Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 10 de 10
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
2.
J Agric Food Chem ; 66(12): 3086-3092, 2018 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-29432005

RESUMO

Herbicides are pesticides used to eradicate unwanted plants in both crop and non-crop environments. These chemistries are toxic to weeds due to inhibition of key enzymes or disruption of essential biochemical processes required for weedy plants to survive. Crops can survive systemic herbicidal applications through various forms of detoxification, including metabolism that can be enhanced by safeners. Field studies were conducted near Louisville, Tennessee and Painter, Virginia to determine how the herbicides mesotrione, topramezone, nicosulfuron, and atrazine applied with or without the safener isoxadifen-ethyl would impact the nutritional quality of "Incredible" sweet corn ( Zea mays L. var. rugosa). Several herbicide treatments increased the uptake of the mineral elements phosphorus, magnesium, and manganese by 8-75%. All herbicide treatments increased protein content by 4-12%. Applied alone, nicosulfuron produced similar levels of saturated, monounsaturated, and polyunsaturated fatty acids when compared to the nontreated check, but when applied with isoxadifen-ethyl, fatty acids increased 8 to 44% relative to the check or control. Nicosulfuron plus isoxadifen-ethyl or topramezone or the combination of all three actives increased the concentrations of fructose and glucose (40-68%), whereas reducing levels of maltose or sucrose when compared to the nontreated check (-15 to -21%). Disruptions in biochemical pathways in plants due to the application of herbicides, safeners, or other pesticides have the potential to alter the nutrient quality, taste, and overall plant health associated with edible crops.


Assuntos
Herbicidas/farmacologia , Zea mays/química , Zea mays/efeitos dos fármacos , Transporte Biológico/efeitos dos fármacos , Cicloexanonas/farmacologia , Ácidos Graxos/metabolismo , Contaminação de Alimentos/análise , Magnésio/metabolismo , Manganês/metabolismo , Valor Nutritivo/efeitos dos fármacos , Fósforo/metabolismo , Proteínas de Plantas/metabolismo , Pirazóis/farmacologia , Piridinas/farmacologia , Compostos de Sulfonilureia/farmacologia , Zea mays/metabolismo
3.
J Am Chem Soc ; 139(8): 2989-2993, 2017 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-28068761

RESUMO

Using two tetraphenylbenzene isomers differing only by the anchoring points to the gold electrodes, we investigate the influence of quantum interference on the single molecule charge transport. The distinct anchor points are realized by selective halogen-mediated binding to the electrodes by formation of surface-stabilized isomers after iodine cleavage. Both isomers are essentially chemically identical and only weakly perturbed by the electrodes avoiding largely parasitic effects, which allows us to focus solely on the relation between quantum interference and the intrinsic molecular properties. The conductance of the two isomers differs by over 1 order of magnitude and is attributed to constructive and destructive interference. Our ab initio based transport calculations compare very well with the accompanying scanning tunneling microscope break junction measurements of the conductance. The findings are rationalized using a two level model, which shows that the interorbital coupling plays the decisive role for the interference effects.

4.
J Am Chem Soc ; 138(2): 679-87, 2016 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-26694660

RESUMO

An exponential decrease of molecular conductance with length has been observed in most molecular systems reported to date, and has been taken as a signature of non-resonant tunneling as the conduction mechanism. Surprisingly, the conductance of iodide-terminated oligothiophene molecules presented herein does not follow the simple exponential length dependence. The lack of temperature dependence in the conductance indicates that tunneling still dominates the conduction mechanism in the molecules. Transition voltage spectroscopy shows that the tunneling barrier of the oligothiophene decreases with length, but the decrease is insufficient to explain the non-exponential length dependence. X-ray photoelectron spectroscopy, stretching length measurement, and theoretical calculations show that the non-exponential length dependence is due to a transition in the binding geometry of the molecule to the electrodes in the molecular junctions as the length increases.

