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Carlosbarbosaite, ideally (UO2)(2)Nb2O6(OH)(2)center dot 2H(2)O, a new hydrated uranyl niobate mineral with tunnels from Jaguaracu, Minas Gerais, Brazil: description and crystal structure

Atencio, D.; Roberts, A. C.; Cooper, M. A.; Menezes Filho, L. A. D.; Coutinho, J. M. V.; Stirling, J. A. R.; Venance, K. E.; Ball, N. A.; Moffatt, E.; Chaves, M. L. S. C.; Brandao, P. R. G.; Romano, A. W.
Fonte: MINERALOGICAL SOC; TWICKENHAM Publicador: MINERALOGICAL SOC; TWICKENHAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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Carlosbarbosaite, ideally (UO2)(2)Nb2O6(OH)(2)center dot 2H(2)O, is a new mineral which occurs as a late cavity filling in albite in the Jaguaracu pegmatite, Jaguaracu municipality, Minas Gerais, Brazil. The name honours Carlos do Prado Barbosa (1917-2003). Carlosbarbosaite forms long flattened lath-like crystals with a very simple orthorhombic morphology. The crystals are elongated along [001] and flattened on (100); they are up to 120 mu m long and 2-5 mu m thick. The colour is cream to pale yellow, the streak yellowish white and the lustre vitreous. The mineral is transparent (as individual crystals) to translucent (massive). It is not fluorescent under either long-wave or short-wave ultraviolet radiation. Carlosbarbosaite is biaxial(+) with alpha = 1.760(5), beta = 1.775(5), gamma = 1.795(5), 2V(meas) = 70(1)degrees, 2V(calc) = 83 degrees. The orientation is X parallel to a, Y parallel to b, Z parallel to c. Pleochroism is weak, in yellowish green shades, which are most intense in the Z direction. Two samples were analysed. For sample I, the composition is: UO3 54.52, CaO 2.07, Ce2O3 0.33, Nd2O3 0.49, Nb2O5 14.11, Ta2O5 15.25, TiO2 2.20, SiO2 2.14, Fe2O3 1.08, Al2O3 0.73, H2O (calc.) 11.49, total 104.41 wt.%; the empirical formula is (square 0.68Ca0.28Nd0.02Ce0.02)(Sigma=1.00)[U-1.44 square O-0.56(2.88)(H2O)(1.12)](Nb0.80Ta0.52Si0.27Ti0.21Al0.11Fe0.10)(Sigma=2.01) O-4.72(OH)(3.20)(H2O)(2.08). For sample 2...

Análise do MTA e do Ca(OH)2 no interior dos tecidos após o processo de reabsorção radicular externa em reimplante dentário tardio

Marão, Heloisa Fonseca
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 96 f. : il. + 1 CD-ROM
POR
Relevância na Pesquisa
47.1201%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Pós-graduação em Odontologia - FOA; A clínica tem mostrado que a maioria dos reimplantes dentários é tardia e nessa condição há necrose das células do ligamento periodontal e as reabsorções patológicas podem se instalar e levar à perda do dente. O objetivo do trabalho foi avaliar o MTA e o Ca(OH)2, no interior dos tecidos, após a reabsorção radicular externa em reimplante tardio de dente de rato. Foram utilizados 20 ratos (Rattus norvegicus albinus) machos que tiveram o incisivo direito extraído e mantido em meio seco por 60 minutos. Em seguida, a papila dentária, o órgão do esmalte, a polpa dentária e o ligamento periodontal foram removidos. Os dentes foram imersos em solução de fluoreto de sódio fosfato acidulado a 2% pH 5,5, por 10 minutos. Em seguida os canais foram secos e divididos em 2 grupos: Grupo I - canais radiculares foram preenchidos com pasta de Ca(OH)2 e soro fisiológico e Grupo II - com MTA. Os alvéolos foram irrigados com soro fisiológico e os dentes reimplantados. Após 80 dias foi possível observar extensas áreas de reabsorção por substituição e algumas inflamatória nos dois grupos experimentais. Houve uma reação inflamatória mais intensa em contato com o Ca(OH)2 quando comparado ao MTA. No fundo do alvéolo houve maior neoformação óssea no grupo do MTA...

