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1.
J Colloid Interface Sci ; 605: 129-137, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-34311307

RESUMO

Lithium-sulfur (Li-S) batteries are greatly expected to be the favored alternatives in the next-generation energy-storage technologies due to their exceptional advantages. However, the shuttle effect and sluggish reaction kinetics of polysulfides largely hamper the practical success of Li-S batteries. Herein, a unique iron carbide (Fe3C) nanoparticles-embedded porous biomass-derived carbon (Fe3C-PBC) is reported as the excellent immobilizer and promoter for polysulfides regulation. Such a distinctive composite strongly couples the vast active sites of Fe3C nanoparticles and the conductive network of porous biomass-derived carbon. Therefore, Fe3C-PBC is endowed with outstanding adsorptivity and catalytic effect toward inhibiting the shuttle effect and facilitating the redox kinetics of polysulfides, demonstrated by the detailed experimental demonstrations and theoretical calculation. With these synergistic effects, the Fe3C-PBC/S electrode embraces a superb capacity retention of 82.7% at 2C over 500 cycles and an excellent areal capacity of 4.81 mAh cm-2 under the high-sulfur loading of 5.2 mg cm-2. This work will inspire the design of advanced hosts based on biomass materials for polysulfides regulation in pursuing the superior Li-S batteries.


Assuntos
Lítio , Nanopartículas , Biomassa , Carbono , Compostos Inorgânicos de Carbono , Compostos de Ferro , Porosidade , Sulfetos , Enxofre
2.
Food Chem ; 366: 130613, 2022 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-34304136

RESUMO

A colorimetric and fluorescence dual-signal method based on sulfur quantum dots (SQDs) was established for determination of iron (II) (Fe2+) and H2O2 in foods. Due to the complexation of Fe2+ with SQD, Fe2+ can cause fluorescence quenching of SQDs, and the color of the mixed solution changed from light yellow to deep green. By use of Fenton reaction, H2O2 can restore the quenched fluorescence of SQDs, and the color of the mixture changed from green to colorless. The concentration of Fe2+ and H2O2 has a good linear relationship with the fluorescence intensity and absorbance in the range of 2.5-55 µM and 1.25-500 µM, and the detection limits were 1.41 µM and 0.54 µM, respectively. For determination of H2O2, the linear ranges were 1.17-1.97 mM and 0.867-1.50 mM, and the detection limits were 0.03 µM and 0.06 µM, respectively.


Assuntos
Pontos Quânticos , Colorimetria , Peróxido de Hidrogênio , Ferro , Enxofre
3.
Food Chem ; 367: 130741, 2022 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-34399272

RESUMO

Volatile sulfur-containing compounds (VSCs) provide an important contribution to foods due to their special odors. In this study, VSCs in 21 cold-pressed rapeseed oils (CROs) from 9 regions in China were extracted and separated by headspace solid-phase microextraction combined with gas chromatography coupled with sulfur chemiluminescence detection. 19 VSCs were identified by authentic standards, and the total concentration of VSCs in all CROs ranged from 49.0 to 18129 µg/kg. Dimethyl sulfide (DMS), with its high odor activity value (7-14574), was the most significant aroma contributor to the CROs. Furthermore, S-methylmethionine (SMM) in rapeseed was first affirmed by ultra-performance liquid chromatography-tandem mass spectrometry and isotope quantitation. The positive correlation coefficient between DMS and SMM was 0.793 (p < 0.05), which confirmed SMM as a crucial precursor of DMS in CROs. This study provided a theoretical basis for selecting rapeseed materials by the distribution of essential VSCs and the source of DMS.


