Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 1.339
Filtrar
Mais filtros










Filtros aplicados

Base de dados
Intervalo de ano de publicação
1.
Nature ; 580(7801): 31-32, 2020 04.
Artigo em Inglês | MEDLINE | ID: mdl-32238937
2.
Chemosphere ; 250: 126298, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32234622

RESUMO

Chlorophenol (CP) is considered as environmentally hazardous material due to its acute toxicity, persistent nature and strong bioaccumulation. The dechlorination of 4-CP was investigated by using various catalysts such as bimetallic (Fe0/Cu0, Al0/Fe0), Pd/C, Raney Ni and Fe0 at room temperature. Among the catalysts studied, Raney Ni proved to be very economical and efficient catalyst that worked without the use of an external reducing agent. The dechlorination of 4-CP by Raney Ni was therefore further explored. Complete dechlorination of 4-CP (30 mg L-1) was achieved in 6 h at an optimum Raney Ni catalyst loading of 3 g L-1. The effect of triethylamine (TEA) and tripropylamine (TPA) was also investigated and it was observed that 100% dechlorination is possible in presence of 45 mg L-1 of TEA. The kinetics of dechlorination of 4-CP was investigated and found to be first order with a rate constant of 0.017 min-1 at 50 οC, and it enhances to 0.109 min-1 with addition of TEA. In the absence of a reducing agent, acidic to neutral pH favors dechlorination of 4-CP. The final product of dechlorination was estimated to be phenol by performing HPLC, LCMS and NMR analysis. Based on the results, a probable dechlorination mechanism of 4-CP is also proposed. It can be concluded that the catalytic hydrodechlorination is an effective and economical technique for dechlorination of 4-CP and it has a potential for the dechlorination of other toxic derivatives of chlorinated aromatics.


Assuntos
Clorofenóis/química , Modelos Químicos , Níquel/química , Catálise , Halogenação , Concentração de Íons de Hidrogênio , Cinética , Substâncias Redutoras
3.
Waste Manag ; 102: 122-130, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-31671359

RESUMO

Some inevitable issues of the acid leaching method used to recycle spent lithium-ion batteries (LIBs), such as toxic gas emission, excessive acid-base consumption, inferior metal selectivity and equipment corrosion, have gradually emerged and restricted the promotion and development of this method. It is therefore essential to develop a sustainable closed-loop recycling technology (reduction-ammoniacal method) for spent LIBs. In this study, the effects of various species of ammonia, ammonium salts and reductants on the leaching of Li, Co, Ni, Mn and Al from spent LIBs were investigated with a hydrothermal method. An increase of the electrode potential of the reductant greatly accelerated the selective leaching of Li, Co and Ni, which agreed with the thermodynamic analysis results. The standard electrode potentials of the LiNixCoyMn1-x-yO2 (NCM) materials were also determined by using approximate calculations. When using (NH4)2SO3 as a reductant in a one-step leaching process, 100% Co, 98.3% Ni and 90.3% Li were extracted into the ammonia-ammonium chloride solutions. From the kinetics analysis, the surface chemical reaction shrinking core model was found to control the leaching behavior of Li, Co, and Ni in the reduction-ammoniacal leaching process. A shell-core structure was composed of a product layer, a diffusion layer of the solid core and an unreacted core. Species in the product layer reduced the leaching efficiencies of Li, Co, and Ni. The results obtained for this hydrothermal reduction-ammoniacal method applied to recycle spent LIBs provide insights for the design of a high-speed, exceptionally selective, closed-loop recycling technique.


Assuntos
Lítio , Níquel , Cobalto , Fontes de Energia Elétrica , Reciclagem , Substâncias Redutoras , Sais
4.
Water Environ Res ; 92(4): 604-611, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31602733