Synthesis, characterization and microwave dielectric properties of flower - like Co(OH)2/C nanocomposites

Feng,Chao; Bi,Nannan; Liu,Xianguo; Jin,Chuangui; Huang,Kai; Xiao,Feng; Sun,Yuping; Or,Siu Wing
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2014 EN
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Flower - like Co(OH)2/C nanocomposites have been synthesized by a facile hydrothermal method. Flower - like Co(OH)2/C nanocomposites were self - assembled by the nanosheets with the thickness distribution of 50 - 80 nm and abundant flocculent carbon structures. With the help of transmission electron microscopy and energy dispersive spectrometer, nanosheets were observed to have core/shell structure, in which Co(OH)2 worked as cores and amorphous C as shells. When the as - prepared products were heated for 6 h at 180 ºC, the Co(OH)2 cores were amorphous. The heating time increased to 10 h, the Co(OH)2 cores became crystalline. The formation mechanism and the self - assembly evolution process were proposed. The microwave dielectric properties of Co(OH)2/C nanocomposites were investigated in the frequency range of 0.03 - 18 GHz. Compared with the amorphous Co(OH)2/C nanocomposites, crystalline nanocomposites had the better conductivity.

The full-length calcium-sensing receptor dampens the calcemic response to 1α,25(OH)2 vitamin D3 in vivo independently of parathyroid hormone

Egbuna, Ogo; Quinn, Steven; Kantham, Lakshmi; Butters, Robert; Pang, Jiang; Pollak, Martin; Goltzman, David; Brown, Edward
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
47.049478%
1α,25(OH)2 vitamin D3 [1,25(OH)2D3] increases serum Ca2+ concentration in vivo, an action counteracted by activation of the Ca2+-sensing receptor (CaSR), which decreases parathyroid hormone (PTH) secretion and increases renal Ca2+ excretion. Relatively little is known of the role the CaSR plays in this response through its potentially direct actions in kidney, gut, and bone independently of PTH. We report PTH-independent roles of the CaSR in modulating the response to exogenous 1,25(OH)2D3 in mice with targeted disruption of both the CaSR and PTH genes (C−P−) compared with that in mice with disruption of the PTH gene alone (C+P−) or wild-type mice (C+P+). After intraperitoneal injection of 0.5 ng/g body wt 1,25(OH)2D3, peak calcemic responses were observed at 24 h in all three genotypes in association with 1) a greater increase in serum Ca2+ in C−P− mice than in the other genotypes on a Ca2+-replete diet that was attenuated by a Ca2+-deficient diet and pamidronate, 2) increased urinary Ca2+-to-creatinine ratios (UCa/Cr) in the C+P− and C+P+ mice but a lowered ratio in the C−P− mice on a Ca2+-replete diet, and 3) no increase in calcitonin (CT) secretion in the C+P+ and C+P− mice and a small increase in the C−P− mice. PTH deficiency had the anticipated effects on the expression of key genes involved in Ca2+ transport at baseline in the duodenum and kidney...

Template Route to Chemically Engineering Cavities at Nanoscale: A Case Study of Zn(OH)2 Template

Wu, Dapeng; Jiang, Yi; Liu, Junli; Yuan, Yafei; Wu, Junshu; Jiang, Kai; Xue, Dongfeng
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 01/08/2010 EN
Relevância na Pesquisa
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A size-controlled Zn(OH)2 template is used as a case study to explain the chemical strategy that can be executed to chemically engineering various nanoscale cavities. Zn(OH)2 octahedron with 8 vertices and 14 edges is fabricated via a low temperature solution route. The size can be tuned from 1 to 30 μm by changing the reaction conditions. Two methods can be selected for the hollow process without loss of the original shape of Zn(OH)2 template. Ion-replacement reaction is suitable for fabrication of hollow sulfides based on the solubility difference between Zn(OH)2 and products. Controlled chemical deposition is utilized to coat an oxide layer on the surface of Zn(OH)2 template. The abundant hydroxyl groups on Zn(OH)2 afford strong coordination ability with cations and help to the coating of a shell layer. The rudimental Zn(OH)2 core is eliminated with ammonia solution. In addition, ZnO-based heterostructures possessing better chemical or physical properties can also be prepared via this unique templating process. Room-temperature photoluminescence spectra of the heterostructures and hollow structures are also shown to study their optical properties.

1,25(OH)2 vitamin D3 promotes FOXP3 expression via binding to vitamin D response elements in its conserved non-coding sequence region

Kang, Seong Wook; Kim, Sang Hyun; Lee, Naeun; Lee, Won-Woo; Hwang, Kyung-A; Shin, Min Sun; Lee, Seung-Hyun; Kim, Wan-Uk; Kang, Insoo
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Forkhead box P3 (FOXP3)-positive regulatory T cells (Treg) are a unique subset of T cells with immune regulatory properties. Treg cells can be induced from non-Treg CD4+ T cells (induced Treg, iTreg) by T cell receptor (TCR) triggering, IL-2 and TGF-β or retinoic acid. 1,25(OH)2 vitamin D3 (VD3) affects the functions of immune cells including T cells. 1,25(OH)2VD3 binds the nuclear vitamin D receptor (VDR) that binds target DNA sequences known as the vitamin D response element (VDRE). Although 1,25(OH)2VD3 can promote FOXP3 expression in CD4+ T cells with TCR triggering and IL-2, it is unknown whether this effect of 1,25(OH)2VD3 is mediated through direct binding of VDR to the FOXP3 gene without involving other molecules. Also, it is unclear whether FOXP3 expression in 1,25(OH)2VD3-induced Treg (VD-iTreg) cells is critical for the inhibitory function of these cells. Here we demonstrated the presence of VDREs in the intronic conserved non-coding sequence (CNS) region +1714 to +2554 of the human FOXP3 gene and the enhancement of the FOXP3 promoter activity by such VDREs in response to 1,25(OH)2VD3. In addition, VD-iTreg cells suppressed the proliferation of target CD4+ T cells and this activity was dependent on FOXP3 expression. These findings suggest that 1...

1,25(OH)2 vitamin D suppresses macrophage migration and reverses atherogenic cholesterol metabolism in type 2 diabetic patients

Riek, Amy E.; Oh, Jisu; Bernal-Mizrachi, Carlos
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
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Reduced monocyte infiltration into the vessel wall and increased macrophage cholesterol efflux are critical components in atherosclerotic plaque regression. During inflammation, monocyte chemotactic protein 1 (MCP-1) signaling activation and cholesterol deposition in macrophages induce endoplasmic reticulum (ER) stress, which promotes an increased inflammatory response. Increased macrophage ER stress shifts macrophages into an M2 macrophage phenotype with increased cholesterol uptake and deposition. In type 2 diabetes, a population with elevated baseline risk of cardiovascular disease (CVD), vitamin D deficiency doubles that risk. We have found that 1,25-dihydroxy vitamin D [1,25(OH)2D] prevents foam cell formation during macrophage differentiation by suppressing ER stress. However, it is unknown whether suppression of ER stress by 1,25(OH)2D decreases monocyte infiltration and reverses atherogenic cholesterol metabolism in previously-differentiated, vitamin D-deplete macrophages. We collected peripheral monocytes from type 2 diabetic patients and differentiated them into macrophages under vitamin D-deplete or 1,25(OH)2D-supplemented conditions. 1, 25(OH)2D supplementation suppressed macrophage migration in response to MCP-1 and mRNA expression of chemokine (C-C motif) receptor 2 (CCR2)...

Ultrahigh capacitive performance from both Co(OH)2/graphene electrode and K3Fe(CN)6 electrolyte

Zhao, Cuimei; Zheng, Weitao; Wang, Xin; Zhang, Hengbin; Cui, Xiaoqiang; Wang, Haoxiang
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 18/10/2013 EN
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Pseudocapacitance is commonly associated to the reversible redox reactions from electrode materials, but the enhancement in pseudocapacitance that only relies on electrode materials is limited. Here, we explore the possibility of enhancing pseudocapacitance through both Co(OH)2/graphene nanosheets (GNS) electrode and K3Fe(CN)6 electrolyte. With a good conductivity and favoring electron transfer, GNS are hybridized with Co(OH)2 to improve the pseudocapacitance of Co(OH)2, including enhancing its rate capability and electrochemical stability. Adding K3Fe(CN)6 into KOH electrolyte further enhances the pseudocapacitance via both directly contributing pseudocapacitance to Co(OH)2/GNS and promoting the electron gain and loss of Co ions. This novel Co(OH)2/GNS-K3Fe(CN)6/KOH electrode system shows an ultrahigh specific capacitance of 7514 Fg−1 at 16 Ag−1 in mixed 1 M KOH and 0.08 M K3Fe(CN)6, more than 100% coulombic efficiency, and long-term cycling stability (the capacitance retention is 75% after 20000 continuous charge-discharge cycles in mixed 1 M KOH and 0.04 M K3Fe(CN)6).

