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1.
Chem Biol Interact ; 311: 108789, 2019 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-31401089

RESUMO

The cytotoxicity of a dinuclear imine-copper (II) complex 2, and its analogous mononuclear complex 1, toward different melanoma cells, particularly human SKMEL-05 and SKMEL-147, was investigated. Complex 2, a tyrosinase mimic, showed much higher activity in comparison to complex 1, and its reactivity was verified to be remarkably activated by UVB-light, while the mononuclear compound showed a small or negligible effect. Further, a significant dependence on the melanin content in the tumor cells, both from intrinsic pigmentation or stimulated by irradiation, was observed in the case of complex 2. Similar tests with keratinocytes and melanocytes indicated a much lower sensitivity to both copper (II) complexes, even after exposition to UV light. Clonogenic assays attested that the fractions of melanoma cells survival were much lower under treatment with complex 2 compared to complex 1, both with or without previous irradiation of the cells. The process also involves generation of reactive oxygen species (ROS), as verified by EPR spectroscopy, and by using fluorescence indicators. Autophagic assays indicated a remarkable formation of cytoplasmic vacuoles in melanomas treated with complex 2, while this effect was not observed in similar treatment with complex 1. Monitoring of specific protein LC3 corroborated the simultaneous occurrence of autophagy. A balance interplay between different modes of cell death, apoptosis and autophagy, occurs when melanomas were treated with the dinuclear complex 2, in contrast to the mononuclear complex 1. These results pointed out to different mechanisms of action of such complexes, depending on its nuclearity.


Assuntos
Complexos de Coordenação/química , Cobre/química , Iminas/química , Monofenol Mono-Oxigenase/metabolismo , Animais , Autofagia/efeitos dos fármacos , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/efeitos da radiação , Complexos de Coordenação/metabolismo , Complexos de Coordenação/farmacologia , Espectroscopia de Ressonância de Spin Eletrônica , Pontos de Checagem da Fase G1 do Ciclo Celular/efeitos dos fármacos , Pontos de Checagem da Fase G1 do Ciclo Celular/efeitos da radiação , Humanos , Melaninas/metabolismo , Melanoma/metabolismo , Melanoma/patologia , Camundongos , Mitocôndrias/efeitos dos fármacos , Mitocôndrias/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Tubulina (Proteína)/metabolismo , Raios Ultravioleta
2.
Phys Chem Chem Phys ; 21(34): 18699-18705, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31423504

RESUMO

Fully hydrated bilayers of monounsaturated palmitoyloleoylphosphatidylcholine (POPC) and diunsaturated dioleoylphosphatidylcholine (DOPC) lipids have low main phase transition temperatures (271 K for POPC and 253 K for DOPC). Two-pulse echo detected spectra, combined with continuous wave electron paramagnetic resonance spectroscopy, are employed to study the low-temperature lamellar phases of the POPC and DOPC unsaturated bilayers that are usually studied in the fluid state. Phosphatidylcholine spin-labeled at C-5 and C-16 carbon atom positions along the acyl chain were used and the temperature varied over the range 77-270 K. Segmental chain librational oscillations of small amplitude and with correlation time in the subnanosecond to nanosecond range are found in both membranes. The mean-square angular amplitude, α2, of librations increases with temperature, is larger close to the bilayer midplane than close to the first acyl chain segments, and is larger in diunsaturated than in monounsaturated bilayers. In the inner hydrocarbon region of both lipid matrices, α2 increases first slowly and linearly with temperature and then more rapidly, and a dynamical transition is detected in the range 190-210 K. Compared to dipalmitoylphosphatidylcholine bilayers of fully saturated symmetric chain lipids, the presence of double bonds in the acyl chain enhances the intensity of librational motion which is characterized by larger angular variations at the terminal methyl ends. These findings highlight biophysical properties of unsaturated bilayers in the frozen state, including a detailed characterization of segmental chain dynamics and the evidence of a dynamical transition that appears to be a generic feature in hydrated macromolecular systems. These results can also be relevant in regulating membrane physical properties and function at higher physiological temperatures.


