Base de dados : MEDLINE
Pesquisa : D02.389.678.900 [Categoria DeCS]
Referências encontradas : 122 [refinar]
Mostrando: 1 .. 10   no formato [Detalhado]

página 1 de 13 ir para página                         

  1 / 122 MEDLINE  
              next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:25813935
[Au] Autor:Pesic M; Podolski-Renic A; Stojkovic S; Matovic B; Zmejkoski D; Kojic V; Bogdanovic G; Pavicevic A; Mojovic M; Savic A; Milenkovic I; Kalauzi A; Radotic K
[Ad] Endereço:Institute for Biological Research "Sinisa Stankovic", University of Belgrade, Despota Stefana 142, 11060 Belgrade, Serbia. Electronic address: camala@ibiss.bg.ac.rs.
[Ti] Título:Anti-cancer effects of cerium oxide nanoparticles and its intracellular redox activity.
[So] Source:Chem Biol Interact;232:85-93, 2015 May 05.
[Is] ISSN:1872-7786
[Cp] País de publicação:Ireland
[La] Idioma:eng
[Ab] Resumo:Data on medical applications of cerium oxide nanoparticles CeO2 (CONP) are promising, yet information regarding their action in cells is incomplete and there are conflicting reports about in vitro toxicity. Herein, we have studied cytotoxic effect of CONP in several cancer and normal cell lines and their potential to change intracellular redox status. The IC50 was achieved only in two of eight tested cell lines, melanoma 518A2 and colorectal adenocarcinoma HT-29. Self-propagating room temperature method was applied to produce CONP with an average crystalline size of 4 nm. The results confirmed presence of Ce(3+) and O(2-) vacancies. The induction of cell death by CONP and the production of reactive oxygen species (ROS) were analyzed by flow-cytometry. Free radicals related antioxidant capacity of the cells was studied by the reduction of stable free radical TEMPONE using electron spin resonance spectroscopy. CONP showed low or moderate cytotoxicity in cancer cell lines: adenocarcinoma DLD1 and multi-drug resistant DLD1-TxR, non-small cell lung carcinoma NCI-H460 and multi-drug resistant NCI-H460/R, while normal cell lines (keratinocytes HaCaT, lung fetal fibroblasts MRC-5) were insensitive. The most sensitive were 518A2 melanoma and HT-29 colorectal adenocarcinoma cell lines, with the IC50 values being between 100 and 200 µM. Decreased rate of TEMPONE reduction and increased production of certain ROS species (peroxynitrite and hydrogen peroxide anion) indicates that free radical metabolism, thus redox status was changed, and antioxidant capacity damaged in the CONP treated 518A2 and HT-29 cells. In conclusion, changes in intracellular redox status induced by CONP are partly attributed to the prooxidant activity of the nanoparticles. Further, ROS induced cell damages might eventually lead to the cell death. However, low inhibitory potential of CONP in the other human cell lines tested indicates that CONP may be safe for human usage in industry and medicine.
[Mh] Termos MeSH primário: Antineoplásicos/farmacologia
Cério/farmacologia
Nanopartículas
[Mh] Termos MeSH secundário: Antioxidantes/metabolismo
Linhagem Celular Tumoral/efeitos dos fármacos
Cério/química
Ensaios de Seleção de Medicamentos Antitumorais
Células HT29/efeitos dos fármacos
Seres Humanos
Nanopartículas/química
Oxirredução
Espécies Reativas de Oxigênio/metabolismo
Triacetonamina-N-Oxil/metabolismo
Triacetonamina-N-Oxil/farmacologia
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, NON-U.S. GOV'T
[Nm] Nome de substância:
0 (Antineoplastic Agents); 0 (Antioxidants); 0 (Reactive Oxygen Species); 2896-70-0 (Triacetoneamine-N-Oxyl); 30K4522N6T (Cerium); 619G5K328Y (ceric oxide)
[Em] Mês de entrada:1506
[Cu] Atualização por classe:150408
[Lr] Data última revisão:
150408
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:150328
[St] Status:MEDLINE


