-frequency side-modes. Our experimental findings manifest a new approach to develop THz slow-light devices.

19.
Adv Mater ; 31(16): e1900458, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30811706

RESUMO

Ionic-liquid-gating- (ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO2.5 , VO2 , WO3 , etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo2 O4 , an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo2 O4 from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution.

20.
Analyst ; 144(8): 2504-2510, 2019 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-30638228

RESUMO

The neurotransmitter norepinephrine (NE) was investigated by broadband terahertz time-domain spectroscopy (THz-TDS) in the air-plasma system range from 0.5 to 18.2 THz. NE has a unique absorption spectrum in the THz band, which can be used as a characteristic fingerprint for molecular detection and identification. The temperature-dependent THz spectra of NE were recorded in the range from 83 to 293 K, and a blue-shift of the absorption peaks was observed as the temperature decreased. A solid-state density functional theory (DFT) calculation was implemented to better understand the low-frequency vibrational property of NE, and the calculated results agree well with the THz experimental observations. This result suggests that the broadband THz system can obtain more abundant spectral signals of NE and each THz resonance peak has its own specific vibrational mode, which corresponds to a specific structure and interaction. Even with the adjacent absorption peaks, the vibrational behaviors are different. The deformation of the aromatic ring and the flexibility of the side chain directly affect the NE molecular conformation, which may be closely associated with the receptor binding preference for the neurotransmitter. The conformational diversity of NE may help to understand the biological function of the neurotransmitter in the nervous system.


Assuntos
Neurotransmissores/química , Norepinefrina/química , Modelos Químicos , Conformação Molecular , Neurotransmissores/efeitos da radiação , Norepinefrina/efeitos da radiação , Teoria Quântica , Temperatura , Radiação Terahertz , Espectroscopia Terahertz/métodos , Vibração
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA