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1.
Arch Virol ; 165(1): 97-104, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31734749

RESUMO

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has spread globally and emerged as an urgent public health threat. Bacteriophages are considered an effective weapon against multidrug-resistant pathogens. In this study, we report a novel lytic phage, kpssk3, which is able to lyse CRKP and degrade exopolysaccharide (EPS). The morphological characteristics of kpssk3 observed by transmission electron microscopy, including a polyhedral head and a short tail, indicate that it belongs to the family Podoviridae. A one-step growth curve revealed that kpssk3 has a latent period of 10 min and a burst size of 200 plaque-forming units (pfu) per cell. kpssk3 was able to lyse 25 out of 27 (92.59%) clinically isolated CRKP strains, and it also exhibited high stability to changes in temperature and pH. kpssk3 has a linear dsDNA genome of 40,539 bp with 52.80% G+C content and 42 putative open reading frames (ORFs). No antibiotic resistance genes, virulence factors, or integrases were identified in the genome. Based on bioinformatic analysis, the tail fiber protein of phage kpssk3 was speculated to possess depolymerase activity towards EPS. By comparative genomics and phylogenetic analysis, it was determined that kpssk3 is a new T7-like virus and belongs to the subfamily Autographivirinae. The characterization and genomic analysis of kpssk3 will promote our understanding of phage biology and diversity and provide a potential strategy for controlling CRKP infection.


Assuntos
Farmacorresistência Bacteriana , Klebsiella pneumoniae/virologia , Podoviridae/classificação , Sequenciamento Completo do Genoma/métodos , Composição de Bases , Carbapenêmicos , Genoma Viral , Concentração de Íons de Hidrogênio , Lisogenia , Microscopia Eletrônica de Transmissão , Filogenia , Podoviridae/genética , Podoviridae/fisiologia , Termodinâmica , Proteínas da Cauda Viral/genética
2.
Acc Chem Res ; 53(1): 20-31, 2020 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-31869209

RESUMO

Oxidative post-translational modifications (OxiPTMs) of cysteine residues are the molecular foundation of thiol-based redox regulation that modulates physiological events such as cell proliferation, differentiation, and migration and, when dysregulated, can lead to biomolecule damage and cell death. Common OxiPTMs of cysteine thiols (-SH) include reversible modifications such as S-sulfenylation (-SOH), S-glutathionylation (-SSG), disulfide formation (-SSR), S-nitrosylation (-SNO), and S-sulfhydration (-SSH) as well as more biologically stable modifications like S-sulfinylation (-SO2H) and S-sulfonylation (-SO3H). In the past decade, our laboratory has developed first-in-class chemistry-based tools and proteomic methods to advance the field of thiol-based redox biology and oxidative stress. In this Account, we take the reader through the historical aspects of probe development and application in our laboratory, highlighting key advances in our understanding of sulfur chemistry, in the test tube and in living systems. Offering superior resolution, throughput, accuracy, and reproducibility, mass spectrometry (MS)-based proteomics coupled to chemoselective "activity-based" small-molecule probes is the most rigorous technique for global mapping of cysteine OxiPTMs. Herein, we describe the evolution of this field from indirect detection to state-of-the-art site-centric quantitative chemoproteomic approaches that enable mapping of physiological and pathological changes in cysteine oxidation. These methods enable protein and site-level identification, mechanistic studies, mapping fold-changes, and modification stoichiometry. In particular, this Account focuses on activity-based methods for profiling S-sulfenylation, S-sulfinylation, and S-sulfhydration with an eye toward new reactions and methodologies developed in our group as well as their applications that have shed new light on fundamental processes of redox biology. Among several classes of sulfenic acid probes, dimedone-based C-nucleophiles possess superior chemical selectivity and compatibility with tandem MS. Cell-permeable dimedone derivatives with a bioconjugation handle are capable of detecting of S-sulfenylation in living cells. In-depth screening of a C-nucleophile library has yielded several entities with significantly enhanced reactivity over dimedone while maintaining selectivity, and reversible linear C-nucleophiles that enable controlled target release. C-Nucleophiles have also been implemented in tag-switch methods to detect S-sulfhydration. Most recently, activity-based detection of protein S-sulfinylation with electrophilic nitrogen species (ENS), such as C-nitroso compounds and electron deficient diazines, offers significant advantages in simplicity-of-use and target specificity compared to label-free methods. When feasible, the rich information provided by site-centric quantitative proteomics should not be tainted by oxidation artifacts from cell lysis. Therefore, chemoselective probes that function in a native environment with low cytotoxicity, good cell-permeability, and competitive kinetics are desired in modern redox chemoproteomics approaches. As our understanding of sulfur chemistry and redox signaling evolves, newly discovered cysteine OxiPTMs in microorganisms, plants, cells, tissues, and disease models should innovatively promote mechanistic and therapeutic research.

