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1.
Talanta ; 212: 120736, 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32113528

RESUMO

The analysis of oil paints present in historical paintings is commonly carried out for research, authenticity and forensic purposes. This paper proposes potentiometric titration and calculation of the fatty acids concentrations with the aid of the Best7 program as an alternative technique to characterize the oil binders used in works of art. The method involves determining the ratio between the levels of palmitic (P) and stearic (S) acids present in the microhydrolysis products of commercial oil binders and paints. The microhydrolysis products were characterized, using FTIR spectroscopy, by displacement of the carbonyl band and the pKa values for the C16 and C18 in the system studied were determined. The P/S ratios found for the microhydrolysis products of linseed, palm and nut oils were 1.65, 5.91 and 2.42, respectively. For the commercial paints analyzed, values ranging from 1.34 to 1.98 were obtained, characterizing the presence of linseed oil. The values were confirmed by GC-MS and are in agreement with those reported in the literature for the oils investigated in this study.

2.
Talanta ; 200: 518-525, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31036218

RESUMO

This paper reports the use of nickel ions supported at activated biochar carbon paste electrode (NiAB-CPME) coupled in a microfluidic thread-based electroanalytical device (µTED) for non-enzymatic glucose determination. Biochar was initially prepared from castor oil cake at 400 °C and activated by HNO3 refluxing. Activation process promoted an increase of functional groups, surface area and porosity in comparison to precursor biochar. Activated biochar (AB) has shown an excellent performance to spontaneous preconcentration of Ni(II) ions. In alkaline conditions a stable voltammetric profile associated to Ni(OH)2/NiOOH redox pair was verified and a significant catalytic effect was observed in presence of glucose which was used for its monitoring. Microfluidic device was assembled at a plastic platform printed using 3D printer being easy to construction using low cost materials. Non-enzymatic amperometric glucose sensor coupled in µTED showed a good repeatability of 3.84% for successive injections of glucose (n = 10), a constant flow rate of 1.11 µL s-1 and an analytical frequency of 61 injections per hour. A linear dynamic range (LDR) from 5.0 to 100.0 µmol L-1, limit of detection (LOD) of 0.137 µmol L-1 and limit of quantification (LOQ) 0.457 µmol L-1 glucose were obtained. The proposed device was applied to glucose determination in real biological samples of human saliva and blood serum. Finally, the method was considered a green analytical procedure with Eco-Scale score of 81.

3.
Environ Technol ; 40(17): 2300-2309, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29436939

RESUMO

This work investigates the sorption of heavy metals by low-cost, byproducts such as charcoal fines (CF), waste green sand, and rice husk ash, in order to examine the feasibility of their use as alternative filter materials for metal-contaminated waters. The sorption of Cd, Cu, Pb, and Zn was investigated in batch experiments and sorption isotherms were constructed. The three byproducts showed high metal removal efficiencies (>95%, regardless of the metal concentration tested). The highest metal sorption distribution coefficients were obtained for CF, with maximum values within the 105-106 L kg-1 range for all the target metals. The sorption isotherms were satisfactorily fitted using the Freundlich equation and a linear model, the latter only being valid for initial metal concentrations lower than 0.4 mmol L-1. Sorption reversibility was very low, with desorption yields lower than 2% and desorption distribution coefficients often higher than 106 L kg-1. The values of the sorption and desorption parameters indicated that the use of these materials, especially CF, could constitute a low-cost alternative for the remediation of contaminated waters.


Assuntos
Metais Pesados , Poluentes Químicos da Água , Adsorção , Carvão Vegetal , Estudos de Viabilidade
4.
Sci Rep ; 8(1): 10677, 2018 07 16.
Artigo em Inglês | MEDLINE | ID: mdl-30013110