Isolation and Characterization of a Dihydroxo-Bridged Iron(III,III)(μ-OH)2 Diamond Core Derived from Dioxygen

Coggins, Michael K.; Toledo, Santiago; Kovacs, Julie A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Dioxygen addition to coordinatively unsaturated [Fe(II)(OMe2N4(6-Me-DPEN))](PF6) (1) is shown to afford a complex containing a dihydroxo-bridged Fe(III)2(μ-OH)2 diamond core, [FeIII(OMe2N4(6-Me-DPEN))]2(μ-OH)2(PF6)2•(CH3CH2CN)2 (2). The diamond core of 2 resembles the oxidized methane monooxygenase (MMOox) resting state, as well as the active site product formed following H-atom abstraction from Tyr-OH by ribonucleotide reductase (RNR). The Fe-OH bond lengths of 2 are comparable with those of the MMOHox suggesting that MMOHox contains a Fe(III)2(μ-OH)2 as opposed to Fe(III)2(μ-OH)(μ-OH2) diamond core as had been suggested. Isotopic labeling experiments with 18O2 and CD3CN indicate that the oxygen and proton of the μ-OH bridges of 2 are derived from dioxygen and acetonitrile. Deuterium incorporation (from CD3CN) suggests that an unobserved intermediate capable of abstracting a H-atom from CH3CN forms en route to 2. Given the high C–H bond dissociation energy (BDE= 97 kcal/mol) of acetonitrile, this indicates that this intermediate is a potent oxidant, possibly a high-valent iron oxo. Consistent with this, iodosylbenzene (PhIO) also reacts with 1 in CD3CN to afford the deuterated Fe(III)2(μ-OD)2 derivative of 2. Intermediates are not spectroscopically observed in either reaction (O2 and PhIO) even at low-temperatures (−80 °C)...

A Computational Investigation of the Oxidative Deboronation of BoroGlycine, H2N–CH2–B(OH)2, Using H2O and H2O2

Larkin, Joseph D.; Markham, George D.; Milkevitch, Matt; Brooks, Bernard R.; Bock, Charles W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/10/2009 EN
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We report results from a computational investigation of the oxidative deboronation of BoroGlycine, H2N–CH2–B(OH)2, using H2O and H2O2 as the reactive oxygen species (ROS) to yield aminomethanol, H2N–CH2–OH; these results complement our study on the protodeboronation of BoroGlycine to produce methylamine, H2N–CH3 (Larkin et al. J. Phys. Chem. A, 111, 6489–6500, 2007). Second-order Møller-Plesset (MP2) perturbation theory with Dunning-Woon correlation-consistent (cc) basis sets were used for the calculations with comparisons made to results from Density Functional Theory (DFT) at the PBE1PBE/6-311++G(d,p)(cc-pVDZ) levels. The effects of a bulk aqueous environment were also incorporated into the calculations employing PCM and CPCM methodology. Using H2O as the ROS, the reaction H2O + H2N–CH2–B(OH)2 → H2N–CH2–OH + H–B(OH)2 was calculated to be endothermic, the value of ΔH2980 was +12.0 kcal/mol at the MP2(FC)/cc-pVTZ computational level in vacuo and +13.7 kcal/mol in PCM aqueous media; the corresponding value for the activation barrier, ΔH‡, was +94.3 kcal/mol relative to the separated reactants in vacuo and +89.9 kcal/mol in PCM aqueous media. In contrast, the reaction H2O2 + H2N–CH2–B(OH)2 → H2N–CH2–OH + B(OH)3 was calculated to be highly exothermic with a ΔH2980 value of −100.9 kcal/mol at the MP2(FC)/cc-pVTZ computational level in vacuo and −99.6 kcal/mol in CPCM aqueous media; the highest-energy transition state for the multi-step process associated with this reaction involved the rearrangement of H2N–CH2–B(OH)(OOH) to H2N–CH2–O–B(OH)2 with a ΔH‡ value of +23.2 kcal/mol in vacuo relative to the separated reactants. These computational results for BoroGlycine are in accord with the experimental observations for the deboronation of the FDA approved anti-cancer drug Bortezomib (Velcade™...

