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1.
Adv Mater ; 32(1): e1905504, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31736228

RESUMO

2D hexagonal boron nitride (hBN) is a wide-bandgap van der Waals crystal with a unique combination of properties, including exceptional strength, large oxidation resistance at high temperatures, and optical functionalities. Furthermore, in recent years hBN crystals have become the material of choice for encapsulating other 2D crystals in a variety of technological applications, from optoelectronic and tunneling devices to composites. Monolayer hBN, which has no center of symmetry, is predicted to exhibit piezoelectric properties, yet experimental evidence is lacking. Here, by using electrostatic force microscopy, this effect is observed as a strain-induced change in the local electric field around bubbles and creases, in agreement with theoretical calculations. No piezoelectricity is found in bilayer and bulk hBN, where the center of symmetry is restored. These results add piezoelectricity to the known properties of monolayer hBN, which makes it a desirable candidate for novel electromechanical and stretchable optoelectronic devices, and pave a way to control the local electric field and carrier concentration in van der Waals heterostructures via strain. The experimental approach used here also shows a way to investigate the piezoelectric properties of other materials on the nanoscale by using electrostatic scanning probe techniques.

2.
ACS Nano ; 13(9): 10520-10534, 2019 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-31393700

RESUMO

Control of impurity concentrations in semiconducting materials is essential to device technology. Because of their intrinsic confinement, the properties of two-dimensional semiconductors such as transition metal dichalcogenides (TMDs) are more sensitive to defects than traditional bulk materials. The technological adoption of TMDs is dependent on the mitigation of deleterious defects and guided incorporation of functional foreign atoms. The first step toward impurity control is the identification of defects and assessment of their electronic properties. Here, we present a comprehensive study of point defects in monolayer tungsten disulfide (WS2) grown by chemical vapor deposition using scanning tunneling microscopy/spectroscopy, CO-tip noncontact atomic force microscopy, Kelvin probe force spectroscopy, density functional theory, and tight-binding calculations. We observe four different substitutional defects: chromium (CrW) and molybdenum (MoW) at a tungsten site, oxygen at sulfur sites in both top and bottom layers (OS top/bottom), and two negatively charged defects (CD type I and CD type II). Their electronic fingerprints unambiguously corroborate the defect assignment and reveal the presence or absence of in-gap defect states. CrW forms three deep unoccupied defect states, two of which arise from spin-orbit splitting. The formation of such localized trap states for CrW differs from the MoW case and can be explained by their different d shell energetics and local strain, which we directly measured. Utilizing a tight-binding model the electronic spectra of the isolectronic substitutions OS and CrW are mimicked in the limit of a zero hopping term and infinite on-site energy at a S and W site, respectively. The abundant CDs are negatively charged, which leads to a significant band bending around the defect and a local increase of the contact potential difference. In addition, CD-rich domains larger than 100 nm are observed, causing a work function increase of 1.1 V. While most defects are electronically isolated, we also observed hybrid states formed between CrW dimers. The important role of charge localization, spin-orbit coupling, and strain for the formation of deep defect states observed at substitutional defects in WS2 as reported here will guide future efforts of targeted defect engineering and doping of TMDs.

3.
Chem Soc Rev ; 46(15): 4387-4399, 2017 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-28640314

RESUMO

This tutorial review presents an overview of the basic theoretical aspects of two-dimensional (2D) crystals. We revise essential aspects of graphene and the new families of semiconducting 2D materials, like transition metal dichalcogenides or black phosphorus. Minimal theoretical models for various materials are presented. Some of the exciting new possibilities offered by 2D crystals are discussed, such as manipulation and control of quantum degrees of freedom (spin and pseudospin), confinement of excitons, control of the electronic and optical properties with strain engineering, or unconventional superconducting phases.