RESUMO

As part of efforts to reduce pressure on the Amazon and other biomes, one approach considered by Brazilian authorities and scientists is more intensive use of the soils of the interior of the northeast of the country, which are generally sandy, with low contents of organic matter and low water holding capacity and are frequently affected by severe droughts. In this work, biochars produced from waste biomasses were tested for the improvement of these soils. The highest BET (Brunauer-Emmett-Teller) specific surface areas were observed for all biochars. In the pH range studied, the water hyacinth plants (WH) sample showed the most negative zeta potentials, as well as the highest water holding capacity (WHC) values, while the zeta potentials of two quartzarenic neosol soils were consistent with their WHC values. The results suggested that despite the effect of porosity on water retention, the zeta potential could be associated with the presence of negative charges by which hydrated cationic counterions were absorbed and retained. The surface energy and its polar and dispersive components were associated with water retention, with sugar cane bagasse, orange peel, and water hyacinth biochars presenting higher SE values and larger polar components.

5.
J Environ Manage ; 190: 122-131, 2017 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-28040588

RESUMO

The aim of this study was to evaluate the interactions of peat, humic acids, and humin with urea dispersed in chitosan, in systems intended for the controlled release of urea. Spheres of chitosan with humic material and urea intentionally added to the media were prepared and characterized by means of elemental analysis (CHN), electron paramagnetic resonance (EPR), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The spheres possessed functional groups related to humic substances that interacted with the chitosan, and the presence of urea in the media was also confirmed after it has been added. Release experiments demonstrated that the samples released urea in a controlled manner that was dependent on pH, increasing in the order: pH 2.5 < pH 4.0 < pH 9.0. In soil experiments, the degree of release of urea (α) increased over time, with values of 0.44 for chitosan-humic acids-urea (CHAU), 0.48 for chitosan-peat-urea (CPTU), and 0.67 for chitosan-humin-urea (CHMU) obtained in the first day of the experiment. The release of urea did not exceed 70% after 7 days. The results demonstrated the potential of using peat, humic acids, and humin, in combination with chitosan, in order to manufacture controlled release urea fertilizers and contribute to reducing adverse environmental and economic impacts.


Assuntos
Quitosana/química , Fertilizantes , Substâncias Húmicas , Nitrogênio/farmacocinética , Solo/química , Ureia/farmacocinética , Preparações de Ação Retardada , Fertilizantes/análise , Substâncias Húmicas/análise , Concentração de Íons de Hidrogênio , Microscopia Eletrônica de Varredura , Nitrogênio/análise , Espectroscopia de Infravermelho com Transformada de Fourier , Ureia/química
6.
Mater Sci Eng C Mater Biol Appl ; 62: 123-9, 2016 May.
Artigo em Inglês | MEDLINE | ID: mdl-26952405

RESUMO

This work describes the construction and application of carbon paste electrodes modified with biochar and antimony microparticles (SbBCPE) for voltammetric determination of paraquat using a simple and sensitive procedure based on voltammetric stripping analysis. Some parameters such as amount of biochar and antimony used in the composition of the carbon paste and instrumental parameters were examined in detail. Under optimized conditions, an analytical curve was obtained for paraquat determination employing SbBCPE, which showed a linear response ranging from 0.2 to 2.9 µmol L(-1), with limit of detection and quantification of 34 nmol L(-1) and 113 nmol L(-1), respectively, after paraquat pre-concentration of 120 s. The repeatability study presented a RSD=2.0% for 10 consecutive measurements using the same electrode surface and the reproducibility study showed a RSD=2.7% for measurements with 10 different electrode surfaces. The proposed sensor was successfully applied for paraquat determination in tap water and citric fruit juice spiked samples and good recoveries were obtained without any sample pre-treatment, showing its promising analytical performance.


Assuntos
Antimônio/química , Carvão Vegetal/química , Técnicas Eletroquímicas , Paraquat/análise , Bebidas/análise , Eletrodos , Água Doce/química , Limite de Detecção , Reprodutibilidade dos Testes
7.
Environ Pollut ; 205: 403-14, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26210796

RESUMO

Spectroscopic and chromatographic techniques can be used together to evaluate hydrocarbon inputs to coastal environments such as the Paranaguá estuarine system (PES), located in the SW Atlantic, Brazil. Historical inputs of aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) were analyzed using two sediment cores from the PES. The AHs were related to the presence of biogenic organic matter and degraded oil residues. The PAHs were associated with mixed sources. The highest hydrocarbon concentrations were related to oil spills, while relatively low levels could be attributed to the decrease in oil usage during the global oil crisis. The results of electron paramagnetic resonance were in agreement with the absolute AHs and PAHs concentrations measured by chromatographic techniques, while near-infrared spectroscopy results were consistent with unresolved complex mixture (UCM)/total n-alkanes ratios. These findings suggest that the use of a combination of techniques can increase the accuracy of assessment of contamination in sediments.


