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991.
Structure of dihydrochalcones and related derivatives and their scavenging and antioxidant activity against oxygen and nitrogen radical species 总被引:1,自引:0,他引:1
Bentes AL Borges RS Monteiro WR de Macedo LG Alves CN 《Molecules (Basel, Switzerland)》2011,16(2):1749-1760
Quantum mechanical calculations at B3LYP/6-31G** level of theory were employed to obtain energy (E), ionization potential (IP), bond dissociation enthalpy (O-H BDE) and stabilization energies (DE(iso)) in order to infer the scavenging activity of dihydrochalcones (DHC) and structurally related compounds. Spin density calculations were also performed for the proposed antioxidant activity mechanism of 2,4,6-trihydroxyacetophenone (2,4,6-THA). The unpaired electron formed by the hydrogen abstraction from the phenolic hydroxyl group of 2,4,6-THA is localized on the phenolic oxygen at 2, 6, and 4 positions, the C? and C? carbon atoms at ortho positions, and the C? carbon atom at para position. The lowest phenolic oxygen contribution corresponded to the highest scavenging activity value. It was found that antioxidant activity depends on the presence of a hydroxyl at the C2 and C4 positions and that there is a correlation between IP and O-H BDE and peroxynitrite scavenging activity and lipid peroxidation. These results identified the pharmacophore group for DHC. 相似文献
992.
This communication describes a new procedure to increase the sensitivity of C(4)D in PDMS/glass microchips. The method consists in doping the insulating layer (PDMS) over the electrodes with nanoparticles of TiO(2), increasing thus its dielectric constant. The experimental protocol is simple, inexpensive, and fast. 相似文献
993.
Zinellu A Sotgia S Usai MF Pintus G Deiana L Carru C 《Analytical and bioanalytical chemistry》2011,399(5):1815-1821
Here, we describe an easy field-amplified sample injection capillary electrophoresis method with UV detection for the separation and detection of free plasma arginine and dimethylated arginines. The analytes were baseline-separated within 22?min by using 50?mmol/L Tris phosphate pH 2.3 as running buffer. The plasma samples were treated with acetonitrile/ammonia for protein elimination, the supernatants were dried, re-swollen in water and directly injected in the capillary without complex cleanup by solid phase extraction and/or tedious sample derivatization procedures. Due to the stacking effects of the electrokinetic injection, it was possible to operate a consistent on-line pre-concentration of the analytes before running the electrophoresis. This procedure allowed to reach a detection limit in the real sample of 10?nmol/L for dimethylated arginines and 20?nmol/L for arginine, thus improving about threefold our previous method, that required a more complicated pre-analytical procedure to concentrate samples. The recovery of plasma ADMA was 99-104% and inter-day CV was less than 3%. The assay performance was evaluated measuring the levels of arginine and its dimethyl derivatives in 50 subjects. The statistical tests for the methods comparison suggest that the data obtained by our new method and by our previous CE assay are similar. 相似文献
994.
Zinellu A Sotgia S De Murtas V Cossu-Rocca P De Miglio MR Muroni MR Mura A Uras MG Contini M Deiana L Carru C 《Analytical and bioanalytical chemistry》2011,399(3):1181-1186
Alterations in global DNA methylation are implicated in several pathobiological processes. The tissues stored as paraffin blocks represent an important source of DNA for retrospective genetic and epigenetic analysis on a large scale. Therefore, we developed the first capillary electrophoresis method able to measure global methylation in formalin-fixed, paraffin-embedded (FFPE) DNA extracts. A field-amplified sample injection capillary electrophoresis method with UV detection for the separation and quantification of cytosine and 5-methylcytosine released following DNA hydrolysis by means of formic acid was employed. Analytes were baseline-separated within 8 min by using 300 mM tris(hydroxymethyl)aminomethane phosphate pH 3.75 as the running buffer. With use of electrokinetic injection the limit of detection (LOD) in real sample was 0.1 nM, thus improving by about 400-fold the LOD of the previously described methods based on capillary electrophoresis. Sample extraction and purification were optimized so that evaluation of the DNA methylation degree was possible starting from 0.5-1 μg of DNA with intra- and interassay relative standard deviations for the 5-methylcytosine to total cytosine ratio of 2.0 and 3.2%, respectively. Because of its high accuracy and throughput, our method will be useful for large-scale applications to determine the implications of genomic DNA methylation levels in tumorigenesis. 相似文献
995.