Hidróxido de cálcio (Ca(OH)2) e bactérias heterofermentativas como aditivos em silagens de cana-de-açúcar (Saccharum officinarum L.) para alimentação de ruminantes

Mohallem, Renata de Freitas Ferreira
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
47.0529%
O objetivo neste trabalho foi estudar as características de fermentação e qualidade nutricional das silagens de cana-de-açúcar, variedade IAC 862480, ensilada pura (tratamento controle-T1), com inoculante bacteriano/enzimático (Propionibacterium sp e enzimas amilolíticas- T2), inoculadas com bactérias heteroláticas (Lactobacillus buchneri- T3), ou tratadas com hidróxido de cálcio (Ca (OH)2) (inclusão de 0,8%- T4, 1,3%-T5 e 1,8%-T6 a massa verde). Avaliou-se a composição químico bromatológica, pH, ácidos graxos voláteis, etanol, nitrogênio amoniacal, digestibilidade in vitro e recuperação de matéria seca (RMS) num delineamento estatístico inteiramente casualisado composto de 6 tratamentos e três repetições cada. Os tratamentos T2 e T3 apresentaram desempenho semelhante ao T1 para todas as variáveis da composição bromatológica das silagens. Silagens contendo aditivos alcalinos (Ca (OH)2) foram mais eficientes na redução dos componentes da parede celular da cana-de-açúcar em relação ao T1, melhorando a DIVMS. Ao avaliar a RMS e as perdas fermentativas no processo de ensilagem, verificou-se mais uma vez muita semelhança do T1 e com a silagem T2, exceto o teor de etanol que foi menor em T2. Fato que não indica superioridade desta silagem em relação ao controle...

Preparación y caracterización de sorbentes magnésico - cálcicos; Preparation and characterization of magnesium - calcium sorbents

Herrera Palencia, Sandra
Fonte: Universidade de Cantabria Publicador: Universidade de Cantabria
Tipo: Trabalho de Conclusão de Curso
SPA
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47.33032%
RESUMEN: Las empresas de producción de óxidos de magnesio al igual que las de óxido de calcio y cementeras están afectadas por la Directiva de Emisiones Industriales 2010/75 / UE, que establece el consumo asociado y los niveles de emisión, animando a seguir ciertas cuestiones clave del medio ambiente, además de cumplir con los estándares de eficiencia. En la empresa MAGNESITAS NAVARRAS S.A. se obtienen tres subproductos en la fabricación de la magnesia que identificamos como: LG-MgO, LG-D y LG-F. En estudios anteriores ya se ha descrito la reutilización de algunos de estos subproductos. El conocido como óxido de magnesio de bajo grado (LG-MgO) ha demostrado ser eficaz en varias aplicaciones ambientales como la eliminación de amonio y fosfatos de aguas residuales industriales. Se puede afirmar que estos subproductos todavía pueden tener una reutilización aprovechable al final de su ciclo de vida, proporcionando un doble beneficio ambiental y económico. Dentro de esta línea de valorización de subproductos en el grupo CADEF del “Departamento de Química e Ingeniería de Procesos y Recursos” de la Universidad de Cantabria en colaboración con la Universidad de Barcelona se plantea la realización de un estudio de modificación de sólidos residuales de base magnésica y cálcica para su posterior uso en la captación de gases ácidos. En este contexto se plantea como objetivos de este proyecto: preparación de la mezclas modelo de Ca (OH)2/Mg(OH)2...

1,25(OH)2 vitamin D3 stimulates membrane phosphoinositide turnover, activates protein kinase C, and increases cytosolic calcium in rat colonic epithelium.