Assuntos
Bicamadas Lipídicas/química , 1,2-Dipalmitoilfosfatidilcolina/química , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Cinética , Conformação Molecular , Movimento (Física) , Transição de Fase , Fosfatidilcolinas/química , Marcadores de Spin , Temperatura Ambiente , Termodinâmica
3.
Biophys Chem ; 252: 106223, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31325894

RESUMO

Simulations of electron paramagnetic resonance spectra of stearic acid spin labels in lipid bilayers are used to illustrate the fact that the apparent order parameter Sapp calculated from the spectral shape does not coincide with the true order parameter S in the case of slow motions. While S reflects a static property as the degree of order of the lipid chains, Sapp depends on both order and dynamics. Thus, calibration procedures intended to obtain bilayer microviscosity values from Sapp in the slow motion regime are not reliable. However, Sapp is a useful tool to describe trends in membrane fluidity.


Assuntos
Bicamadas Lipídicas/química , Ácidos Esteáricos/química , Espectroscopia de Ressonância de Spin Eletrônica , Estrutura Molecular , Marcadores de Spin , Viscosidade
4.
J Sci Food Agric ; 99(14): 6364-6371, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31273805

RESUMO

BACKGROUND: Biofortification with selenium (Se) elevates its concentration in feed and fodder plants and helps to prevent health problems in animals and humans. The aim of this study was to describe Se-induced modifications in the accumulation of elements important for the proper functioning of wheat, one of the most popular cereals. The presence of Se correlated with carbohydrate synthesis and electron paramagnetic resonance (EPR). This explained the mechanisms of Se's antioxidant activity. RESULTS: Selenium accumulation in vegetative and generative leaves, and in the grains of three wheat genotypes (cv. Parabola, cv. Raweta and cv. Manu), differing in their stress tolerance and grown hydroponically in the presence of 10 or 20 µM Na2 SeO4, , was proportional to its content in the medium. Stronger Se accumulation was typical of a stress-sensitive genotype. Selenium generally promoted the uptake of macronutrients and micronutrients but their distribution depended on tissue and genotype. Changes in the Se-induced EPR signals of paramagnetic metals and organic radicals corresponded with stress tolerance of the tested genotypes. CONCLUSIONS: Se application increased the accumulation of nutrients and carbohydrates that are vital for proper plant growth and development. Accelerated uptake of molybdenum (Mo), an element improving dietary properties of grains, may be an additional advantage of Se fertilization. The mechanisms of Se-induced changes in removing Mn and iron (Fe) ions from macromolecules may be one of the factors that differentiate plant tolerance to oxidative stress. © 2019 Society of Chemical Industry.


Assuntos
Selênio/metabolismo , Açúcares/metabolismo , Triticum/crescimento & desenvolvimento , Triticum/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica , Genótipo , Ferro/análise , Ferro/metabolismo , Micronutrientes/análise , Micronutrientes/metabolismo , Folhas de Planta/química , Folhas de Planta/metabolismo , Selênio/análise , Açúcares/análise , Triticum/química , Triticum/genética
5.
Chem Biol Interact ; 310: 108752, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31330126

RESUMO

Atopic dermatitis (AD) is a chronic inflammatory skin disease whose pathogenesis is still not fully understood. Since inflammatory processes correlate with oxidative stress, the redox status may play a key role in AD. In this study, electron paramagnetic resonance (EPR) spectroscopy was mainly used to investigate the redox status in normal and inflammatory skin equivalents mimicking characteristics of AD in vitro using EPR spin probes (TEMPO, PCA) and a spin trap (DMPO). The total antioxidant status in the hydrophilic and lipophilic compartments of skin (microenvironment) showed no differences between the skin equivalents. In the inflammatory skin equivalents, a decreased glutathione concentration in the epidermis and an increased metabolic radical production could be observed compared to normal skin equivalents. The induction of external stress by simulated solar irradiation (UVB-NIR) resulted in the same amount and type of radicals in normal and inflammatory skin equivalents. For the first time, the antioxidant and oxidant status of inflammatory in vitro skin equivalents was analyzed by EPR to elucidate their redox status using different methods which focus on various microenvironments. Our investigations suggested that the redox status in atopic skin could be different, but this should be investigated more comprehensively, because the results can vary depending on the used methods and where the investigations take place.