6.
Mol Genet Metab ; 119(4): 338-343, 2016 12.
Artigo em Inglês | MEDLINE | ID: mdl-27743858

RESUMO

Annexin A6 is a multicompetent, multifunctional protein involved in several biological processes within and outside of the cell. Whereas HeLa cells express annexin A6 only as a 68/67-kDa doublet, indicating alternative splicing (Smith PD et al. (1994) Proc Natl Acad Sci USA 91, 2713-2717), the GMO2784 human fibroblast cell line expresses two additional isoforms at 64 and 58kDa. In both cell lines, annexin A6 is located intracellularly and on the plasma membrane. In vitro eukaryotic protein synthesis of pIRESneoAnxA6 cDNA and pIRESneoAnxA6/Met1- or Met33- using a reticulocyte lysate coupled transcription/translation system revealed that this gene contains two translation start codons, Met1 and Met33. Immunoprecipitation of the products obtained from the transcription/translation system using various anti-annexin A6 antibodies confirmed the presence of several isoforms and suggested that this protein might be present in different configurations.


Assuntos
Processamento Alternativo/genética , Anexina A6/genética , Iniciação Traducional da Cadeia Peptídica , Isoformas de Proteínas/genética , Anexina A6/biossíntese , Sequência de Bases , Linhagem Celular , Membrana Celular , Códon de Iniciação/genética , DNA Complementar , Fibroblastos , Regulação da Expressão Gênica/genética , Humanos , Isoformas de Proteínas/biossíntese
7.
Nano Lett ; 16(5): 2931-7, 2016 05 11.
Artigo em Inglês | MEDLINE | ID: mdl-27042865

RESUMO

Controlling the bandgap through local-strain engineering is an exciting avenue for tailoring optoelectronic materials. Two-dimensional crystals are particularly suited for this purpose because they can withstand unprecedented nonhomogeneous deformations before rupture; one can literally bend them and fold them up almost like a piece of paper. Here, we study multilayer black phosphorus sheets subjected to periodic stress to modulate their optoelectronic properties. We find a remarkable shift of the optical absorption band-edge of up to ∼0.7 eV between the regions under tensile and compressive stress, greatly exceeding the strain tunability reported for transition metal dichalcogenides. This observation is supported by theoretical models that also predict that this periodic stress modulation can yield to quantum confinement of carriers at low temperatures. The possibility of generating large strain-induced variations in the local density of charge carriers opens the door for a variety of applications including photovoltaics, quantum optics, and two-dimensional optoelectronic devices.

8.
J Phys Condens Matter ; 27(31): 313201, 2015 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-26199038

RESUMO

One of the fascinating properties of the new families of two-dimensional crystals is their high stretchability and the possibility to use external strain to manipulate, in a controlled manner, their optical and electronic properties. Strain engineering, understood as the field that study how the physical properties of materials can be tuned by controlling the elastic strain fields applied to it, has a perfect platform for its implementation in the atomically thin semiconducting materials. The object of this review is to give an overview of the recent progress to control the optical and electronics properties of 2D crystals, by means of strain engineering. We will concentrate on semiconducting layered materials, with especial emphasis in transition metal dichalcogenides (MoS2, WS2, MoSe2 and WSe2). The effect of strain in other atomically thin materials like black phosphorus, silicene, etc, is also considered. The benefits of strain engineering in 2D crystals for applications in nanoelectronics and optoelectronics will be revised, and the open problems in the field will be discussed.

9.
Nano Lett ; 15(1): 218-23, 2015 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-25457561

RESUMO

Two-dimensional (2D) hexagonal boron nitride (BN) nanosheets are excellent dielectric substrate for graphene, molybdenum disulfide, and many other 2D nanomaterial-based electronic and photonic devices. To optimize the performance of these 2D devices, it is essential to understand the dielectric screening properties of BN nanosheets as a function of the thickness. Here, electric force microscopy along with theoretical calculations based on both state-of-the-art first-principles calculations with van der Waals interactions under consideration, and nonlinear Thomas-Fermi theory models are used to investigate the dielectric screening in high-quality BN nanosheets of different thicknesses. It is found that atomically thin BN nanosheets are less effective in electric field screening, but the screening capability of BN shows a relatively weak dependence on the layer thickness.

10.
Phys Rev Lett ; 113(10): 106802, 2014 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-25238376

RESUMO

Black phosphorus exhibits a high degree of band anisotropy. However, we find that its in-plane static screening remains relatively isotropic for momenta relevant to elastic long-range scattering processes. On the other hand, the collective electronic excitations in the system exhibit a strong anisotropy. Band nonparabolicity, due to interband couplings, leads to a plasmon frequency which scales as nß, where n is the carrier concentration, and ß<1/2. Screening and charge distribution in the out-of-plane direction are also studied using a nonlinear Thomas-Fermi model.

11.
Nucleic Acids Res ; 42(11): 6885-900, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24771346

RESUMO

The estrogen receptor alpha (ERα) is a ligand-activated transcription factor that possesses two activating domains designated AF-1 and AF-2 that mediate its transcriptional activity. The role of AF-2 is to recruit coregulator protein complexes capable of modifying chromatin condensation status. In contrast, the mechanism responsible for the ligand-independent AF-1 activity and for its synergistic functional interaction with AF-2 is unclear. In this study, we have identified the protein Na+/H+ Exchanger RegulatoryFactor 2 (NHERF2) as an ERα-associated coactivator that interacts predominantly with the AF-1 domain of the nuclear receptor. Overexpression of NHERF2 in breast cancer MCF7 cells produced an increase in ERα transactivation. Interestingly, the presence of SRC-1 in NHERF2 stably overexpressing MCF7 cells produced a synergistic increase in ERα activity. We show further that NHERF2 interacts with ERα and SRC-1 in the promoter region of ERα target genes. The binding of NHERF2 to ERα in MCF7 cells increased cell proliferation and the ability of MCF7 cells to form tumors in a mouse model. We analyzed the expression of NHERF2 in breast cancer tumors finding a 2- to 17-fold increase in its mRNA levels in 50% of the tumor samples compared to normal breast tissue. These results indicate that NHERF2 is a coactivator of ERα that may participate in the development of estrogen-dependent breast cancer tumors.


Assuntos
Neoplasias da Mama/genética , Receptor alfa de Estrogênio/metabolismo , Fosfoproteínas/metabolismo , Trocadores de Sódio-Hidrogênio/metabolismo , Ativação Transcricional , Animais , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Linhagem Celular Tumoral , Núcleo Celular/química , Núcleo Celular/metabolismo , Proliferação de Células , Estradiol/farmacologia , Receptor alfa de Estrogênio/análise , Receptor alfa de Estrogênio/química , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Camundongos , Camundongos Nus , Coativador 1 de Receptor Nuclear/metabolismo , Fosfoproteínas/análise , Fosfoproteínas/genética , Regiões Promotoras Genéticas , Estrutura Terciária de Proteína , RNA Mensageiro/metabolismo , Trocadores de Sódio-Hidrogênio/análise , Trocadores de Sódio-Hidrogênio/genética , Fator Trefoil-1 , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismo
12.
Mol Genet Metab ; 111(3): 321-330, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24239178

RESUMO

In human cells, HCS catalyzes the biotinylation of biotin-dependent carboxylases and mediates the transcriptional control of genes involved in biotin metabolism through the activation of a cGMP-dependent signal transduction pathway. HCS also targets to the cell nucleus in association with lamin-B suggesting additional gene regulatory functions. Studies from our laboratory in Drosophila melanogaster showed that nuclear HCS is associated with heterochromatin bands enriched with the transcriptionally repressive mark histone 3 trimethylated at lysine 9. Further, HCS was shown to be recruited to the core promoter of the transcriptionally inactive hsp70 gene suggesting that it may participate in the repression of gene expression, although the mechanism involved remained elusive. In this work, we expressed HCS as a fusion protein with the DNA-binding domain of GAL4 to evaluate its effect on the transcription of a luciferase reporter gene. We show that HCS possesses transcriptional repressor activity in HepG2 cells. The transcriptional function of HCS was shown by in vitro pull down and in vivo co-immunoprecipitation assays to depend on its interaction with the histone deacetylases HDAC1, HDAC2 and HDAC7. We show further that HCS interaction with HDACs and its function in transcriptional repression is not affected by mutations impairing its biotin-ligase activity. We propose that nuclear HCS mediates events of transcriptional repression through a biotin-independent mechanism that involves its interaction with chromatin-modifying protein complexes that include histone deacetylases.


Assuntos
Carbono-Nitrogênio Ligases/metabolismo , Histona Desacetilase 1/genética , Histona Desacetilase 2/genética , Histona Desacetilases/genética , Biotina/metabolismo , Carbono-Nitrogênio Ligases/genética , Cromatina , Proteínas de Ligação a DNA/metabolismo , Proteínas de Drosophila/metabolismo , Células Hep G2 , Heterocromatina/genética , Histona Desacetilase 1/metabolismo , Histona Desacetilase 2/metabolismo , Histona Desacetilases/metabolismo , Humanos , Regiões Promotoras Genéticas , Fatores de Transcrição/metabolismo , Transcrição Genética
13.
Nano Lett ; 13(11): 5361-6, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24083520

RESUMO

Controlling the bandstructure through local-strain engineering is an exciting avenue for tailoring optoelectronic properties of materials at the nanoscale. Atomically thin materials are particularly well-suited for this purpose because they can withstand extreme nonhomogeneous deformations before rupture. Here, we study the effect of large localized strain in the electronic bandstructure of atomically thin MoS2. Using photoluminescence imaging, we observe a strain-induced reduction of the direct bandgap and funneling of photogenerated excitons toward regions of higher strain. To understand these results, we develop a nonuniform tight-binding model to calculate the electronic properties of MoS2 nanolayers with complex and realistic local strain geometries, finding good agreement with our experimental results.

15.
Mol Genet Metab ; 95(4): 201-5, 2008 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-18974016

RESUMO

We investigated in a patient with holocarboxylase synthetase deficiency, the relation between the biochemical and genetic factors of the mutant protein with the pharmacokinetic factors of successful biotin treatment. A girl exhibited abnormal skin at birth, and developed in the first days of life neonatal respiratory distress syndrome and metabolic abnormalities diagnostic of multiple carboxylase deficiency. Enzyme assays showed low carboxylase activities. Fibroblast analysis showed poor incorporation of biotin into the carboxylases, and low transfer of biotin by the holocarboxylase synthetase enzyme. Kinetic studies identified an increased Km but a preserved Vmax. Mutation analysis showed the child to be a compound heterozygote for a new nonsense mutation Q379X and for a novel missense mutation Y663H. This mutation affects a conserved amino acid, which is located the most 3' of all recorded missense mutations thus far described, and extends the region of functional biotin interaction. Treatment with biotin 100mg/day gradually improved the biochemical abnormalities in blood and in cerebrospinal fluid (CSF), corrected the carboxylase enzyme activities, and provided clinical stability and a normal neurodevelopmental outcome. Plasma concentrations of biotin were increased to more than 500 nM, thus exceeding the increased Km of the mutant enzyme. At these pharmacological concentrations, the CSF biotin concentration was half the concentration in blood. Measuring these pharmacokinetic variables can aid in optimizing treatment, as individual tailoring of dosing to the needs of the mutation may be required.