5.
J Am Chem Soc ; 135(9): 3319-22, 2013 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-23405987

RESUMO

We report controlling the formation of single-molecule junctions by means of electrochemically reducing two axialdiazonium terminal groups on a molecule, thereby producing direct Au-C covalent bonds in situ between the molecule and gold electrodes. We report a yield enhancement in molecular junction formation as the electrochemical potential of both junction electrodes approach the reduction potential of the diazonium terminal groups. Step length analysis shows that the molecular junction is significantly more stable, and can be pulled over a longer distance than a comparable junction created with amine anchoring bonds. The stability of the junction is explained by the calculated lower binding energy associated with the direct Au-C bond compared with the Au-N bond.


Assuntos
Compostos de Diazônio/síntese química , Técnicas Eletroquímicas , Compostos de Diazônio/química , Estrutura Molecular , Oxirredução
6.
J Am Board Fam Med ; 25(4): 511-21, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22773719

RESUMO

We describe how collaboration with outpatient community health centers and other disciplines resulted in the creation of a novel interdisciplinary inpatient maternal child health system that focuses on safety and collaboration. Our maternal child health faculty team includes a mix of fellowship- and non-fellowship-trained, inpatient- and outpatient-based family physicians. Our team provides a sustainable framework for faculty to practice both inpatient and outpatient maternity care and provides strong role models for our trainees.


Assuntos
Competência Clínica/normas , Comportamento Cooperativo , Parto Obstétrico , Serviços de Saúde Materna , Equipe de Assistência ao Paciente/organização & administração , Assistência Perinatal , Boston , Centros Comunitários de Saúde , Feminino , Humanos , Comunicação Interdisciplinar , Estudos de Casos Organizacionais , Segurança do Paciente , Gravidez , Garantia da Qualidade dos Cuidados de Saúde/métodos
7.
Nat Nanotechnol ; 6(4): 226-31, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-21336268

RESUMO

In recent years, various single-molecule electronic components have been demonstrated. However, it remains difficult to predict accurately the conductance of a single molecule and to control the lateral coupling between the π orbitals of the molecule and the orbitals of the electrodes attached to it. This lateral coupling is well known to cause broadening and shifting of the energy levels of the molecule; this, in turn, is expected to greatly modify the conductance of an electrode-molecule-electrode junction. Here, we demonstrate a new method, based on lateral coupling, to mechanically and reversibly control the conductance of a single-molecule junction by mechanically modulating the angle between a single pentaphenylene molecule bridged between two metal electrodes. Changing the angle of the molecule from a highly tilted state to an orientation nearly perpendicular to the electrodes changes the conductance by an order of magnitude, which is in qualitative agreement with theoretical models of molecular π-orbital coupling to a metal electrode. The lateral coupling is also directly measured by applying a fast mechanical perturbation in the horizontal plane, thus ruling out changes in the contact geometry or molecular conformation as the source for the conductance change.


Assuntos
Hidrocarbonetos Aromáticos com Pontes/química , Hidrocarbonetos Aromáticos/química , Nanotecnologia/métodos , Condutividade Elétrica , Eletrodos , Microscopia de Tunelamento , Modelos Moleculares
8.
J Am Chem Soc ; 132(33): 11658-64, 2010 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-20669945

RESUMO

The charge transport characteristics of a family of long conjugated molecular wires have been studied using the scanning tunneling microscope break junction technique. The family consists of four wires ranging from 3.1 to 9.4 nm in length. The two shortest wires show highly length dependent and temperature invariant conductance behavior, whereas the longer two wires show weakly length dependent and temperature variant behavior. This trend is consistent with a model whereby conduction occurs by two different mechanisms in the family of wires: by a coherent tunneling mechanism in the shorter two and by an incoherent charge hopping process in the longer wires. The temperature dependence of the two conduction mechanisms gives rise to a phenomenon whereby at elevated temperatures longer molecules that conduct via charge hopping can yield a higher conductance than shorter wires that conduct via tunneling. The evolution of molecular junctions as the tip retracts has been studied and explained in context of the characteristics of individual transient current decay curves.