Assuntos
Dermatite Atópica/patologia , Pele/patologia , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Glutationa/análise , Humanos , Inflamação/metabolismo , Oxirredução , Pele/metabolismo
6.
J Phys Chem A ; 123(32): 7075-7086, 2019 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-31310526

RESUMO

The nitric oxide synthase (NOS) enzyme consists of multiple domains connected by flexible random coil tethers. In a catalytic cycle, the NOS domains move within the limits determined by the length and flexibility of the interdomain tethers and form docking complexes with each other. This process represents a key component of the electron transport from the flavin adenine dinucleotide/reduced nicotinamide adenine dinucleotide phosphate binding domain to the catalytic heme centers located in the oxygenase domain. Studying the conformational behavior of NOS is therefore imperative for a full understanding of the overall catalytic mechanism. In this work, we have investigated the equilibrium positional distributions of the NOS domains and the bound calmodulin (CaM) by using Monte Carlo calculations of the NOS conformations. As a main experimental reference, we have used the magnetic dipole interaction between a bifunctional spin label attached to T34C/S38C mutant CaM and the NOS heme centers, which was measured by pulsed electron paramagnetic resonance. In general, the calculations of the conformational distributions allow one to determine the range and statistics of positions occupied by the tethered protein domains, assess the crowding effect of the multiple domains on each other, evaluate the accessibility of various potential domain docking sites, and estimate the interaction energies required to achieve target populations of the docked states. In the particular application described here, we have established the specific mechanisms by which the bound CaM facilitates the flavin mononucleotide (FMN)/heme interdomain docking in NOS. We have also shown that the intersubunit FMN/heme domain docking and electron transfer in the homodimeric NOS protein are dictated by the existing structural makeup of the protein. Finally, from comparison of the calculated and experimental docking probabilities, the characteristic stabilization energies for the CaM/heme domain and the FMN domain/heme domain docking complexes have been estimated as -4.5kT and -10.5kT, respectively.


Assuntos
Óxido Nítrico Sintase/química , Espectroscopia de Ressonância de Spin Eletrônica , Modelos Moleculares , Método de Monte Carlo , Óxido Nítrico Sintase/metabolismo , Conformação Proteica
7.
Biophys Chem ; 252: 106191, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31177024

RESUMO

Bacterial cell characteristics, such as size, morphology, and membrane integrity, are affected by environmental conditions. Thermal treatment results in related structural changes, extent of which is determined by the microorganism's survival skills and inactivation kinetics. The objective of this study was to characterize changes in cell structure of Escherichia coli during heating using the combined analysis of dynamic light scattering (DLS), electron paramagnetic resonance (EPR) spectroscopy, and transmission electron microscopy (TEM) techniques. The size of E. coli cells increased from 2.3 µm to 3.0 µm with heating up to 50 °C followed by a shrinkage with further heating up to 70 °C. The morphological changes were verified using transmission electron microscopy. Related changes in membrane integrity was quantified via the mobility of 16-doxylstearic acid (16-DSA) spin probe using EPR spectroscopy. Two order parameters S1 and S2 defined on x- and y-axes, respectively, decreased with increasing temperature indicating loss of membrane integrity. The combined techniques as in this study can be used to further understand factors that play role in survival behavior of microorganisms.


Assuntos
Membrana Celular/química , Escherichia coli/química , Escherichia coli/citologia , Calefação , Difusão Dinâmica da Luz , Espectroscopia de Ressonância de Spin Eletrônica , Hidrodinâmica , Microscopia Eletrônica de Transmissão , Tamanho da Partícula , Propriedades de Superfície
8.
Anal Bioanal Chem ; 411(17): 3801-3810, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31172237

RESUMO

The convenience of colorimetric sensors is useful for practical applications. In this work, we constructed a novel colorimetric sensor with magnetic separation ability that can be operated in nearly neutral conditions and achieve one-step detection of metabolites. Magnetic Cu doped Fe3O4@FeOOH magnetic nanocomposite (Cu/Fe3O4@FeOOH) with an oxygen vacancy was prepared by a one-step self-assembly hydrothermal method, and fully characterized by different methods. The oxygen vacancy generated by the incorporation of Cu2+ cations into the Fe3O4@FeOOH structure was confirmed to be a vital reactive site for enhancing the catalytic activity, which opens up a new way of designing highly efficient enzyme mimics. Benefiting from its inherent horseradish-peroxidase-like activity, a simple and selective enzyme-based colorimetric sensor was developed for one-step detection of H2O2 and cholesterol, and 3,3',5,5'-tetramethylbenzidine was catalyzed by H2O2 to generate a colored product of oxidized 3,3',5,5'-tetramethylbenzidine for signaling. H2O2 and cholesterol can be linearly detected in the same range from 0.01 to 0.4 mmol L-1 with detection limits of 0.0075 mmol L-1 and 0.0082 mmol L-1, respectively. The proposed colorimetric sensor has satisfactory reusability, accuracy, and practicability in human serum samples, indicating its potential application for the detection of different metabolites in the fields of life science and analytical science. Graphical abstract.