Assuntos
Compostos de Enxofre , Compostos Orgânicos Voláteis , Cromatografia Líquida de Alta Pressão , Cromatografia Líquida , Cromatografia Gasosa-Espectrometria de Massas , Odorantes/análise , Óleo de Brassica napus , Sulfetos , Enxofre , Compostos de Enxofre/análise , Espectrometria de Massas em Tandem , Compostos Orgânicos Voláteis/análise
4.
Food Chem ; 371: 131123, 2022 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-34555706

RESUMO

The anabolism of aroma volatiles in response to non-biological factors during the drying process of shiitake mushrooms was analyzed. Temperatures (40 °C, 50 °C, and 60 °C) had secondary activation effects on the synthetase activity. The enzymatic reaction time could last 4-5 h under medium-temperature drying process (40 °C and 50 °C), and 1.5-2 h under a high-temperature drying process (60 °C and 70 °C). The aroma synthesis dominated by non-enzymatic reactions were chemical reactions between amino acids and reducing sugars. The hot-air drying process of shiitake mushroom was consistent with the cubic model and the key control points influencing the enzymatic reaction parameters were in the order of moisture rate > temperature > drying time > drying rate. The non-enzymatic reaction parameters were in the order of temperature > drying time > drying rate > moisture rate. The total sulfur volatiles produced in the optimized process were significantly higher, and the drying time of the process could be completed within 6 h.


Assuntos
Cogumelos Shiitake , Dessecação , Conservação de Alimentos , Odorantes/análise , Enxofre
5.
J Colloid Interface Sci ; 606(Pt 1): 688-695, 2022 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-34416458

RESUMO

Herein, we systematically investigated the mechanisms of OH production and arsenic (As(III)) oxidation induced by sulfur vacancy greigite (Fe3S4) under anoxic and oxic conditions. Reactive oxygen species analyses revealed that sulfur vacancy-rich Fe3S4 (SV-rich Fe3S4) activated molecular oxygen to produce hydrogen peroxide (H2O2) via a two-electron reduction pathway under oxic conditions. Subsequently, H2O2 was decomposed to OH via the Fenton reaction. Additionally, H2O was directly oxidized to OH by surface high-valent iron (Fe(IV)) resulting from the abundance of sulfur vacancies in Fe3S4 under anoxic/oxic conditions. These differential OH-generating mechanisms of Fe3S4 resulted in higher OH production of SV-rich Fe3S4 compared to sulfur vacancy-poor Fe3S4 (SV-poor Fe3S4). Moreover, the OH production rate of SV-rich Fe3S4 under oxic conditions (19.3 ± 1.0 µM•h-1) was 1.6 times greater than under anoxic conditions (11.8 ± 0.4 µM•h-1). As(III) removal experiments and X-ray photoelectron spectra (XPS) showed that both OH production pathways were favorable for As(III) oxidation, and a higher concentration of As(V) was immobilized on the surface of SV-rich Fe3S4 under oxic conditions. This study provides new insights concerning OH production and environmental pollutants removal mechanisms on surface defects of Fe3S4 under anoxic and oxic conditions.


Assuntos
Arsênio , Peróxido de Hidrogênio , Radical Hidroxila , Ferro , Oxirredução , Sulfetos , Enxofre
6.
Spectrochim Acta A Mol Biomol Spectrosc ; 265: 120365, 2022 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-34509893

RESUMO

Sulfur quantum dots (S-dots) show great potential for applications in various field, due to their favorable biocompatibility, high stability, and antibacterial properties. However, the use of S-dots in chemical sensing is limited by the lack of functional groups on the surface. In this work, a fluorescence glutathione (GSH) assay is developed based on the GSH modulated quenching effect of Cu2O nanoparticles (NP) on S-dots. The fluorescence of S-dots is effectively quenched after forming complex with Cu2O NP through a static quenching effect (SQE). Introducing of GSH can trigger the decomposition of Cu2O NP into GSH-Cu(I) complex, which leads to the weaken of SQE and the partial recover of the fluorescence. The intensity of recovered fluorescence shows a positive correlation with the concentration of GSH in the concentration range of 20 to 500 µM. The fluorescence GSH assay shows excellent selectivity and robustness towards various interferences and high concentration salt, which endow the successful detection of GSH in human blood sample. The presented results provide a new door for the design of fluorescence assays, which also provides a platform for the applications in nanomedicine and environmental science.