Assuntos
Biotina/administração & dosagem , Carbono-Nitrogênio Ligases/deficiência , Deficiência de Holocarboxilase Sintetase/tratamento farmacológico , Sequência de Aminoácidos , Biotina/metabolismo , Carbono-Nitrogênio Ligases/química , Carbono-Nitrogênio Ligases/genética , Células Cultivadas , Feminino , Deficiência de Holocarboxilase Sintetase/genética , Deficiência de Holocarboxilase Sintetase/metabolismo , Humanos , Recém-Nascido , Cinética , Dados de Sequência Molecular , Mutação , Alinhamento de Sequência
16.
J Biol Chem ; 283(49): 34150-8, 2008 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-18845537

RESUMO

Biotinidase catalyzes the hydrolysis of the vitamin biotin from proteolytically degraded biotin-dependent carboxylases. This key reaction makes the biotin available for reutilization in the biotinylation of newly synthesized apocarboxylases. This latter reaction is catalyzed by holocarboxylase synthetase (HCS) via synthesis of 5'-biotinyl-AMP (B-AMP) from biotin and ATP, followed by transfer of the biotin to a specific lysine residue of the apocarboxylase substrate. In addition to carboxylase activation, B-AMP is also a key regulatory molecule in the transcription of genes encoding apocarboxylases and HCS itself. In humans, genetic deficiency of HCS or biotinidase results in the life-threatening disorder biotin-responsive multiple carboxylase deficiency, characterized by a reduction in the activities of all biotin-dependent carboxylases. Although the clinical manifestations of both disorders are similar, they differ in some unique neurological characteristics whose origin is not fully understood. In this study, we show that biotinidase deficiency not only reduces net carboxylase biotinylation, but it also impairs the expression of carboxylases and HCS by interfering with the B-AMP-dependent mechanism of transcription control. We propose that biotinidase-deficient patients may develop a secondary HCS deficiency disrupting the altruistic tissue-specific biotin allocation mechanism that protects brain metabolism during biotin starvation.


Assuntos
Biotina/fisiologia , Deficiência de Biotinidase/enzimologia , Biotinidase/química , Carbono-Nitrogênio Ligases/biossíntese , Sequência de Aminoácidos , Animais , Sequência de Bases , Biotina/química , Deficiência de Biotinidase/metabolismo , Encéfalo/metabolismo , Técnicas de Cultura de Células , GMP Cíclico/química , Deficiência de Holocarboxilase Sintetase/enzimologia , Deficiência de Holocarboxilase Sintetase/genética , Humanos , Modelos Biológicos , Dados de Sequência Molecular , Transcrição Genética
17.
Arch. psiquiatr ; 69(3): 159-170, jul.-sept. 2006.
Artigo em Espanhol | IBECS | ID: ibc-051528

RESUMO

La clínica psiquiátrica actual aspira a poseer referentes fisiopatológicos fundados y síntomas diana válidos y fiables de sus elementos clasificables y que llo sea la base de su teoría general del enfermar psiquiátrico. Sin embargo, existe confusión entre lo que significa y representa ello para la enfermedad y para el enfermar psiquiátrico, como constructos teóricos y sus repercusiones en la clínica. En este sentido se aborda, como una contribución a la teoría psiquiátrica, los hechos y valores que conllevan los términos enfermedad y enfermar psiquiátrico, teniendo en cuenta las vertientes objetivas y subjetivas de los mismos, las referencias sociales de la variabilidad sintomática y las modificaciones que ello produce en los órdenes taxonómicos y evaluativos


In current clinical psychiatry the aims is to have well founded physiopathological references and valid target symptoms with reliably classifiable elements on which to base a general theory of psychiatric illness. Nevertheless there is some confusion over the meaning and implication of this for psychiatric illness and the process of falling ill, in terms of theoretical constructs and their repercussions in clinical practice. As a contribution to psychitric theory, we tackle the facts and values bound up in the terms psychiatric illness and falling psychiatrically ill, bearing in mind both their objective and subjective aspects, the social references of variations in symptoms and the consequent modifications in taxonomy and evaluation


Assuntos
Humanos , Atitude Frente a Saúde , Pessoas Mentalmente Doentes/psicologia , Transtornos Mentais/psicologia , Psiquiatria
18.
J Biol Chem ; 279(50): 52312-8, 2004 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-15456772