In the ecosystem of Serra Da Estrela, some plant species have the potential to be used as raw material for extraction of bioactive products. The goal of this work was to determine the phenolic, flavonoid, tannin and alkaloid contents of the methanolic extracts of some shrubs (Echinospartum ibericum, Pterospartum tridentatum, Juniperus communis, Ruscus aculeatus, Rubus ulmifolius, Hakea sericea, Cytisus multiflorus, Crataegus monogyna, Erica arborea and Ipomoea acuminata), and then to correlate the phenolic compounds and flavonoids with the antioxidant activity of each extract. The Folin-Ciocalteu's method was used for the determination of total phenols, and tannins were then precipitated with polyvinylpolypyrrolidone (PVPP); a colorimetric method with aluminum chloride was used for the determination of flavonoids, and a Dragendorff's reagent method was used for total alkaloid estimation. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) and beta-carotene bleaching tests were used to assess the antioxidant activity of extracts. The identification of phenolic compounds present in extracts was performed using RP-HPLC. A positive linear correlation between antioxidant activity index and total phenolic content of methanolic extracts was observed. The RP-HPLC procedure showed that the most common compounds were ferulic and ellagic acids and quercetin. Most of the studied shrubs have significant antioxidant properties that are probably due to the existence of phenolic compounds in the extracts. It is noteworthy to emphasize that for Echinospartum ibericum, Hakea sericea and Ipomoea acuminata, to the best of our knowledge, no phytochemical studies have been undertaken nor their use in traditional medicine been described. 相似文献
996.
William B. Fernandes Angelo Q. Arago Felipe T. Martins Caridad Noda‐Perez Carlito Lariucci Hamilton B. Napolitano 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(7):o226-o229
Two arylsulfonamide derivatives, N‐(4‐acetylphenyl)benzenesulfonamide, C14H13NO3S, and N‐(4‐acetylphenyl)‐2,5‐dichlorobenzenesulfonamide, C14H11Cl2NO3S, differing by the absence or presence of two chloro substituents on one of the phenyl rings, were synthesized and characterized in order to establish structural relationships and the role of chloro substitution on the molecular conformation and crystal assembly. Both arylsulfonamides form inversion‐related dimers through C—H...π and π–π interactions. These dimers pack in a similar way in the two structures. The substitution of two H atoms at the 2‐ and 5‐positions of one phenyl ring by Cl atoms did not substantially alter the molecular conformation or the intermolecular architecture displayed by the unsubstituted sulfonamide. The structural information controlling the assembly of such compounds in their crystal phases is in the (phenyl)benzenesulfonamide molecular framework. 相似文献
997.
Angelo Di Egidio Fabrizio Vestroni 《International Journal of Solids and Structures》2011,48(13):1894-1905
The aim of the paper is the numerical and experimental validation of a previously developed nonlinear one-dimensional model of inextensional, shear undeformable, thin-walled beam with an open cross-section. Nonlinear in-plane and out-of-plane warping and torsional elongation effects are included in the model. To better understand the role of these new contributions a beam with a section with one symmetry axis, undergoing moderately large flexural curvatures and large torsional curvature is taken into account. To obtain a section of a cantilever beam for which the torsional curvature is expected to prevail with respect to the flexural ones, a preliminary study is performed. The attention is focused on the response to static forces and on the stability of the equilibrium branches. Analytical results are compared with results of two different nonlinear finite element models and mainly with experimental results to confirm the validity of the analytical model. Interesting results are obtained for the critical values of the flexural–torsional instability loads. 相似文献
998.
999.
Angelo Morro 《Journal of Elasticity》2011,105(1-2):93-105
Objectivity and compatibility with thermodynamics of evolution equations are examined in connection with the modelling of viscoelastic solids. The purpose of the paper is to show that the evolution equation for the stress is eventually obtained by means of a tensorial internal variable within the framework of the reference configuration. The non-simple character is realized by gradients of the internal variable. The thermodynamic analysis is developed by investigating the entropy inequality in the reference configuration and allowing for a non-zero extra-entropy flux. It follows that the evolution for the Cauchy stress tensor involves the Oldroyd derivative, irrespective of the form of the non-local terms. 相似文献
1000.
Tommaso Benincasa Angelo Favini Costică Moroşanu 《Journal of Optimization Theory and Applications》2011,148(1):14-30
The paper establishes existence, uniqueness and regularity for the solution of a phase-field transition system with non-homogeneous
Cauchy-Neumann boundary conditions. Moreover, some estimates for the solution are given. The non-linear parabolic problem
considered here can be used to modeling the solidification (liquidification) process to a matter. The non-homogeneous boundary
conditions (depending both on time and space variables) can be understood as a boundary control. 相似文献