Assuntos
Monitoramento Ambiental/métodos , Estuários , Sedimentos Geológicos/química , Hidrocarbonetos/análise , Hidrocarbonetos Policíclicos Aromáticos/análise , Poluentes Químicos da Água/análise , Brasil , Espectroscopia de Ressonância de Spin Eletrônica , Espectroscopia de Luz Próxima ao Infravermelho
8.
Environ Monit Assess ; 187(1): 4123, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25399121

RESUMO

The aim of this work was to evaluate the concentrations of polycyclic aromatic hydrocarbons (PAHs) in soils to which solid shale materials (SSMs) were added as soil conditioners. The SSMs were derived from the Petrosix pyrolysis process developed by Petrobras (Brazil). An improved ultrasonic agitation method was used to extract the PAHs from the solid samples (soils amended with SSMs), and the concentrations of the compounds were determined by gas chromatography coupled to mass spectrometry (GC-MS). The procedure provided satisfactory recoveries, detection limits, and quantification limits. The two-, three-, and four-ring PAHs were most prevalent, and the highest concentration was obtained for phenanthrene (978 ± 19 µg kg(-1) in a pyrolyzed shale sample). The use of phenanthrene/anthracene and fluoranthene/pyrene ratios revealed that the PAHs were derived from petrogenic rather than pyrogenic sources. The measured PAH concentrations did not exceed national or international limit values, suggesting that the use of SSMs as soil conditioners should not cause environmental damage.


Assuntos
Monitoramento Ambiental , Hidrocarbonetos Policíclicos Aromáticos/análise , Eliminação de Resíduos/métodos , Poluentes do Solo/análise , Solo/química , Brasil , Cromatografia Gasosa-Espectrometria de Massas , Incineração , Minerais/análise
9.
Mater Sci Eng C Mater Biol Appl ; 33(7): 3916-22, 2013 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-23910296

RESUMO

Reaction of highly soluble orally active, non-peptide antihypertensive drug losartan with copper(II) leads to the spontaneous formation of a very insoluble 2:1 covalent complex, which self assembles in a hydrophobic supramolecular structure of nanometric dimensions. Thermal analysis showed that Los/Cu(II) complex presents intermediate stability in comparison with its precursors KLos and Cu(OAc)2·H2O. Isothermal titration calorimetry indicated complexation to be a stepwise process, driven by enthalpy and entropy. Zeta potential and DLS measurements showed that it is possible to control the size and charge of nanoprecipitates by adjusting the relative concentration of Los(-) and Cu(II).


Assuntos
Precipitação Química , Complexos de Coordenação/química , Cobre/química , Interações Hidrofóbicas e Hidrofílicas , Losartan/química , Tamanho da Partícula , Varredura Diferencial de Calorimetria , Espectroscopia de Ressonância de Spin Eletrônica , Cinética , Luz , Dinâmica não Linear , Análise de Regressão , Espalhamento de Radiação , Solubilidade , Soluções , Eletricidade Estática , Termodinâmica , Termogravimetria , Titulometria , Água/química
10.
Artigo em Inglês | MEDLINE | ID: mdl-22513170

RESUMO

Zinc(II) and copper(II) complexes of a tridentate Mannich base L1 derived from 2-hydroxy-1,4-naphthoquinone, pyridinecarboxyaldehyde and 2-aminomethylpyridine, [ZnL1Cl(2)]·H(2)O 1 and [CuL1Cl(2)]·2H(2)O 2, have been synthesized and fully characterized. The structure of complex 1 has been elucidated by a single crystal X-ray diffraction study: the zinc atom is pentacoordinate and the coordination geometry is a distorted square base pyramid, with a geometric structural parameter τ equal to 0.149. Vibrational spectroscopy and ab initio DFT calculations of both compounds have confirmed that the two complexes exhibit similar structures. Full assignment of the vibrational spectra was also supported by careful analysis of the distorted geometries generated by the normal modes.


