1451
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Crispino CC, Fernandes KG, Kamogawa MY, Nóbrega JA, Nogueira ARA, Ferreira MMC. Multivariate Classification of Cigarettes According to Their Elemental Content Determined by Inductively Coupled Plasma Optical Emission Spectrometry. ANAL SCI 2007; 23:435-8. [PMID: 17420548 DOI: 10.2116/analsci.23.435] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
In this paper we describe our study on the characterization of cigarette samples according to their mineral content. Acid digestion assisted by microwaves was employed, and inductively coupled plasma optical emission spectrometry was the analytical technique used for the determination of Al, Ba, Ca, Cu, Fe, K, Mg, Mn, Na, P and Sr in conventional, light, and flavorized cigarettes. Multivariate techniques, such as hierarchical clusters analysis (HCA) and principal-component analysis (PCA), were applied to discriminate among different types of cigarettes. Cluster analysis and principal-component analysis showed differences in cigarettes according to the type and mineral composition. The cigarette samples were divided within the 3 groups according to their mineral composition. Ca, Sr, Cu, K and Na were the most important elements for cigarette classification, and only these 5 variables were sufficient for the classification and discrimination of the evaluated types of cigarettes.
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Affiliation(s)
- Carla C Crispino
- Grupo de Análise Instrumental Aplicada, Departamento de Química, Universidade Federal de São Carlos, Brazil
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1452
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Benedetti AV, Fugivara CS, Cilense MÁR, Rabockai T. Reference Electrodes in Dimethylformamide. ANAL LETT 2006. [DOI: 10.1080/00032718308065250] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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1453
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A solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica for differential pulse adsorptive stripping analysis of nickel in ethanol fuel. Anal Chim Acta 2006; 584:295-301. [PMID: 17386618 DOI: 10.1016/j.aca.2006.11.069] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2006] [Revised: 11/21/2006] [Accepted: 11/27/2006] [Indexed: 11/27/2022]
Abstract
A solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica (SiAt-SPCPE) was applied to Ni(2+) determination in commercial ethanol fuel samples. The proposed method comprised four steps: (1) Ni(2+) preconcentration at open circuit potential directly in the ethanol fuel sample, (2) transference of the electrode to an electrochemical cell containing DMG, (3) differential pulse voltammogram registering and (4) surface regeneration by polishing the electrode. The proposed method combines the high Ni(2+) adsorption capacity presented by 2-aminothiazole organofunctionalized silica with the electrochemical properties of the Ni(DMG)(2) complex, whose electrochemical reduction provides the analytical signal. All experimental parameters involved in the proposed method were optimized. Using a preconcentration time of 20 min, it was obtained a linear range from 7.5 x 10(-9) to 1.0 x 10(-6) mol L(-1) with detection limit of 2.0 x 10(-9) mol L(-1). Recovery values between 96.5 and 102.4% were obtained for commercial samples spiked with 1.0 micromol L(-1) Ni(2+) and the developed electrode was totally stable in ethanolic solutions. The contents of Ni(2+) found in the commercial samples using the proposed method were compared to those obtained by graphite furnace atomic absorption spectroscopy by using the F- and t-test. Neither the F- nor t-values exceeded the critical values at 95% confidence level, confirming that there are not statistical differences between the results obtained by both methods. These results indicate that the developed electrode can be successfully employed to reliable Ni(2+) determination in commercial ethanol fuel samples without any sample pretreatment or dilution step.
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1454
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Santini A, de Oliveira J, Pezza H, Pezza L. A new potentiometric ibuprofenate ion sensor immobilized in a graphite matrix for determination of ibuprofen in tablets. Microchem J 2006. [DOI: 10.1016/j.microc.2006.04.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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1455
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Favaro-Trindade CS, Bernardi S, Bodini RB, De Carvalho Balieiro JC, De Almeida E. Sensory Acceptability and Stability of Probiotic Microorganisms and Vitamin C in Fermented Acerola (Malpighia emarginata DC.) Ice Cream. J Food Sci 2006. [DOI: 10.1111/j.1750-3841.2006.00100.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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1456
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Tartarotti FO, de Oliveira MF, Balbo VR, Stradiotto NR. Determination of Nickel in Fuel Ethanol Using a Carbon Paste Modified Electrode Containing Dimethylglyoxime. Mikrochim Acta 2006. [DOI: 10.1007/s00604-006-0638-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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1457
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Oriňáková R, Turoňová A, Kladeková D, Gálová M, Smith RM. Recent developments in the electrodeposition of nickel and some nickel-based alloys. J APPL ELECTROCHEM 2006. [DOI: 10.1007/s10800-006-9162-7] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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1458
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Espinosa Bosch M, Ruiz Sánchez AJ, Sánchez Rojas F, Bosch Ojeda C. Determination of paracetamol: historical evolution. J Pharm Biomed Anal 2006; 42:291-321. [PMID: 16716555 DOI: 10.1016/j.jpba.2006.04.007] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2006] [Revised: 04/03/2006] [Accepted: 04/10/2006] [Indexed: 10/24/2022]
Abstract
Paracetamol is a common analgesic and antipyretic drug that is used for the relief of fever, headaches and other minor aches and pains. Their determination in pharmaceuticals is of paramount importance, since an overdose of paracetamol can cause fulminating hepatic necrosis and other toxic effects. Many analytical methodologies have been proposed for the determination of paracetamol. The aim of the present study is to evaluate the utility of different techniques for quantification of paracetamol content in pharmaceutical formulations and biological samples.
