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61.
Spiegel DA Wiberg KB Schacherer LN Medeiros MR Wood JL 《Journal of the American Chemical Society》2005,127(36):12513-12515
Trialkylboranes (BMe3, BEt3, and BBu3) have been shown to mediate reductive deoxygenation reactions of O-alkyl-S-methyl dithiocarbonates (methyl xanthates) in which water or deuterium oxide functions as the source of hydrogen or deuterium. This method has proven versatile with regard to substrate scope and is capable of providing protio- or deuterioalkane products in high yields with excellent levels of D-incorporation. Ab initio calculations suggest that the trialkylborane-water complex possesses an unusually low O-H bond dissociation energy (73 kcal/mol) and support a radical chain mechanism for this process. Taken together, this report provides evidence for fundamentally novel and previously overlooked modes of reactivity for water and trialkylboranes of wide ranging importance in both theoretical and applied investigations. 相似文献
62.
Alipázaga MV Moreno RG Linares E Medeiros MH Coichev N 《Dalton transactions (Cambridge, England : 2003)》2005,(23):3738-3744
NiIIGGH (GGH = glycylglycylhistidine) reacts rapidly with S(IV), in air-saturated solution, to produce NiIIIGGH. A mechanism is proposed where initial NiIII oxidizes SO3(2-) to SO3*-, which reacts with dissolved oxygen to produce SO5*-, initiating radical chain reactions. DNA strand breaks and 8-oxo-7,8-dihydro-2'-deoxyguanosine formation were observed in air-saturated solutions containing micromolar concentrations of Ni(II) and S(IV). The extent of DNA damage showed dependence on the ratio of the NiIIGGH : S(IV) concentrations and the ionic strength. 相似文献
63.
Miyamoto S Martinez GR Martins AP Medeiros MH Di Mascio P 《Journal of the American Chemical Society》2003,125(15):4510-4517
Peroxynitrite (ONOO-), a biologically active species, can induce lipid peroxidation in biological membranes, thereby leading to the formation of various hydroperoxides. We report herein on the formation of singlet molecular oxygen [O(2) ((1)Delta(g))] in the reaction of peroxynitrite with linoleic acid hydroperoxide (LAOOH) or (18)O-labeled LAOOH. The formation of O(2) ((1)Delta(g)) was characterized by (i) dimol light emission in the red spectral region (lambda > 570 nm) using a red-sensitive photomultiplier; (ii) monomol light emission in the near-infrared region (lambda = 1270 nm) with a liquid nitrogen-cooled germanium diode or a photomultiplier coupled to a monochromator; (iii) the enhacing effect of deuterium oxide on chemiluminescence intensity, as well as the quenching effect of sodium azide; and (iv) chemical trapping of O(2) ((1)Delta(g)) or (18)O-labeled O(2) ((1)Delta(g)) with the 9,10-diphenylanthracene (DPA) and detection of the corresponding DPAO(2) or (18)O-labeled DPA endoperoxide by HPLC coupled to tandem mass spectrometry. Moreover, the presence of O(2) ((1)Delta(g)) was unequivocally demonstrated by a direct spectral characterization of the near-infrared light emission attributed to the transition of O(2) ((1)Delta(g)) to the triplet ground state. For the sake of comparison, O(2) ((1)Delta(g)) deriving from the thermolysis of the endoperoxide of 1,4-dimethylnaphthalene or from the H(2)O(2)/hypochlorite and H(2)O(2)/molybdate systems were also monitored. These novel observations identified the generation of O(2) ((1)Delta(g)) in the reaction of LAOOH with peroxynitrite, suggesting a potential O(2) ((1)Delta(g))-dependent mechanism that contributes to cytotoxicity mediated by lipid hydroperoxides and peroxynitrite reactions in biological systems. 相似文献
64.
Fernanda M. Prado Alexsandra C. Scalfo Sayuri Miyamoto Marisa H.G. Medeiros Paolo Di Mascio 《Photochemistry and photobiology》2020,96(3):560-569
Singlet molecular oxygen is a reactive species involved in biological oxidative processes. The major cellular targets of singlet molecular oxygen are unsaturated fatty acids in the membrane, as well as nucleic acids and proteins. The aim of this study was to investigate whether lipids and commercial hydroperoxides generate singlet molecular oxygen, in presence of nitronium and activated nitronium ion. For this purpose, monomol light emitted in the near-infrared region (λ = 1270 nm) was used to monitor singlet molecular oxygen decay in different solvents, with different hydroperoxides and in the presence of azide. Direct measurements of the singlet molecular oxygen spectrum at 1270 nm recorded during the reaction between lipids and commercial hydroperoxides and nitronium ions unequivocally demonstrated the formation of this excited species. 相似文献
65.
Andrade Breno Henrique da Silva Caluête Rafael Evaristo de Oliveira Danniel Ferreira Gomes Rodinei Medeiros Melo Tadeu Antônio de Azevedo 《Journal of Thermal Analysis and Calorimetry》2020,139(2):905-911
Journal of Thermal Analysis and Calorimetry - Cu–Al–Be polycrystalline SMAs modified with the addition of inoculants show improved ductility, which accredits them for technological... 相似文献
66.
Danilo Augusto Ferreira Fontes Magaly Andreza Marques de Lyra Jeyce Kelle Ferreira de Andrade Giovanna Christinne Rocha de Medeiros Schver Larissa Araújo Rolim Teresinha Gonçalves da Silva José Lamartine Soares-Sobrinho Severino Alves-Júnior Pedro José Rolim-Neto 《Journal of inclusion phenomena and macrocyclic chemistry》2016,85(3-4):281-288
67.
68.
Fernanda Germano Alves Francisco Maugeri Filho Janaína Fernandes de Medeiros Burkert Susana Juliano Kalil 《Applied biochemistry and biotechnology》2010,160(5):1528-1539
In this work, the agitation and aeration effects in the maximization of the β-galactosidase production from Kluyveromyces marxianus CCT 7082 were investigated simultaneously, in relation to the volumetric enzyme activity and the productivity, as well as
the analysis of the lactose consumption and production of glucose, and galactose of this process. Agitation and aeration effects
were studied in a 2 L batch stirred reactor. A central composite design (22 trials plus three central points) was carried out. Agitation speed varied from 200 to 500 rpm and aeration rate from 0.5
to 1.5 vvm. It has been shown in this study that the volumetric enzyme production was strongly influenced by mixing conditions,
while aeration was shown to be less significant. Linear models for activity and productivity due to agitation and aeration
were obtained. The favorable condition was 500 rpm and 1.5 vvm, which lead to the best production of 17 U mL−1 for enzymatic activity, 1.2 U mL−1 h−1 for productivity in 14 h of process, a cellular concentration of 11 mg mL−1, and a 167.2 h−1 volumetric oxygen transfer coefficient. 相似文献
69.
Everaldo Medeiros 《Nonlinear Analysis: Theory, Methods & Applications》2009,71(9):3654-3660
In this paper we study a quasilinear elliptic problem with the Dirichlet boundary condition in a bounded domain involving the operator Au=−Δpu−Δqu. Assuming that the nonlinearity has a concave-convex behavior we obtain some multiplicity results. More precisely, we obtain five nontrivial solutions; two by a minimization argument, two by the mountain pass theorem, and the other by a cohomological linking theorem. 相似文献
70.
In this paper we study existence and properties of solutions of the problem Δw=0 on the half-space with nonlinear boundary condition ∂w/∂η+w=|w|p−2w where 2<p<2(N−1)/(N−2) and N?3. We obtain a ground state solution w=w(x1,…,xN−1,t) which is radial and has exponential decay in the first N−1 variables. Moreover, w has sharp polynomial decay in the variable t. 相似文献