Assuntos
Cobre/química , Bases de Mannich/síntese química , Modelos Moleculares , Naftoquinonas/síntese química , Teoria Quântica , Vibração , Zinco/química , Complexos de Coordenação/síntese química , Complexos de Coordenação/química , Cristalografia por Raios X , Espectroscopia de Ressonância de Spin Eletrônica , Elétrons , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Bases de Mannich/química , Conformação Molecular , Naftoquinonas/química , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman , Termodinâmica
11.
Inorg Chem ; 51(3): 1569-89, 2012 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-22260179

RESUMO

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper(II) complexes, using the unsymmetrical ligands N',N',N-tris(2-pyridylmethyl)-N-(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L1) and N',N'-bis(2-pyridylmethyl)-N,N-(2-hydroxybenzyl)(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L2). The structures of the complexes [Cu(2)(L1)(µ-OAc)](ClO(4))(2)·(CH(3))(2)CHOH (1) and [Cu(2)(L2)(µ-OAc)](ClO(4))·H(2)O·(CH(3))(2)CHOH (2) were determined by X-ray crystallography. The complex [Cu(2)(L3)(µ-OAc)](2+) [3; L3 = N-(2-hydroxybenzyl)-N',N',N-tris(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. Inorg. Chim. Acta2005, 358, 1807-1822). Magnetic data show that the Cu(II) centers in 1 and 2 are antiferromagnetically coupled and that the difference in the exchange coupling J found for these complexes (J = -4.3 cm(-1) for 1 and J = -40.0 cm(-1) for 2) is a function of the Cu-O-Cu bridging angle. In addition, 1 and 2 were tested as catalysts in the oxidation of the model substrate 3,5-di-tert-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu(II)-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis(dinitrophenyl)phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu(II) center that contains the phenol group with tert-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (K(ass.) and k(cat.)) of 1 and 2 in comparison with that found for complex 3. In fact, complexes 1 and 2 show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity.


Assuntos
Catecol Oxidase/química , Cobre/química , Hidrolases/química , Modelos Moleculares , Catálise , Cristalografia por Raios X , Espectroscopia de Ressonância de Spin Eletrônica , Espectrofotometria Infravermelho
12.
Artigo em Inglês | MEDLINE | ID: mdl-20044305

RESUMO

The reaction between p-benzoquinone (PBQ) and casein (protein) in the solid state was studied. After reaction with protein, the FT-IR spectra showed a new band at 1215 cm(-1), with an intense sign attributed for casein/PBQ product. An optimum amount of PBQ for determination of the product when mixed with casein was 100mg and a reaction time of 30 min. The product was stable for a period of 24h after the reacting by heating. The interaction of PBQ with casein was investigated by FT-IR, reflectance, Raman and EPR spectroscopies. The reaction between PBQ and casein in the solid state yields a radical species (p-benzosemiquinone) that it is stabilized by the presence of p-biphenolate and p-benzoquinone species in the solid state.


Assuntos
Benzoquinonas/química , Benzoquinonas/metabolismo , Caseínas/química , Caseínas/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman
13.
J Inorg Biochem ; 103(4): 474-9, 2009 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-19264361

RESUMO

A vanadyl complex with the ligand (bis(1-methylimidazol-2-yl)methyl)(2-(pyridyl-2-yl)ethyl)amine was synthesized and fully characterized by X-ray crystallography, elemental analyses, cyclic voltammetry and infrared, electronic and electron paramagnetic resonance spectroscopies. This compound was designed under the so called hybrid concept. It shows to be able to promiscuously use hydrogen peroxide to oxidize bromide and to catalyze the oxidation of benzene and cyclohexane with very good selectivities.