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Affiliation(s)
- M Espinosa Bosch
- Department of Analytical Chemistry, Faculty of Sciences, University of Málaga, Campus Teatinos, 29071 Málaga, Spain
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1459
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Wada A, Harada M, Okada T. Kinetic Monitoring of Electrophoretically Induced Solute Reaction by Axial Absorption Detection with Liquid-Core Waveguide. Anal Chem 2006; 78:4709-12. [PMID: 16808486 DOI: 10.1021/ac060175c] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Teflon AF-2400 capillary has been used for capillary electrophoretic separation as well as for liquid-core waveguide for axial absorption detection. This separation/detection scheme has allowed continuous monitoring of electrophoretically induced reactions. In this paper, the decomposition of Cd2+ complex with 4-(2-pyridylazo)resorcinol has been tested, and its decomposition kinetics has been studied. A simple modeling has predicted the single-exponential decay of the absorbance detected by the present axial absorption detector and has allowed the estimation of the decomposition rate constant for this reaction.
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Affiliation(s)
- Akira Wada
- Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan
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1460
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Gomes J, Pires AM, Serra OA. Nanocrystalline RE2O3:Tm3+ (RE: Gd3+, Y3+) Blue Phosphors Synthesized via the Combustion Method. J Fluoresc 2006; 16:411-21. [PMID: 16791505 DOI: 10.1007/s10895-006-0090-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Accepted: 02/27/2006] [Indexed: 10/24/2022]
Abstract
This work reports on the preparation of a luminescent blue-emitting rare earth (RE) Tm-doped oxide phosphor. Nanocrystalline RE2O3:Tm3+ particles were prepared via the combustion method using citric acid, glycine, or urea as fuels. Samples were doped with different percentages of the activator Tm3+. The post-annealing treatment was performed in air for all the samples, at temperatures ranging from 800 to 1100 degrees C, for 4 h. The samples were characterized by X-ray diffraction (XRD), photoluminescence spectroscopy (PL) and scanning electron and transmission microscopies (SEM and TEM) in order to determine the best synthetic procedure. The post-annealed powders showed blue emission with maximum at 452 nm characteristics for Tm3+ transition 1D2 --> 3H4 (under UV excitation at 360 nm). Samples, presented a tri-dimensional porous structure (50-200 nm) formed of spheroid particles with a diameter between 20 and 60 nm. The best luminescent material was obtained when urea was used to prepare nanoparticles of Gd2O3 doped with 0.5% Tm3+, and 1100 degrees C was used as the post-annealing temperature.
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Affiliation(s)
- Janaína Gomes
- Laboratório de Terras Raras, Departamento de Química, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, São Paulo, Brazil.
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1461
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de Souza Gonçalves A, Antonio Marques de Lima S, Rosaly Davolos M, Gutierrez Antônio S, de Oliveira Paiva-Santos C. The effects of ZnGa2O4 formation on structural and optical properties of ZnO:Ga powders. J SOLID STATE CHEM 2006. [DOI: 10.1016/j.jssc.2006.01.046] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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1462
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De Souza D, de Toledo R, Suffredini H, Mazo L, Machado S. Characterization and Use of Copper Solid Amalgam Electrode for Electroanalytical Determination of Triazines-Based Herbicides. ELECTROANAL 2006. [DOI: 10.1002/elan.200503441] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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1463
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Saczk AA, Okumura LL, Oliveira MFD, Zanoni MVB, Stradiotto NR. Determination of Aldehydes and Ketones in Fuel Ethanol by High-Performance Liquid Chromatography with Electrochemical Detection. Chromatographia 2006. [DOI: 10.1365/s10337-005-0698-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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1464
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Oliveira Neto A, Dias RR, Ribeiro VA, Spinacé EV, Linardi M. Eletro-oxidação de etanol sobre eletrocatalisadores PtRh/C, PtSn/C e PtSnRh/C preparados pelo método da redução por álcool. ECLÉTICA QUÍMICA 2006. [DOI: 10.1590/s0100-46702006000100010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Os eletrocatalisadores PtRh/C, PtSn/C e PtSnRh/C foram preparados pelo método da redução por álcool e caracterizados pelas técnicas de EDX, difração de raios X e voltametria cíclica. A eletro-oxidação direta de etanol foi estudada por voltametria cíclica utilizando a técnica do eletrodo de camada fina porosa. Na região de interesse para aplicações em células a combustível a etanol direto (0,3 a 0,4 V) os eletrocatalisadores PtSn/C e PtSnRh/C se mostraram mais ativos que os eletrocatalisadores PtRh/C.