  2 / 122 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
PubMed Central Texto completo
Texto completo
[PMID]:25594422
[Au] Autor:Merunka D; Peric M; Peric M
[Ad] Endereço:Department of Physics and Astronomy and The Center for Supramolecular Studies, California State University at Northridge , Northridge, California 91330, United States.
[Ti] Título:Study of nanostructural organization of ionic liquids by electron paramagnetic resonance spectroscopy.
[So] Source:J Phys Chem B;119(7):3185-93, 2015 Feb 19.
[Is] ISSN:1520-5207
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:The X-band electron paramagnetic resonance spectroscopy (EPR) of a stable, spherical nitroxide spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (pDTO) has been used to study the nanostructural organization of a series of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids (ILs) with alkyl chain lengths from two to eight carbons. By employing nonlinear least-squares fitting of the EPR spectra, we have obtained values of the rotational correlation time and hyperfine coupling splitting of pDTO to high precision. The rotational correlation time of pDTO in ILs and squalane, a viscous alkane, can be fit very well to a power law functionality with a singular temperature, which often describes a number of physical quantities measured in supercooled liquids. The viscosity of the ILs and squalane, taken from the literature, can also be fit to the same power law expression, which means that the rotational correlation times and the ionic liquid viscosities have similar functional dependence on temperature. The apparent activation energy of both the rotational correlation time of pDTO and the viscous flow of ILs and squalane increases with decreasing temperature; in other words, they exhibit strong non-Arrhenius behavior. The rotational correlation time of pDTO as a function of η/T, where η is the shear viscosity and T is the temperature, is well described by the Stokes-Einstein-Debye (SED) law, while the hydrodynamic probe radii are solvent dependent and are smaller than the geometric radius of the probe. The temperature dependence of hyperfine coupling splitting is the same in all four ionic liquids. The value of the hyperfine coupling splitting starts decreasing with increasing alkyl chain length in the ionic liquids in which the number of carbons in the alkyl chain is greater than four. This decrease together with the decrease in the hydrodynamic radius of the probe indicates a possible existence of nonpolar nanodomains.
[Mh] Termos MeSH primário: Líquidos Iônicos/química
Nanoestruturas/química
[Mh] Termos MeSH secundário: Boratos/química
Deutério
Espectroscopia de Ressonância de Spin Eletrônica/métodos
Hidrazonas/química
Hidrodinâmica
Análise dos Mínimos Quadrados
Dinâmica não Linear
Rotação
Esqualeno/análogos & derivados
Esqualeno/química
Temperatura Ambiente
Fatores de Tempo
Triacetonamina-N-Oxil
Viscosidade
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, N.I.H., EXTRAMURAL
[Nm] Nome de substância:
0 (Borates); 0 (Hydrazones); 0 (Ionic Liquids); 14046-96-9 (carbonyl 3-chlorophenylhydrazone); 2896-70-0 (Triacetoneamine-N-Oxyl); 7QWM220FJH (Squalene); AR09D82C7G (Deuterium); GW89575KF9 (squalane)
[Em] Mês de entrada:1602
[Cu] Atualização por classe:170220
[Lr] Data última revisão:
170220
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:150117
[St] Status:MEDLINE
[do] DOI:10.1021/jp512487y


