RESUMO
Proteases can be used in several biotechnological processes including detergent, food and leather industries. In the leather industry, dehairing is carried out by chemicals, which pollute the environment. Therefore, to make the hair removal process environmentally friendly, a protease produced by Aspergillus terreus has been purified, biochemically characterized and had an efficient ability to remove hair from bovine leather. The protease was produced using 1% wheat bran and was purified 2.3-fold using two chromatographic steps showing a molecular weight of 90 kDa. Optimal temperature and pH were 50 °C and 6.5, respectively. Thermal stability was up to 1 h at 50 °C. Protease was stable to detergents like Tween 80 and to organic solvents. The activity was activated by Ca2+ and inhibited by Hg2+ and Cu2+. The enzyme was classified as serine protease, by the inhibition by PMSF and was stable to reducing agents. It hydrolyzed casein, azocasein, BSA, egg albumin and BTpNA. The Km and Vmax values were 0.65 ± 0.03 mg/mL and 3.66 ± 0.18 µmol/min, respectively. Remarkable properties about temperature, pH, stability to detergents and reducing agents ensure that the protease from A. terreus can be an excellent candidate for industrial applications, particularly in the leather industry.
Assuntos
Aspergillus/enzimologia , Proteínas Fúngicas/química , Proteínas Fúngicas/metabolismo , Química Verde/métodos , Remoção de Cabelo/métodos , Serina Proteases/química , Serina Proteases/metabolismo , Animais , Biotecnologia/métodos , Cálcio/metabolismo , Bovinos , Cobre/metabolismo , Detergentes/química , Ativação Enzimática , Estabilidade Enzimática , Proteínas Fúngicas/isolamento & purificação , Concentração de Íons de Hidrogênio , Hidrólise , Mercúrio/metabolismo , Peso Molecular , Substâncias Redutoras/química , Serina Proteases/isolamento & purificação , Solventes/química , TemperaturaRESUMO
Corn cob is an agricultural byproduct that produces an estimated waste burden in the thousands of tons annually, but it is also a good source of xylan, an important bioactive polysaccharide. Silver nanoparticles containing xylan (nanoxylan) were produced using an environmentally friendly synthesis method. To do this, we extracted xylan from corn cobs using an ultrasound technique, which was confirmed by both chemical and NMR analyses. This xylan contained xylose, glucose, arabinose, galactose, mannose, and glucuronic acid in a molar ratio of 50:21:14:9:2.5:2.5, respectively. Nanoxylan synthesis was analyzed using UV-vis spectroscopy at kmax = 469 nm and Fourier transform infrared spectroscopy (FT-IR), which confirmed the presence of both silver and xylan in the nanoxylan product. Dynamic light scattering (DLS) and atomic force microscopy (AFM) revealed that the nanoxylan particles were ~102.0 nm in size and spherical in shape, respectively. DLS also demonstrated that nanoxylan was stable for 12 months and coupled plasma optical emission spectrometry (ICP-OES) showed that the nanoxylan particles were 19% silver. Nanoxylan reduced Leishmania amazonensis promastigote viability with a half maximal inhibitory concentration (IC50) value of 25 µg/mL, while xylan alone showed no effective. Additionally, nanoxylan exhibited antifungal activity against Candida albicans (MIC = 7.5 µg/mL), C. parapsilosis (MIC = 7.5 µg/mL), and Cryptococcus neoformans (MIC = 7.5 µg/mL). Taken together, these data suggest that it is possible to synthesize silver nanoparticles using xylan and that these nanoxylan exert improved antileishmanial and antifungal activities when compared to the untreated polysaccharide or silver nitrate used for their synthesis. Thus, nanoxylan may represent a promising new class of antiparasitic agents for use in the treatment of these microorganisms.