Assuntos
Hidrocarbonetos Aromáticos/química , Temperatura Ambiente , Estrutura Molecular
9.
Haematologica ; 95(10): 1691-6, 2010 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-20494933

RESUMO

BACKGROUND: Bone marrow biopsy is considered essential for the staging and risk-adapted treatment of Hodgkin's lymphoma with unfavorable risk features. We reviewed the cases of pediatric Hodgkin's lymphoma in our institution to determine the impact of bone marrow involvement on treatment, relapse, and survival. DESIGN AND METHODS: We reviewed the clinical characteristics and outcome of 383 patients treated for Hodgkin's lymphoma at St. Jude Children's Research Hospital between August 1990 and August 2008. The 5-year survival estimates for patients with and without bone marrow involvement were compared. RESULTS: Of 228 patients who had a bone marrow biopsy at diagnosis, 21 had bone marrow involvement. Bone marrow findings changed the disease stage in only seven patients (3.1%): from IB to IVB (n=1), from IIA (with bulky disease) to IVA (n=1), from IIB to IVB (n=1), and from IIIB to IVB (n=4). One patient's risk assignment changed from intermediate to unfavorable risk without his chemotherapy being altered. No statistically significant difference was observed between patients with stage IV Hodgkin's lymphoma who did (n=21) and did not (n=61) have bone marrow involvement in 5-year relapse-free survival (89.6± 7% versus 73.9±6.1%; P=0.25) or 5-year overall survival (95.2±8.2% versus 87.3±4.9%; P=0.82). CONCLUSIONS: Although bone marrow involvement changed the stage in 3.1% of pediatric Hodgkin's lymphoma patients, it did not change risk-adapted treatment or prognosis. We conclude that bone marrow biopsy need not be performed at diagnosis in patients who have unfavorable risk features, although this finding should be confirmed by larger prospective studies.


Assuntos
Exame de Medula Óssea , Doença de Hodgkin/diagnóstico , Adolescente , Antineoplásicos/uso terapêutico , Exame de Medula Óssea/estatística & dados numéricos , Criança , Pré-Escolar , Doença de Hodgkin/mortalidade , Doença de Hodgkin/patologia , Humanos , Estadiamento de Neoplasias , Estudos Retrospectivos , Medição de Risco , Adulto Jovem
10.
Pediatr Blood Cancer ; 51(2): 198-203, 2008 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-18428430

RESUMO

BACKGROUND: Positron emission tomography (PET) and gallium scans facilitate diagnosis and staging, evaluation of response to therapy, and monitoring for relapse in Hodgkin lymphoma (HL), but have not been compared in pediatric HL. PROCEDURE: We performed concurrent PET and gallium scans on 44 pediatric HL patients at diagnosis, early response, off chemotherapy, and off-therapy evaluations. PET and gallium scans were compared to each other and to computed tomography (CT) alone to determine whether either modality led to a change in stage or modified the results of the early response evaluation, which was used to determine the radiation dose. RESULTS: PET upstaged four patients at diagnosis (2 from stage I to II, one II to III, and one III to IV), but did not lead to a change in therapy in any of them. It changed response category in two patients at early response evaluation, leading to a change in radiation dose for 1 patient (25.5 Gy instead of 15 Gy to the spleen). Gallium did not change the stage of treatment for any patient. The negative predictive values for eventual lymphoma relapse of PET and gallium scans at off therapy were 89% and 83%, respectively; the positive predictive value of PET at off therapy is 29%. CONCLUSION: PET appears to be superior to gallium in pediatric HL; future studies will determine the optimal timing of PET to assess early response and the utility of quantitative interpretation of the avidity of specific nodal sites.


Assuntos
Radioisótopos de Gálio , Doença de Hodgkin/diagnóstico por imagem , Tomografia por Emissão de Pósitrons , Adolescente , Criança , Pré-Escolar , Feminino , Seguimentos , Humanos , Lactente , Masculino , Estadiamento de Neoplasias , Tomografia Computadorizada por Raios X
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA