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941.
João Marcos do Ó Everaldo Medeiros 《Journal of Mathematical Analysis and Applications》2008,345(1):286-304
In this paper we study a class of nonhomogeneous Schrödinger equations
−Δu+V(x)u=f(u)+h(x) 相似文献
942.
Leandro M. de Carvalho Paulo C. do Nascimento Denise Bohrer Raquel Stefanello Eduardo J. Pilau Marcelo B. da Rosa 《Electroanalysis》2008,20(7):776-781
This paper describes a new voltammetric procedure for the inorganic speciation of As(III) and As(V) in water samples. The procedure is based on the chemical reduction of arsenate [As(V)] to arsenite [As(III)] followed by the voltammetric determination of total arsenic as As(III) at the hanging mercury drop electrode (HMDE) by adsorptive cathodic stripping voltammetry (AdCSV) in the presence of sodium diethyl dithiocarbamate (SDDC). The reduction step involved the reaction with a mixture of Na2S2O5 and Na2S2O3 in the concentrations 2.5 and 0.5 mg mL?1, respectively, and the sample heating at 80 °C for 45 min. The linear range for the determination of total arsenic as As(III) in the presence of SDDC was between 5 and 150 μg L?1 for a deposition time of 60 s (r=0.992). A detection limit of 1.05 μg L?1 for total As was calculated for the method in water samples using a deposition time of 60 s. The detection limits of 4.2 μg L?1 and 15.0 μg L?1 for total As in seawater and dialysis concentrates, respectively, were calculated using a deposition time of 60 s. The relative standard deviations calculated were 2.5 and 4.0% for five measurements of 20 μg L?1 As(V) as As(III) in water and dialysis concentrates, respectively, after chemical reduction under optimized conditions. The method was applied for the determination of As(III) and total As in samples of dialysis water, mineral water, seawater and dialysis concentrates. Recovery values between 86.0 and 104.0% for As(III) and As(V) added to the samples prove the satisfactory accuracy and applicability of the procedure for the arsenic monitoring. 相似文献
943.
Zecca A Trainotti E Chiari L Bettega MH Sanchez Sd Varella MT Lima MA Brunger MJ 《The Journal of chemical physics》2012,136(12):124305
In this paper we report original measurements of total cross sections (TCSs) for positron scattering from the cyclic ethers oxirane (C(2)H(4)O), 1,4-dioxane (C(4)H(8)O(2)), and tetrahydropyran (C(5)H(10)O). The present experiments focus on the low energy range from ~0.2 to 50 eV, with an energy resolution smaller than 300 meV. This study concludes our systematic investigation into TCSs for a class of organic compounds that can be thought of as sub-units or moieties to the nucleotides in living matter, and which as a consequence have become topical for scientists seeking to simulate particle tracks in matter. Note that as TCSs specify the mean free path between collisions in such simulations, they have enjoyed something of a recent renaissance in interest because of that application. For oxirane, we also report original Schwinger multichannel elastic integral cross section (ICS) calculations at the static and static plus polarisation levels, and with and without Born-closure that attempts to account for the permanent dipole moment of C(2)H(4)O. Those elastic ICSs are computed for the energy range 0.5-10 eV. To the best of our knowledge, there are no other experimental results or theoretical calculations against which we can compare the present positron TCSs. However, electron TCSs for oxirane (also known as ethylene oxide) and tetrahydropyran do currently exist in the literature and a comparison to them for each species will be presented. 相似文献
944.
LS Soares E Silva LS da Santos da Silva L Brumano PC Stringheta M Aparecida de Oliveira Pinto LO Moreira Dias C de Sá Martins Muller E Scio RL Fabri HC Castro M da Penha Henriques do Amaral 《Molecules (Basel, Switzerland)》2012,17(9):10344-10354
Guaco (Mikania glomerata Sprengel) syrup is one of the most popular herbal medicines used to treat the symptoms of asthmatic bronchitis, cough and hoarseness. The coumarin 2H-1-benzopyran-2-one, is one of the major constituents of Guaco and contributes to its pharmacological effects. The pharmaceutical capsule form of dry extract of Guaco is recommended by the Brazilian Program of Medicinal Plants and Herbal Medicines and used in primary health care. In order to identify a new protocol to obtain the raw material for Guaco capsule production we evaluated two methods, including a freeze-drying process (lyophilization) and the spray-dryer technique, as well as the use of two adjuvants, Maltodextrins and Aerosil?, in different concentrations. The coumarin levels of the dried extracts were analyzed by UV-spectrophotometry and HPLC-UV/DAD. The adjuvant Aerosil? 8% showed better dry powder physical appearance. Lyophilization was observed to be the best process to obtain the dry extract of Guaco based on the measured coumarin levels. 相似文献
945.