Assuntos
Cobre , Nanopartículas , Pontos Quânticos , Corantes Fluorescentes , Glutationa , Humanos , Limite de Detecção , Enxofre
7.
Chemosphere ; 286(Pt 1): 131599, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-34315084

RESUMO

In this study, 11 low/uncontaminated (including Lufa 2.2) and 9 contaminated field soils with varying geophysical and physicochemical characteristics were evaluated for toxicities based on oxygen consumption of sulfur-oxidizing bacteria (SOB). Oxygen consumption of the low/uncontaminated soils ranged between 7.9 mL and 9.5 mL, while contaminated soils ranged between 0.4 mL and 5.4 mL. Inherent test variability (CVi), variation due to soil natural properties (CVns) and minimal detectable difference (MDD) values ranged 1.2%-3.9%, 3.5%-16.9%, and 2.1%-4.3%, respectively. The toxicity threshold of 20% was established for soil toxicity based maximal tolerable inhibition (MTI). All the contaminated soils were found to be toxic and showed inhibition between 42% and 100% above the 20% threshold value. Increased proportions of clay and slit enhanced the of inhibitory effect of contaminants on SOB by reducing the oxygen consumption. Current study provides a suitable method for the rapid toxicity assessment of contaminated field soils with the advantages of ease of handling and rapidity without employing elutriates and sophisticated equipments and tools.


Assuntos
Poluentes do Solo , Solo , Bactérias , Bioensaio , Oxirredução , Poluentes do Solo/análise , Poluentes do Solo/toxicidade , Enxofre/toxicidade
8.
Sci Total Environ ; 802: 149780, 2022 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-34461478

RESUMO

In order to evaluate the potential risk of surface water acidification in regions with historically-elevated acid deposition and to measure the recovery of such ecosystems after policy changes, critical loads and their exceedances were estimated for 349 headwater streams across China using a modified SSWC model. Such a model considered the acid-neutralizing capacity derived from high base cation deposition and the robust retention of sulfate and nitrate. Results indicated that China's streams had higher critical loads (averaged at 4.7 keq·ha-1·yr-1) and were less sensitive to acid deposition as compared to Europe and North America. The proportion of surveyed streams with acid deposition exceeded critical load decreased from 40.4% in 2005 to 29.5% in 2018, indicating a significant decrease in risk of surface water acidification, and thus a benefit from the emission abatement in recent years. Nonetheless, a relatively high risk of acidification still existed in southeast China with lower critical loads and most critical load exceedances. More efforts should be put into implementing emission control policies in the future.


Assuntos
Ecossistema , Rios , China , Monitoramento Ambiental , Água Doce , Sulfatos , Enxofre/análise
9.
Environ Pollut ; 291: 118221, 2021 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-34740294

RESUMO

Sulfur, an essential macronutrient, plays important roles in plant development and stress mitigation. Sulfur deficiency, a common problem in agricultural soils, may disturb plant stress resistance and xenobiotic detoxification. In the present study, the function and mechanism of limited sulfur nutrition on the residues and phtotoxicity of imidacloprid were investigated in lettuce plants. Sulfur deficiency significantly increased imidacloprid accumulation in lettuce tissues, exacerbated imidacloprid biological toxicity by enhancing the accumulation of toxic metabolites, like imidacloprid-olefin. Simultaneously, imidacloprid-induced detoxification enzymes including cytochromes P450, glutathione S-transferases (GSTs) and glycosyltransferases were inhibited under limited sulfur supply. On the other hand, sulfur deficiency further enhanced the generation of reactive oxygen species and exacerbated lipid peroxidation in lettuce tissues. Sulfur deficiency mainly reduced the abundance of thiol groups, which are essential redox modulators as well as xenobiotic conjugators, and significantly inhibited GSTs expression. These results clearly suggested that sulfur deficiency inhibited the synthesis of sulfur-containing compounds, leading to increased accumulation of pesticide residues and toxic metabolites as well as reduced detoxification capacity, consequently leading to oxidative damage to plants. Therefore, moderate sulfur supply in regions where neonicotinoid insecticides are intensively and indiscriminately used may be an efficient strategy to reduce pesticide residues and the potential risk to ecosystem.


