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381.
Cadet J Ravanat JL Martinez GR Medeiros MH Di Mascio P 《Photochemistry and photobiology》2006,82(5):1219-1225
This survey focuses on recent aspects of the singlet oxygen oxidation of the guanine moiety of nucleosides, oligonucleotides, isolated and cellular DNA that has been shown to be the exclusive DNA target for this biologically relevant photogenerated oxidant. A large body of mechanistic data is now available from studies performed on nucleosides in both aprotic solvents and aqueous solutions. A common process to both reaction conditions is the formation of 8-oxo-7,8-dihydroguanine by reduction of 8-hydroperoxyguanine that arises from the rearrangement of initially formed endoperoxide across the 4,8-bond of the purine moiety. However, in organic solvent the hydroperoxide is converted as a major degradation pathway into a dioxirane that subsequently decomposes into a complex pattern of oxidation products. A different reaction that involved the formation of a highly reactive quinonoid intermediate consecutively to the loss of a water molecule from the 8-hydroperoxide has been shown to occur in aqueous solution. Subsequent addition of a water molecule at C5 leads to the generation of a spiroiminodihy-dantoin compound via a rearrangement that involves an acyl shift. However, in both isolated and cellular DNA the latter decomposition pathway is at the best a minor process, because only 8-oxo-7,8-dihydroguanine has been found to be generated. It is interesting to point out that singlet oxygen has been shown to contribute predominantly to the formation of 8-oxo-7,8-dihydroguanine in the DNA of bacterial and human cells upon exposure to UVA radiation. It may be added that the formation of secondary singlet-oxygen oxidation products of 8-oxo-7,8-dihydroguanine, including spiroiminodihydantoin and oxaluric acid that were characterized in nucleosides and oligonucleotide, respectively, have not yet been found in cellular DNA. 相似文献
382.
Apparent reactivity ratios and detailed NMR analysis of copolymerizations of eight membered ring-opening allylic sulfide monomers; 3-methylene-1,5-oxathiocan-2-one 2 and 2,2,4-trimethyl-7-methylene-1,5-dithiocane 5 with methyl methacrylate and styrene are presented. The activated double bond of 2 and unactivated double bond and additional methyl substituents of 5 were found to have a profound affect on reactivity. The copolymerization rates were analyzed based on the lumped parameter kp(f/kt)0.5, which was estimated as a function of monomer composition in the feed. 相似文献
383.
Experimental evidence have been suggesting that the toxicity of metals may involve inflammatory processes, with subsequent sustained overproduction of pro-oxidant reactive species, leading to indirect toxic effects, namely genotoxicity. Neutrophils, as important mediators of the innate defence systems, may have a hitherto not known role on these metal-induced adverse effects. Thus, the aim of the present study was to evaluate the putative activation of human neutrophils' oxidative burst by two groups of metals, the first group being able to undergo redox-cycling reactions (iron, copper, chromium and cobalt), whilst the primary route for the toxicity of the second group is not dependent on redox reactions (mercury and cadmium). The generation of reactive oxygen species (ROS) by metal-stimulated neutrophils was measured using the chemiluminometric probe luminol. Appropriate scavengers and metabolizing enzymes were subsequently used to identify the reactive species produced. The modulatory effects of metals on phorbol myristate acetate (PMA)-activated neutrophils were also studied. To evaluate the contribution of protein kinase C (PKC) on metal stimulatory effect, we used the specific inhibitor of PKC Gö6983. The obtained results showed that, in the present experimental conditions, only Cd (II) has the ability to stimulate the production of superoxide radical (O2−), hydrogen peroxide (H2O2), and hypochlorous acid (HOCl) in isolated human neutrophils. The same metal showed a synergistic effect with PMA. It was also demonstrated that Cd (II) induces neutrophils' oxidative burst mainly via activation of PKC, precluding a significant contribution of other cellular pathways for ROS generation mediated by this metal. These observations indicate that the sustained activation of human neutrophils may contribute for the long term adverse effects on human health mediated by Cd (II). 相似文献
384.
Vívian Aparecida Ricardo Teixeira Ernesto Clóvis Augusto Ribeiro Ossamu Hojo Fernando Luis Fertonani Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2009,97(2):653-656
Bagasse samples from four different sugarcane were directly collected as the residues of milling in a processing plant. The
samples were dried at 105 °C, compressed to small granules and then their TG/DTA and DSC curves in synthetic air were recorded.
Similar thermogravimetric curves were obtained for the different samples and they exhibited four mass loss steps. However,
the analysis of the exotherm DSC peaks showed that the oxidation of the organic matter resulted different enthalpy values
(ΔH/kJ g−1). 相似文献
385.
Additive manufacturing or 3D printing is the advanced method of manufacturing monolithic adsorbent materials. Unlike beads or pellets, 3D monolithic adsorbents possess the advantages of widespread structural varieties, low heat and mass transfer resistance, and low channeling of fluids. Despite a large volume of research on 3D printing of adsorbents having been reported, such studies on porous carbons are highly limited. In this work, we have reported direct ink 3D printing of porous carbon; the ink consisted of commercial activated carbon, a gel of poly(4-vinylphenol) and Pluronic F127 as plasticizer, and bentonite as the binder. The 3D printing was performed in a commercial 3D printer that has been extensively modified in the lab. Upon 3D printing and carbonization, the resultant 3D printed porous carbon demonstrated a stable structure with a BET area of 400 m2/g and a total pore volume of 0.27 cm3/g. The isotherms of six pure-component gases, CO2, CH4, C2H6, N2, CO, and H2, were measured on this carbon monolith at 298 K and pressure up to 1 bar. The selectivity of four gas pairs, C2H6/CH4, CH4/N2, CO/H2, and CO2/N2, was calculated by Ideally Adsorbed Solution Theory (IAST) and reported. Ten continuous cycles of adsorption and desorption of CO2 on this carbon confirmed no loss of working capacity of the adsorbent. 相似文献
386.
387.
Jefferson L. M. A. Gomes Nlio Henderson Marisa C. G. Rocha 《Macromolecular theory and simulations》2001,10(9):816-826
This work presents the vapor–liquid equilibrium calculations in an isothermal flash, applied to polymer solutions, using the Peng–Robinson cubic equation of state modified by Stryjek–Vera, and the mixing rule introduced by Wong–Sandler. This rule allows combining the rigid lattice thermodynamic model of Flory–Huggins to the Peng–Robinson–Stryjek–Vera equation of state. As the Gibbs free energy must be minimum in the equilibrium state, a stochastic optimization method, the simulated annealing algorithm, was used to find out the extreme of this thermodynamic potential. 相似文献
388.
389.
Smart PVCL-based nanogels for photosensitizers were prepared following the thermo precipitation methodology. PVCL-based imprinted and non-imprinted NGs are reported with different percentages of N,N′-methylenebisacrylamide (BIS) as crosslinker agent. Zn(II)phthalocyanine (ZnPc) is employed as a model photosensitizer and incorporated as a template molecule for imprinted NGs or it loads post-synthesis for non-imprinted NGs. In order to analyze the chemical structure, NGs were characterized using infrared microscopy. Hydrodynamic diameter was determined by dynamic light scattering. The phase transition temperature was measured by UV–vis spectroscopy. The phase transition temperature and Dh values were regulated by the percentage of crosslinker and the presence of the photosensitizer as a template or post-synthesis load. In all cases, the yields were acceptable and the smart nanodevices were stable. 相似文献