3.
Med Sci Monit ; 25: 8352-8362, 2019 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-31693655

RESUMO

BACKGROUND Increasing antibiotic resistance and multidrug resistance (MDR) in patients with bloodstream infection (BSI) has resulted in treatment using bacteriophage. This study aimed to identify Gram-negative bacilli and Gram-positive cocci and antibiotic resistance in patients with BSI in a burn intensive care unit (BICU). The environment, including sewage systems, were investigated for the presence of lytic bacteriophage. MATERIAL AND METHODS Between January 2011 to December 2017, 486 patients with BSI were admitted to the BICU. Blood culture identified the main infectious organisms. Bacterial screening tests for antibiotic resistance included the D test and the modified Hodge test (MHT). Lytic bacteriophage was isolated from the environment. RESULTS In 486 patients with BSI, the main causative organisms were Gram-negative bacilli (64.6%), Gram-positive cocci (27.7%), and fungi (7.7%). The main pathogenic organisms that showed multidrug resistance (MDR) were Acinetobacter baumannii (26.0%), Staphylococcus aureus (16.8%), and Pseudomonas aeruginosa (14.2%). Bacteriophage was mainly isolated from Gram-negative bacilli. Screening of hospital and residential sewage systems identified increased levels of bacteriophage in hospital sewage. CONCLUSIONS The causative organisms of BSI and the presence of MDR in a hospital BICU were not typical, which supports the need for routine bacterial monitoring. Hospital sewage provides a potential source of bacteriophage for the treatment of MDR pathogenic bacteria.

4.
Plants (Basel) ; 8(10)2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31652528

RESUMO

Freezing tolerant tea cultivars are urgently needed. The tea cultivars with highly freezing tolerance showed resistance to freezing stress induced photoinhibition. Freezing sensitivity index (H) of 47 tea clonal cultivars was investigated after severe freezing winter in 2016. To develop instrumental methods for freezing tolerance selection, the maximum photochemical efficiency of photosystem II (PSII) (Fv/Fm) and leaf color indicator a on the Hunter color scale were determined on control group (non-frozen) and frozen group (being frozen at -15 °C for 2 h and then stood at 20 °C for 5 h) of the cultivars. When the two indicators were expressed as the ratios (RFv/Fm and Ra) of frozen group to control group, linear regression of the freezing sensitivity index (H) upon the RFv/Fm and Ra produced significant relationship respectively, i.e., H = 60.31 - 50.09 RFv/Fm (p < 0.01) and H = 30.03 - 10.82 Ra (p < 0.01). Expression of gene psbA encoding D1 protein and gene psbD encoding D2 protein in PSII showed that the frezzing tolerant tea cultivars maintained a high expression level of psbA after freezing stress, which is considered to be beneficial to de novo synthesis of D1 protein and sustaining PSII activity. These findings can provide instrumental tools for assessing freezing tolerance of tea cultivars in tea breeding program.

5.
Int J Mol Sci ; 20(10)2019 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-31108845

RESUMO

Anthracnose is a major leaf disease in tea plant induced by Colletotrichum, which has led to substantial losses in yield and quality of tea. The molecular mechanism with regards to responses or resistance to anthracnose in tea remains unclear. A de novo transcriptome assembly dataset was generated from healthy and anthracnose-infected leaves on tea cultivars "Longjing-43" (LJ43) and "Zhenong-139" (ZN139), with 381.52 million pair-end reads, encompassing 47.78 billion bases. The unigenes were annotated versus Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), National Center for Biotechnology Information (NCBI) non-redundant protein sequences (Nr), evolutionary genealogy of genes: Non-supervised Orthologous Groups (eggNOG) and Swiss-prot. The number of differential expression genes (DEGs) detected between healthy and infected leaves was 1621 in LJ43 and 3089 in ZN139. The GO and KEGG enrichment analysis revealed that the DEGs were highly enriched in catalytic activity, oxidation-reduction, cell-wall reinforcement, plant hormone signal transduction and plant-pathogen interaction. Further studies by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and high-performance liquid chromatography (HPLC) showed that expression of genes involved in endogenous salicylic acid biosynthesis and also accumulation of foliar salicylic acid are involved in the response of tea plant to anthracnose infection. This study firstly provided novel insight in salicylic acid acting as a key compound in the responses of tea plant to anthracnose disease. The transcriptome dataset in this study will facilitate to profile gene expression and metabolic networks associated with tea plant immunity against anthracnose.


Assuntos
Camellia sinensis/genética , Colletotrichum/patogenicidade , Perfilação da Expressão Gênica/métodos , Redes Reguladoras de Genes , Camellia sinensis/metabolismo , Camellia sinensis/microbiologia , Regulação da Expressão Gênica de Plantas , Ontologia Genética , Sequenciamento de Nucleotídeos em Larga Escala , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Folhas de Planta/genética , Proteínas de Plantas/genética , Ácido Salicílico/metabolismo
6.
Arch Virol ; 164(6): 1527-1533, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30900072

RESUMO

A novel virulent bacteriophage, φAbp2, infecting multidrug-resistant (MDR) Acinetobacter baumannii was isolated from the wastewater of a sewage management centre at Southwest Hospital, China. Transmission electron microscopy and phylogenetic analysis revealed that φAbp2 belongs to the subfamily Peduovirinae. A one-step growth curve demonstrated that φAbp2 had a latent period of 15 min, a lysis period of 35 min, and a burst size of 222 particles per infected host cell. Moreover, φAbp2 showed a relatively broad host range in local A. baumannii, and it also exhibited tolerance over a wider range of thermal and pH conditions. Genomic sequencing revealed that φAbp2 has a circular double-stranded DNA genome with no sequence similarity to our previously isolated φAbp1. Eighty-eight putative open reading frames (ORFs) encoding 41 proteins of known function and 47 of unknown function were identified, and the G/C content was 37.84%. φAbp2 is a new member of the subfamily Peduovirinae of the family Myoviridae. Its genome sequence is very similar to that of the A. baumannii phage LZ35.


Assuntos
Acinetobacter baumannii/virologia , Genoma Viral , Myoviridae/classificação , Myoviridae/genética , Análise de Sequência de DNA/métodos , Bacteriófagos/classificação , Bacteriófagos/genética , Bacteriófagos/isolamento & purificação , Composição de Bases , Farmacorresistência Bacteriana Múltipla , Microscopia Eletrônica de Transmissão , Anotação de Sequência Molecular , Myoviridae/isolamento & purificação , Fases de Leitura Aberta , Filogenia , Águas Residuárias/virologia
7.
Molecules ; 24(5)2019 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-30857144

RESUMO

There is epidemiological evidence showing that drinking green tea can lower the risk of esophageal cancer (EC). The effect is mainly attributed to tea polyphenols and their most abundant component, (-)-epigallocatechin-3-gallate (EGCG). The possible mechanisms of tumorigenesis inhibition of EGCG include its suppressive effects on cancer cell proliferation, angiogenesis, DNA methylation, metastasis and oxidant stress. EGCG modulates multiple signal transduction and metabolic signaling pathways involving in EC. A synergistic effect was also observed when EGCG was used in combination with other treatment methods.


Assuntos
Catequina/análogos & derivados , Neoplasias Esofágicas/tratamento farmacológico , Antineoplásicos/química , Antineoplásicos/farmacologia , Catequina/química , Catequina/farmacologia , Proliferação de Células/efeitos dos fármacos , Metilação de DNA/efeitos dos fármacos , Humanos , Polifenóis/química , Transdução de Sinais/efeitos dos fármacos , Chá
8.
Nat Commun ; 9(1): 5363, 2018 12 18.
Artigo em Inglês | MEDLINE | ID: mdl-30560893

RESUMO

The gain-of-function MUC5B promoter variant rs35705950 is the dominant risk factor for developing idiopathic pulmonary fibrosis (IPF). Here we show in humans that MUC5B, a mucin thought to be restricted to conducting airways, is co-expressed with surfactant protein C (SFTPC) in type 2 alveolar epithelia and in epithelial cells lining honeycomb cysts, indicating that cell types involved in lung fibrosis in distal airspace express MUC5B. In mice, we demonstrate that Muc5b concentration in bronchoalveolar epithelia is related to impaired mucociliary clearance (MCC) and to the extent and persistence of bleomycin-induced lung fibrosis. We also establish the ability of the mucolytic agent P-2119 to restore MCC and to suppress bleomycin-induced lung fibrosis in the setting of Muc5b overexpression. Our findings suggest that mucociliary dysfunction might play a causative role in bleomycin-induced pulmonary fibrosis in mice overexpressing Muc5b, and that MUC5B in distal airspaces is a potential therapeutic target in humans with IPF.


