RESUMO
Single-molecules have been widely investigated in the last decades due to their promises as devices in molecular electronics. One of the advantages in the use of natural compounds in molecular electronics is the economy of material and molecular synthesis, which makes the process both cheaper and self-sustaining. Although many studies have considered electronic transport in single molecules, there are few studies associated with isomeric effects in biologically appealing systems. In the present work, we have studied ballistic electron transport in two isomeric forms of a retinol molecule: 11-cis and all-trans-retinol. The molecules were connected between two Au(111) electrodes and calculations were performed with the NEGF-DFT methodology. Current-voltage, differential conductance, and rectification curves were obtained and compared for two structures. While 11-cis-retinol shows a more symmetrical current-voltage curve, all-trans-retinol acts as molecular diode for low applied voltages. Our results suggest that a simple isomeric effect modulates the molecular device from nanowires to diodes with potential applications as field-effect transistors.
RESUMO
In the present work we propose a novel treatment to investigate ballistic electron transport under mechanical strain in a 1-D molecular bridge composed of alternating simple and triple bonds (polyyne) connected between two Single-Wall Carbon Nanotube (SWCNT) electrodes. Calculations with the DFT-NEGF methodology were performed in order to analyze this system at low values of mechanical strain (compression and distension) and at equilibrium length in the presence of bias voltages applied along the longitudinal direction. The results show that, while the mechanical strain displaces the energy levels and changes the band gap in the nanotube caps, the applied bias breaks the degeneracy in the nanotube cap states and defines the electrical conductance along the system. The analysis of the PDOS suggests that the main contribution to the electrical current comes from the superposition of the nanotube cap states, which is in agreement with the transmission calculation, and this device can be employed as a transistor observed in the I-V curve.
RESUMO
We propose an efficient single-molecule rectifier based on a derivative of opioid. Electron transport properties are investigated within the non-equilibrium Green's function formalism combined with density functional theory. The analysis of the current-voltage characteristics indicates obvious diode-like behavior. While heroin presents rectification coefficient R>1, indicating preferential electronic current from electron-donating to electron-withdrawing, 3 and 6-acetylmorphine and morphine exhibit contrary behavior, R<1. Our calculations indicate that the simple inclusion of acetyl groups modulate a range of devices, which varies from simple rectifying to resonant-tunneling diodes. In particular, the rectification rations for heroin diodes show microampere electron current with a maximum of rectification (R=9.1) at very low bias voltage of â¼0.6 V and (R=14.3)â¼1.8 V with resistance varying between 0.4 and 1.5 M Ω. Once most of the current single-molecule diodes usually rectifies in nanoampere, are not stable over 1.0 V and present electrical resistance around 10 M. Molecular devices based on opioid derivatives are promising in molecular electronics.
Assuntos
Analgésicos Opioides/química , Eletrônica , ElétronsRESUMO
The use of strains of Salmonella enterica serovar Typhimurium with different metabolic capacities can indicate the class or classes of compounds present in an environmental sample and enable the diagnosis of the mutagenic activity of these pollutants adsorbed on particulate matter (PM) in the air. In the present study, the sensitivity of Salmonella strains TA98NR, TA98/1,8-DNP6, YG1021, and YG1024 to detect nitro compounds adsorbed on samples of PM 2.5 was compared from three sites in Rio de Janeiro city. Samples were collected using a high-volume sampler at three sites: one with light traffic and two with heavy traffic. The assays were performed in the presence of 10-50 µg/ plate organic extracts with and without exogenous metabolization. The YG1021 and YG1024 strains showed the highest rev/m(3) values, confirming their enhanced sensitivity. As YG1024 also demonstrated sensitivity to nitro and amino compounds, we suggest its use in research into environmental contamination.