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Affiliation(s)
| | - R. R. Dias
- Instituto de Pesquisas Energéticas e Nucleares, Brasil
| | - V. A. Ribeiro
- Instituto de Pesquisas Energéticas e Nucleares, Brasil
| | - E. V. Spinacé
- Instituto de Pesquisas Energéticas e Nucleares, Brasil
| | - M. Linardi
- Instituto de Pesquisas Energéticas e Nucleares, Brasil
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1465
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1466
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Ferenc W, Walków-Dziewulska A, Sarzynski J, Paszkowska B. Magnetic, thermal and spectral properties of Ni(II) 2,3- , 3,5- and 2,6-dimethoxybenzoates. ECLÉTICA QUÍMICA 2006. [DOI: 10.1590/s0100-46702006000300007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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1467
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Fonseca JCL, Silva MRA, Bautitz R, Nogueira RFP, Marchi MRR. Avaliação da confiabilidade analítica das determinações de carbono orgânico total (COT). ECLÉTICA QUÍMICA 2006. [DOI: 10.1590/s0100-46702006000300006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Observando a literatura pode ser verificado um crescente número de trabalhos que determinam potenciais contaminantes presentes em matrizes de interesse ambiental. É importante ressaltar que quando se estuda o ambiente, os dados analíticos são uma das ferramentas usadas para se avaliar a extensão dos problemas observados que conseqüentemente influenciam as tomadas de decisão. Assim a confiabilidade desses dados é de extrema importância. Neste contexto, este trabalho visa avaliar a confiabilidade analítica das determinações de Carbono Orgânico Total (COT), ferramenta empregada no monitoramento da matéria orgânica em diversos estudos ambientais. Para essa avaliação foram analisados alguns parâmetros de desempenho como limite de detecção e quantificação, repetibilidade e linearidade.
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1468
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Lourenço LM, Martins FG, Balbo VR, Pimenta AC, Castro JRM, Andrade JF. Spectrophotometric study of the chromium(III)/azide system in the ultraviolet region and its analytical application. ECLÉTICA QUÍMICA 2006. [DOI: 10.1590/s0100-46702006000400004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A sensitive and alternative method for the spectrophotometric determination of chromium(III) based on the formation of chromium(III)/azide complexes was established by investigating a new band in the ultraviolet region. The best experimental conditions for the analytical determination of this metallic ion were: ligand and perchloric acid analytical concentration = 493 and 12.0 mmol L-1, respectively; aqueous medium; T = 25.0 ºC; contact time = 1 hour. The maximum molar absorptivity coefficient occurred at 287 nm (average 1.481 ± 0.008 <FONT FACE=Symbol>´</FONT> 10(4) L mol-1 cm-1), leading to the determination of metal ion concentrations one hundred times lower than the ones formerly determined in the visible region. The system obeys Beer's Law and is suitable for chromium determination in the 0.702-2.81 mg L-1 concentration range (15-65% T, 1.00 cm-width quartz cells). Analytical applications of the current method were tested with a nutritional supplement containing chromium. Results were compared with those obtained with atomic absorption spectrometry.
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1469
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ANTOLINI E, SALGADO J, SANTOS L, GARCIA G, TICIANELLI E, PASTOR E, GONZALEZ E. Carbon supported Pt–Cr alloys as oxygen-reduction catalysts for direct methanol fuel cells. J APPL ELECTROCHEM 2005. [DOI: 10.1007/s10800-005-9072-0] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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1470
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De Souza D, de Toledo R, Mazo L, Machado S. Utilization of a Copper Solid Amalgam Electrode for the Analytical Determination of Atrazine. ELECTROANAL 2005. [DOI: 10.1002/elan.200503331] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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1471
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Santana RAC, Prasad S, Campos ARN, Araújo FO, Silva GPD, Lima-Neto PD. Electrodeposition and corrosion behaviour of a Ni–W–B amorphous alloy. J APPL ELECTROCHEM 2005. [DOI: 10.1007/s10800-005-9046-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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1472
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Alcântara AFC, Silveira D, Chiari E, Oliveira AB, Guimarães JE, Raslan DS. Comparative analysis of the trypanocidal activity and chemical properties of E-lychnophoric acid and its derivatives using theoretical calculations. ECLÉTICA QUÍMICA 2005. [DOI: 10.1590/s0100-46702005000300005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
E-Lychnophoric acid 1, its derivative ester 2 and alcohol 3 killed 100% of trypomastigote blood forms of Trypanosoma cruzi at the concentrations of 13.86, 5.68, and 6.48 µg/mL, respectively. Conformational distribution calculations (AM1) of 1, 2 and 3 gave minimum energies for the conformers a, b, c, and d, which differ from each other only in the cyclononene ring geometry. Calculations (DFT/BLYP/6-31G*) of geometry optimization and chemical properties were performed for conformers of 1, 2, and 3. The theoretical results were numerically compared to the trypanocidal activity. Calculated values of atomic charge, orbital population, and vibrational frequencies showed that the C-4-C-5 pi-endocyclic bond does not affect the trypanocidal activity of the studied compounds. Nevertheless, the structure of the group at C-4 strongly influences the activity. However, the theoretical results indicated that the intra-ring (C-1 and C-9) and pi-exocycle (C-8 and C-14) carbons of caryophyllene-type structures promote the trypanocidal activity of these compounds.