Assuntos
Técnicas Biossensoriais/métodos , Colorimetria/métodos , Cobre/química , Óxido Ferroso-Férrico/química , Peroxidase do Rábano Silvestre/química , Concentração de Íons de Hidrogênio , Magnetismo , Nanopartículas Metálicas/química , Benzidinas/química , Colesterol/sangue , Espectroscopia de Ressonância de Spin Eletrônica , Peróxido de Hidrogênio/análise , Microscopia Eletrônica de Transmissão , Oxirredução , Espectroscopia Fotoeletrônica , Reprodutibilidade dos Testes , Análise Espectral Raman , Difração de Raios X
9.
Dokl Biochem Biophys ; 485(1): 135-137, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31201634

RESUMO

Singlet fission of carotenoid excitation is studied in purple phototrophic bacterium Thermochromatium tepidum. Using time-resolved EPR and magnetic field-induced modulation of fluorescence yield it is shown that the concept of intramolecular excitation fission developed in a number of publications is not supported by the experimental results. The obtained data favor intermolecular fission mechanism involving two carotenoid molecules.


Assuntos
Carotenoides/química , Chromatiaceae/química , Fluorescência , Carotenoides/metabolismo , Chromatiaceae/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica
10.
Medicine (Baltimore) ; 98(23): e15972, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31169728

RESUMO

BACKGROUND: This study aimed to evaluate the value of 3-dimensional pseudocontinuous arterial spin labeling (3D-pcASL) and susceptibility-weighted imaging (SWI) for the early disease-sensitive markers of conversion from amnestic MCI (aMCI) to Alzheimer disease (AD) in this process. METHODS: Forty patients with aMCI and AD respectively were recruited in the study, and 40 healthy subjects were taken as controls. Data were recorded using 3T MR scanner. We assessed the cerebral blood flow (CBF) in 11 different regions of interest, and counted number of microhemorrhages (MB) in 3 regions of brain lobes, bilateral basal ganglia/thalamus, and brain stem/cerebellum, and then investigated correlations between Montreal Cognitive Assessment (MoCA) scores, CBF, and susceptibility-weighted imaging (SWI) features in these 3 groups. RESULTS: The results revealed that for AD patients, the MoCA scores and CBF values in frontal gray matter (FGM), occipital gray matter (OGM), temporal gray matter (TGM), parietal gray matter (PGM), hippocampus, anterior cingulate cortex (ACC), precuneus, posterior cingulate cortex (PCC), precuneus, basal ganglia and thalamus decreased compared with aMCI patients and control group, and significant difference was revealed among the 3 groups. While in cerebellum, statistical significance was only found between AD patients and control group. On SWI, the average numbers of hemorrhage in regions of lobes for AD patients were significantly higher than aMCI patients and control group. The same results occurred in the bilateral basal ganglia/thalamus. We further found the MoCA score was positively correlated with CBF, but negatively correlated with hypointense signal on SWI. CONCLUSION: 3D-pCASL and SWI have promising potential to be biomarkers for conversion from aMCI to AD in this process.


Assuntos
Doença de Alzheimer/diagnóstico por imagem , Amnésia/diagnóstico por imagem , Disfunção Cognitiva/diagnóstico por imagem , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Angiografia por Ressonância Magnética/métodos , Idoso , Doença de Alzheimer/psicologia , Amnésia/complicações , Circulação Cerebrovascular/fisiologia , Disfunção Cognitiva/complicações , Estudos Transversais , Progressão da Doença , Feminino , Humanos , Imagem Tridimensional , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Medição de Risco/métodos , Marcadores de Spin
11.
Chem Commun (Camb) ; 55(60): 8840-8843, 2019 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-31168558

RESUMO

Redox reactions and paramagnetic intermediates are ubiquitous in biological chemistry. We report a new method, protein film electrochemical electron paramagnetic resonance spectroscopy (PFE-EPR), that enables the direct and accurate potential control of proteins on the electrode surface for both electrochemical and EPR spectroscopic characterisation of their redox centres.