  3 / 122 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
PubMed Central Texto completo
Texto completo
[PMID]:25240151
[Au] Autor:Yu Z; Quine RW; Rinard GA; Tseitlin M; Elajaili H; Kathirvelu V; Clouston LJ; Boratynski PJ; Rajca A; Stein R; Mchaourab H; Eaton SS; Eaton GR
[Ad] Endereço:Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA.
[Ti] Título:Rapid-scan EPR of immobilized nitroxides.
[So] Source:J Magn Reson;247:67-71, 2014 Oct.
[Is] ISSN:1096-0856
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:X-band electron paramagnetic resonance spectra of immobilized nitroxides were obtained by rapid scan at 293 K. Scan widths were 155 G with 13.4 kHz scan frequency for (14)N-perdeuterated tempone and for T4 lysozyme doubly spin labeled with an iodoacetamide spirocyclohexyl nitroxide and 100 G with 20.9 kHz scan frequency for (15)N-perdeuterated tempone. These wide scans were made possible by modifications to our rapid-scan driver, scan coils made of Litz wire, and the placement of highly conducting aluminum plates on the poles of a Bruker 10″ magnet to reduce resistive losses in the magnet pole faces. For the same data acquisition time, the signal-to-noise for the rapid-scan absorption spectra was about an order of magnitude higher than for continuous wave first-derivative spectra recorded with modulation amplitudes that do not broaden the lineshapes.
[Mh] Termos MeSH primário: Espectroscopia de Ressonância de Spin Eletrônica/métodos
Óxidos de Nitrogênio/química
[Mh] Termos MeSH secundário: Deutério
Campos Eletromagnéticos
Indicadores e Reagentes
Muramidase/química
Radioisótopos de Nitrogênio
Marcadores de Spin
Triacetonamina-N-Oxil/química
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, N.I.H., EXTRAMURAL; RESEARCH SUPPORT, U.S. GOV'T, NON-P.H.S.
[Nm] Nome de substância:
0 (Indicators and Reagents); 0 (Nitrogen Oxides); 0 (Nitrogen Radioisotopes); 0 (Spin Labels); 2896-70-0 (Triacetoneamine-N-Oxyl); AR09D82C7G (Deuterium); EC 3.2.1.17 (Muramidase)
[Em] Mês de entrada:1511
[Cu] Atualização por classe:170830
[Lr] Data última revisão:
170830
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:140921
[St] Status:MEDLINE


  4 / 122 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
PubMed Central Texto completo
Texto completo
[PMID]:24874024
[Au] Autor:Peric I; Merunka D; Bales BL; Peric M
[Ad] Endereço:Department of Physics and Astronomy and The Center for Supramolecular Studies, California State University at Northridge , Northridge, California 91330, United States.
[Ti] Título:Hydrodynamic and nonhydrodynamic contributions to the bimolecular collision rates of solute molecules in supercooled bulk water.
[So] Source:J Phys Chem B;118(25):7128-35, 2014 Jun 26.
[Is] ISSN:1520-5207
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:Bimolecular collision rate constants of a model solute are measured in water at T = 259-303 K, a range encompassing both normal and supercooled water. A stable, spherical nitroxide spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl, is studied using electron paramagnetic resonance spectroscopy (EPR), taking advantage of the fact that the rotational correlation time, τ(R), the mean time between successive spin exchanges within a cage, τ(RE), and the long-time-averaged spin exchange rate constants, K(ex), of the same solute molecule may be measured independently. Thus, long- and short-time translational diffusion behavior may be inferred from K(ex) and τ(RE), respectively. In order to measure K(ex), the effects of dipole-dipole interactions (DD) on the EPR spectra must be separated, yielding as a bonus the DD broadening rate constants that are related to the dephasing rate constant due to DD, W(dd). We find that both K(ex) and W(dd) behave hydrodynamically; that is to say they vary monotonically with T/η or η/T, respectively, where η is the shear viscosity, as predicted by the Stokes-Einstein equation. The same is true of the self-diffusion of water. In contrast, τ(RE) does not follow hydrodynamic behavior, varying rather as a linear function of the density reaching a maximum at 276 ± 2 K near where water displays a maximum density.
[Mh] Termos MeSH primário: Hidrodinâmica
Água/química
[Mh] Termos MeSH secundário: Espectroscopia de Ressonância de Spin Eletrônica
Modelos Teóricos
Resistência ao Cisalhamento
Temperatura Ambiente
Triacetonamina-N-Oxil/química
Viscosidade
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, N.I.H., EXTRAMURAL
[Nm] Nome de substância:
059QF0KO0R (Water); 2896-70-0 (Triacetoneamine-N-Oxyl)
[Em] Mês de entrada:1505
[Cu] Atualização por classe:170220
[Lr] Data última revisão:
170220
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:140531
[St] Status:MEDLINE
[do] DOI:10.1021/jp501330x