Wali, R K; Baum, C L; Sitrin, M D; Brasitus, T A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1990 EN
Relevância na Pesquisa
47.16401%
The hormonal form of vitamin D, 1,25(OH)2 vitamin D3 [1,25(OH)2D3], regulates colonic calcium absorption and colonocyte proliferation and differentiation. In this study, we have examined the effect of 1,25(OH)2D3 on membrane phosphoinositide turnover, protein kinase C activation, and regulation of intracellular calcium concentration [( Ca+2]i) in isolated rat colonic epithelium. In a concentration-dependent manner, 1,25(OH)2D3 stimulated breakdown of membrane phosphoinositides within 15 s, generating diacylglycerol and inositol 1,4,5-triphosphate (IP3). 1,25(OH)2D3 rapidly activated colonic protein kinase C, with maximal translocation of activity from the cytosol to the membrane occurring within 1 min of exposure to the secosteroid. Studies performed in isolated colonocytes with the fluorescent dye fura-2 demonstrated that 10(-8) M 1,25(OH)2D3 caused a rapid rise in [Ca+2]i which then transiently decreased before rising to a new plateau value. When these experiments were performed in a calcium-free buffer, an increase in [Ca+2]i was observed, but both the transient and secondary rise were diminished in magnitude, suggesting that 1,25(OH)2D3 may stimulate both release of intracellular calcium stores and calcium influx. 1,25(OH)2D3 stimulated [3H]thymidine uptake in rat colonocytes...

Antidepressants differentially related to 1,25-(OH)2 vitamin D3 and 25-(OH) vitamin D3 in late-life depression

Oude Voshaar, R C; Derks, W J; Comijs, H C; Schoevers, R A; de Borst, M H; Marijnissen, R M
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
47.206445%
A low plasma 25-OH vitamin D3 level is a universal risk factor for a wide range of diseases and has also been implicated in late-life depression. It is currently unknown whether the biologically active form of vitamin D, that is, 1,25-(OH)2 vitamin D3, is also decreased in late-life depression, or whether vitamin D levels correlate with specific depression characteristics. We determined plasma 25-OH vitamin D3, 1,25-(OH)2 vitamin D3 and parathormone levels in 355 depressed older persons and 124 non-depressed comparison subjects (age⩾60 years). Psychopathology was established with the Composite International Diagnostic Interview 2.1, together with potential confounders and depression characteristics (severity, symptom profile, age of onset, recurrence, chronicity and antidepressant drug use). Adjusted for confounders, depressed patients had significantly lower levels of 25-OH vitamin D33 (Cohen's d =0.28 (95% confidence interval: 0.07–0.49), P=0.033) as well as 1,25-(OH)2 vitamin D3 (Cohen's d =0.48 (95% confidence interval: 0.27–0.70), P<0.001) than comparison subjects. Of all depression characteristics tested, only the use of tricyclic antidepressants (TCAs) was significantly correlated with lower 1,25-(OH)2 vitamin D3 levels (Cohen's d =0.86 (95% confidence interval: 0.53–1.19)...

2D titanium carbonitrides and their hydroxylated derivatives: Structural, electronic properties and stability of MXenes Ti3C2-xNx and Ti3C2-xNx(OH)2

Enyashin, A. N.; Ivanovskii, A. L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
47.036855%
3D titanium carbonitrides TiCxNy possess excellent physical, chemical, and mechanical properties, attractive for various industrial applications. Most recently, the uncommon nano-sized layers of 2D-like titanium carbonitrides were fabricated from MAX phases. Herein, the structural, electronic properties and stability of these new compounds as well as their hydroxylated derivatives - so-called MXenes Ti3C2-xNx and Ti3C2-xNx(OH)2 are probed by means of SSC-DFTB calculations. The genesis of the properties is discussed in the sequence: binary MXenes Ti3C2 (Ti3N2) -> their hydroxylated forms Ti3C2(OH)2 (Ti3N2(OH)2) -> pristine MXene Ti3C2-xNx -> hydroxylated Ti3C2-xNx(OH)2. Our results show that the examined materials are metallic-like. The most favorable type of OH-covering is presented by the occupation of the hollow sites between three neighboring carbon (nitrogen) atoms. The formation of 2D MXene carbonitrides with random distribution of C and N atoms was found to be thermodynamically more favorable.