Assuntos
Inseticidas , Plântula , Ecossistema , Inseticidas/toxicidade , Alface , Neonicotinoides/toxicidade , Nitrocompostos/toxicidade , Compostos de Sulfidrila , Enxofre
10.
J Int Med Res ; 49(11): 3000605211059936, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34786994

RESUMO

Sulphur-containing compounds have been linked to colorectal cancer by factors such as the presence of methyl mercaptan in intestinal gas and long-term dietary intake associated with sulphur-metabolizing microbiota. Therefore, this current case report hypothesized that active sulphur metabolism in colorectal cancer results in the formation of sulphur compounds in the intestine and, thus, examined sulphur metabolites possibly associated with sulphur respiration in colon cancer tissues. The patient was a 73-year-old female that underwent laparoscopic right hemicolectomy for ascending colon cancer. During the surgery, colon cancer tissues and normal intestinal mucosa samples were collected. After optimizing the sample concentrations for homogenization (pre-treatment), the samples were stabilized using a hydroxyphenyl-containing derivative and the relevant metabolites were quantified using liquid chromatography with tandem mass spectrometry. The results showed that cysteine persulfide and cysteine trisulfide levels were higher in colon cancer tissues than in normal mucosal tissues. Thus, sulphur metabolism, possibly sulphur respiration, is enhanced in colon cancer tissues.


Assuntos
Neoplasias do Colo , Idoso , Cromatografia Líquida , Feminino , Humanos , Mucosa Intestinal , Enxofre , Espectrometria de Massas em Tandem
11.
J Synchrotron Radiat ; 28(Pt 6): 1825-1838, 2021 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-34738936

RESUMO

Sulfur K-edge X-ray absorption spectroscopy (XAS) was employed to experimentally characterize the coordinative bond between the thiourea (TU) or thiocarbamide ligand and transition metal (TM) ions Zn2+, Co2+ and Ni2+ in distorted tetrahedral and octahedral homoleptic coordination environments. Comparisons of XAS spectra of the free TU ligand and [Zn(TU)4]2+, [Co(TU)4]2+ and [Ni(TU)6]2+ complexes clearly identify spectral features unique to TM2+-S(TU) bonding. Quantitative analysis of pre-edge intensities describes the covalency of Ni2+-S(TU) and Co2+-S(TU) bonding to be at most 21% and 9% as expressed by the S 3p contributions per TM 3d electron hole. Using relevant Ni2+ complexes with dithiocarbamate and thioether ligands, we evaluated the empirical S 1s → 3p transition dipole integrals developed for S-donor ligands and their dependence on heteroatom substitutions. With the aid of density functional theory-based ground electronic state calculations, we found evidence for the need of using a transition dipole that is dependent on the presence of conjugated heteroatom (N) substitution in these S-donor ligands.


Assuntos
Compostos Organometálicos , Tioureia , Eletrônica , Enxofre , Espectroscopia por Absorção de Raios X , Zinco
12.
Int J Syst Evol Microbiol ; 71(11)2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34739363

RESUMO

An anaerobic, alkaliphilic, halotolerant, Gram-stain-positive and rod-shaped bacterium, designated Q10-2T, was isolated from mangrove sediment sampled at the Jiulong river estuary, PR China. The cells of strain Q10-2T were motile and 0.5×2-4 µm in size. Strain Q10-2T grew at 8-45 °C (optimum, 32 °C), at pH 7.0-10.5 (optimum, pH 8.5) and in the presence of 0-6 % (w/v) NaCl (optimum, 3 %). It could use complex organic compounds and carbohydrates including d-fructose, d-galactose, d-glucose, d-mannitol, d-xylose, trehalose, lactose, maltose, sucrose and starch as carbon sources and electron donors. It could reduce sulphate, thiosulphate and elemental sulphur to sulphide, but not sulphite. Fe (Ⅲ) citrate, ferrihydrite, haematite and goethite in the presence of glucose as the electron donor were also reduced. Acetate, butyrate, ethanol, CO2 and H2 were end products of glucose fermentation. The predominant cellular fatty acids were composed of C14 : 0, C16 : 0 and summed features containing C16 : 1 ω7c and/or iso-C15 : 0 2-OH and iso-C17 : 1 and/or anteiso-C17 : 1 B. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the novel strain was most closely related to Fusibacter paucivorans DSM 12116T (95.5 % sequence similarity). The genome size of strain Q10-2T was 5.0 Mb, with a G+C content of 37.4 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strain Q10-2T and F. paucivorans DSM 12116T were 69.1 and 21.8 %, respectively. The combined genotypic and phenotypic data showed that strain Q10-2T represents a novel species of the genus Fusibacter, for which the name Fusibacter ferrireducens sp. nov. is proposed. The type strain is Q10-2T (=MCCC 1A16257T=KCTC 15906T).