Assuntos
Óxidos N-Cíclicos/química , Técnicas Eletroquímicas/métodos , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Superóxido Dismutase-1/química , Animais , Bovinos , Técnicas Eletroquímicas/instrumentação , Eletrodos , Oxirredução
12.
J Agric Food Chem ; 67(26): 7526-7529, 2019 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-31184887

RESUMO

A limitation of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability (DRSA) due to the presence of pigments and colors in the extracts of plant-based foods was addressed. The pigments present in the test samples absorb in the same wavelength region as the DPPH radicals; this interferes with the elaborate absorbance readings of the DPPH radicals. In this contribution, electron paramagnetic resonance (EPR) spectroscopy for DPPH assay is proposed in order to avoid this limitation. In the EPR-DPPH assay, the underestimation of the radical scavenging abilities of four different pigment-containing extracts was corrected and this reflected up to a 16.1% change compared to the original values. Thus, the EPR-DPPH assay eliminated interference from the pigments coexisting in the reaction medium and improved the accuracy of the DPPH radical scavenging potential of such extracts. The principle of the proposed solution might also be employed in other assays which suffer from pigment interference.


Assuntos
Compostos de Bifenilo/química , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Depuradores de Radicais Livres/química , Picratos/química , Pigmentos Biológicos/química , Extratos Vegetais/química , Beta vulgaris/química , Capsicum/química , Cor , Rubus/química
13.
Chemosphere ; 233: 975-982, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31230826

RESUMO

To remove the harmful dye contaminants via an efficient, facile and low energy consumption route is a grave challenge in current chemical industry. Though the great progresses of TiO2 photocatalysis and enzymatic degradation have been witnessed, the strategy for satisfying the above requirements is still worth exploring. Herein, we develop a biomimetic catalysis strategy for the fast decolorization of organic dyes catalyzed by iron octacarboxylic phthalocyanine (FeOCPc) complexes assisted with tert-butyl hydroperoxide (BuOOH). Methyl orange (MO) and methylene blue (MB) were used as the model pollutants and experimental results show that the decolorization degree of 25 mg/L MO could achieve 100% within 20 min and 80% for 25 mg/L MB within 30 min. The molar ratio for FeOCPc/MO and FeOCPc/MB is 0.146 and 0.142, respectively. Interestingly, other than the high-valent iron-oxygen active species, tert-butyl peroxyl radicals and hydroxyl radicals were detected as the active species generated during the catalytic oxidation by the electron paramagnetic resonance (EPR) measurement. This work not only provides a distinctive biomimetic catalysis system of FeOCPc-BuOOH for the fast bleaching of dye pollutants, but also proposes the new insight on a mechanism based on the cooperation catalysis of iron-oxygen active species, tert-butyl peroxyl radicals and hydroxyl radicals.


Assuntos
Corantes/química , Compostos Ferrosos/química , Indóis/química , Poluentes Químicos da Água/química , Compostos Azo , Catálise , Espectroscopia de Ressonância de Spin Eletrônica , Radical Hidroxila , Ferro/química , Azul de Metileno/química , Modelos Químicos , Oxirredução , Peróxidos , Espécies Reativas de Oxigênio , terc-Butil Hidroperóxido
14.
Biochemistry (Mosc) ; 84(5): 570-574, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31234771

RESUMO

Studying pigment-protein interactions in the photosynthetic reaction centers (RCs) is important for the understanding of detailed mechanisms of the photochemical process. This paper describes spectral and photochemical characteristics, pigment composition, and stability of the Rhodobacter sphaeroides RCs with the I(L177)Y and I(M206)Y amino acid substitutions. The obtained data are compared with the properties of I(L177)H, I(L177)D, and I(M206)H RCs reported previously. It is shown that the I(L177)Y and I(M206)Y mutations cause a similar shift of the QYP band in the absorption spectra of the mutant RCs and do not affect the distribution of the electron spin density within the photo-oxidized P+ dimer. The differences in the position and amplitude of the QYB band in the I(L177)Y and I(M206)Y RCs were determined. The results indicate the possibility of new pigment-protein interactions in the vicinity of monomeric bacteriochlorophylls in the A and B chains, which might be of interest for future research.