RESUMO

Activating permanganate with reductants has gained increasing attention recently for efficient organic contaminants abatement via reactive intermediate Mn species. However, few studies have been conducted to explore the role of pyrophosphate (PP), a typical complexing agent for intermediate Mn species, in activated permanganate systems. In this study, taking sulfamethoxazole (SMX) as a probe compound, the influences of PP on SMX degradation by permanganate/thiosulfate and permanganate/hydroxylamine were extensively studied. It was found that both thiosulfate and hydroxylamine were able to activate permanganate for oxidation of SMX in the absence of PP. However, upon the introduction of PP, opposite effects were observed in the two systems where PP further improved the activation of permanganate by thiosulfate but dampened the performance of permanganate/hydroxylamine markedly. For permanganate/hydroxylamine system, MnO2 was determined to be the only reactive oxidative species accounting for SMX degradation in the absence of PP, and its generation could be completely inhibited by PP. While in permanganate/thiosulfate system, both Mn(V) and MnO2 were responsible for SMX oxidation, and the introduction of PP could strengthen the oxidative ability of Mn(V). These results could shed some insights on the suitability of applying PP to explore the kinetics and mechanisms of manganese involved redox reactions. PRACTITIONER POINTS: Both Na2 S2 O3 and NH2 OH·HCl can activate KMnO4 for SMX removal without PP. MnO2 is the reactive oxidative species involved in KMnO4 /NH2 OH·HCl system. Mn(V) and MnO2 account for the SMX oxidation by KMnO4 /Na2 S2 O3 system. PP could inhibit the formation of MnO2 but enhance the oxidative ability of Mn(V).


Assuntos
Compostos de Manganês , Óxidos , Difosfatos , Oxirredução , Substâncias Redutoras , Sulfametoxazol
5.
Chemosphere ; 238: 124636, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31470308

RESUMO

Electrochemical reduction process is a promising method for wastewater treatment, and its performance is determined by cathode material. Nitrogen doped carbon is a kind of favorable cathode material for electrochemical reduction, but deep understanding for the effect of nitrogen concentration and reduction pathway is still needed. In this paper, nitrogen doped porous carbon (NPC) with different nitrogen concentration were fabricated by directly carbonization of ZIF-8 under various temperatures. The electrochemical reduction performance of NPCs was evaluated by reducing nitrobenzene (NB), and the effects of nitrogen concentration were discussed. NPC with 22.7% nitrogen concentration exhibited the best NB reduction performance with the NB removal constant about 1.0 h-1 under optimal conditions; the NB removal rate and aniline (AN) production on this NPC are 4.2 and 8.5 times higher than graphite electrode. Further H* quenching experiment indicates the NPC electrochemical reduction process mainly following an indirect hydrogenation reduction pathway. These results offer some insights into the electrochemical reduction process on nitrogen doped carbon, which may facilitate the design of efficient metal free carbon based catalyst for wastewater electrochemical pretreatment.


Assuntos
Carbono , Técnicas Eletroquímicas/métodos , Nitrobenzenos/química , Nitrogênio , Substâncias Redutoras/química , Compostos de Anilina/síntese química , Catálise , Eletrodos , Porosidade , Águas Residuárias/química , Purificação da Água/métodos
6.
Contact Dermatitis ; 82(1): 39-44, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31652346

RESUMO

BACKGROUND: Allergic contact dermatitis caused by Cr(VI) is often severe and difficult to treat. Therefore, primary prevention is a main goal but, secondary prevention can be valuable to ease the symptoms or prevent relapse of Cr(VI) dermatitis when sensitization has occurred. Barrier creams have been tried for many chemical substances, but until now there is no successful barrier cream against Cr(VI). OBJECTIVES: To investigate the ability of reducing agents to transform Cr(VI) into Cr(III) in an experimental situation, in order to find suitable chemicals to investigate for possible use in a barrier cream. METHODS: The capacity to reduce the amount of Cr(VI) was analyzed in water solutions of acetylcysteine, cysteine, dihydroxyacetone, glutathione, and iron sulfate heptahydrate. Thereafter the reducing capacity of acetylcysteine, dihydroxyacetone, glutathione, and iron sulfate on the amount of Cr(VI) in cement extracts was investigated. The content of Cr(VI) in the test solutions and in the cement extracts was estimated by the diphenyl carbazide spot test. RESULTS: All of the chosen chemicals reduced the amount of Cr(VI) in the test solutions and in the cement extracts to some extent. The reducing capacity was most prominent for iron sulfate. CONCLUSION: A reducing capacity was found for all chosen chemicals.