Assuntos
Antifúngicos/síntese química , Antiprotozoários/síntese química , Nanopartículas Metálicas/química , Prata/química , Células 3T3 , Animais , Antifúngicos/química , Antiprotozoários/química , Candida albicans/efeitos dos fármacos , Candida parapsilosis/efeitos dos fármacos , Cryptococcus neoformans/efeitos dos fármacos , Estabilidade de Medicamentos , Difusão Dinâmica da Luz , Excipientes/química , Excipientes/isolamento & purificação , Química Verde/métodos , Humanos , Leishmania mexicana/efeitos dos fármacos , Nanopartículas Metálicas/ultraestrutura , Camundongos , Testes de Sensibilidade Microbiana , Tamanho da Partícula , Substâncias Redutoras/química , Substâncias Redutoras/isolamento & purificação , Espectrofotometria , Xilanos/química , Xilanos/isolamento & purificação , Xilanos/ultraestrutura , Zea mays/químicaRESUMO
This paper provides a novel and facile method to synthesize antibacterial phase change microcapsules (microPCMs) decorated with silver particles, where lignin was acting as both the Pickering stabilizer and the reducing agent for silver. First lignin Pickering emulsions at various oil-to-water ratios and lignin loading were prepared. Then, n-eicosane encapsulated in polyurea (PU) shells was prepared via interfacial polymerization of isophorone diisocyanate (IPDI) and ethylene diamine/diethylene triamine (EDA/DETA) in a Pickering emulsion stabilized by lignin particles. The results showed that the lignin particles were embedded in the microPCMs shell. These lignin particles were utilized to reduce silver ions, resulting in silver particles decorated microPCMs (Ag/lignin microPCMs). The resulting Ag/lignin microPCMs exhibited a well-defined core-shell spherical morphology with high phase-transition enthalpy (177.6 J/g), high encapsulation efficiency (69.0%) and good thermal durability. As well, the Ag/lignin microPCMs presented good antibacterial activity, showing great potential in industrial applications such as biomedical, textile and construction areas.
Assuntos
Antibacterianos/química , Cápsulas/química , Emulsões/química , Lignina/química , Substâncias Redutoras/química , Prata/química , Alcanos/química , Antibacterianos/farmacologia , Estabilidade de Medicamentos , Escherichia coli/efeitos dos fármacos , Isocianatos/química , Microesferas , Tamanho da Partícula , Transição de Fase , Poliaminas/química , Polímeros/química , Staphylococcus aureus/efeitos dos fármacos , Propriedades de Superfície , TermodinâmicaRESUMO
The germin-like protein (GLP) purified from Thevetia peruviana, Peruvianin-I, is the only one described as having proteolytic activity. Therefore, the goal of this study was to investigate the structural features responsible for its enzymatic activity. Although the amino acid sequence of Peruvianin-I showed high identity with other GLPs, it exhibited punctual mutations, which were responsible for the absence of oxalate oxidase activity. The phylogenetic analysis showed that Peruvianin-I does not belong to any classification of GLP subfamilies. Moreover, Peruvianin-I contains a catalytic triad found in all plant cysteine peptidases. Molecular docking simulations confirmed the role of the catalytic triad in its proteolytic activity. Synchrotron radiation circular dichroism assays confirmed that Peruvianin-I was stable at pH ranging from 5.0 to 8.0 and that it presented significant structural changes only above 60⯰C. The addition of iodoacetamide caused changes in its native conformation, but only a slight effect was observed after adding a reducing agent. This study reports an unusual protein with germin-like structure, lacking typical oxalate oxidase activity. Instead, the proteolytic activity observed suggests that the protein is a cysteine peptidase. These structural peculiarities make PeruvianinI an interesting model for further understanding of the action of laticifer fluids in plant defense.