Assuntos
Poluentes Atmosféricos/toxicidade , Mutagênicos/toxicidade , Nitrocompostos/toxicidade , Salmonella typhi/efeitos dos fármacos , Cidades , Humanos , Testes de Mutagenicidade , Salmonella typhi/genéticaRESUMO
Risk assessment can provide a comprehensive estimate of potential effects of contaminants under specific, well-defined, and well-described circumstances, providing quantitative relationships between exposure and effects to identify and to define areas of concern. We investigated the mutagenic activity of particulate matter in air samples collected from three sites in Rio de Janeiro city. Samples were collected using a high-volume sampler at Avenida Brasil, at Campus of Universidade do Estado do Rio de Janeiro, and at Rebouças Tunnel. Six polycyclic aromatic hydrocarbons were quantified by gas chromatography/mass spectrometry. Salmonella typhimurium TA98 and the derivative strains TA98/1.8-DNP(6), YG1021, and YG1024, commonly used in mutagenicity assays, were treated (10-50 µg/plate), with and without exogenous metabolization. The highest values for the polycyclic aromatic hydrocarbons were detected at Rebouças Tunnel. For chrysene, as an example, the concentration was nearly 200 times higher than that established by the US Environmental Protection Agency. Frequent traffic jams can place bus drivers who go through the Rebouças Tunnel at risk of exposure to up to 0.69 ng/m(3) benzo(a) pyrene. Independent of exogenous metabolization, mutagenicity was detected in strains YG1021 and YG1024 at all the sites, suggesting nitro and amino derivatives of polycyclic aromatic hydrocarbons. Rebouças Tunnel air samples gave the highest values for rev/µg and rev/m(3). This could be due to the fact that the long, enclosed passageway through a mountain restricts ventilation. The cancer risk estimate in this study was 10(-3) for the benzo(a)pyrene, at the two sites, indicating a high risk.
Assuntos
Poluentes Atmosféricos/análise , Cidades , Exposição Ambiental/efeitos adversos , Hidrocarbonetos Policíclicos Aromáticos/análise , Poluentes Atmosféricos/toxicidade , Brasil , Crisenos/análise , Crisenos/toxicidade , Cromatografia Gasosa-Espectrometria de Massas , Humanos , Testes de Mutagenicidade , Material Particulado/análise , Material Particulado/toxicidade , Hidrocarbonetos Policíclicos Aromáticos/toxicidade , Medição de Risco , Fatores de Risco , Salmonella typhimurium/efeitos dos fármacosRESUMO
Terson's syndrome is characterized by the presence of a subarachnoid hemorrhage accompanied by retinal and vitreous hemorrhage leading to a not very favorable prognosis. We describe a case with a good outcome, probably because of a early diagnosis and medical intervention. We emphasize the routine optician's check up as very important in the evaluation of a prognosis in the cases of a suspect intracranial hemorrhage.
Assuntos
Hemorragia Retiniana/diagnóstico , Hemorragia Subaracnóidea/diagnóstico , Hemorragia Vítrea/diagnóstico , Adulto , Feminino , Seguimentos , Humanos , Hemorragia Retiniana/complicações , Hemorragia Subaracnóidea/complicações , Síndrome , Hemorragia Vítrea/complicaçõesRESUMO
780 patients with recurrent conjunctival infections or persistent complaints of itching, burning pain, lacrimation and conjunctival hyperemia were subject to conjunctival smear examination for cytology and the presence of inclusion bodies. Two hundred and forty seven (31.7%) showed cytoplamic inclusions; 235 of them were subject to a direct specific immunofluorescency test with 90 (38.3%) positive results. The importance of the clinical manifestations and laboratory methods (direct immunofluorescence and research cytoplasmic inclusions) were considered. The patients are clients of a private clinic and have a moderate to hightor socioeconomic level.
Assuntos
Infecções por Chlamydia/epidemiologia , Conjuntivite/microbiologia , Infecções Oculares Bacterianas/epidemiologia , Adolescente , Adulto , Idoso , Brasil , Criança , Pré-Escolar , Estudos de Coortes , Hospitais Privados , Humanos , Lactente , Recém-Nascido , Pessoa de Meia-IdadeRESUMO
Os autores apresentam o caso de um recemnascido, com 17 dias de idade, portador de infeccao disseminada (incluindo meningencefalite) pelo Herpes simplex, cultivado a partir de material obtido de lesoes cutaneas. A evolucao foi arrastada, com o aparecimento de novas vesiculas, em que pese o tratamento com adenina-arabinosideo na dose de 15mg/kg/dia. A crianca desnutriu-se, superou uma pneumonia aspirativa aos 7 meses de idade e veio a falecer com nove meses em virtude de nova pneumonia aspirativa. Os autores justificam a presente publicacao tendo em vista: a) e o primeiro caso registrado no Brasil com identificacao do agente etiologico; b) a evolucao atipica e recidivante e c) o insucesso do tratamento com a adenina-arabinosideo