Effect of annealing temperature on morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2

Zhang, Min; Jin, Zhensheng; Zhang, Jingwei; Guo, Xinyong; Yang, Jianjun; Li, Wei; Wang, Xiaodong; Zhang, Zhijun
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/09/2010
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47.0529%
Nanotubed titanic acid (H2Ti2O4(OH)2) was prepared from nanotubed sodium titanate (Na2Ti2O4(OH)2) by an ion exchange reaction in a pH=1 HCl solution. The effect of annealing temperature on the morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2 was studied by means of TEM, XRD, DTG, DSC, BET and ESR. The results showed that nanotubed H2Ti2O4(OH)2 is thermally unstable. Its dehydration consists of two steps. In the first-step dehydration, single-electron-trapped oxygen vacancies (SETOVs) were generated. Accompanying the second-step dehydration, the transition of crystal form from orthorhombic system to anatase took place, at the same time the nanotubes broke. At T>300 {\deg}C, when the SETOV concentration greatly increased, the interaction between SETOV happened. (VOo)x formed could play the role of recombination center of photogenerated e--h+ and make the photocatalytic behavior of TiO2 (anatase, obtained from 500 {\deg}C-treated nanotubed H2Ti2O4(OH)2) to become bad.; Comment: 8 pages, 11 figures

Kinetics and Mechanism of Indene C–H Bond Activation by [(COD)Ir(μ_2-OH)]_2

Ahmed, Tonia S.; Tonks, Ian A.; Labinger, Jay A.; Bercaw, John E.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf; chemical/x-cif
Publicado em 10/06/2013
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The hydroxy-bridged dimer [(COD)Ir(μ_2-OH)]_2 (COD = 1,5-cyclooctadiene) cleanly cleaves C–H bonds in indene and cyclopentadiene to produce (COD)Ir(η^3-indenyl) and (COD)Ir(η^5-C_(5)H_5), respectively. The kinetics of the formation of (COD)Ir(η^3-indenyl) are consistent with a mechanism that involves coordination of indene to [(COD)Ir(μ_2-OH)]_2 followed by rate-determining C–H activation from the iridium dimer–indene unit. Transition-state analysis of the Ir and Rh hydroxy dimers indicates that the C–H activation proceeds through a direct deprotonation of indene by the M–OH unit rather than a stepwise oxidative addition/reductive elimination mechanism. The crystal structure of [(COD)Ir]_5(μ_4-O)(μ_3-O)(μ_2-OH), a dehydration product of [(COD)Ir(μ_2-OH)]_2, is presented.

Aspectos histomicrobiológicos do sistema de canais radiculares e das lesões periapicais em dentes de cães após instrumentação automatizada e medicação intracanal com pastas de Ca(OH)2; Histomicrobiologic aspects of the root canal system and periapical lesions in dogs' teeth after rotary instrumentation and intracanal dressing with Ca(OH)2 pastes

Soares, Janir Alves; Leonardo, Mário Roberto; Silva, Léa Assed Bezerra da; Tanomaru Filho, Mário; Ito, Izabel Yoko
Fonte: Universidade de São Paulo. Faculdade de Odontologia de Bauru Publicador: Universidade de São Paulo. Faculdade de Odontologia de Bauru
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 01/10/2006 ENG
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OBJETIVO: Neste estudo avaliou-se a distribuição dos microrganismos no sistema de canais radiculares (SCR) e região periapical (RP) de cães após instrumentação automatizada e utilização de pastas à base de hidróxido de cálcio CaO(H)2. MATERIAL E MÉTODOS: Lesões periapicais crônicas foram induzidas em 80 raízes de pré-molares de quatro cães. Após a instrumentação com o sistema Profile auxiliado pela solução de hipoclorito de sódio a 5,25%, aplicou-se as seguintes pastas contendo Ca(OH)2: grupo 1-Calen (n=18), grupo 2-Calen/PMCC (n=20), grupo 3-hidróxido de cálcio p.a. + solução anestésica (n=16) e grupo 4-hidróxido de cálcio p.a. + solução de digluconato de clorexidina a 2% (n=18), por 21 dias. Oito canais radiculares sem tratamento endodôntico constituíram o grupo-controle. Nas secções histológicas coradas por Brown & Brenn, avaliou-se a presença de microrganismos nos 3mm apicais do SCR e RP, incluindo o canal radicular principal, deltas, cementoplastos, túbulos dentinários, reabsorções cementárias e lesão periapical. Os resultados foram analisados pelo teste de Mann-Whitney (p;0.05). Nos grupos 1, 2, 3, 4 e controle, os percentuais de sítios do SCR contendo microrganismos foram: 67.6%...