Assuntos
Alérgenos/efeitos adversos , Cromatos/efeitos adversos , Dermatite Alérgica de Contato/prevenção & controle , Substâncias Redutoras/uso terapêutico , Prevenção Secundária/métodos , Creme para a Pele/uso terapêutico , Dermatite Alérgica de Contato/etiologia , Humanos , Resultado do Tratamento
7.
Colloids Surf B Biointerfaces ; 185: 110579, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-31689675

RESUMO

Graphene-based nanomaterials (GBNs) have many applications as biomedical materials in tissue engineering and regenerative medicine. We report on the preparation of starch-(functionalized) reduced graphene oxide nanosheets (SRGO) using soluble starch as a reducing agent in a hydrothermal method, and their in vitro interactions with human skin fibroblasts and red blood cells (RBCs). Our results indicate that soluble SRGO nanosheets were prepared using graphene oxide (GO) as a raw material. SRGO-1 and -10, which were prepared using different concentrations of soluble starch after hydrothermal treatment, were characterized by ultraviolet-visible spectroscopy and showed a peak shift at 260 nm corresponding to the deoxygenation of GO and restoration of the conjugated aromatic structure. Dynamic light scattering and zeta potential measurements were used to determine Z-average sizes and surface charges of GO and SRGOs. X-ray diffractometry, attenuated total reflectance Fourier-transform infrared spectroscopy, and Raman spectroscopy revealed the progressive elimination of labile oxygen functional groups during hydrothermal treatment and restoration of the π-conjugated network. X-ray photoelectron spectroscopy showed de-oxidation of SRGOs, which had high carbon to oxygen ratios (C/O) as compared with GO. Interactions of SRGO-1 and -10 with skin fibroblasts showed excellent biocompatibility even at a concentration of 200 µg/ml with cell viabilities up to 88% and 90%, respectively, whereas notable cytotoxicity was observed for GO at 20 µg/ml. Similarly, SRGO-1 and -10 did not exhibit toxicity to RBCs compared to GO. Biofilm formation and metabolic activities of biofilm by the bacterium Staphylococcus aureus were also evaluated using a crystal violet and a tetrazolium reduction assay, respectively. The described hydrothermal method used to synthesize SRGO provides a cheap, facile, and environmentally friendly means of producing water-dispersible, biocompatible and hemocompatible reduced GOs for the fabrication of novel GBNs for various biomedical applications.


Assuntos
Fibroblastos/efeitos dos fármacos , Grafite/farmacologia , Hemólise/efeitos dos fármacos , Nanoestruturas/química , Substâncias Redutoras/química , Staphylococcus aureus/efeitos dos fármacos , Amido/química , Antibacterianos/química , Antibacterianos/farmacologia , Materiais Biocompatíveis/química , Biofilmes/efeitos dos fármacos , Biofilmes/crescimento & desenvolvimento , Sobrevivência Celular , Células Cultivadas , Fibroblastos/citologia , Grafite/química , Humanos , Pele/citologia , Pele/efeitos dos fármacos
8.
Int J Mol Sci ; 20(22)2019 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-31726728

RESUMO

The development of Pt(IV) anticancer prodrugs to overcome the detrimental side effects of Pt(II)-based anticancer drugs is of current interest. The kinetics and reaction mechanisms of the reductive activation of the carboplatin Pt(IV) prodrug cis,trans-[Pt(cbdca)(NH3)2Cl2] (cbdca = cyclobutane-1,1-dicarboxylate) by the major small-molecule reductants in human plasma were analyzed in this work. The reductants included ascorbate (Asc), the thiol-containing molecules L-cysteine (Cys), DL-homocysteine (Hcy), and glutathione (GSH), and the dipeptide Cys-Gly. Overall second-order kinetics were established in all cases. At the physiological pH of 7.4, the observed second-order rate constants k' followed the order Asc << Cys-Gly ~ Hcy < GSH < Cys. This reactivity order together with the abundances of the reductants in human plasma indicated Cys as the major small-molecule reductant in vivo, followed by GSH and ascorbate, whereas Hcy is much less important. In the cases of Cys and GSH, detailed reaction mechanisms and the reactivity of the various protolytic species at physiological pH were derived. The rate constants of the rate-determining steps were evaluated, allowing the construction of reactivity-versus-pH distribution diagrams for Cys and GSH. The diagrams unraveled that species III of Cys (-SCH2CH(NH3+)COO-) and species IV of GSH (-OOCCH(NH3+)CH2CH2CONHCH(CH2S-)- CONHCH2COO-) were exclusively dominant in the reduction process. These two species are anticipated to be of pivotal importance in the reduction of other types of Pt(IV) prodrugs as well.