  5 / 122 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:24695794
[Au] Autor:Enkin N; Liu G; Tkach I; Bennati M
[Ad] Endereço:Max-Planck Institute for Biophysical Chemistry, Am Fassberg, 37077 Göttingen, Germany. guoquan.liu@mpibpc.mpg.de marina.bennati@mpibpc.mpg.de.
[Ti] Título:High DNP efficiency of TEMPONE radicals in liquid toluene at low concentrations.
[So] Source:Phys Chem Chem Phys;16(19):8795-800, 2014 May 21.
[Is] ISSN:1463-9084
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:We show that at low concentrations (≤5 mM) TEMPONE radicals in liquid toluene exhibit higher DNP efficiency than in water. In spite of reduced coupling factors, the improved DNP performance in toluene results from favourable saturation and leakage factors, as determined by pulse electron-electron double resonance (ELDOR) and NMR relaxation, respectively. The extracted coupling factors at 0.35 Tesla support theoretical predictions of the Overhauser mechanism.
[Mh] Termos MeSH primário: Tolueno/química
Triacetonamina-N-Oxil/química
[Mh] Termos MeSH secundário: Radicais Livres/química
Espectroscopia de Ressonância Magnética
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, NON-U.S. GOV'T
[Nm] Nome de substância:
0 (Free Radicals); 2896-70-0 (Triacetoneamine-N-Oxyl); 3FPU23BG52 (Toluene)
[Em] Mês de entrada:1504
[Cu] Atualização por classe:140416
[Lr] Data última revisão:
140416
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:140404
[St] Status:MEDLINE
[do] DOI:10.1039/c4cp00854e


  6 / 122 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
Texto completo
[PMID]:24411834
[Au] Autor:Hirama T; Minezaki S; Yamaguchi T; Kishi E; Kodama K; Egashira H; Kobayashi K; Nagata M; Ishii T; Nemoto M; Tanaka M; Fukunaga K; Kanazawa M; Hagiwara K
[Ad] Endereço:Department of Respiratory Medicine, Saitama Medical University, Moroyama-machi, Saitama 350-0495, Japan. Electronic address: mycobacteriumtuberculosis@hotmail.com.
[Ti] Título:HIRA-TAN: a real-time PCR-based system for the rapid identification of causative agents in pneumonia.
[So] Source:Respir Med;108(2):395-404, 2014 Feb.
[Is] ISSN:1532-3064
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:UNLABELLED: Identification of the causative pathogen(s) of pneumonia would allow the selection of effective antibiotics and thus reduce the mortality rate and the emergence of drug-resistant pathogens. To identify such pathogens and to obtain these benefits, it is necessary that a clinical test is rapid, accurate, easily performed, and cost-effective. Here, we devised a PCR-based test, named HIRA-TAN, which is able to discriminate therapeutic targets from commensal organisms (e.g. Streptococcus pneumoniae or Haemophilus influenzae) and to detect foreign organisms (e.g. Mycoplasma pneumoniae or Legionella pneumophila) in the sputum. The utility of this system was validated in a prospective study, using sputum samples from patients with pneumonia. 568 patients were enrolled and the HIRA-TAN assay identified the causative pathogens with an accuracy of 96.7% for H. influenzae; 93.2% for Pseudomonas aeruginosa; 80.6% for Klebsiella pneumoniae; 90.9% for Moraxella catarrhalis; 87.5% for Escherichia coli; 78.1% for MRSA and 91.6% for S. pneumoniae. Overall the HIRA-TAN procedure was able to identify the causative pathogens of pneumonia in 60% of the cases. Additionally, this procedure was able to determine when the pneumonia-causing organism was a commensal organism or a foreign organism in a single assay. The HIRA-TAN approach yielded reproducible results and provided valuable information to plan the course of treatment of pneumonia. Through the rapid identification of the causative pathogens, the HIRA-TAN will promote targeted treatments for pneumonias. CLINICAL TRIALS REGISTRATION: UMIN000001694.
[Mh] Termos MeSH primário: Bactérias/isolamento & purificação
Pneumonia Bacteriana/diagnóstico
[Mh] Termos MeSH secundário: Adulto
Idoso
Idoso de 80 Anos ou mais
Feminino
Seres Humanos
Masculino
Meia-Idade
Estudos Prospectivos
Reação em Cadeia da Polimerase em Tempo Real/métodos
Sensibilidade e Especificidade
Escarro/microbiologia
Simbiose
Triacetonamina-N-Oxil
Adulto Jovem
[Pt] Tipo de publicação:JOURNAL ARTICLE; MULTICENTER STUDY; OBSERVATIONAL STUDY; VALIDATION STUDIES
[Nm] Nome de substância:
2896-70-0 (Triacetoneamine-N-Oxyl)
[Em] Mês de entrada:1409
[Cu] Atualização por classe:151119
[Lr] Data última revisão:
151119
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:140114
[St] Status:MEDLINE