Assuntos
Glicoproteínas/química , Glicoproteínas/metabolismo , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Proteólise , Thevetia/enzimologia , Sequência de Aminoácidos , Domínio Catalítico , Dicroísmo Circular , Concentração de Íons de Hidrogênio , Simulação de Acoplamento Molecular , Oxirredutases/metabolismo , Filogenia , Inibidores de Proteases/farmacologia , Substâncias Redutoras/química , Análise de Sequência de Proteína , Especificidade por Substrato/efeitos dos fármacos , TemperaturaRESUMO
Silver nanoparticles (AgNPs) are known mainly because of their bactericidal properties. Among the different types of synthesis, there is the biogenic synthesis, which allows the synergy between the nanocomposites and substances from the organism employed for the synthesis. This study describes the synthesis of AgNPs using infusion of roots (AgNpR) and extract (AgNpE) of the plant Althaea officinalis. After the synthesis through reduction of silver nitrate with compounds of A. officinalis, physico-chemical analyzes were performed by UV-Vis spectroscopy, nanoparticles tracking analysis (NTA), dynamic light scattering (DLS) and scanning electron microscopy (SEM). Toxicity was evaluated through Allium cepa assay, comet test with cell lines, cell viability by mitochondrial activity and image cytometry and minimal inhibitory concentration on pathogenic microorganisms. Biochemical analyzes (CAT - catalase, GPx - glutathione peroxidase e GST - glutationa S-transferase) and genotoxicity evaluation in vivo on Zebrafish were also performed. AgNpE and AgNpR showed size of 157 ± 11 nm and 293 ± 12 nm, polydispersity of 0.47 ± 0.08 and 0.25 ± 0.01, and zeta potential of 20.4 ± 1.4 and 26.5 ± 1.2 mV, respectively. With regard to toxicity, the AgNpE were the most toxic when compared with AgNpR. Biochemical analyzes on fish showed increase of CAT activity in most of the organs, whereas GPx showed few changes and the activity of GST decreased. Also regarding to bactericidal activity, both nanoparticles were effective, however AgNpR showed greater activity. Althaea officinalis can be employed as reducing agent for the synthesis of silver nanoparticles, although it is necessary to consider its potential toxicity and ecotoxicity.
Assuntos
Althaea/química , Nanopartículas Metálicas , Extratos Vegetais/química , Extratos Vegetais/farmacologia , Substâncias Redutoras/química , Substâncias Redutoras/farmacologia , Prata , Animais , Anti-Infecciosos , Apoptose/efeitos dos fármacos , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Fenômenos Químicos , Dano ao DNA/efeitos dos fármacos , Humanos , Nanopartículas Metálicas/química , Camundongos , Testes de Sensibilidade Microbiana , Extratos Vegetais/toxicidade , Substâncias Redutoras/toxicidade , Prata/química , Toxicologia/métodos , Peixe-ZebraRESUMO
Cysteine proteases play multiple roles in basically all aspects of physiology and development. In plants, they are involved in growth and development and in accumulation and mobilization of storage proteins. Furthermore, they are engaged in signalling pathways and in the response to biotic and abiotic stresses. In animals and also in humans, they are responsible for senescence and apoptosis, prohormone processing, and ECM remodelling. When analyzed by zymography, the enzyme must be renaturated after SDS-PAGE. SDS must be washed out and substituted by Triton X-100. Gels are then further incubated under ideal conditions for activity detection. Cysteine proteases require an acidic pH (5.0-6.0) and a reducing agent, usually DTT. When screening biological samples, there is generally no previous clue on what peptidase class will be present, neither optimal proteolysis conditions are known. Hence, it is necessary to assess several parameters, such as incubation time, pH, temperature, influence of ions or reducing agents, and finally evaluate the inhibition profile. For detection of cysteine peptidase activity, the use of specific inhibitors, such as E-64, can be used to prevent the development of cysteine peptidase activity bands and positively confirm its presence. Here four different protocols to assess cysteine protease activity from different sources are presented.
Assuntos
Cisteína Proteases/análise , Eletroforese em Gel de Poliacrilamida/métodos , Ensaios Enzimáticos/métodos , Animais , Catepsinas/análise , Catepsinas/metabolismo , Cisteína Proteases/metabolismo , Inibidores de Cisteína Proteinase/metabolismo , Humanos , Concentração de Íons de Hidrogênio , Leucina/análogos & derivados , Leucina/metabolismo , Desnaturação Proteica , Substâncias Redutoras/químicaRESUMO
OBJECTIVES: To evaluate the effect of photoinitiators and reducing agents on cure efficiency and color stability of resin-based composites using different LED wavelengths. METHODS: Model resin-based composites were associated with diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO), phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (BAPO) or camphorquinone (CQ) associated with 2-(dimethylamino) ethyl methacrylate (DMAEMA), ethyl 4-(dimethyamino) benzoate (EDMAB) or 4-(N,N-dimethylamino) phenethyl alcohol (DMPOH). A narrow (Smartlite, Dentisply) and a broad spectrum (Bluephase G2, Ivoclar Vivadent) LEDs were used for photo-activation (20 J/cm(2)). Fourier transform infrared spectroscopy (FT-IR) was used to evaluate the cure efficiency for each composite, and CIELab parameters to evaluated color stability (ΔE00) after aging. The UV-vis absorption spectrophotometric analysis of each photoinitiator and reducing agent was determined. Data were analyzed using two-way ANOVA and Tukey's test for multiple comparisons (α=0.05). RESULTS: Higher cure efficiency was found for type-I photoinitiators photo-activated with a broad spectrum light, and for CQ-systems with a narrow band spectrum light, except when combined with an aliphatic amine (DMAEMA). Also, when combined with aromatic amines (EDMAB and DMPOH), similar cure efficiency with both wavelength LEDs was found. TPO had no cure efficiency when light-cured exclusively with a blue narrowband spectrum. CQ-systems presented higher color stability than type-I photoinitiators, especially when combined with DMPOH. CONCLUSIONS: After aging, CQ-based composites became more yellow and BAPO and TPO lighter and less yellow. However, CQ-systems presented higher color stability than type-I photoinitiators, as BAPO- and TPO-, despite their higher cure efficiency when photo-activated with corresponding wavelength range. CLINICAL SIGNIFICANCE: Color matching is initially important, but color change over time will be one of the major reasons for replacing esthetic restorations; despite the less yellowing of these alternative photoinitiators, camphorquinone presented higher color stability.