Assuntos
Carboplatina , Plasma/metabolismo , Pró-Fármacos , Substâncias Redutoras/metabolismo , Carboplatina/química , Carboplatina/farmacocinética , Humanos , Cinética , Pró-Fármacos/química , Pró-Fármacos/farmacocinética
9.
Phys Chem Chem Phys ; 21(35): 19226-19233, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31441492

RESUMO

As one of the main air pollutants, nitrogen oxides (NOx) have serious effects on human health and the environment. In our previous study, we found that Mn-MOF-74 shows excellent catalytic performance for the selective catalytic reduction (SCR) reaction with NH3 being the reductant (NH3-SCR) at low temperature. To obtain a further understanding of the NH3-SCR mechanism in Mn-MOF-74, in this paper, we investigated two important parts of the NH3-SCR process in Mn-MOF-74 using the density functional theory (DFT) method. On the one hand, the structural characteristics of two types of oxygen vacancies of Mn-MOF-74, namely carboxyl oxygen vacancies and hydroxyl oxygen vacancies, and their adsorption properties to reaction species were calculated. It was found that the oxygen vacancies not only activate the reaction species, but also promote the desorption of NO2 molecules from metal sites for the subsequent rapid SCR reactions. On the other hand, we studied the effect of H2O on the structural stability and catalytic performance of Mn-MOF-74. It was found that the interaction of Mn-O bonds was weakened by H2O. Therefore, the influence of H2O should be considered for the future design of MOF-based catalysts for the SCR process.


Assuntos
Teoria da Densidade Funcional , Estruturas Metalorgânicas/química , Oxigênio/química , Água/química , Poluentes Atmosféricos/química , Poluentes Atmosféricos/isolamento & purificação , Catálise , Óxidos de Nitrogênio/química , Óxidos de Nitrogênio/isolamento & purificação , Substâncias Redutoras/química
10.
Chem Commun (Camb) ; 55(61): 9019-9022, 2019 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-31290863

RESUMO

DNA nanohydrogel assembled AuNPs were proposed as a high-throughput multidimensional sensing strategy for small molecule reductant profiling in rat brain. The equilibrium among AuNPs, DNA nanohydrogel and targets produced a unique fingerprint-like pattern for differentiating the reducing capacity.


Assuntos
Encéfalo/metabolismo , DNA de Cadeia Simples/química , Ouro/química , Hidrogéis/química , Nanopartículas Metálicas/química , Substâncias Redutoras/análise , Animais , Colorimetria/métodos , Análise Discriminante , Glutationa/líquido cefalorraquidiano , Oxirredução , Tamanho da Partícula , Ratos
11.
J Pharm Biomed Anal ; 174: 518-524, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31252308

RESUMO

Identification and localization of modifications in peptides containing multiple disulfide bonds is challenging due to inefficient fragmentation in mass spectrometry (MS) analysis. In cases where MS fragmentation techniques such as electron capture dissociation (ECD), electron transfer dissociation (ETD), and ultraviolet photodissociation (UVPD) fail to achieve efficient fragmentation, off-line disulfide bond reduction techniques are typically employed prior to MS analysis. Some commonly used reducing agents include dithiothreitol (DTT) and tris(2-carboxyethyl)phosphine (TCEP). In this work, we describe the detection and identification of an unexpected impurity that formed during the reduction of Peptide A, containing multiple disulfide bonds, while using DTT or TCEP as reducing agents and acetonitrile as a co-solvent. The DTT reduced products were found to be a mixture of the expected linear Peptide A (fully reduced) and an unknown product (>50%) with a mass corresponding to linear Peptide A plus 41 Da ([reduced-M + 41]). A series of experiments were subsequently performed to investigate the identity and origin of this impurity. Disulfide bond reduction with DTT was performed in aqueous mixtures containing acetonitrile, methanol, and deuterated acetonitrile; and with TCEP in aqueous mixtures containing acetonitrile. Additionally, glycine amino acid was used as a surrogate to investigate the mechanism. The liquid chromatography-mass spectrometry (LCMSMS) results demonstrated that the [reduced-M + 41] impurity was an acetonitrile addition on the peptide's N-terminal glycine. The corresponding impurity [M + 41] was also found in the native Peptide A (non-reduced), suggesting that small amounts of this impurity may also be generated during the synthesis in the upstream process steps. By understanding the formation of this process-related impurity [M + 41], one could potentially reduce or eliminate its presence in Peptide A through chemical controls. Finally, this observation provides caution against using acetonitrile as a co-solvent during DTT- or TCEP-promoted reduction of peptides with an uncapped N-terminus primary amine.