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Affiliation(s)
| | | | - E. Chiari
- Universidade Federal de Minas Gerais
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1473
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Moon JW, Moon HS, Kim H, Roh Y. Remediation of TCE-contaminated groundwater using zero valent iron and direct current: experimental results and electron competition model. ACTA ACUST UNITED AC 2005. [DOI: 10.1007/s00254-005-0023-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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1474
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Carbon-Supported Pt-Ni Alloys Prepared by the Borohydride Method as Electrocatalysts for DMFCs. ACTA ACUST UNITED AC 2005. [DOI: 10.1149/1.1870632] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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1475
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Barbosa LCA, Maltha CRA, Demuner AJ, Silva VL, Oliveira FM, Borges EEL. Fitotoxicidade de novos álcoois e alquenos derivados do 2alfa,4alfa-dimetil-8-oxabiciclo[3.2.1]oct-6-en-3-ona. ECLÉTICA QUÍMICA 2005. [DOI: 10.1590/s0100-46702005000400005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A reação de cicloadição [4+3] entre o furano e o cátion oxialílico, gerado in situ a partir da 2,4-dibromopentan-3-ona, forneceu o 2alfa,4alfa-dimetil-8-oxabiciclo[3.2.1]oct-6-en-3-ona (1). A oxidação catalítica do oxabiciclo 1 com tetróxido de ósmio em presença de peróxido de hidrogênio em excesso levou à formação do acetonídeo 10, a partir do qual foram obtidos os álcoois 2, 11-15, com rendimentos de 23-86%. O tratamento dos álcoois 11-13 com cloreto de tionila, em presença de piridina, resultou nos respectivos alquenos 17 (94%), 18 (89%) e 19 (80%). A atividade herbicida dos compostos foi avaliada sobre o desenvolvimento do sistema radicular de Sorghum bicolor L. e Cucumis sativus L., nas concentrações de 100 e 250 ppm.
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1476
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Rosa MFD, Savariz FC. Síntese e estudo da fotoestabilidade de derivados azalactônicos encapsulados em beta-ciclodextrina. ECLÉTICA QUÍMICA 2005. [DOI: 10.1590/s0100-46702005000400010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neste trabalho foram sintetizados 12 derivados azalactônicos pela metodologia clássica de Plöchl-Erlenmeyer. Destes, um foi avaliado quanto a fotoestabilidade em solução por meio de experimentos de fotodegradação utilizando agentes encapsulantes e diferentes solventes. Para a irradiação das amostras foi empregada uma lâmpada de mercúrio de 80W. Os resultados mostram que a fotodegradação do corante ocorre muito mais rapidamente em solventes polares e que o agente encapsulante é fundamental na sua fotoestabilidade.
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Affiliation(s)
- M. F. da Rosa
- Grupo Interdisciplinar de Pesquisa em Fotoquímica e Eletroanalítica Ambiental Química, Brasil
| | - F. C. Savariz
- Grupo Interdisciplinar de Pesquisa em Fotoquímica e Eletroanalítica Ambiental Química, Brasil
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1477
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Soylak M. Solid Phase Extraction of Cu(II), Pb(II), Fe(III), Co(II), and Cr(III) on Chelex‐100 Column Prior to Their Flame Atomic Absorption Spectrometric Determinations. ANAL LETT 2004. [DOI: 10.1081/al-120034064] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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1478
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Peres P, Lombardi FR, Dos Santos GC, Olivieri JR, Canduri F, Bonilla-Rodriguez GO, de Azevedo WF. Molecular modeling and small angle X-ray scattering studies of Hoplosternum littorale cathodic haemoglobin. Biochem Biophys Res Commun 2004; 325:487-93. [PMID: 15530418 DOI: 10.1016/j.bbrc.2004.10.061] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2004] [Indexed: 11/19/2022]
Abstract
Considerable interest is currently focused on fish haemoglobins in order to identify the structural basis for their diversity of functional behavior. Hoplosternum littorale is a catfish that presents bimodal gill (water)/gut (air)-breathing, which allows this species to survive in waters with low oxygen content. The hemolysate of this fish showed the presence of two main haemoglobins, cathodic and anodic. This work describes structural features analyzed here by integration of molecular modeling with small angle X-ray scattering. Here is described a molecular model for the cathodic haemoglobin in the unliganded and liganded states. The models were determined by molecular modeling based on the high-resolution crystal structure of fish haemoglobins. The structural models for both forms of H. littorale haemoglobin were compared to human haemoglobin.
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Affiliation(s)
- P Peres
- Programa de Pós-graduação em Biofísica Molecular, Departamento de Física, UNESP, R. Cristóvão Colombo, 2265 São José do Rio Preto, SP 15054-000, Brazil
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1479
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1480
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Valadares MC, Klein SI, Queiroz MLS. Titanocene modulation of cytokine imbalance induced by Ehrlich ascites tumour progression. Eur J Pharmacol 2004; 503:203-8. [PMID: 15496315 DOI: 10.1016/j.ejphar.2004.08.047] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2004] [Revised: 08/09/2004] [Accepted: 08/18/2004] [Indexed: 11/21/2022]
Abstract
In the present work, we have studied the effects of two titanocenes, biscyclopentadienyldichlorotitanium IV (DDCT) and its derivative, biscyclopentadienylditiocianatetitanium IV (BCDT), on the production of cytokines [interferon-gamma (IFN-gamma), interelukin-1, interleukin (IL) 2, IL-4, and IL-10] by concanavalin A (Con A)-stimulated T cells obtained from Ehrlich ascites tumour (EAT)-bearing BALB/c mice. The treatment consisted of intraperitoneal (i.p) administration of 15 mg/kg/day DDCT for 2 days or 10 mg/kg/day BCDT for 3 days. We observed that the levels of IFN-gamma, but not IL-2, were dramatically increased in the early phase of EAT development. With tumour evolution, however, a sharp and progressive decrease in the levels of both IFN-gamma and IL-2 was found concomitantly to an enhancement in the levels of IL-10. Treatment of these mice with both titanocene compounds demonstrated that DDCT is more effective in modulating the cytokine imbalance induced by the tumour since it could prevent the early enhancement of IFN-gamma, the late decline of IFN-gamma and IL-2, and the increase in the IL-10. The administration of BCDT, in spite of preventing early IFN-gamma enhancement and increase in IL-10, did not produce any change in the IL-2 levels and did not prevent the decline of IFN-gamma levels during tumour evolution. Collectively, these results reveal that the ability of titanocenes to reverse tumour-induced immunosuppression and delay tumour growth is more evident in the DDCT compound, thus indicating that the substitution of the halides halogens by pseudohalogens, present in the molecular structure of BCDT, leads to a less effective antitumoral compound.