Assuntos
Brometos/química , Etilaminas/química , Hidrocarbonetos/química , Imidazóis/química , Piridinas/química , Vanádio/química , Catálise , Cristalografia por Raios X , Espectroscopia de Ressonância de Spin Eletrônica , Etilaminas/síntese química , Imidazóis/síntese química , Ligantes , Compostos Organometálicos/química , Oxirredução , Piridinas/síntese química
14.
Chemosphere ; 73(8): 1162-6, 2008 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-18778847

RESUMO

Conformational changes in the structures of humic acids (HA) extracted from compost with varying degrees of maturity were monitored by high performance size exclusion chromatography (HPSEC). The molecular size distribution of HA was compared in solutions containing sodium or ammonium counterions at pH 7 and pH 4.5. These findings indicate that the humates' molecular size depended not only on the nature of the counterions but also on their concentration in the solution. The physicochemical nature of sodium counterions determined smaller molecular sizes than those of the more hydrated ammonium counterions, at low concentrations of humates. Conversely, at higher humate concentrations, the more compact conformation of sodium humates produced larger molecular sizes than those of ammonium humates due to the aggregation of more hydrophobic surfaces in the sodium humates. Composting led to the degradation of labile microbial components with accumulation of hydrophobic constituents. This caused self-association of hydrophobic compounds into humic superstructures of larger molecular size over composting time. At lower pH, changes in conformational stability by the addition of acetic acid to humate solutions were explained by the supramolecular model of humified organic matter.


Assuntos
Substâncias Húmicas , Solo , Cromatografia em Gel , Concentração de Íons de Hidrogênio , Conformação Molecular , Reprodutibilidade dos Testes , Fatores de Tempo
15.
Eur J Med Chem ; 43(5): 939-48, 2008 May.
Artigo em Inglês | MEDLINE | ID: mdl-17709156

RESUMO

N(4)-methyl-4-nitroacetophenone thiosemicarbazone (H4NO(2)Ac4M, 1), N(4),N(4)-dimethyl-4-nitroacetophenone thiosemicarbazone (H4NO(2)Ac4DM, 2) and N(4)-piperidyl-4-nitroacetophenone thiosemicarbazone (H4NO(2)Ac4Pip, 3) and their copper(II) complexes [Cu(4NO(2)Ac4M)(2)] (4), [Cu(4NO(2)Ac4DM)(2)] (5) and [Cu(4NO(2)Ac4Pip)(2)] (6) were tested for their in vitro ability to inhibit the growth of Trypanosoma cruzi epimastigote forms. H4NO(2)Ac4DM (2), [Cu(4NO(2)Ac4M)(2)] (4) and [Cu(4NO(2)Ac4DM)(2)] (5) proved to be as active as the clinical reference drugs nifurtimox and benznidazol. Taking into consideration the serious side effects and the poor efficacy of the reference drugs, as well as the appearance of resistance during treatment, the studied compounds could constitute a new class of anti-trypanosomal drug candidates.


Assuntos
Acetofenonas/síntese química , Quelantes/síntese química , Cobre , Tiossemicarbazonas/síntese química , Tripanossomicidas/síntese química , Acetofenonas/química , Acetofenonas/farmacologia , Animais , Quelantes/química , Cristalografia por Raios X , Eletroquímica , Espectroscopia de Ressonância de Spin Eletrônica , Humanos , Técnicas In Vitro , Macrófagos/efeitos dos fármacos , Macrófagos/parasitologia , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Tiossemicarbazonas/química , Tiossemicarbazonas/farmacologia , Tripanossomicidas/química , Tripanossomicidas/farmacologia , Trypanosoma cruzi/efeitos dos fármacos
16.
Inorg Chem ; 45(26): 10642-50, 2006 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-17173419

RESUMO

This work reports the incorporation of ferrocene into a porous silica glass under ambient temperature and atmosphere. After or during the ferrocene incorporation, the spontaneous formation of ferricinium ions was observed by electron paramagnetic resonance (EPR), UV-visible, X-ray absorption near-edge structure (XANES), and 57Fe Mössbauer measurements. It was shown that the oxidation of ferrocene molecules to ferricinium ions was promoted by air and that the Si-O- groups on the surface of the pores act as counteranions. Pyrolysis of the porous glass/ferricinium material under argon atmosphere and variable temperature yields different glass/carbon nanocomposites, which were subsequently treated with an HF solution in order to remove the glassy fraction. The resulting insoluble carbon materials were characterized by transmission electron microscopy (TEM), Raman, and EPR spectroscopy and consisted of amorphous carbon when the pyrolysis was carried out at 900 or 1000 degrees C and of a mixture of carbon nanotubes and carbonaceous materials at a pyrolysis temperature of 1100 degrees C. When the pyrolysis was conducted under air, the incorporated ferricinium forms alpha-Fe2O3, and the resulting material is a transparent and highly homogeneous glass/iron oxide nanocomposite.

17.
J Inorg Biochem ; 100(5-6): 992-1004, 2006 May.
Artigo em Inglês | MEDLINE | ID: mdl-16563512

RESUMO

The new homodinuclear complexes, [Cu(2)(II)(HLdtb)(mu-OCH(3))](ClO(4))(2) (1) and [Cu(2)(II)(Ldtb)(mu-OCH(3))](BPh(4)) (2), with the unsymmetrical N(5)O(2) donor ligand (H(2)Ldtb) - {2-[N,N-Bis(2-pyridylmethyl)aminomethyl]-6-[N',N'-(3,5-di-tert-butylbenzyl-2-hydroxy)(2-pyridylmethyl)]aminomethyl}-4-methylphenol have been synthesized and characterized in the solid state by X-ray crystallography. In both cases the structure reveals that the complexes have a common {Cu(II)(mu-phenoxo)(mu-OCH(3))Cu(II)} structural unit. Magnetic susceptibility studies of 1 and 2 reveal J values of -38.3 cm(-1) and -2.02 cm(-1), respectively, and that the degree of antiferromagnetic coupling is strongly dependent on the coordination geometries of the copper centers within the dinuclear {Cu(II)(mu-OCH(3))(mu-phenolate)Cu(II)} structural unit. Solution studies in dichloromethane, using UV-Visible spectroscopy and electrochemistry, indicate that under these experimental conditions the first coordination spheres of the Cu(II) centers are maintained as observed in the solid state structures, and that both forms can be brought into equilibrium ([Cu(2)(HLdtb)(mu-OCH(3))](2+)=[Cu(2)(Ldtb)(mu-OCH(3))](+)+H(+)) by adjusting the pH with Et(3)N (Ldtb(2-) is the deprotonated form of the ligand). On the other hand, potentiometric titration studies of 1 in an ethanol/water mixture (70:30 V/V; I=0.1M KCl) show three titrable protons, indicating the dissociation of the bridging CH(3)O(-) group.The catecholase activity of 1 and 2 in methanol/water buffer (30:1 V/V) demonstrates that the deprotonated form is the active species in the oxidation of 3,5-di-tert-butylcatechol and that the reaction follows Michaelis-Menten behavior with k(cat)=5.33 x 10(-3)s(-1) and K(M)=3.96 x 10(-3)M. Interestingly, 2 can be electrochemically oxidized with E(1/2)=0.27 V vs.Fc(+)/Fc (Fc(+)/Fc is the redox pair ferrocinium/ferrocene), a redox potential which is believed to be related to the formation of a phenoxyl radical. Since these complexes are redox active species, we analyzed their activity toward the nucleic acid DNA, a macromolecule prone to oxidative damage. Interestingly these complexes promoted DNA cleavage following an oxygen dependent pathway.