Assuntos
Acetonitrilos/química , Dissulfetos/química , Ditiotreitol/química , Peptídeos/química , Fosfinas/química , Aminas/química , Cromatografia Líquida , Glicina/química , Proteína Oncogênica pp60(v-src)/química , Oxirredução , Fragmentos de Peptídeos/química , Domínios Proteicos , Substâncias Redutoras/química , Espectrometria de Massas por Ionização por Electrospray , Raios Ultravioleta
12.
Food Chem ; 293: 23-31, 2019 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-31151606

RESUMO

Cyclic voltammetry (CV) and high performance liquid chromatography (HPLC), were compared to quantify uric acid and antioxidant reducing agents in 36 milk samples. The enzymes uricase and ascorbate oxidase were used to remove uric and ascorbic acids and showed that the peaks obtained by CV and HPLC did not contain contributions from other unknown compounds. The levels of uric acid obtained by CV compared well to those determined using HPLC, with only a few exceptions, and the average difference was around 6%. CV measurements were made using the main anodic peak seen at approximately 330 mV (Ag/AgCl), while a later oxidation peak at approximately 650 mV can be associated with further reducing agents present in milk. The electrochemical method was quicker to apply than HPLC that included a pre-treatment step, and provides an inexpensive and simple method for the reliable analysis of uric acid in milk.


Assuntos
Técnicas Eletroquímicas , Leite/química , Substâncias Redutoras/análise , Ácido Úrico/análise , Animais , Antioxidantes/química , Ascorbato Oxidase/metabolismo , Cromatografia Líquida de Alta Pressão , Eletrodos , Concentração de Íons de Hidrogênio , Temperatura , Urato Oxidase/metabolismo
13.
Chemosphere ; 234: 98-107, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31203046

RESUMO

The reaction kinetics of groundwater contaminants are integral to evaluating the fate and transport of toxic metals in the environment. For redox sensitive contaminants, such as chromium, the kinetics of different reaction pathways can vary by orders of magnitude. Species-specific rate constants for iron-chromium oxidation-reduction reactions are unknown for many systems, especially in the presence of sorbing surfaces. We investigate the role of quartz and amorphous silica (SiO2(am)) surfaces in mediating abiotic reduction of Cr(VI)aq by aqueous and sorbed Fe(II) using batch sorption and redox experiments. Sorption edges indicate outer-sphere (Fe(II)ads,OS) and inner-sphere (Fe(II)ads,IS) complexes are present on both silica surfaces, and their abundance depends on pH, ionic strength, and surface disorder. The rate constants for Cr(VI)aq reduction by Fe(II) species increase in the following order: kaq ≪ kads,OS,quartz < kads,OS,SiO2(am) < kads,IS,quartz < kads,IS,SiO2(am), suggesting that increasing proximity of Fe(II) to the negatively charged silica surface enhances the rate of reduction of Cr(VI)aq. However, we observe that experiments with larger amounts of sorbed Fe(II) reduce less total Cr(VI)aq over time, which we attribute to a portion of the sorbed Fe(II) being sequestered into the Cr(III)-Fe(III)-oxyhydroxide precipitates forming on the silica surface. Therefore, the balance between increases in the rate and decreases in the total amount of Cr(VI)aq reduction by various sorbed Fe(II) species must be considered when devising remediation strategies.