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Affiliation(s)
- Marize C Valadares
- Departamento de Farmacologia e Hemocentro, Faculdade de Ciências Médicas, FCM, Universidade Estadual de Campinas, UNICAMP, PO Box 6111, Campinas, SP CEP 13083-970, Brazil
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1481
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Giacomelli MBO, Silva JBBD, Saint'Pierre TD, Curtius AJ. Use of iridium plus rhodium as permanent modifier to determine As, Cd and Pb in acids and ethanol by electrothermal atomic absorption spectrometry. Microchem J 2004. [DOI: 10.1016/j.microc.2004.02.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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1482
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Canduri F, dos Santos DM, Silva RG, Mendes MA, Basso LA, Palma MS, de Azevedo WF, Santos DS. Structures of human purine nucleoside phosphorylase complexed with inosine and ddI. Biochem Biophys Res Commun 2004; 313:907-14. [PMID: 14706628 DOI: 10.1016/j.bbrc.2003.11.179] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Human purine nucleoside phosphorylase (PNP) is a ubiquitous enzyme which plays a key role in the purine salvage pathway, and PNP deficiency in humans leads to an impairment of T-cell function, usually with no apparent effect on B-cell function. PNP is highly specific for 6-oxopurine nucleosides and exhibits negligible activity for 6-aminopurine nucleosides. The catalytic efficiency for inosine is 350,000-fold greater than for adenosine. Adenine nucleosides and nucleotides are deaminated by adenosine deaminase and AMP deaminase to their corresponding inosine derivatives which, in turn, may be further degraded. Here we report the crystal structures of human PNP in complex with inosine and 2('),3(')-dideoxyinosine, refined to 2.8A resolution using synchrotron radiation. The present structures provide explanation for ligand binding, refine the purine-binding site, and can be used for future inhibitor design.
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Affiliation(s)
- Fernanda Canduri
- Departamento de Física, UNESP, São José do Rio Preto, SP 15054-000, Brazil
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1483
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Roldan PS, Alcântara IL, Rocha JC, Padilha CCF, Padilha PM. Determination of Copper, Iron, Nickel and Zinc in fuel kerosene by FAAS after adsorption and pre-concentration on 2-aminothiazole-modified silica gel. ECLÉTICA QUÍMICA 2004. [DOI: 10.1590/s0100-46702004000200005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Silica gel chemically modified with 2-Aminotiazole groups, abbreviated as SiAT, was used for preconcentration of copper, zinc, nickel and iron from kerosene, normally used as a engine fuel for airplanes. Surface characteristics and surface area of the silica gel were obtained before and after chemical modification using FT-IR, Kjeldhal and surface area analysis (B.E.T.). The retention and recovery of the analyte elements were studied by applying batch and column techniques. The experimental parameters, such as shaking time in batch technique, flow rate and concentration of the eluent (HCl- 0.25-2.00 mol L-1) and the amount of silica, on retention and elution, have been investigated. Detection limits of the method for copper, iron, nickel and zinc are 0.77, 2.92, 1.73 and 0.097 mg L-1, respectively. The sorption-desorption of the studied metal ions made possible the development of a preconcentration method for metal ions at trace level in kerosene using flame AAS for their quantification.
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1484
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Santini AO, Silva Júnior ESD, Pezza HR, Pezza L. Determinação de parâmetros físico-químicos com um sensor potenciométrico sensível ao íon p-aminobenzoato. ECLÉTICA QUÍMICA 2004. [DOI: 10.1590/s0100-46702004000100002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Este trabalho descreve a construção e a determinação de parâmetros físico-químicos com um eletrodo de segunda ordem do tipo, Pt|Hg|Hg2(PAB)2|Grafite, sensível ao íon p-aminobenzoato (PAB). O eletrodo é construído facilmente, apresenta um rápido tempo de resposta, é de baixo custo e tem um tempo de vida útil superior a 12 meses. Utilizando o referido eletrodo foi possível estimar os coeficientes de atividade iônica individuais do PAB, a 25ºC, em força iônica ajustada entre 0,700-3,000 mol L-1 com NaClO4, em solução aquosa. O potencial molal padrão do eletrodo determinado a 25ºC é de (445,5 ± 0,5) mV. A constante termodinâmica do produto de solubilidade, T Kps (I=0) do Hg2(PAB)2 determinada com o eletrodo é de (T Kps = 2,50 x 10-12 mol³ L-3 , a 25ºC). Uma característica favorável consiste no fato de que o eletrodo pode ser utilizado para determinar a concentração de íons p-aminobenzoato livres em sistemas complexos de íons metálicos.