Assuntos
Bis-Fenol A-Glicidil Metacrilato/química , Cor , Lâmpadas de Polimerização Dentária/classificação , Cura Luminosa de Adesivos Dentários/métodos , Fotoiniciadores Dentários/química , Substâncias Redutoras/química , Resinas Acrílicas/química , Cânfora/análogos & derivados , Cânfora/química , Resinas Compostas/química , Luz , Teste de Materiais , Metacrilatos/química , Fosfinas/química , Poliuretanos/química , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
Anisotropic and branched gold nanoparticles have great potential in optical, chemical and biomedical applications. However their syntheses involve multi-step protocols and the use of cytotoxic agents. Here, we report a novel one-step method for the preparation of gold nanostructures using only Hantzsch 1,4-dihydropyridines as mild reducing agents. The substituent pattern of the dihydropyridine nucleus was closely related to the ease of formation, morphology and stability of the nanoparticles. We observed nanostructures such as spheres, rods, triangles, pentagons, hexagons, flowers, stars and amorphous. We focused mainly on the synthesis and characterization of well-defined gold nanostars, which were produced quickly at room temperature (25°C) in high yield and homogeneity. These nanostars presented an average size of 68 nm with mostly four or six tips. Based on our findings, we propose that the growth of the nanostars occurs in the (111) lattice plane due to a preferential deposition of the gold atoms in the early stages of particle formation. Furthermore, the nanostars were easily modified with peptides remaining stable for more than six months in their colloidal state and showing a better stability than unmodified nanostars in different conditions. We report a new approach using dihydropyridines for the straightforward synthesis of gold nanostructures with controlled shape, feasible for use in future applications.
Assuntos
Di-Hidropiridinas/química , Ouro/química , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Substâncias Redutoras/química , Nanotecnologia/métodosRESUMO
El objetivo de este trabajo es estudiar, desde una perspectiva feminista, la diversidad y homogeneidad en las trayectorias profesionales de las médicas de familia que ejercían en Andalucía a comienzos del siglo XXI, a través del análisis de los significados que ellas mismas confieren a su desarrollo profesional y de la influencia de los factores personales, familiares y laborales. Realizamos un estudio cualitativo con seis grupos de discusión. Participaron 32 médicas de familia que se encontraban trabajando en los centros de salud urbanos de la red sanitaria pública de Andalucía. El análisis del discurso revela que la mayoría de las médicas no planifican sus metas profesionales y que, cuando lo hacen, las van entrelazando con las necesidades familiares. Esto se traduce en que sus trayectorias profesionales sean discontinuas. Por el contrario, las trayectorias orientadas al desarrollo profesional y a la planificación consciente de metas son más frecuentes entre las médicas que ocupan cargos de dirección en centros de salud.
The purpose of this article was to study, from a feminist perspective, the diversity and homogeneity in the career paths of female primary care physicians from Andalusia, Spain in the early 21st century, by analyzing the meanings they give to their careers and the influence of personal, family and professional factors. We conducted a qualitative study with six discussion groups. Thirty-two female primary care physicians working in urban health centers of the public health system of Andalusia participated in the study. The discourse analysis revealed that most of the female physicians did not plan for professional goals and, when they did plan for them, the goals were intertwined with family needs. Consequently, their career paths were discontinuous. In contrast, career paths oriented towards professional development and the conscious planning of goals were more common among the female doctors acting as directors of health care centers.
Assuntos
Humanos , Compostos Férricos/química , Compostos Ferrosos/química , Ferro/química , Sarcosina/análogos & derivados , Proteínas tau/química , Alumínio/química , Química Encefálica , Cloretos , Immunoblotting , Substâncias Macromoleculares , Fosfatos/química , Fosforilação , Ligação Proteica/fisiologia , Substâncias Redutoras/química , Sarcosina/químicaRESUMO
This enzyme immobilization approach involves the formation of disulfide (-S-S-) bonds with the support. Thus, enzymes bearing exposed nonessential thiol (SH) groups can be immobilized onto thiol-reactive supports provided with reactive disulfides or disulfide oxides under mild conditions. The great potential advantage of this approach is the reversibility of the bonds formed between the activated solid phase and the thiol-enzyme, because the bound protein can be released with an excess of a low-molecular-weight thiol (e.g., dithiothreitol [DTT]). This is of particular interest when the enzyme degrades much faster than the adsorbent, which can be reloaded afterwards. The possibility of reusing the polymeric support after inactivation of the enzyme may be of interest for the practical use of immobilized enzymes in large-scale processes in industry, where their use has often been hampered by the high cost of the support material. Disulfide oxides (thiolsulfinate or thiolsulfonate groups) can be introduced onto a wide variety of support materials with different degrees of porosity and with different mechanical resistances. Procedures are given for the preparation of thiol-activated solid phases and the covalent attachment of thiol-enzymes to the support material via disulfide bonds. The possibility of reusing the polymeric support is also shown.
Assuntos
Dissulfetos/química , Enzimas Imobilizadas/química , Sefarose/análogos & derivados , Adsorção , Reagentes de Ligações Cruzadas/química , Ditiotreitol/química , Ensaios Enzimáticos , Proteínas Fúngicas/química , Oxirredução , Substâncias Redutoras/química , Sefarose/química , Titulometria , beta-Galactosidase/químicaRESUMO
High-resolution photoemission spectroscopy is used to characterize adlayers of ethane-, hexane-, and nonanedithiol molecules grown on Au(111) surfaces by the immersion method. The effect of using a reducing agent during and after the immersion to inhibit or eliminate S-S bonds is investigated. Our results demonstrate that immersion 24 h in millimolar dithiol ethanolic solutions gives rise to the formation of multilayers; this effect is more pronounced in the case of ethanedithiol, the shortest molecule. A post-treatment with a disulfide reducing agent is effective to produce monolayers of standing-up molecules; this effect is again more pronounced in the case of ethanedithiol. Finally, the immersion 24 h in a solution containing dithiol and the reducing agent gives an unexpected result: most molecules remain adsorbed in the lying-down configuration; in this case, the almost complete suppression of the standing-up phase occurs equally with the three types of molecules, which suggests that the formation of S-S bonds must be important for the lifting of the molecules.
Assuntos
Alcanos/química , Dissulfetos/química , Ouro/química , Substâncias Redutoras/química , Compostos de Sulfidrila/química , Propriedades de SuperfícieRESUMO
The reactivity of coordinated nitroxyl (HNO) has been explored with the [Fe(II)(CN)(5)HNO](3-) complex in aqueous medium, pH 6. We discuss essential biorelevant issues as the thermal and photochemical decompositions, the reactivity toward HNO dissociation, the electrochemical behavior, and the reactions with oxidizing and reducing agents. The spontaneous decomposition in the absence of light yielded a two-electron oxidized species, the nitroprusside anion, [Fe(II)(CN)(5)NO](2-), and a negligible quantity of N(2)O, with k(obs)≈5×10(-7)s(-1), at 25.0°C. The value of k(obs) represents an upper limit for HNO release, comparable to values reported for other structurally related L ligands in the [Fe(II)(CN)(5)L](n-) series. These results reveal that the FeN bond is strong, suggesting a significant σ-π interaction, as already postulated for other HNO-complexes. The [Fe(II)(CN)(5)HNO](3-) ion showed a quasi-reversible oxidation wave at 0.32 V (vs normal hydrogen electrode), corresponding to the [Fe(II)(CN)(5)HNO](3-)/[Fe(II)(CN)(5)NO](3-),H(+) redox couple. Hexacyanoferrate(III), methylviologen and the nitroprusside ion have been selected as potential oxidants. Only the first reactant achieved a complete oxidation process, initiated by a proton-coupled electron transfer reaction at the HNO ligand, with nitroprusside as a final oxidation product. Dithionite acted as a reductant of [Fe(II)(CN)(5)HNO](3-), in a 4-electron process, giving NH(3). The high stability of bound HNO may resemble the properties in related Fe(II) centers of redox active enzymes. The very minor release of N(2)O shows that the redox conversions may evolve without disruption of the FeN bonds, under competitive conditions with the dissociation of HNO.