Arruda M Viana H Rainha N Neng NR Rosa JS Nogueira JM Barreto Mdo C 《Molecules (Basel, Switzerland)》2012,17(3):3082-3092
Acetylcholinesterase inhibition, antioxidant and cytotoxic activities of Hedychium gardnerianum leaf essential oils from S. Miguel Island were determined. All the oils inhibited acetylcholinesterase, with IC(50) values of approximately 1 mg/mL, showing no statistical differences between collection sites. Three oils presented mixed inhibition, whilst one was almost truly competitive. This activity can be attributed to the presence of sesquiterpenes, which constituted more than 60% of the composition of the oils. Regarding the antioxidant activity as measured by the DPPH method, all the oils presented activities similar to reference compounds, although with statistical differences between collection sites. Cytotoxicity measured using Artemia salina classified these oils as moderately toxic, with LC(50) values ranging from 300 to 500 μg/mL. These results indicate a possible application of these oils in aromatherapy as coadjuvants in the treatment of cognitive diseases such as Alzheimer, since they may contribute to increase acetylcholine in cholinergic neurons and simultaneously fight deleterious oxidations responsible by neurological degeneration. 相似文献
946.
dos Santos EO Meira M do Vale AE David JM de Queiróz LP David JP 《Natural product communications》2012,7(6):781-783
Two new ceramides were isolated from the bulbs of Lepidaploa cotoneaster (Willd. ex Spreng.) H. Rob. [Vernonia cotoneaster (Willd. ex Spreng.) Less.)], in addition to germanicol, beta-sitosterol, stigmasterol, 3-beta-O-beta-D-glucopyranosyl-sitosterol, lupeol, lupeoyl acetate and tiliroside. The structures of the new compounds were elucidated by spectral techniques (MS, 1H NMR, 13C NMR, HSQC, HMBC, DEPT, and TOCSY) and were compared with data reported in literature, and were established as 2S*,2'R*,3S*,4R*,11E)-N-[2'-hydroxyhenicosanoyl]-2-amino-nonadec-11-ene-1,3,4-triol (1) and (2S*,2'R*,3S*,4R*,8E)-N-[2'-hydroxytricosanoyl]-2-amino-nonadec-8-ene-1,3,4-triol (2). To establish the structure and to locate the double bond, the methyl ester of the fatty acid and dimethyl disulfide (DMDS) derivatives were prepared for both ceramides. 相似文献
947.
Hossain Md Anawar Maria do Carmo Freitas Nuno Canha Isabel Dionísio Ho Manh Dung Catarina Galinha A. M. G. Pacheco 《Journal of Radioanalytical and Nuclear Chemistry》2012,294(3):377-381
Native plant species, lichens and tailings, sampled from a copper?Csulphide mining area located in southern?Ceastern Portugal, were analysed by neutron activation analysis (INAA) for determination of rare earth elements (REEs). Values of ??REEs and individual REEs concentration of tailing samples are higher than those of natural background concentrations. The higher values of REEs are found in modern slags and the mixture of oxidized gossan and sulphide disseminated country rocks when compared with the alluvial sediments contaminated by mine tailings. The total concentrations of light REEs are higher than those of heavy REEs in all tailing samples. Distribution patterns of PAAS-normalized REEs in mine tailings show slightly LREE enriched and flat HREE pattern with negative Eu anomaly. Lichens accumulated higher concentration of lanthanides than vascular plants. The elevated levels of REEs in lichen, native plant species and tailing samples reflect the contamination of REEs in S?o Domingos mining area. The Carlina corymbosa, Erica australis and Lavandula luisierra accumulated the higher amounts of La, Ce and other REEs than the other plant species grown in this mining area. 相似文献
948.