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Affiliation(s)
| | | | | | - L. Pezza
- Universidade Estadual Paulista, Brasil
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1485
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Muraoka TK, Zutin K, Ananias SR, Mauro AE, Nogueira VM, Rechenberg HR. Investigação por espectroscopia Mössbauer de compostos de ferro(0) contendo dissulfeto de carbono. ECLÉTICA QUÍMICA 2004. [DOI: 10.1590/s0100-46702004000200004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neste trabalho são apresentados resultados proveniente da aplicação da Espectroscopia Mössbauer na investigação de compostos carbonilferro contendo o ligante CS2, [Fe(CO)2(h²-CS2 )(PPh3)2] e [Fe(CO)2(h²-CS2) {P(OPh)3}2]. Nas sínteses dessas espécies, a utilização de TMNO (trimetilaminóxido) como agente descarbonilante mostrou-se bastante eficiente, superando aquelas descritas na literatura que requerem inclusive preparação de compostos precursores. Os resultados de espectroscopia Mössbauer, juntamente com dados no IV e de RMN de 31P, foram conclusivos na proposição da geometria octaédrica distorcida ao redor do átomo de ferro para ambos os compostos investigados.
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1486
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Moro AC, Mauro AE, Ananias SR. Clivagem dos ciclopaladados diméricos [Pd(dmba)(m-X)]2 (dmba = N,N-dimetilbenzilamina; X = Cl, N3, NCO) por tiouréia. ECLÉTICA QUÍMICA 2004. [DOI: 10.1590/s0100-46702004000100007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ciclopaladados diméricos do tipo [Pd(dmba)(m-X)]2 (dmba = N,N-dimetilbenzilamina; X = Cl, N3, NCO) reagem com tiouréia (tu), à temperatura ambiente, resultando espécies mononucleares do tipo [Pd(dmba)(X)(tu)]. Todos os compostos foram caracterizados por análise elementar, espectroscopias no IV e de RMN de ¹H e com base nessas técnicas as estruturas, desses compostos, foram propostas. Os espectros de absorção no infravermelho mostraram que a coordenação da tiouréia, ao paládio, ocorre através do átomo de enxofre. O anel ciclometalado foi confirmado através da espectroscopia de RMN de ¹H.
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1487
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Ramos LA, Cassiano NM, Capelato MD. Utilização de um eletrodo de grafite recoberto com PbO2 incorporado em matriz de PVC como eletrodo indicador em titulações coulométricas. ECLÉTICA QUÍMICA 2004. [DOI: 10.1590/s0100-46702004000200010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A aplicação de um eletrodo sensível a íons H3O+, obtido pelo recobrimento de um eletrodo de grafite com uma membrana polimérica contendo PbO2 incorporado em uma matriz de PVC (PbO2-PVC), como eletrodo indicador em titulações coulométricas de neutralização, foi investigada. As leituras dos potenciais foram feitas usando o eletrodo indicador de PbO2-PVC e para comparação dos resultados foi usado um eletrodo de vidro combinado (EVC). As curvas de titulação monitoradas com o eletrodo de PbO2-PVC apresentaram características semelhantes àquelas monitoradas com o EVC e os tempos de equivalência obtidos foram concordantes a um nível de confiança de 95%. O eletrodo de PbO2-PVC apresentou resposta linear no intervalo de pH 2 a 12 com inclinação de Nernst de -57,6 ± 0,1 mV/pH (r= 0,9998), sendo o tempo de resposta deste eletrodo bem menor do que aquele obtido com o EVC. O eletrodo de PbO2-PVC é de fácil construção, possui baixo custo e tempo de vida útil superior a 4 meses, equivalente a (pelo menos 1200 determinações por membrana polimérica).
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1488
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Schnitzler E, Kobelnik M, Sotelo GFC, Bannach G, Ionashiro M. Thermoanalytical study of purine derivatives compounds. ECLÉTICA QUÍMICA 2004. [DOI: 10.1590/s0100-46702004000100009] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Thermal methods of analysis are now used in a very large range of scientific investigations. In this work simultaneous thermogravimetry-differential thermal analysis (TG-DTA), X-Ray powder diffractometry and infrared spectroscopy were used to study the derivative compounds of purine, i. e. aminophylline, theophylline, caffeine and uric acid. The results led to informations about the thermal stability and thermal decomposition of these compounds.
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Affiliation(s)
| | - M. Kobelnik
- Universidade Estadual de Ponta Grossa, Brasil
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1489
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de Azevedo WF, Canduri F, dos Santos DM, Pereira JH, Bertacine Dias MV, Silva RG, Mendes MA, Basso LA, Palma MS, Santos DS. Crystal structure of human PNP complexed with guanine. Biochem Biophys Res Commun 2003; 312:767-72. [PMID: 14680831 DOI: 10.1016/j.bbrc.2003.10.190] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2003] [Indexed: 11/22/2022]
Abstract
Purine nucleoside phosphorylase (PNP) catalyzes the phosphorolysis of the N-ribosidic bonds of purine nucleosides and deoxynucleosides. PNP is a target for inhibitor development aiming at T-cell immune response modulation and has been submitted to extensive structure-based drug design. More recently, the 3-D structure of human PNP has been refined to 2.3A resolution, which allowed a redefinition of the residues involved in the substrate-binding sites and provided a more reliable model for structure-based design of inhibitors. This work reports crystallographic study of the complex of Human PNP:guanine (HsPNP:Gua) solved at 2.7A resolution using synchrotron radiation. Analysis of the structural differences among the HsPNP:Gua complex, PNP apoenzyme, and HsPNP:immucillin-H provides explanation for inhibitor binding, refines the purine-binding site, and can be used for future inhibitor design.