Assuntos
Ácidos Graxos , Compostos Férricos , Anaerobiose , Técnicas de Tipagem Bacteriana , Composição de Bases , China , Clostridiales , DNA Bacteriano/genética , Ácidos Graxos/química , Fosfolipídeos , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Enxofre
13.
Nat Commun ; 12(1): 5925, 2021 10 11.
Artigo em Inglês | MEDLINE | ID: mdl-34635654

RESUMO

Iron-sulfur (FeS) proteins are ancient and fundamental to life, being involved in electron transfer and CO2 fixation. FeS clusters have structures similar to the unit-cell of FeS minerals such as greigite, found in hydrothermal systems linked with the origin of life. However, the prebiotic pathway from mineral surfaces to biological clusters is unknown. Here we show that FeS clusters form spontaneously through interactions of inorganic Fe2+/Fe3+ and S2- with micromolar concentrations of the amino acid cysteine in water at alkaline pH. Bicarbonate ions stabilize the clusters and even promote cluster formation alone at concentrations >10 mM, probably through salting-out effects. We demonstrate robust, concentration-dependent formation of [4Fe4S], [2Fe2S] and mononuclear iron clusters using UV-Vis spectroscopy, 57Fe-Mössbauer spectroscopy and 1H-NMR. Cyclic voltammetry shows that the clusters are redox-active. Our findings reveal that the structures responsible for biological electron transfer and CO2 reduction could have formed spontaneously from monomers at the origin of life.


Assuntos
Cisteína/química , Ferro/química , Modelos Químicos , Origem da Vida , Sulfetos/química , Enxofre/química , Bicarbonatos/química , Dióxido de Carbono/química , Técnicas Eletroquímicas , Transporte de Elétrons , Concentração de Íons de Hidrogênio , Oxirredução , Espectroscopia de Mossbauer
14.
PLoS One ; 16(10): e0258166, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34606515

RESUMO

Understanding the spatial spreading patterns of plant-available sulphur (S) (AS) and plant-available micronutrients (available zinc (AZn), available iron (AFe), available copper (ACu), available manganese (AMn) and available boron (AB)) in soils, especially in coastal agricultural soils subjected to various natural and anthropogenic activities, is vital for sustainable crop production by adopting site-specific nutrient management (SSNM) strategies. We studied the spatial distribution patterns of AS, AZn, AFe, ACu, AMn, and AB in cultivated soils of coastal districts of India using geostatistical approaches. Altogether 39,097 soil samples from surface (0 to 15 cm depth) layers were gathered from farm lands of 68 coastal districts. The analysis of soil samples was carried out for soil pH, electrical conductivity (EC), soil organic carbon (SOC) and AS, AZn, AFe, ACu, AMn, and AB. Soil pH, EC and SOC varied from 3.70 to 9.90, 0.01 to 7.45 dS m-1 and 0.02 to 3.74%, respectively. The concentrations of AS, AZn, AFe, ACu, AMn, and AB varied widely in the study area with their corresponding mean values were 37.4±29.4, 1.50±1.53, 27.9±35.1, 2.14±1.74, 16.9±18.4 and 1.34±1.52 mg kg-1, respectively. The coefficient of variation values of analyzed soil parameters varied from 14.6 to 126%. The concentrations of AS, AZn, AFe, ACu, AMn, and AB were negatively and significantly correlated with soil pH and positively and significantly correlated with SOC. The geostatistical analysis indicated stable, Gaussian and exponential best-fit semivariogram models with moderate to strong spatial dependence for available nutrients. The generated spatial spreading maps revealed different distribution patterns for AS, AZn, AFe, ACu, AMn, and AB. There were variations in spatial spreading patterns of AS, AZn, AFe, ACu, AMn, and AB in east- and west-coastal area. About 62, 35, 12, 0.4, 23 and 45% of the study area had deficiency of AS, AZn, AFe, ACu, AMn, and AB, respectively. The spatial spreading maps will be highly useful for SSNM in the cultivated coastal soils of the country. This study could also be used as a base for assessing spatial spreading patterns of soil parameters in cultivated coastal areas of other parts of the world.