Assuntos
Cromo/química , Compostos Ferrosos/química , Dióxido de Silício/química , Adsorção , Cinética , Oxirredução , Substâncias Redutoras/química , Propriedades de Superfície
14.
Colloids Surf B Biointerfaces ; 180: 457-465, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31100672

RESUMO

A simple method for preparing AgNPs/clay nanocomposites using an adsorption process without any reducing agent was developed in which saponite iron-rich clay was both the solid inorganic support and reducing agent. Silver adsorption by ion exchange of silver ions and saponite ferrous ions resulted in simultaneous silver reduction and silver nanoparticle formation. The maximum loading of silver was determined as 48 mg/g (4.8 mass %). Microscopy showed a homogeneous distribution of sphere-like silver nanoparticles which are composed from smaller crystallites in the form of twinned triangular prisms. The silver particle sizes ranged from 1 nm to 50 nm but predominantly between 8 and 10 nm. The optimum pH range for silver immobilization on saponite support was between 4 and 8. Characterization of the clay samples and synthesized AgNPs/saponite nanocomposites was performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), porosimetry (low temperature nitrogen adsorption-desorption) and zeta potential measurements. The antibacterial activities of raw saponite and AgNPs/saponite nanocomposite samples were tested against clinical relevant Gram-positive Staphylococcus aureus, Staphylococcus epidermidis, and Gram-negative Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis bacteria by the well diffusion method.


Assuntos
Antibacterianos/farmacologia , Nanopartículas Metálicas/química , Nanocompostos/química , Substâncias Redutoras/química , Prata/farmacologia , Adsorção , Silicatos de Alumínio/química , Concentração de Íons de Hidrogênio , Cinética , Nanopartículas Metálicas/ultraestrutura , Testes de Sensibilidade Microbiana , Nanocompostos/ultraestrutura , Espectroscopia de Infravermelho com Transformada de Fourier , Fatores de Tempo , Difração de Raios X
15.
Drug Discov Ther ; 13(2): 70-79, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31080206

RESUMO

The aim of this study was to synthesize silver nanoparticles (AgNPs) by using cellulose derivatives as a reducing agent. Methyl cellulose (MC), hydroxy ethylcellulose (HEC), and hydroxypropyl methylcellulose (HPMC) were compared for their reducing property. HPMC presented the highest reducing power, with equilibrium concentration (EC) of 84.6 ± 4.5 µmol Fe2+/g, followed by MC and HEC, with the EC of 62.3 ± 1.4, and 38.1 ± 3.2 µmol Fe2+/g, respectively. Using these cellulose derivatives as a reducing agent and silver nitrate as a precursor in fabrication of silver nanoparticles (AgNPs), three cellulose-AgNPs, HEC-AgNPs, MC-AgNPs, and HPMC-AgNPs, were obtained. The cellulose-AgNPs showed different maximum absorptions confirming AgNPs spectra at 415, 425, and 418 nm, respectively. Reaction parameters such as pH, temperature, and period of reaction affected intensity of the maximum absorptions and size of AgNPs. Using 0.3% cellulose solution at pH 9 and reaction at 70°C for 90 min, the particle size of MC-AgNPs, HEC-AgNPs, and HPMC-AgNPs was 97.7 ± 2.4, 165.6 ± 10.6, and 51.8 ± 1.6 nm, respectively. AgNPs obtained from different cellulose derivatives and various preparation parameters possess different inhibition potential against Escherichia coli and Staphylococcus aureus. The cellulose-AgNPs have higher effective against E. coli than S. aureus. HPMC-AgNPs showed significantly higher antibacterial activity than MC- AgNPs and HEC-AgNPs, respectively. These results suggest that the type of cellulose derivatives and the reaction parameters of the synthesis such as pH, temperature, and reaction period play an important role to the yield and physicochemical property of the obtained AgNPs.