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1490
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Davies R, Martinelli M, Wheatley A, White A, Williams D. Structural Studies of Lithium Telluro‐ and Seleno‐Phosphorus Compounds. Eur J Inorg Chem 2003. [DOI: 10.1002/ejic.200300234] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Robert P. Davies
- Dept of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, U.K., Fax: (internat.) +44‐20/7594‐5804
| | - M. Giovanna Martinelli
- Dept of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, U.K., Fax: (internat.) +44‐20/7594‐5804
| | - Andrew E. H. Wheatley
- Dept of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, U.K., Fax: (internat.) +44‐1223/336‐362
| | - Andrew J. P. White
- Dept of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, U.K., Fax: (internat.) +44‐20/7594‐5804
| | - David J. Williams
- Dept of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, U.K., Fax: (internat.) +44‐20/7594‐5804
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1491
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Valadares MC, Klein SI, Guaraldo AMA, Queiroz MLS. Enhancement of natural killer cell function by titanocenes in mice bearing Ehrlich ascites tumour. Eur J Pharmacol 2003; 473:191-6. [PMID: 12892838 DOI: 10.1016/s0014-2999(03)01967-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In the present work, we studied the effects of two titanocenes, biscyclopentadienyldichlorotitanium IV, (DDCT) and its derivative, biscyclopentadienylditiocianatetitanium IV (BCDT), on the activity of natural killer (NK) cells in Ehrlich ascites tumour (EAT)-bearing BALB/c mice. In order to investigate a more direct effect of these compounds on NK cell function, we performed experiments with severe combined immunodeficiency (SCID) mice, which exhibit a normal NK cell response in the absence of T and B cells. The treatment consisted of intraperitoneal (i.p.) administration of 15 mg/kg/day of DDCT for 2 days or 10 mg/kg/day of BCDT for 3 days. In addition, to verify whether the effects produced by the titanocenes were compound specific or related to a direct antitumour effect, we also investigated the effects of a 3-day treatment with 100 mg/kg of cyclophosphamide cyclophosphamide on NK cell activity. Our results demonstrated that, in BALB/c and SCID mice, NK cell function declined to subnormal levels after inoculation of the tumour. In these animals, although treatment with DDCT and BCDT significantly enhanced NK cell function, only DDCT restored NK cell activity to normal values in all stages studied. Conversely, treatment with cyclophosphamide reduced NK cell function in nontumour bearing SCID mice and was also unable to restore the decreased NK activity of tumour-bearing SCID mice, thus demonstrating that the enhancement of NK cell function by titanocenes is compound specific. The same effect of cyclophosphamide was observed with BALB/c mice. In the present study, the up-modulatory effects of these two compounds on NK cell function reveal a new aspect of the mechanism of antitumoural action of titanocenes.
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Affiliation(s)
- Marize C Valadares
- Departamento de Farmacologia/Hemocentro, Faculdade de Ciências Médicas, FCM, Universidade Estadual de Campinas, UNICAMP, P.O. Box 6111, CEP 13083-970, Campinas, SP, Brazil
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1492
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Villafranca AC, Moraes MD, Pezza L. Avaliação e caracterização da pastilha sensora de um eletrodo de segunda espécie sensível a oxalato. ECLÉTICA QUÍMICA 2003. [DOI: 10.1590/s0100-46702003000100011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
O eletrodo Pt|Hg|Hg2Ox|Grafite (Ox = íon oxalato) foi estudado utilizando NaClO4 como eletrólito de suporte. Foram feitas experiências preliminares utilizando o NaNO3 como eletrólito de suporte seguindo a mesma metodologia do trabalho anterior e verificou-se que havia uma diminuição na sensibilidade do eletrodo em função do tempo de uso. Visando compreender a diferença de comportamento do eletrodo em meio de NaClO4 e NaNO3 foram feitas experiências de obtenção de curvas de potencial em função do tempo para verificar seu comportamento em função do tempo e em diferentes meios iônicos. A morfologia da superfície da pastilha sensora usada em meio de NaNO3 apresentou alteração, a qual sugere que este meio favorece reações na superfície da pastilha sensora que fica em contato com a solução.
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Affiliation(s)
| | | | - L. Pezza
- Universidade Estadual Paulista, Brasil
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1493
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Bannach G, Schnitzler E, Ionashiro M. Synthesis, characterization and thermal behaviour of solid state compounds of 2-chlorobenzylidenepyruvate with trivalent aluminium, gallium, indium and scandium metals. ECLÉTICA QUÍMICA 2003. [DOI: 10.1590/s0100-46702003000100002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Solid state compounds M-2-Cl-BP, where 2-Cl-BP is 2-chlorobenzylidenepyruvate and M represents Al, Ga, In, and Sc were prepared. X-ray powder diffractometry, infrared spectroscopy and simultaneous thermogravimetry-differential thermal analysis (TG-DTA), have been used to characterize and to study the thermal behavior of these compounds. The results provided information concerning the stoichiometry, crystallinity, thermal stability and thermal decomposition of the compounds.