Assuntos
Micronutrientes/análise , Solo/química , Enxofre/análise , Agricultura , Geografia , Índia , Estatística como Assunto
15.
Anal Chem ; 93(40): 13450-13458, 2021 10 12.
Artigo em Inglês | MEDLINE | ID: mdl-34597513

RESUMO

Elemental and molecular imaging play a crucial role in understanding disease pathogenesis. To accurately correlate elemental and molecular markers, it is desirable to perform sequential elemental and molecular imaging on a single-tissue section. However, very little is known about the impact of performing these measurements in sequence. In this work, we highlight some of the challenges and successes associated with performing elemental mapping in sequence with mass spectrometry imaging. Specifically, the feasibility of molecular mapping using the mass spectrometry imaging (MSI) techniques matrix-assisted laser desorption ionization (MALDI) and desorption electrospray ionization (DESI) in sequence with the elemental mapping technique particle-induced X-ray emission (PIXE) is explored. Challenges for integration include substrate compatibility, as well as delocalization and spectral changes. We demonstrate that while sequential imaging comes with some compromises, sequential DESI-PIXE imaging is sufficient to correlate sulfur, iron, and lipid markers in a single tissue section at the 50 µm scale.


Assuntos
Oligoelementos , Lipídeos , Imagem Molecular , Espectrometria de Massas por Ionização por Electrospray , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz , Enxofre
16.
Nano Lett ; 21(20): 8895-8900, 2021 10 27.
Artigo em Inglês | MEDLINE | ID: mdl-34617776

RESUMO

The hitherto unexplored surface structural and dynamical properties of the thermoelectric material ß-Cu2S chalcocite, are uncovered using ab initio molecular dynamics simulations at 450 K. The material exhibits a hybrid crystalline-liquid behavior, with the liquidlike dynamics of the Cu atoms and the crystalline order of the sulfur sublattice. The topmost nanoscale region of the material is predicted to undergo significant structural relaxation, resulting in a ∼10% increase in the distance between the topmost S-layers accompanied by an increased Cu density. Cu diffusion in the interlayer regions of the surface S-sublattice is enhanced (doubled) compared to the bulk value, and an underlying microscopic mechanism, entailing marked emergent surface-induced softening of the S-sublattice vibrational dynamics, is described.


Assuntos
Simulação de Dinâmica Molecular , Enxofre , Difusão
17.
Mar Pollut Bull ; 171: 112917, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34488148

RESUMO

Very Low Sulfur Fuel Oils (VSLFO, <0.5% S) are a new class of marine fuel oils, introduced to meet recent International Maritime Organization regulations. The MV Wakashio was reported to have released 1000 t of VLSFO when it grounded on a reef in Mauritius on 25th July 2020. A field sample of oily residue contaminating the Mauritian coast was collected on 16th August 2020 and compared with the Wakashio fuel oil. Both oils were analyzed for organic and elemental content, and stable isotope ratios δ13C and δ2H measured. Comprehensive two-dimensional gas chromatography with high-resolution mass spectrometry was used to identify and compare biomarkers resistant to weathering. The aromatic content in the VLSFO was relatively low suggesting that the potential for ecosystem harm arising from exposure to toxic components may be less than with traditional fuel oil spills. The Wakashio oil spill is, to our knowledge, the first documented spill involving VLSFO.


Assuntos
Óleos Combustíveis , Poluição por Petróleo , Ecossistema , Maurício , Enxofre
18.
Anal Chim Acta ; 1178: 338805, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34482864