Assuntos
Complexos de Coordenação/química , Compostos Ferrosos/química , Óxidos de Nitrogênio/química , Complexos de Coordenação/síntese química , Ditionita/química , Eletroquímica , Ferricianetos/química , Compostos Ferrosos/síntese química , Cinética , Nitroprussiato/química , Oxidantes/química , Oxirredução , Paraquat/química , Processos Fotoquímicos , Substâncias Redutoras/química , Soluções , Espectrofotometria UltravioletaRESUMO
This study evaluated the interference of the amino acids tryptophan, cysteine, histidine, tyrosine, hydroxyproline, leucine, proline, serine, glycine, valine, glutamic acid, phenylalanine, and methionine on the measurement of reducing sugars using a phenol-free 3,5-dinitrosalicylic acid (DNS) reagent. It was found that in reaction mixtures containing 20mM of either tryptophan, cysteine, histidine, tyrosine, or hydroxyproline the measurement of 3.7 mM glucose was overestimated by 76%, 50%, 35%, 18%, and 10%, respectively. The amino acids valine, glutamic acid, and phenylalanine did not affect the DNS reaction, while methionine decreased the color development by 5%. The measurement of glucose, xylose, arabinose, and cellobiose at the 3.7-12.4 mM range in the presence of 20 mM cysteine resulted in an overestimated concentration of 34.8-50%. Enzymatic assays for measuring xylanolytic and filter paper activity (FPAse) were conducted in the presence of 20-60 mM cysteine, and compared to cysteine-free assays. In the presence of cysteine, the measured xylanase activity increased threefold and the FPAse activity increased twofold due to the overestimation of the reducing sugar concentrations in the assays. The interference from cysteine was reduced to a maximum of 8.6% when a DNS reagent containing phenol was used.
Assuntos
Aminoácidos/metabolismo , Artefatos , Carboidratos/química , Ensaios Enzimáticos/métodos , Glicosídeo Hidrolases/metabolismo , Substâncias Redutoras/química , Salicilatos/metabolismo , Colorimetria , Glicosídeo Hidrolases/análise , Substâncias Redutoras/metabolismo , Salicilatos/químicaRESUMO
Hexavalent chromium is of particular environmental concern due to its toxicity and mobility and is challenging to remove from industrial wastewater. It is a strong oxidizing agent that is carcinogenic and mutagenic and diffuses quickly through soil and aquatic environments. It does not form insoluble compounds in aqueous solutions, so separation by precipitation is not feasible. While Cr(VI) oxyanions are very mobile and toxic in the environment, Cr(III) cations are not. Like many metal cations, Cr(III) forms insoluble precipitates. Thus, reducing Cr(VI) to Cr(III) simplifies its removal from effluent and also reduces its toxicity and mobility. In this review, we describe the environmental implications of Cr(VI) presence in aqueous solutions, the chemical species that could be present and then we describe the technologies available to efficiently reduce hexavalent chromium.