Assuntos
Proteínas de Bactérias/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Bacterioclorofilas/química , Bacterioclorofilas/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica , Mutagênese Sítio-Dirigida , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/genética , Estrutura Terciária de Proteína , Rhodobacter sphaeroides/metabolismo , Espectrofotometria
15.
Chem Commun (Camb) ; 55(54): 7752-7755, 2019 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-31204733

RESUMO

Metal-binding peptides are versatile building blocks in supramolecular chemistry. We recently reported a class of crystalline materials formed through a combination of coiled-coil peptide self-association and metal coordination. Here, we probe the serendipitously discovered metal binding motif that drives the assembly and apply these insights to exert rational control over structure and morphology in the materials.


Assuntos
Metaloproteínas/química , Motivos de Aminoácidos , Sequência de Aminoácidos , Cobre/química , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Metaloproteínas/síntese química , Engenharia de Proteínas/métodos , Multimerização Proteica , Piridinas/química
16.
Environ Int ; 129: 154-163, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31128436

RESUMO

This paper presents the interaction of benzo[a]pyrene (B[a]P) with Cu(II)-montmorillonite to investigate the formation, evolution and potential toxicity of environmentally persistent free radicals (EPFRs) under dark and visible light irradiation conditions. Degradation of B[a]P and the generated transformative products on clay mineral are monitored by gas chromatography-mass spectrometry (GC-MS) technique. Hydroxyl-B[a]P and B[a]P-diones are observed during the transformation of B[a]P under dark condition. B[a]P-3,6-dione and B[a]P-6,12-dione are the main products under visible light irradiation. B[a]P transformation is accompanied by the formation of EPFRs, which are quantified by electron paramagnetic resonance (EPR) spectroscopy. With increasing reaction time, the concentrations of the produced EPFRs are initially increased and then gradually decrease to an undetectable level. The deconvolution results of EPR spectra reveal formation of three types of organic radicals (carbon-centered radicals, oxygen-centered radicals, and carbon-centered radicals with a conjugated oxygen), which also co-exist. Correspondingly, visible-light irradiation promotes the formation and the decay of these EPFRs. The produced B[a]P-type EPFRs induce the generation of reactive oxygen species (ROS), such as superoxide (O2-) and hydroxide radicals (OH), which may cause oxidative stress to cells and tissues of organisms. The toxicity of degradation products is evaluated by the livability of human gastric epithelial GES-1cells. The toxicity is initially increased and then decreases with the elapsed reaction time, which correlates with the evolution of EPFRs concentrations. The present work provides direct evidence that the formation of EPFRs in interaction of PAHs with metal-contaminated clays may result in negative effects to human health.


Assuntos
Bentonita/química , Benzo(a)pireno/química , Cobre/química , Espécies Reativas de Oxigênio/química , Linhagem Celular , Espectroscopia de Ressonância de Spin Eletrônica , Radicais Livres/química , Humanos
17.
Dalton Trans ; 48(21): 7451-7461, 2019 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-31086893

RESUMO

A significant abundance of copper (Cu) and iron in amyloid ß (Aß) plaques, and several heme related metabolic disorders are directly correlated with Alzheimer's disease (AD), and these together with co-localization of Aß plaques with heme rich deposits in the brains of AD sufferers indicates a possible association of the said metals with the disease. Recently, the Aß peptides have been found to bind heme and Cu individually as well as simultaneously. Another significant finding relevant to this is the lower levels of nitrite and nitrate found in the brains of patients suffering from AD. In this study, a combination of absorption and electron paramagnetic resonance spectroscopy and kinetic assays have been used to study the interaction of nitrite with the metal bound Aß complexes. The data indicate that heme(III)-Cu(i)-Aß, heme(II)-Cu(i)-Aß, heme(II)-Aß and Cu(i)-Aß can reduce nitrite to nitric oxide (NO), an important biological messenger also related to AD, and thus behave as nitrite reductases. However these complexes reduce nitrite at different rates with heme(III)-Cu(i)-Aß being the fastest following an inner sphere electron transfer mechanism. The rest of the metal-Aß adducts follow an outer sphere electron transfer mechanism during nitrite reduction. Protonation from the Arg5 residue triggering the N-O bond heterolysis in heme(III) bound nitrite with a simultaneous electron transfer from the Cu(i) center to produce NO is the rate determining step, indicating a proton transfer followed by electron transfer (PTET) mechanism.