Assuntos
Antibacterianos/síntese química , Celulose/análogos & derivados , Escherichia coli/efeitos dos fármacos , Substâncias Redutoras/química , Prata/química , Staphylococcus aureus/efeitos dos fármacos , Antibacterianos/química , Antibacterianos/farmacologia , Celulose/química , Concentração de Íons de Hidrogênio , Derivados da Hipromelose/química , Nanopartículas Metálicas/química , Metilcelulose/química , Testes de Sensibilidade Microbiana , Tamanho da Partícula , Prata/farmacologia , Temperatura
16.
Chemosphere ; 226: 238-245, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30928716

RESUMO

The individual degradation rates of the three dominant stereoisomers (α, ß, γ) of hexabromocyclododecane (HBCDD) with bisulfide and polysulfides were investigated at pH 9 in methanol/water solutions at two different temperatures (25 °C and 40 °C). Under all conditions investigated, α-HBCDD reacts 10 to 20 times slower with bisulfide than ß-HBCDD and γ-HBCDD. The difference in reactivity of HBCDD isomers can be explained by the different populations of stable conformers with large dihedral angle between the vicinal bromine atoms. It was also observed that the reaction of HBCDD with polysulfides is about six times faster than with bisulfide. The experiments performed in solvent mixtures with increased water content at 40 °C indicated that the reaction of HBCDD with bisulfide is faster with higher percentage of water. The much slower abiotic reaction of α-HBCDD compared to ß-HBCDD and γ-HBCDD could potentially contribute to the fact that α-HBCDD is more persistent in the environment than γ-HBCDD. Only one isomer of tetrabromocyclododecene (TBCDe-5) was identified as a degradation product of the reaction of HBCDD with reduced sulfur species. TBCDe-5 itself reacts about ten times slower with bisulfide and twenty times slower with polysulfide than HBCDD. The study demonstrates that polysulfides and bisulfides can reduce HBCDD sufficiently in natural anoxic environments and the dominant pathway for the degradation of HBCDD by reduced sulfur species is very likely to be the reductive debromination of vicinal dibromides via concerted anti-elimination.


Assuntos
Hidrocarbonetos Bromados/química , Estereoisomerismo , Enxofre/química , Metanol/química , Substâncias Redutoras , Sulfetos/química , Água/química , Poluentes Químicos da Água/análise
17.
Methods Mol Biol ; 1977: 83-97, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30980324

RESUMO

Reduction and alkylation are common processing steps in sample preparation for qualitative and quantitative proteomic analyses. In principle, these steps mitigate the limitations resulting from the presence of disulfide bridges. There has been recurring debate in the proteomics community around their use, with concern over negative impacts that result from overalkylation (off-target, non-thiol sites) or incomplete reduction and/or S-alkylation of cysteine. This chapter integrates findings from a number of studies on different reduction and alkylation strategies, to guide users in experimental design for their optimal use in proteomic workflows.


Assuntos
Cisteína/metabolismo , Processamento de Proteína Pós-Traducional/efeitos dos fármacos , Proteômica , Alquilantes/farmacologia , Alquilação/efeitos dos fármacos , Oxirredução/efeitos dos fármacos , Proteômica/métodos , Substâncias Redutoras/farmacologia , Fluxo de Trabalho
18.
Chemosphere ; 227: 63-71, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30981971

RESUMO

The catalytic reduction of diverse pollutants by noble metal catalysts in the presence of reductants is a highly effective and widely used method. However, the considerable cost of noble metal catalysts impedes the practical application of this method, and the recovery of excessive reductants has not been reported previously. In this work, we prepared inexpensive biochar-supported magnetic noble metallic nanoparticles (NPs) and efficiently recovered the excessive reductants in the form of H2. The as-synthesized biochar-supported noble metallic NPs exhibited high H2 recovery during the 4-nitrophenol reduction reaction. Results showed that the catalysts with low noble metallic content have higher H2 recovery rate than commercial Pd/C, Ag/C, and Pt/C. The catalytic mechanism of magnetic biochar-supported noble metallic NPs was demonstrated to be a "synergetic effect", where biochar and Fe3O4 acted as accelerants that enable noble metallic NPs to produce active hydrogen for the reduction reaction, and the excess active hydrogen atoms combined to form H2.