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1494
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Synthesis, characterization, properties and thermal study of nickel(II)/di-2-pyridyl ketone benzoylhydrazone complex. Polyhedron 2002. [DOI: 10.1016/s0277-5387(02)01185-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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1495
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Valadares MC, Queiroz MLS. The effect of a Titanocene Dichloride derivative, Ti IV (C5H5)(2) NCS(2), on the haematopoietic response of Ehrlich tumour-bearing mice. Eur J Pharmacol 2002; 439:35-42. [PMID: 11937090 DOI: 10.1016/s0014-2999(02)01411-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The effects of the [Ti IV (C(5)H(5))(2) NCS(2)] metallocene (BCDT), a Titanocene Dichloride derivative, on the growth and differentiation of granulocyte-macrophage progenitor cells [colony-forming unit-granulocyte-macrophage (CFU-GM)] and bone marrow cellularity in normal and Ehrlich ascites tumour-bearing mice were studied. As expected for the Ehrlich ascites tumour-model, concomitant myelosuppression, increased number of spleen CFU-GM and changes in bone marrow cellularity were observed. The treatment of Ehrlich ascites tumour-bearing mice with BCDT (10-30 mg/kg/day) produced a dose-dependent increase in myelopoiesis, a reduction in splenic colonies and a restoration in the total and differential marrow cell counts. We also observed an increase in CFU-GM number when bone marrow cells obtained from normal mice were incubated in vitro with serum from normal mice treated with BCDT. In addition, BCDT prolonged, in a dose-dependent manner, the survival of mice inoculated with Ehrlich ascites tumour. Although it has been previously reported that substitutions in the two halides of the titanocene do not interfere with antitumoural effect, our results with BCDT demonstrated a reduction in antitumour efficacy when compared to previous results with the original titanocene produced in our laboratory.
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Affiliation(s)
- Marize C Valadares
- Departamento de Farmacologia/Hemocentro, Faculdade de Ciências Médicas, Universidade Estadual de Campinas (UNICAMP), P.O. Box 6111, CEP 13083-970, SP, Campinas, Brazil
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1496
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SCHNITZLER E, LAZZAROTTO M, CARVALHO-FILHO MADS, IONASHIRO M. Thermoanalytical study of the complexes of 4-dimetilaminocinnamylidenepiruvate with manganese (II), cobalt (II), nickel (II), cupper (II), zinc (II) and lead (II), in the solid state. ECLÉTICA QUÍMICA 2002. [DOI: 10.1590/s0100-46702002000100004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Solid state compounds M-4-DMCP, where 4-DMCP is 4-dimethylaminocinnamylidenepyruvate and M represents Mn (II), Co (II), Ni (II), Cu (II), Zn (II) and Pb (II) were prepared. These compounds were studied by thermoanalitycal techniques: thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), X-ray diffraction powder patterns and complexometric titration with EDTA. From the results obtained by the complexometric titration with EDTA, TG, DTG and DSC curves, was possible to establish the hydration degree, stoichiometry and thermal stability of the prepared compounds.
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1497
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1498
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ADORNO AT, GUERREIRO MR, BENEDETTI AV. Determinação das energias de ativação para nucleação de precipitados e difusão da prata na liga cu-2%al com adições de prata. ECLÉTICA QUÍMICA 2001. [DOI: 10.1590/s0100-46702001000100008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
As energias de ativação para nucleação de precipitados ricos em prata e de difusão da prata no cobre, em ligas de Cu-2%Al contendo 2, 4, 6, 8, 10 e 12%Ag, em peso, foram determinadas utilizando-se medidas de variação da microdureza com a temperatura e o tempo de envelhecimento. Os resultados indicaram que, com o método utilizado, é possível obter valores para as energias de ativação para nucleação da fase rica em prata e de difusão da prata no cobre bastante próximos daqueles citados na literatura.
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1499
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FERNANDES AP, MORAES MD, GOMES NETO JA. Potencialidades e aplicações do ligante dietilditiofosfato de amônio em análises químicas. ECLÉTICA QUÍMICA 2001. [DOI: 10.1590/s0100-46702001000100016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Este trabalho descreve uma revisão a respeito do uso do ligante dietilditiofosfato de amônio em química analítica e suas potencialidades no campo da análise química espectrofotométrica (UV/VIS) e espectrométrica (AAS, ICP-AES, ICP-MS) em diferentes matrizes e meios. A discriminação de espécies químicas por meio de complexações seletivas de elementos químicos com dietilditiofosfato e a hifenação de técnicas espectroscópicas a etapas de separação como extração em fase sólida, extração líquido-líquido, extração por "cloud point", são outros assuntos abordados neste trabalho.
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1500
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CAPELA MV, MAGNANI R, ADORNO AT, CAPELA JMV. Comparação do ajuste dos modelos de morgan-mercer-flodin e de johnson-mehl-avrami na reação de precipitação na liga cu-3%al-5%ag. ECLÉTICA QUÍMICA 2001. [DOI: 10.1590/s0100-46702001000100015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Em geral, os modelos de crescimento empregados na descrição de processos cinéticos do estado sólido utilizam as funções de Morgan-Mercer-Flodin (MMF) e Johnson-Mehl-Avrami (JMA). Neste trabalho comparou-se o comportamento das estimativas dos parâmetros dessas funções, em duas parametrizações, quando ajustadas aos dados experimentais de variação isotérmica da microdureza da liga Cu-3%Al-5%Ag com o tempo de envelhecimento, em cinco temperaturas diferentes. Na estimativa dos parâmetros aplicou-se o método dos mínimos quadrados à função linearizada do modelo e para o refinamento da solução, os procedimentos da regressão não linear. Foram obtidas as distribuições de freqüências das estimativas dos parâmetros, por simulação, e determinados seus erros relativos. Observou-se que, em uma das parametrizações das funções, a estimativa do parâmetro cinético apresentou maior estabilidade. Apesar dessas funções serem anteriormente consideradas distintas, verificou-se que a função de MMF é uma aproximação da função de JMA, sendo que esta, com a parametrização adequada, é a mais indicada para descrever o processo cinético considerado.
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