Assuntos
Cobre/química , DNA/química , Enzimas/química , Cristalografia por Raios X , Eletroquímica , Espectroscopia de Ressonância de Spin Eletrônica , Hidrólise , Cinética , Modelos Moleculares
18.
Inorg Chem ; 44(4): 921-9, 2005 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-15859269

RESUMO

The crystal structures and redox and UV-vis/EPR spectroscopic properties of two new mononuclear copper(II) complexes, [Cu(HL1)Cl2] (1) and [Cu(L1)Cl] (2), prepared through the reaction between copper(II) chloride and the ligand 2-[(bis(pyridylmethyl)amino)methyl]-4-methyl-6-formylphenol (HL1) under distinct base conditions, are reported along with solution studies. Also, we demonstrate that these CuII complexes are able to cleave unactivated peptide bonds from bovine serum albumin (BSA) and the thermostable enzyme Taq DNA polymerase at micromolar concentration, under mild pH and temperature conditions. The cleavage activity seems to be specific with defined proteolytic fragments appearing after protein treatment. The location of the specific cleavage sites was tentatively assigned to solvent-accessible portions of the protein. These are two of the most active Cu(II) complexes described to date, since their cleavage activity is detected in minutes and evidence is here presented for a hydrolytic mechanism mediating protein cleavage by these complexes.


Assuntos
Cobre/química , Compostos Organometálicos/química , Proteínas/metabolismo , Animais , Cátions Bivalentes , Bovinos , Cristalografia por Raios X , DNA/química , DNA/metabolismo , Eletroquímica , Concentração de Íons de Hidrogênio , Hidrólise , Ligantes , Estrutura Molecular , Compostos Organometálicos/metabolismo , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Proteínas/química , Albumina Sérica/química , Albumina Sérica/metabolismo , Soluções , Espectrofotometria Ultravioleta , Taq Polimerase/química , Taq Polimerase/metabolismo , Fatores de Tempo
19.
Inorg Chem ; 42(25): 8353-65, 2003 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-14658888

RESUMO

The tridentate Schiff base [(2-(imidazol-4-yl)ethyl)(1-methylimidazol-2-yl)methyl)imine (HISMIMI) and its reduced form HISMIMA were synthesized and characterized, as well their mononuclear cis-dihalo copper(II) complexes 1 and 2, respectively. In addition, the dinuclear [CuII(mu-OH)2CuII](2+) complexes (3) and (4) obtained from complexes 1 and 2, respectively, were also isolated and characterized by several physicochemical techniques, including magnetochemistry, electrochemistry, and EPR and UV-vis spectroscopies. The crystal structures of 1 and 2 were determined by X-ray crystallography and revealed two neutral complexes with their tridentate chelate ligands meridionally coordinated. Completing the coordination spheres of the square-pyramidal structures, a chloride ion occupies the apical position and another is bonded in the basal plane. In addition, complexes 1 and 2 were investigated by infrared, electronic, and EPR spectroscopies, cyclic voltammetry, and potentiometric equilibrium studies. The hydrolytic activity on phosphate diester cleavage of 1 and 2 was investigated utilizing 2,4-BDNPP as substrate. These experiments were carried out at 50 degrees C, and the data treatment was based on the Michaelis-Menten approach, giving the following kinetic parameters (complex 1/complex 2): vmax (mol L(-1) s(-1))=16.4x10(-9)/7.02x10(-9); KM (mol L(-1))=17.3x10(-3)/3.03x10(-3); kcat (s(-1))=3.28x10(-4)/1.40x10(-4). Complex 1 effectively promoted the hydrolytic cleavage of double-strand plasmid DNA under anaerobic and aerobic conditions, with a rate constant of 0.28 h(-1) for the decrease of form I, which represents about a 10(7) rate increase compared with the estimated uncatalyzed rate of hydrolysis.


Assuntos
Cobre/química , Dano ao DNA/efeitos dos fármacos , Imidazóis/química , Imidazóis/farmacologia , Compostos Organometálicos/química , Fosfatos/química , Anaerobiose , Animais , Bovinos , Cristalografia por Raios X , DNA/química , DNA/efeitos dos fármacos , DNA/genética , Espectroscopia de Ressonância de Spin Eletrônica , Ésteres/química , Hidrólise , Indicadores e Reagentes , Cinética , Ligantes , Espectroscopia de Ressonância Magnética , Magnetismo , Modelos Moleculares , Conformação Molecular , Plasmídeos/genética , Potenciometria , Espectrofotometria Infravermelho
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