Assuntos
Predisposição Genética para Doença , Fibrose Pulmonar Idiopática/genética , Mucina-5B/genética , Mucina-5B/metabolismo , Depuração Mucociliar/genética , Mucosa Respiratória/patologia , Animais , Bleomicina/toxicidade , Modelos Animais de Doenças , Células Epiteliais/metabolismo , Células Epiteliais/patologia , Expectorantes/farmacologia , Expectorantes/uso terapêutico , Feminino , Mutação com Ganho de Função , Humanos , Fibrose Pulmonar Idiopática/induzido quimicamente , Fibrose Pulmonar Idiopática/tratamento farmacológico , Fibrose Pulmonar Idiopática/patologia , Pulmão/citologia , Pulmão/metabolismo , Pulmão/patologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Depuração Mucociliar/efeitos dos fármacos , Regiões Promotoras Genéticas/genética , Proteína C Associada a Surfactante Pulmonar/metabolismo , Mucosa Respiratória/citologia , Mucosa Respiratória/metabolismo
9.
Molecules ; 23(9)2018 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-30217074

RESUMO

Many in vitro studies have shown that tea catechins had vevarious health beneficial effects. However, inconsistent results between in vitro and in vivo studies or between laboratory tests and epidemical studies are observed. Low bioavailability of tea catechins was an important factor leading to these inconsistencies. Research advances in bioavailability studies involving absorption and metabolic biotransformation of tea catechins were reviewed in the present paper. Related techniques for improving their bioavailability such as nanostructure-based drug delivery system, molecular modification, and co-administration of catechins with other bioactives were also discussed.


Assuntos
Camellia sinensis/química , Catequina/farmacocinética , Animais , Disponibilidade Biológica , Catequina/química , Sistemas de Liberação de Medicamentos , Humanos , Nanoestruturas/administração & dosagem , Nanoestruturas/química , Extratos Vegetais/química , Extratos Vegetais/farmacocinética
10.
Sci Rep ; 8(1): 10106, 2018 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-29973624

RESUMO

Oceanic mesoscale eddies are common, especially in areas where zonal currents with meridional shear exists. The nonlinear effects complicate the analysis of mesoscale eddy dynamics. This study proposes a solitary (eddy) solution based on an asymptotic expansion of the nonlinear potential vorticity equation with a constant meridional shear of zonal current. This solution reveals several important consequences. For example, cyclonic (anticyclonic) eddies can be generated by the negative (positive) shear of the zonal current. Furthermore, the meridional structure of an eddy is asymmetrical, and the center of a cyclonic (anticyclonic) eddy tilts poleward (equatorward). Eddy width is inversely proportional to shear intensity. Eddy phase speed is proportional to shear intensity and the wave amplitude, and their spatial distribution show band-like pattern as they propagate westward. This nonlinear solitary solution is an extension of classical linear Rossby theory. Moreover, these findings could be applied to other areas with similar zonal current shear.

11.
Nutrients ; 10(5)2018 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-29789466

RESUMO

Neurodegenerative disease Alzheimer's disease (AD) is attracting growing concern because of an increasing patient population among the elderly. Tea consumption is considered a natural complementary therapy for neurodegenerative diseases. In this paper, epidemiological studies on the association between tea consumption and the reduced risk of AD are reviewed and the anti-amyloid effects of related bioactivities in tea are summarized. Future challenges regarding the role of tea in preventing AD are also discussed.


Assuntos
Doença de Alzheimer/prevenção & controle , Peptídeos beta-Amiloides/antagonistas & inibidores , Encéfalo/efeitos dos fármacos , Fármacos Neuroprotetores/uso terapêutico , Extratos Vegetais/uso terapêutico , Chá , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/epidemiologia , Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/metabolismo , Animais , Encéfalo/metabolismo , Encéfalo/patologia , Camellia sinensis/química , Cognição/efeitos dos fármacos , Humanos , Memória/efeitos dos fármacos , Pessoa de Meia-Idade , Degeneração Neural , Fármacos Neuroprotetores/isolamento & purificação , Estresse Oxidativo/efeitos dos fármacos , Extratos Vegetais/isolamento & purificação , Prognóstico , Fatores de Proteção , Recomendações Nutricionais , Fatores de Risco
12.
Molecules ; 23(2)2018 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-29462972

RESUMO

(-)-Epigallocatechin gallate (EGCG) has attracted significant research interest due to its health-promoting effects such as antioxidation, anti-inflammation and anti-cancer activities. However, its instability and poor bioavailability have largely limited its efficacy and application. Food-grade materials such as proteins, carbohydrates and lipids show biodegradability, biocompatibility and biofunctionality properties. Food-grade encapsulation systems are usually used to improve the bioavailability of EGCG. In the present paper, we provide an overview of materials and techniques used in encapsulating EGCG, in which the adsorption mechanisms of food-grade systems during in vitro digestion are reviewed. Moreover, the potential challenges and future work using food-grade encapsulates for delivering EGCG are also discussed.


Assuntos
Catequina/análogos & derivados , Composição de Medicamentos , Alimentos , Carboidratos/química , Catequina/química , Humanos , Lipídeos/química , Chá/química
13.
Materials (Basel) ; 10(2)2017 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-28772492

RESUMO

The nucleation undercooling of TiB2/7075 Al matrix composites, the microstructure observed after solidification at different cooling rate, and the size and distribution of TiB2 particles were investigated. The experimental results have shown that the grain sizes of TiB2/7075 Al matrix composites firstly decreased, then increased, and finally decreased again with the increase of TiB2 content. The nucleation undercooling of TiB2/7075 Al matrix composites first increased, then decreased, and finally increased again with the increase of TiB2 content when the cooling rates was 5 and 10 °C/min respectively, but kept decreasing with the increase of TiB2 content at a cooling rate of 20 °C/min. The melting and solidification process showed no significant change with the decrease of cooling rate in 9.0% TiB2/7075 Al matrix composites. Most small particles can act as heterogeneous nucleus, which induced grain growth and were captured into the grain by the solid/liquid interface. At the same time, most of the larger particles and a minority of the small TiB2 particles are pushed into the grain boundary; locating in the grain boundary can hinder the Al atoms from diffusing during the solidification process and restrain α-Al phase growth. The influence of particles shifted from dominating by locating to dominating by nucleation as the quantity of TiB2 particles increased.

14.
Bioorg Med Chem ; 25(11): 2817-2824, 2017 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-28404523

RESUMO

The pentacyclic guanidinium alkaloids (PGAs) are a family of marine natural products that possess a polycyclic guanidine-containing core and a long alkyl chain tethered spermidine-derived tail that is rarely observed in other natural products. These natural products exhibit potent activities on a wide range of organisms and therefore have attracted the attention of many synthetic chemists; however, the structure-activity relationships and mechanisms of action of PGAs remain largely elusive. Herein we summarize the structure, synthesis, toxicity and mechanisms of action of PGAs and highlight their potential as chemical probes and/or therapeutic leads.


Assuntos
Alcaloides/farmacologia , Antibacterianos/farmacologia , Antifúngicos/farmacologia , Antineoplásicos/farmacologia , Antiprotozoários/farmacologia , Antivirais/farmacologia , Guanidina/farmacologia , Alcaloides/síntese química , Alcaloides/química , Animais , Antibacterianos/síntese química , Antibacterianos/química , Antifúngicos/síntese química , Antifúngicos/química , Antineoplásicos/síntese química , Antineoplásicos/química , Antiprotozoários/síntese química , Antiprotozoários/química , Antivirais/síntese química , Antivirais/química , Guanidina/síntese química , Guanidina/química , Humanos , Estrutura Molecular , Relação Estrutura-Atividade
15.
Sci Rep ; 7: 40044, 2017 01 05.
Artigo em Inglês | MEDLINE | ID: mdl-28053307

RESUMO

Materials with a high density of heterophase interfaces, which are capable of absorbing and annihilating radiation-induced point defects, can exhibit a superior radiation tolerance. In this paper, we investigated the interaction behaviors of point defects and heterophase interfaces by implanting helium atoms into the ZrN/TaN multilayered nanofilms. It was found that the point defect-interface interaction on the two sides of the ZrN/TaN interface was asymmetric, likely due to the difference in the vacancy formation energies of ZrN and TaN. The helium bubbles could migrate from the ZrN layers into the TaN layers through the heterophase interfaces, resulting in a better crystallinity of the ZrN layers and a complete amorphization of the TaN layers. The findings provided some clues to the fundamental behaviors of point defects near the heterophase interfaces, which make us re-examine the design rules of advanced radiation-tolerant materials.

16.
Org Lett ; 18(20): 5308-5311, 2016 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-27690467

RESUMO

Plagiogyrin A (1) was first isolated from the fronds of Plagiogyria matsumureana. Structurally, it features an α-ketoaldehyde functional group in its hemiacetal form, fused in a cis-substituted lactone ring. We have successfully synthesized the skeleton of this natural product by employing a stereocontrolled aldol reaction followed by the installation of the α-ketoaldehyde moiety derived from the mild oxidation of an α-diazoketone. Finally, anhydrous acidic conditions released the protected diol and provided the required cyclized hemiacetal.

17.
Sci Rep ; 5: 18021, 2015 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-26658128

RESUMO

Many features like spin-orbit coupling, bias and magnetic fields applied, and so on, can strongly influence the Kondo effect. One of the consequences is Kondo peak splitting. However, Kondo peak splitting led by a local moment has not been investigated systematically. In this research we study theoretically electronic transport through a single-level quantum dot exchange coupled to a local magnetic moment in the Kondo regime. We focus on the Kondo peak splitting induced by an anisotropic exchange coupling between the quantum dot and the local moment, which shows rich splitting behavior. We consider the cases of a local moment with S = 1/2 and S = 1. The longitudinal (z-component) coupling plays a role of multivalued magnetic fields and the transverse (x, y-components) coupling lifts the degeneracy of the quantum dot, both of which account for the fine Kondo peak splitting structures. The inter-level or intra-level transition processes are identified in detail. Moreover, we find a Kondo dip at the Fermi level under the proper parameters. The possible experimental observations of these theoretical results should deepen our understanding of Kondo physics.

18.
Opt Lett ; 40(14): 3380-3, 2015 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-26176474

RESUMO

The generation and control of valley pseudospin currents are the core of valleytronics. Here, the photonic analogy for generation and control of valley pseudospin currents using the pseudomagnetic fields induced in strained graphene is investigated in a microwave regime. In photonic graphene with uniaxial distortion, photons in two different valleys experience pseudomagnetic fields with opposite signs, and valley-dependent propagations in bended paths are observed. The external-field-free photonic transportation behavior may be very useful in controlling the flow of light in future valley-polarized devices.

19.
Opt Express ; 23(4): 5126-33, 2015 Feb 23.
Artigo em Inglês | MEDLINE | ID: mdl-25836546

RESUMO

At the Dirac-like point at the Brillouin zone center, the photonic crystals (PhCs) can mimic a zero-index medium. In the band structure, an additional flat band of longitudinal mode will intersect the Dirac cone. This longitudinal mode can be excited in PhCs with finite sizes at the Dirac-like point. By introducing positional shift in the PhCs, we study the dependence of the longitudinal mode on the disorder. At the Dirac-like point, the transmission peak induced by the longitudinal mode decreases as the random degree increases. However, at a frequency slightly above the Dirac-like point, in which the longitudinal mode is absent, the transmission is insensitive to the disorder because the effective index is still near zero and the effective wavelength in the PhC is very large.

20.
Org Lett ; 17(4): 968-71, 2015 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-25642987

RESUMO

Monanchocidin A is a recently isolated pentacyclic guanidinium alkaloid that contains an unusual highly oxidized morpholinone fragment. Herein we report a rapid synthesis of this heterocyclic scaffold and confirm its structure. The key reaction involves an acid promoted hemiketalization/hemiaminalization of an α-hydroxyamide and α-ketoaldehyde that proceeds with exclusive regioselectivity and high diastereoselectivity to form the natural scaffold in moderate to high yield.


Assuntos
Alcaloides/síntese química , Guanidina/análogos & derivados , Morfolinas/síntese química , Alcaloides/química , Guanidina/síntese química , Guanidina/química , Estrutura Molecular , Morfolinas/química , Estereoisomerismo
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