  7 / 122 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
PubMed Central Texto completo
Texto completo
[PMID]:23527059
[Au] Autor:Wang YJ; Liu W; Chen C; Yan LM; Song J; Guo KY; Wang G; Wu QH; Gu WW
[Ad] Endereço:Department of Laboratory Animal Center, Southern Medical University, Guangzhou, Guangdong, China.
[Ti] Título:Irradiation induced injury reduces energy metabolism in small intestine of Tibet minipigs.
[So] Source:PLoS One;8(3):e58970, 2013.
[Is] ISSN:1932-6203
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:BACKGROUND: The radiation-induced energy metabolism dysfunction related to injury and radiation doses is largely elusive. The purpose of this study is to investigate the early response of energy metabolism in small intestinal tissue and its correlation with pathologic lesion after total body X-ray irradiation (TBI) in Tibet minipigs. METHODS AND RESULTS: 30 Tibet minipigs were assigned into 6 groups including 5 experimental groups and one control group with 6 animals each group. The minipigs in these experimental groups were subjected to a TBI of 2, 5, 8, 11, and 14 Gy, respectively. Small intestine tissues were collected at 24 h following X-ray exposure and analyzed by histology and high performance liquid chromatography (HPLC). DNA contents in this tissue were also examined. Irradiation causes pathologic lesions and mitochondrial abnormalities. The Deoxyribonucleic acid (DNA) content-corrected and uncorrected adenosine-triphosphate (ATP) and total adenine nucleotides (TAN) were significantly reduced in a dose-dependent manner by 2-8 Gy exposure, and no further reduction was observed over 8 Gy. CONCLUSION: TBI induced injury is highly dependent on the irradiation dosage in small intestine and inversely correlates with the energy metabolism, with its reduction potentially indicating the severity of injury.
[Mh] Termos MeSH primário: Metabolismo Energético/efeitos da radiação
Intestino Delgado/metabolismo
Intestino Delgado/efeitos da radiação
Lesões por Radiação/metabolismo
Porco Miniatura/metabolismo
[Mh] Termos MeSH secundário: Nucleotídeos de Adenina/metabolismo
Animais
Dano ao DNA/efeitos da radiação
Intestino Delgado/patologia
Masculino
Mitocôndrias/metabolismo
Mitocôndrias/efeitos da radiação
Mitocôndrias/ultraestrutura
Dose de Radiação
Suínos
Fatores de Tempo
Triacetonamina-N-Oxil/metabolismo
Irradiação Corporal Total
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, NON-U.S. GOV'T
[Nm] Nome de substância:
0 (Adenine Nucleotides); 2896-70-0 (Triacetoneamine-N-Oxyl)
[Em] Mês de entrada:1309
[Cu] Atualização por classe:150427
[Lr] Data última revisão:
150427
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:130326
[St] Status:MEDLINE
[do] DOI:10.1371/journal.pone.0058970