Simultaneous Determination of Ba(OH)2 Content by Conductometric and Potentiometric Titration: A Suggestion of an Experiment to Eletrochemical Teaching in Instrumental Analysis; Determinação Simultânea do Teor de Ba(OH)2 por Titulação Condutométrica e Potenciométrica: Uma Sugestão de Prática para o Ensino de Eletroquímica em Análise Instrumental

Eros Izidoro Amaral; Universidade Federal Fluminense; Marco Antônio G. Teixeira; Universidade Federal Fluminense
Fonte: Revista Virtual de Química Publicador: Revista Virtual de Química
Tipo: ; Formato: binary/octet-stream
Publicado em 18/09/2015 PT
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Conductometric titrations present potential utility in any chemical reaction in which ionic content is much lower in the equivalence point in comparison to another steps of the titration. Conductometric titrations could be performed in some different kinds of reactions, including neutralization and precipitation. The reaction chosen to the experiment was the neutralization between Ba(OH)2 and H2SO4, which is also a precipitation reaction, with formation of BaSO4 as final product. This choice is justified due to the utilization of stocked solutions of Ba(OH)2 to acid gases absorption in the laboratories. The determination of its real content as well as the losses in function of the reaction with naturally present CO2 could be done by titration. The combination of potentiometric and conductometric methods was a choice done in function of the intention to compare them and to show to the students different ways to solve the same problem, coupling two analytical techniques to help them in the development of integrated learning. The results obtained with this experiment were excellent, with very near final points by the two different techniques in the same titration. DOI: 10.5935/1984-6835.20150108; As titulações condutométricas apresentam potencial utilidade em qualquer reação onde o conteúdo iônico seja bem menor no ponto de equivalência em comparação às outras etapas da titulação. Podem ser realizadas titulações condutométricas de diferentes tipos de reação...

Theoretical Chemistry at the Service of the Chemical Defense: Degradation of Nerve Agents in Magnesium Oxide and Hydroxide Surface; A Química Teórica a Serviço da Defesa Química: Degradação de Agentes Neurotóxicos em Superfícies de Óxido e Hidróxido de Magnésio

Raphael S. Alvim; Universidade Federal de Juiz de Fora; Viviane S. Vaiss; Universidade Federal de Juiz de Fora; Alexandre A. Leitão; Universidade Federal de Juiz de Fora; Itamar Borges Júnior; Instituto Militar de Engenharia
Fonte: Revista Virtual de Química Publicador: Revista Virtual de Química
Tipo: ; Formato: binary/octet-stream
Publicado em 24/04/2014 PT
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The Pró-Defesa funding of projects was a joint initiative of CAPES and the Ministry of Defense to fund research in defense. In this article we review the main scientific results obtained in the project “Formação de Pessoal Qualificado em Química Quântica Computacional para Atuação na Área de Defesa Química”, funded by the first edition of Pró-Defesa in 2005, which involved a collaboration between the Departments of Chemistry of the Federal University of Juiz de Fora and of the Military Institute of Engineering. The main goal of this project was to study, using theoretical-computational methods, the potential of magnesium oxide and hydroxide surfaces to degrade organophosphorus (OP) substances used as warfare agents, also known as neurotoxics. These substances inhibit the acetylcholinesterase, enzyme of fundamental role in the central nervous system. The VX (O-ethyl-S-(2-diisopropylethylamino) ethyl methylphosphonothioate) and sarin (isopropyl methylphosphonofluoridate) agents are some of the main neurotoxic agents, thus the search for ways to degrade them is considerably important. In this paper, we present theoretical investigations of two chemical degradation processes of organophosphates: the hydrolysis of a VX-like OP compound (O...