Assuntos
Cromo/isolamento & purificação , Substâncias Redutoras/química , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Biodegradação Ambiental , Técnicas Eletroquímicas/métodos , Oxirredução , Solubilidade , SoluçõesRESUMO
The present investigation is the first part of an initiative to prepare a regional map of the natural abundance of selenium in various areas of Brazil, based on the analysis of bean and soil samples. Continuous-flow hydride generation electrothermal atomic absorption spectrometry (HG-ET AAS) with in situ trapping on an iridium-coated graphite tube has been chosen because of the high sensitivity and relative simplicity. The microwave-assisted acid digestion for bean and soil samples was tested for complete recovery of inorganic and organic selenium compounds (selenomethionine). The reduction of Se(VI) to Se(IV) was optimized in order to guarantee that there is no back-oxidation, which is of importance when digested samples are not analyzed immediately after the reduction step. The limits of detection and quantification of the method were 30 ng L(-1) Se and 101 ng L(-1) Se, respectively, corresponding to about 3 ng g(-1) and 10 ng g(-1), respectively, in the solid samples, considering a typical dilution factor of 100 for the digestion process. The results obtained for two certified food reference materials (CRM), soybean and rice, and for a soil and sediment CRM confirmed the validity of the investigated method. The selenium content found in a number of selected bean samples varied between 5.5±0.4 ng g(-1) and 1726±55 ng g(-1), and that in soil samples varied between 113±6.5 ng g(-1) and 1692±21 ng g(-1).
Assuntos
Fabaceae/química , Selênio/análise , Solo/análise , Espectrofotometria Atômica/métodos , Ácidos/química , Oxirredução , Substâncias Redutoras/química , Valores de Referência , Selênio/química , Selenometionina/análise , Selenometionina/química , Glycine max/química , TemperaturaRESUMO
OBJECTIVES: The aim of this study was to evaluate the degree of conversion (DC), rate of polymerization (R(p)(max)), Knoop hardness (KHN) and bond strength between tooth/restoration of composite resins containing different photo-initiators photo-activated by different light-curing units (LCUs). MATERIALS AND METHODS: A mixture of BisGMA, UDMA, BisEMA and TEGDMA was prepared along with the following photo-initiators: camphorquinone (CQ), phenyl-propanedione (PPD) or the association (CQ/PPD) and 65 wt% of silanated filler particles. The LCUs included a halogen lamp XL 2500 and two LEDs: UltraBlueIS and UltraLume5. The conversion profiles during photo-polymerization were investigated using middle-infrared spectroscopy (mid-IR). Bond strength was evaluated using push-out test in ninety teeth with prepared cavities. Before the push-out test, Knoop hardness (KH) was verified in the top and at the base of the restorations. RESULTS: PPD obtained lower R(p)(max) values, regardless of the LCU used. It also provided a greater bond strength than CQ when the LEDs LCUs were used. The degree of conversion after 40s of irradiation was the same for all composite resins, except PPD photo-activated for XL 2500, which showed lower DC values than CQ and CQ/PPD. In the top and at the base of the restorations, PPD showed the lowest KH values when photo-activated with XL 2500. XL 2500 produced higher KH values than UltraBlueIS when used with CQ or CQ/PPD photo-initiators. CONCLUSION: Because it increased the bond strength without compromising the properties of composite resins when photo-activated by an LED, PPD can be used as an alternative photo-initiator.
Assuntos
Chalconas/química , Resinas Compostas/química , Colagem Dentária , Materiais Dentários/química , Fotoiniciadores Dentários/química , Bis-Fenol A-Glicidil Metacrilato/química , Lâmpadas de Polimerização Dentária/classificação , Restauração Dentária Permanente , Vidro/química , Dureza , Humanos , Teste de Materiais , Metacrilatos/química , Processos Fotoquímicos , Polietilenoglicóis/química , Polimerização , Ácidos Polimetacrílicos/química , Poliuretanos/química , Substâncias Redutoras/química , Silanos/química , Dióxido de Silício/química , Espectrofotometria Infravermelho , Estresse Mecânico , Terpenos/químicaRESUMO
OBJECTIVES: To evaluate the influence of different tertiary amines on degree of conversion (DC), shrinkage-strain, shrinkage-strain rate, Knoop microhardness, and color and transmittance stabilities of experimental resins containing BisGMA/TEGDMA (3:1wt), 0.25wt% camphorquinone, 1wt% amine (DMAEMA, CEMA, DMPT, DEPT or DABE). Different light-curing protocols were also evaluated. METHODS: DC was evaluated with FTIR-ATR and shrinkage-strain with the bonded-disk method. Shrinkage-strain-rate data were obtained from numerical differentiation of shrinkage-strain data with respect to time. Color stability and transmittance were evaluated after different periods of artificial aging, according to ISO 7491:2000. Results were evaluated with ANOVA, Tukey, and Dunnett's T3 tests (α=0.05). RESULTS: Studied properties were influenced by amines. DC and shrinkage-strain were maximum at the sequence: CQAssuntos