  8 / 122 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
PubMed Central Texto completo
Texto completo
[PMID]:23320940
[Au] Autor:Kurban MR
[Ad] Endereço:Department of Physics and Astronomy and The Center for Supramolecular Studies, California State University at Northridge, Northridge, California 91330, USA. mkurban@alumni.usc.edu
[Ti] Título:Determination of very rapid molecular rotation by using the central electron paramagnetic resonance line.
[So] Source:J Phys Chem A;117(7):1466-73, 2013 Feb 21.
[Is] ISSN:1520-5215
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:Picosecond rotational correlation times of perdeuterated tempone (PDT) are found in alkane and aromatic liquids by directly using the spectral width of the central electron paramagnetic resonance line. This is done by mathematically eliminating the nonsecular spectral density from the spectral parameter equations, thereby removing the need to assume a particular form for it. This is preferable to fitting a constant correction factor to the spectral density, because such a factor does not fit well in the low picosecond range. The electron-nuclear spin dipolar interaction between the probe and solvent is shown to be negligible for the very rapid rotation of PDT in these liquids at the temperatures of the study. The rotational correlation times obtained with the proposed method generally agree to within experimental uncertainty with those determined by using the traditional parameters. Using the middle line width offers greater precision and smoother trends. Previous work with the central line width is discussed, and past discrepancies are explained as possibly resulting from residual inhomogeneous broadening. The rotational correlation time almost forms a common curve across all of the solvents when plotted with respect to isothermal compressibility, which shows the high dependence of rotation on liquid free volume.
[Mh] Termos MeSH primário: Espectroscopia de Ressonância de Spin Eletrônica
Marcadores de Spin
[Mh] Termos MeSH secundário: Rotação
Fatores de Tempo
Triacetonamina-N-Oxil/química
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, N.I.H., EXTRAMURAL
[Nm] Nome de substância:
0 (Spin Labels); 2896-70-0 (Triacetoneamine-N-Oxyl)
[Em] Mês de entrada:1308
[Cu] Atualização por classe:170220
[Lr] Data última revisão:
170220
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:130117
[St] Status:MEDLINE
[do] DOI:10.1021/jp310890h


  9 / 122 MEDLINE  
              first record previous record next record last record
seleciona
para imprimir
Fotocópia
PubMed Central Texto completo
Texto completo
[PMID]:23123770
[Au] Autor:Biller JR; Meyer VM; Elajaili H; Rosen GM; Eaton SS; Eaton GR
[Ad] Endereço:Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA.
[Ti] Título:Frequency dependence of electron spin relaxation times in aqueous solution for a nitronyl nitroxide radical and perdeuterated-tempone between 250 MHz and 34 GHz.
[So] Source:J Magn Reson;225:52-7, 2012 Dec.
[Is] ISSN:1096-0856
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:Electron spin relaxation times of perdeuterated tempone (PDT) 1 and of a nitronyl nitroxide (2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) 2 in aqueous solution at room temperature were measured by 2-pulse electron spin echo (T(2)) or 3-pulse inversion recovery (T(1)) in the frequency range of 250 MHz to 34 GHz. At 9 GHz values of T(1) measured by long-pulse saturation recovery were in good agreement with values determined by inversion recovery. Below 9 GHz for 1 and below 1.5 GHz for 2,T(1)~T(2), as expected in the fast tumbling regime. At higher frequencies T(2) was shorter than T(1) due to incomplete motional averaging of g and A anisotropy. The frequency dependence of 1/T(1) is modeled as the sum of spin rotation, modulation of g and A-anisotropy, and a thermally-activated process that has maximum contribution at about 1.5 GHz. The spin lattice relaxation times for the nitronyl nitroxide were longer than for PDT by a factor of about 2 at 34 GHz, decreasing to about a factor of 1.5 at 250 MHz. The rotational correlation times, τ(R) are calculated to be 9 ps for 1 and about 25 ps for 2. The longer spin lattice relaxation times for 2 than for 1 at 9 and 34 GHz are due predominantly to smaller contributions from spin rotation that arise from slower tumbling. The smaller nitrogen hyperfine couplings for the nitronyl 2 than for 1 decrease the contribution to relaxation due to modulation of A anisotropy. However, at lower frequencies the slower tumbling of 2 results in a larger value of ωτ(R) (ω is the resonance frequency) and larger values of the spectral density function, which enhances the contribution from modulation of anisotropic interactions for 2 to a greater extent than for 1.
[Mh] Termos MeSH primário: Óxidos de Nitrogênio/química
Marcadores de Spin
Triacetonamina-N-Oxil/química
[Mh] Termos MeSH secundário: Anisotropia
Deutério
Espectroscopia de Ressonância de Spin Eletrônica
Indicadores e Reagentes
Oxigênio/química
Soluções
Água
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, N.I.H., EXTRAMURAL
[Nm] Nome de substância:
0 (Indicators and Reagents); 0 (Nitrogen Oxides); 0 (Solutions); 0 (Spin Labels); 059QF0KO0R (Water); 2896-70-0 (Triacetoneamine-N-Oxyl); AR09D82C7G (Deuterium); GFQ4MMS07W (nitroxyl); S88TT14065 (Oxygen)
[Em] Mês de entrada:1305
[Cu] Atualização por classe:170220
[Lr] Data última revisão:
170220
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:121106
[St] Status:MEDLINE


  10 / 122 MEDLINE  
              first record previous record
seleciona
para imprimir
Fotocópia
PubMed Central Texto completo
Texto completo
[PMID]:22288424
[Au] Autor:Peric M; Bales BL; Peric M
[Ad] Endereço:Department of Physics and Astronomy and The Center for Supramolecular Studies, California State University at Northridge, Northridge, California 91330, USA. peric@usc.edu
[Ti] Título:Electron paramagnetic resonance line shifts and line shape changes due to heisenberg spin exchange and dipole-dipole interactions of nitroxide free radicals in liquids 8. Further experimental and theoretical efforts to separate the effects of the two interactions.
[So] Source:J Phys Chem A;116(11):2855-66, 2012 Mar 22.
[Is] ISSN:1520-5215
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:The work in part 6 of this series (J. Phys. Chem. A 2009, 113, 4930), addressing the task of separating the effects of Heisenberg spin exchange (HSE) and dipole-dipole interactions (DD) on electron paramagnetic resonance (EPR) spectra of nitroxide spin probes in solution, is extended experimentally and theoretically. Comprehensive measurements of perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (pDT) in squalane, a viscous alkane, paying special attention to lower temperatures and lower concentrations, were carried out in an attempt to focus on DD, the lesser understood of the two interactions. Theoretically, the analysis has been extended to include the recent comprehensive treatment by Salikhov (Appl. Magn. Reson. 2010, 38, 237). In dilute solutions, both interactions (1) introduce a dispersion component, (2) broaden the lines, and (3) shift the lines. DD introduces a dispersion component proportional to the concentration and of opposite sign to that of HSE. Equations relating the EPR spectral parameters to the rate constants due to HSE and DD have been derived. By employing nonlinear least-squares fitting of theoretical spectra to a simple analytical function and the proposed equations, the contributions of the two interactions to items 1-3 may be quantified and compared with the same parameters obtained by fitting experimental spectra. This comparison supports the theory in its broad predictions; however, at low temperatures, the DD contribution to the experimental dispersion amplitude does not increase linearly with concentration. We are unable to deduce whether this discrepancy is due to inadequate analysis of the experimental data or an incomplete theory. A new key aspect of the more comprehensive theory is that there is enough information in the experimental spectra to find items 1-3 due to both interactions; however, in principle, appeal must be made to a model of molecular diffusion to separate the two. The permanent diffusion model is used to illustrate the separation in this work. In practice, because the effects of DD are dominated by HSE, negligible error is incurred by using the model-independent extreme DD limit of the spectral density functions, which means that DD and HSE may be separated without appealing to a particular model.
[Mh] Termos MeSH primário: Óxidos de Nitrogênio/química
Esqualeno/análogos & derivados
Triacetonamina-N-Oxil/química
[Mh] Termos MeSH secundário: Difusão
Espectroscopia de Ressonância de Spin Eletrônica
Cinética
Análise dos Mínimos Quadrados
Modelos Químicos
Teoria Quântica
Soluções/química
Esqualeno/química
Temperatura Ambiente
Termodinâmica
Viscosidade
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, N.I.H., EXTRAMURAL
[Nm] Nome de substância:
0 (Nitrogen Oxides); 0 (Solutions); 2896-70-0 (Triacetoneamine-N-Oxyl); 7QWM220FJH (Squalene); GFQ4MMS07W (nitroxyl); GW89575KF9 (squalane)
[Em] Mês de entrada:1207
[Cu] Atualização por classe:170220
[Lr] Data última revisão:
170220
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:120201
[St] Status:MEDLINE
[do] DOI:10.1021/jp210057x



página 1 de 13 ir para página                         
   


Refinar a pesquisa
  Base de dados : MEDLINE Formulário avançado   

    Pesquisar no campo  
1  
2
3
 
           



Search engine: iAH v2.6 powered by WWWISIS

BIREME/OPAS/OMS - Centro Latino-Americano e do Caribe de Informação em Ciências da Saúde