Peroxidase immobilized on Amberlite IRA-743 resin for on-line spectrophotometric detection of hydrogen peroxide in rainwater 总被引:1,自引:0,他引:1
The importance of atmospheric hydrogen peroxide (H2O2) in the oxidation of SO2 and other compounds has been well established. A spectrophotometric method for the determination of hydrogen peroxide in rainwater is proposed. This method is based on selective oxidation of hydrogen peroxide using an on-line tubular reactor containing peroxidase immobilized on Amberlite IRA-743 resin. The hydrogen peroxide in the presence of phenol, 4-aminoantipyrine and peroxidase, produces a red compound (λ = 505 nm). Beer's law is obeyed in a concentration range of 1–100 μmol l−1 hydrogen peroxide with an excellent correlation coefficient (r = 0.9991), at pH 7.0, with a relative standard deviation (R.S.D.) <2%. The detection limit of the method is 0.7 μmol l−1 (4.8 ng of H2O2 in a 200 μl sample). Measurements of hydrogen peroxide in rain samples were carried out over the period from November 2003 to January 2005, in the central area of the Juiz de Fora city, Brazil. The concentration of H2O2 varied from values lower than the detection limit to 92.5 μmol l−1. The effects of the presence of nonseasalt (NSS) SO42−, NO3− and H+ in the concentration of hydrogen peroxide in the rainwater had been evaluated. The average concentrations of H2O2, NO3−, NSS SO42− and SO42− are 23.4, 18.9, 7.9 and 10.3 μmol l−1, respectively. The pH values for 82% of the collected samples are greater than 5.0. The spectrophotometeric method developed in this work that uses enzyme immobilized on the resin ion-exchange compared with the amperometric method did not present any significant difference in the results. 相似文献
949.
In this work, a hydrophilic clay, Na-montmorillonite from Wyoming, USA, was rendered organophilic by exchanging the inorganic interlayer cations for hexadecyltrimethylammonium ions (HDTA), with the formulae of [(CH3)3N(C16H33)]+ ion. Based on fact that organo-clay has high affinities for non-ionic organic molecules, 1,3,4-thiadiazole-2,5-dithiol was loaded on the HDTA-montmorillonite surface, resulting in the 1,3,4-thiadiazole-2,5-dithiol-HDTA-montmorillonite complex (TDD-organo-clay).The following properties of TDD-organo-clay are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II).The main point of this paper is the construction of a selective sensor, a carbon paste electrode modified with TDD-organo-clay, its properties and its application to the determination of mercury(II) ions, as this element belongs to the most toxic metals. The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination. 相似文献
950.
de Sousa GF Deflon VM Gambardella MT Francisco RH Ardisson JD Niquet E 《Inorganic chemistry》2006,45(11):4518-4525
The synthesis and the IR, NMR (1H, 13C, and 119Sn), and M?ssbauer spectroscopies and single-crystal X-ray diffraction studies of seven-coordinated diorganotin(IV) complexes, namely, [Ph2Sn(Hdapsc)]Cl.H2O.DMF [7; H(2)dapsc = 2,6-diacetylpyridine bis(semicarbazone)], [Me(2)Sn(H2,6Achexim)]Br.H2O [8; H(2)2,6Achexim = 2,6-diacetylpyridine bis(3-hexamethyleneiminylthiosemicarbazone)], [Me(2)Sn(dapmts)] [9; H(2)dapmts = 2,6-diacetylpyridine bis(4-methythiosemicarbazone)], and [nBu2Sn(dapmdtc)] [10; H(2)dapmdtc = 2,6-diacetylpyridine bis(S-methydithiocarbazate)], were done. The determination of the structures of [Ph(2)Sn(Hdapsc)]+, [Me2Sn(H2,6Achexim)]+ and [Me2Sn(dapmts)], [nBu2Sn(dapmdtc)] revealed the presence of monocationic and neutral complexes, respectively. The structures consist of monomeric units in which the Sn(IV) ions exhibit distorted pentagonal-bipyramidal geometries, with the X,N,N,N,X-donor (X = O, S) systems of the ligands lying in the equatorial plane and the organic groups in the apical positions. The C-Sn-C angle in the seven-coordinated diorganotin(IV) complexes was estimated using a correlation between M?ssbauer and X-ray data based on the point-charge model and using new values obtained in this work for [alkyl] = -1.00 mm s(-1) and [aryl] = -0.80 mm s(-1) for complexes containing O,N,N,N,O-pentadentate ligands and new values for [alkyl] = -0.87 mm s(-1) and [aryl] = -0.75 mm s(-1) for complexes containing S,N,N,N,S-pentadentate ligands. 相似文献