RESUMO

The development of real-time monitoring sensors for pyro-metallurgical processes is an analytical challenge, mainly due to adverse environmental conditions, high spectral interferences and multiphase (molten and gas) reactions. This work demonstrates the suitability of stand-off LIBS (ST-LIBS) for real time monitoring of the desulfurization of blister copper which is carried out in molten phase. Here sulfur is removed by the formation of SO2 by supplying oxygen in molten phase. Using ST-LIBS the relative emission intensities of Cu(I) at 351.06 nm, O at 777.34 nm and S at 921.29 nm in both molten and gaseous phase were considered simultaneously during the process. This was possible only by the use high energy laser pulse over up to 270 mJ per pulse. In the case of copper, the selection of emission lines was assessed considering non-linear behavior, which is caused by self-absorption. For the first time, real time determination of sulfur in ppm range is reported by ST-LIBS using low sensitive lines from the NIR region. These results were validated with differential optical absorption spectroscopy (DOAS) as gold standard method. The analytical information obtained by LIBS can precisely determine the critical end-point of the desulfurization where the removal of sulfur is finished, and copper started to oxidize.


Assuntos
Vesícula , Cobre , Humanos , Lasers , Análise Espectral , Enxofre
19.
J Phys Chem B ; 125(38): 10779-10795, 2021 09 30.
Artigo em Inglês | MEDLINE | ID: mdl-34546762

RESUMO

The structure of aqueous Cu(II)-bis-thiosemicarbazide, [Cu(tsc)2]2+, is reported following EXAFS and MXAN analyses of the copper K-edge X-ray absorption (XAS) spectrum. The rising K-edge feature at 8987.1 eV is higher energy than those of crystalline models, implying unique electronic and structural solution states. EXAFS analysis (k = 2-13 Å-1; 2 × Cu-N = 2.02 ± 0.01 Å; 2 × Cu-S = 2.27 ± 0.01 Å; Cu-Oax = 2.41 ± 0.04 Å) could not resolve 5- versus 6-coordinate models. However, MXAN fits converged to an asymmetric broken symmetry 6-coordinate model with cis-disposed TSC ligands (Cu-Oax = 2.07 and 2.54 Å; Cu-N = 1.94 Å, 1.98 Å; Cu-S = 2.20 Å, 2.41 Å). Transition dipole integral evaluation of the sulfur K-edge XAS 1s → 3p valence transition feature at 2470.7 eV yielded a Cu-S covalence of 0.66 e-, indicating Cu1.34+. The high Cu-S covalence and short Cu-S bond in aqueous [Cu(tsc)2(H2O)2]2+ again contradict the need for a protein rack to explain the unique structure of the blue copper active site. MXAN models of dissolved Cu(II) complex ions have invariably featured broken centrosymmetry. The potential energy ground state for dissolved Cu(II) evidently includes the extended solvation field, providing a target for improved physical theory. A revised solvation model for aqueous Cu(II), |[Cu(H2O)5]·14H2O|2+, is presented.


Assuntos
Cobre , Enxofre , Ligantes , Modelos Moleculares , Água
20.
Med Mycol J ; 62(3): 63-65, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34471037

RESUMO

BACKGROUND: Dermoscopy is a new method to diagnose and manage nail disorders. The definite dermoscopic finding for onychomycosis, however, is still debatable. OBJECTIVE: To identify the dermoscopic features that help differentiate between onychomycosis (OM) and traumatic onychodystrophy (TOD). METHODS: A prospective study of 65 patients with toenail abnormalities was conducted. The patients were classified into OM and TOD groups using mycological tests (potassium hydroxide test, fungal culture, and histological examination). OM was diagnosed from positive results for all tests, while TOD was decided based on negative results for all tests and evidence of foot trauma. Dermoscopic features were recorded and compared between the two groups. RESULTS: Most patients of the 65 patients were female (72.3%), and had a mean age of 67.9 years. Twenty-seven patients (41.5%) were diagnosed with OM, all of which were distal and lateral subungual onychomycosis. TOD, on the other hand, was determined in 38 patients. Dermoscopic findings revealed that the yellow, clumping, sulphur-nugget-like debris in the ruin appearance was significantly associated with onychomycosis (p = 0.002), while ruin appearance without sulphur nugget was not statistically correlated with onychomycosis (p = 0.068). CONCLUSION: The presence of sulphur nuggets in the ruin appearance is a new and helpful dermoscopic feature for onychomycosis diagnosis.


Assuntos
Dermatoses do Pé , Onicomicose , Idoso , Dermoscopia , Feminino , Humanos , Onicomicose/diagnóstico por imagem , Estudos Prospectivos , Enxofre
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