Assuntos
Peptídeos beta-Amiloides/química , Cobre/química , Heme/química , Nitrito Redutases/química , Espectroscopia de Ressonância de Spin Eletrônica , Transporte de Elétrons , Humanos , Ferro/química , Cinética , Óxido Nítrico/química , Nitritos/química , Oxirredução , Placa Amiloide/química
18.
Environ Sci Technol ; 53(11): 6454-6461, 2019 06 04.
Artigo em Inglês | MEDLINE | ID: mdl-31081617

RESUMO

The effect of Cr(VI) and bisphenol A (BPA) on U(VI) photoreduction by C3N4 photocatalyst was demonstrated by the batch experiments, electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) techniques. The batch experiments manifested that Cr(VI) and BPA enhanced the photocatalytic activity of C3N4 for U(VI) photoreduction, whereas U(VI) photoreduction was significantly diminished with increased pH from 4.0 to 8.0. According to radical scavengers and ESR analysis, U(VI) was photoreduced to U(IV) by photogenerated electrons of conduction band edge, whereas Cr(VI) was reduced to Cr(III) by H2O2. BPA and its products such as organic acid and alcohols can capture photoinduced holes, which resulted in the enhancement of U(VI) photoreduction to U(IV). XPS and XANES analyses demonstrated that U(VI) was gradually photoreduced to U(IV) by C3N4 within irradiation 60 min, whereas U(IV) was reoxidized to U(VI) with increasing irradiation time. EXAFS analysis determined that the dominant interaction mechanisms of U(VI) on C3N4 after irradiation for 240 min were reductive precipitation and inner-sphere surface complexation. This work highlights the synergistic removal of radionuclides, heavy metals, and persistent organic pollutants by C3N4, which is crucial for the design and application of a high-performance photocatalyst in actual environmental cleanup.


Assuntos
Peróxido de Hidrogênio , Compostos Benzidrílicos , Cromo , Espectroscopia de Ressonância de Spin Eletrônica , Fenóis , Espectroscopia Fotoeletrônica
19.
Chemphyschem ; 20(14): 1860-1868, 2019 07 16.
Artigo em Inglês | MEDLINE | ID: mdl-31054266

RESUMO

It is an open question whether the conformations of proteins sampled in dilute solutions are the same as in the cellular environment. Here we address this question by double electron-electron resonance (DEER) distance measurements with Gd(III) spin labels to probe the conformations of calmodulin (CaM) in vitro, in cell extract, and in human HeLa cells. Using the CaM mutants N53C/T110C and T34C/T117C labeled with maleimide-DOTA-Gd(III) in the N- and C-terminal domains, we observed broad and varied interdomain distance distributions. The in vitro distance distributions of apo-CaM and holo-CaM in the presence and absence of the IQ target peptide can be described by combinations of closed, open, and collapsed conformations. In cell extract, apo- and holo-CaM bind to target proteins in a similar way as apo- and holo-CaM bind to IQ peptide in vitro. In HeLa cells, however, in the presence or absence of elevated in-cell Ca2+ levels CaM unexpectedly produced more open conformations and very broad distance distributions indicative of many different interactions with in-cell components. These results show-case the importance of in-cell analyses of protein structures.


Assuntos
Calmodulina/química , Calmodulina/metabolismo , Calmodulina/genética , Extratos Celulares/química , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Gadolínio/química , Células HeLa , Humanos , Mutação , Conformação Proteica , Marcadores de Spin
20.
Int J Mol Sci ; 20(10)2019 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-31091724

RESUMO

Low-frequency electron paramagnetic resonance (EPR) spectra were obtained for the Co complex of ethylene diamine tetraacetic acid (CoEDTA). It was found that the cobalt hyperfine at geff-mid is better resolved at a low frequency, L-band (1.37 GHz), and not resolved at X-band (9.631 GHz), which is the conventional frequency used for most spectra for metal complexes. Resolved cobalt hyperfine lines lead to additional EPR parameters like A-mid for cobalt and a more-accurate determination of g-mid. Resolved hyperfine lines in the L-band, but not the S-band, spectra were obtained at a concentration of 1 mM. Knowing these additional EPR parameters provides a means to better determine the electron density in the ground state orbital for each cobalt complex, as well as to determine differences upon a change of ligation. If zinc sites can be replaced by cobalt, the cobalt spectra for these sites will enhance the characterization of the zinc sites.


Assuntos
Cobalto/química , Ácido Edético/química , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Compostos de Zinco/química
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