RESUMO

Holocarboxylase synthetase (HCS) catalyzes the biotinylation of five carboxylases in human cells, and mutations of HCS cause multiple carboxylase deficiency (MCD). Although HCS also participates in the regulation of its own mRNA levels, the relevance of this mechanism to normal metabolism or to the MCD phenotype is not known. In this study, we show that mRNA levels of enzymes involved in biotin utilization, including HCS, are down-regulated during biotin deficiency in liver while remaining constitutively expressed in brain. We propose that this mechanism of regulation is aimed at sparing the essential function of biotin in the brain at the expense of organs such as liver and kidney during biotin deprivation. In MCD, it is possible that some of the manifestations of the disease may be associated with down-regulation of biotin utilization in liver because of the impaired activity of HCS and that high dose biotin therapy may in part be important to overcoming the adverse regulatory impact in such organs.


Assuntos
Biotina/metabolismo , Encéfalo/metabolismo , Fígado/metabolismo , Deficiência Múltipla de Carboxilase/genética , Deficiência Múltipla de Carboxilase/metabolismo , Animais , Sequência de Bases , Biotina/deficiência , Carbono-Nitrogênio Ligases/genética , Carbono-Nitrogênio Ligases/metabolismo , Linhagem Celular , DNA Complementar/genética , Deficiência de Holocarboxilase Sintetase/genética , Deficiência de Holocarboxilase Sintetase/metabolismo , Humanos , Masculino , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Distribuição Tecidual
19.
Rev. colomb. ortop. traumatol ; 18(3): 20-26, sept. 2004.
Artigo em Espanhol | LILACS | ID: lil-619216

RESUMO

CONCLUSIONES: 1) Se Considera que el enclavijamiento es el mejor tratamiento de las fracturas diafisarias del fémur. 2) Se hace un análisis de su indicación en las fracturas abiertas recientes, así como también de las abiertas infectadas y llegamos a la conclusión de que a pesar de que la Casuística es reducida en muchos de estos casos debe ser usado el enclavijamiento. 3) El tiempo de hospitalización promedio es de doce días, cifra muy baja si se compara con los otros métodos. 4) En las fracturas de tibia, húmero y antebrazo los resultados son buenos, pero nunca comparables con los obtenidos en fémur, por las causas ya anotadas.


Assuntos
Fixação Intramedular de Fraturas , Fixação Intramedular de Fraturas/métodos , Fixação Intramedular de Fraturas
20.
Clin Infect Dis ; 36(4): 491-8, 2003 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-12567308

RESUMO

To evaluate the factors associated with the evolution of chronic hepatitis C in human immunodeficiency virus (HIV)-infected patients, a cross-sectional analysis of 41 HIV-infected patients with chronic hepatitis C (known as "HIV-HCV [hepatitis C virus]-coinfected patients") and a control group of patients with chronic hepatitis C who did not have HIV infection (known as "non-HIV-infected patients") was performed. The association of histological variables with demographic parameters, HCV load and genotype, HIV load, CD4(+) T cell count, and response to highly active antiretroviral therapy (HAART) was evaluated. HIV-HCV-coinfected patients showed a significantly higher HCV load, more-advanced fibrosis, and a higher liver fibrosis progression rate (FPR) than did non-HIV-infected patients. A high HCV load and a low CD4(+) T cell count were associated with a higher FPR. The immune response induced by HAART did not influence this progression. In conclusion, HIV-HCV-infected patients, mainly such patients with a high HCV load and an immunodepressed state, have a higher FPR. An independent effect of the immune response to HAART was not evident.


Assuntos
Fibrose/etiologia , Infecções por HIV/complicações , HIV , Hepacivirus , Hepatite C Crônica/complicações , Cirrose Hepática/etiologia , Adulto , Terapia Antirretroviral de Alta Atividade , Contagem de Linfócito CD4 , Progressão da Doença , Feminino , Infecções por HIV/tratamento farmacológico , Infecções por HIV/patologia , Hepatite C Crônica/patologia , Humanos , Masculino , Pessoa de Meia-Idade
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