Bis-Fenol A-Glicidil Metacrilato/química
, Resinas Compostas/química
, Polietilenoglicóis/química
, Ácidos Polimetacrílicos/química
, Substâncias Redutoras/química
, Ácido 4-Aminobenzoico/química
, Compostos de Anilina/química
, Cor
, Dureza
, Humanos
, Luz
, Metacrilatos/química
, Fotoiniciadores Dentários/química
, Polimerização
, Espectroscopia de Infravermelho com Transformada de Fourier
, Estresse Mecânico
, Terpenos/química
, Fatores de Tempo
, Toluidinas/química
, para-Aminobenzoatos
RESUMO
A new and straightforward method for screening highly catalytically active silver nanoparticle-polymer composites derived from branched polyethyleneimine (PEI) is reported. The one-step systematic derivatization of the PEI scaffold with alkyl (butyl or octyl) and ethanolic groups led to a structural diversity correlated to the stabilization of silver nanoparticles and catalysis. Analysis of PEI derivative libraries identified a silver nanoparticle-polymer composite that was able to efficiently catalyze the p-nitrophenol reduction by NaBH(4) in water with a rate constant normalized to the surface area of the nanoparticles per unit volume (k(1)) of 0.57 s(-1) m(-2) L. Carried out in the presence of excess NaBH(4), the catalytic reaction was observed to follow pseudo-first-order kinetics and the apparent rate constant was linearly dependent on the total surface area of the silver nanoparticles (Ag-NPs), indicating that catalysis takes place on the surface of the nanoparticles. All reaction kinetics presented induction periods, which were dependent on the concentration of substrates, the total surface of the nanoparticles, and the polymer composition. All data indicated that this induction time is related to the resistance to substrate diffusion through the polymer support. Hydrophobic effects are also assumed to play an important role in the catalysis, through an increase in the local substrate concentration.
Assuntos
Nanopartículas Metálicas/química , Polietilenoimina/análogos & derivados , Polietilenoimina/química , Prata/química , Boroidretos/química , Catálise , Interações Hidrofóbicas e Hidrofílicas , Hidroquinonas/química , Cinética , Nitrofenóis/química , Oxirredução , Tamanho da Partícula , Substâncias Redutoras/química , Nitrato de Prata/química , Água/químicaRESUMO
The organometallic complexes ([Ru(COD)(2-methylallyl)2] and [Ni(COD)2] (COD=1,5-cyclooctadiene) dissolved in imidazolium ionic liquids (ILs) undergo reduction and decomposition, respectively, to afford stable ruthenium and nickel metal(0) nanoparticles (Ru(0)-NPs and Ni(0)-NPs) in the absence of classical reducing agents. Depending on the case, the reduction/auto-decomposition is promoted by either the cation and/or anion of the neat imidazolium ILs.
Assuntos
Complexos de Coordenação/química , Imidazóis/química , Líquidos Iônicos/química , Nanopartículas Metálicas/química , Compostos Organometálicos/química , Complexos de Coordenação/síntese química , Nanopartículas Metálicas/ultraestrutura , Níquel/química , Oxirredução , Substâncias Redutoras/química , Rutênio/químicaRESUMO
UNLABELLED: Dental amalgam residues are probably the most important chemical residues generated from clinical dental practice because of the presence of heavy metals among its constituents, mainly mercury and silver. OBJECTIVE: The purpose of this study was to develop an alternative method for the recovery of silver residues from dental amalgam. MATERIAL AND METHODS: The residue generated after vacuum distillation of dental amalgam for the separation of mercury was initially diluted with 32.5% HNO3, followed by precipitation with 20% NaCl. Sequentially, under constant heating and agitation with NaOH and sucrose, the sample was reduced to metallic silver. However, the processing time was too long, which turned this procedure not viable. In another sequence of experiments, the dilution was accomplished with concentrated HNO3 at 90 degrees C, followed by precipitation with 20% NaCl. After washing, the pellet was diluted with concentrated NH4OH, water and more NaCl in order to facilitate the reaction with the reducer. RESULTS: Ascorbic acid was efficiently used as reducer, allowing a fast reduction, thus making the procedure viable. CONCLUSIONS: The proposed methodology is of easy application and does not require sophisticated equipment or expensive reagents.