Assuntos
Carvão Vegetal/química , Poluentes Ambientais/química , Nanopartículas Metálicas/química , Modelos Químicos , Catálise , Hidrogênio , Nitrofenóis , Substâncias Redutoras
19.
Magn Reson Imaging ; 60: 32-37, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-30922833

RESUMO

PURPOSE: Investigate the possibility of measuring changes in glutathione (GSH) concentration using the MRS PRESS and MEGA-PRESS sequences by tracking the natural oxidation of GSH, and to examine the accuracy of the two methods. METHODS: 122 GSH edited MEGA-PRESS and PRESS acquisitions were acquired on a "braino" based phantom +3.0 mM GSH during a period of 11 days. All spectra were analyzed in LCModel. (The MEGA-PRESS data were first preprocessed in Matlab). Degradation curves were modeled. A one year follow-up on the same phantom and measurements from a similar phantom without GSH and one pure GSH phantom were also included. RESULTS: Both MEGA-PRESS and PRESS showed degradation of the measured GSH signal. Modeling the exponential decay of the GSH signal in MEGA-PRESS and PRESS gave for t = 0; 2.9 i.u. for MEGA-PRESS and 2.3 i.u. for PRESS. As t increased, the GSH concentration converged to zero for MEGA-PRESS but not for PRESS (0.7 i.u.). GSH for the one year follow up were 0.0 i.u. for MEGA-PRESS and 0.6 i.u. for PRESS. Similar phantom without GSH yielded 0.0 i.u. for both MEGA-PRESS and PRESS. CONCLUSION: It is possible to measure changes in GSH concentration in a phantom using both PRESS and MEGA-PRESS techniques, however the PRESS spectrum appears to include oxidized GSH (GSSG). In addition, GSH edited MEGA-PRESS measurement gives more precise values at lower GSH concentrations.


Assuntos
Glutationa/química , Espectroscopia de Ressonância Magnética , Oxigênio/química , Antioxidantes/química , Encéfalo/diagnóstico por imagem , Radicais Livres , Dissulfeto de Glutationa/química , Humanos , NADP/química , Imagens de Fantasmas , Substâncias Redutoras/química , Reprodutibilidade dos Testes , Razão Sinal-Ruído
20.
Inorg Chem ; 58(6): 3851-3860, 2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-30843385

RESUMO

The reduction mechanism of Pt(IV) anticancer prodrugs, still today a matter of debate, assisted by one of the dominant reductants in human plasma, that is l-ascorbic acid in its monodeprotonated form, has been computationally examined in this work. In order to check what should be the influence on the reduction rate of the identity of the ligands in axial and equatorial position, both cisplatin and oxaliplatin derivatives have been studied, varying the ligands in axial position in connection with the role they should play as bridges, trans leaving species, and proton acceptors. OH, OAc, Cl, and Br ligands have been tested as bridging/leaving ligands, whereas Cl and aspirin have been used as trans labile and less labile ligands, respectively. The most recent theoretical and experimental investigations have demonstrated that the generally adopted grouping of reduction mechanisms into inner- and outer-sphere does not properly take into account all the viable alternatives. Therefore, inner-sphere mechanisms, classified as ligand-bridged, ligand-bridged-H transfer and enolate ß-carbon attack, have been explored for all the complexes under investigation. Concerning the outer-sphere mechanism, redox potentials have been calculated adopting a recently proposed procedure based on the separation between electrochemical and chemical events to evaluate their propensity to be reduced. Moreover, according to the hypothesis that the outer-sphere reduction mechanism involves the sequential addition of two electrons causing the formation of a Pt(III) intermediate, the possibility that singlet and triplet pathways can cross for the Pt(IV) cisplatin derivative having two chlorido ligands in axial position has been explored in detail. Results show that the mechanism indicated as base-assisted outer sphere can become competitive with respect to the inner one if two singlet-triplet spin inversions occur. Results presented here are helpful in addressing synthetic strategies as they show that Pt(IV) prodrugs propensity to be reduced can be properly tuned and give indications on how this aim can be accomplished.


Assuntos
Antineoplásicos/metabolismo , Ácido Ascórbico/metabolismo , Compostos Organoplatínicos/metabolismo , Pró-Fármacos/metabolismo , Substâncias Redutoras/metabolismo , Antineoplásicos/química , Cisplatino/química , Cisplatino/metabolismo , Transporte de Elétrons , Humanos , Modelos Moleculares , Compostos Organoplatínicos/química , Oxirredução , Pró-Fármacos/química , Termodinâmica
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA