► The chalcopyrite electrode was shown to be passive for potentials up to 0.90VSHE. ► Metal-deficient sulfide film passivates chalcopyrite. ► Transpassive dissolution is linked to oxidation of ...sulfide to elemental sulfur. ► No S0 or polysulfide species were detected for potentials below 0.90VSHE. ► Potentiodynamic polarization cannot demonstrate chalcopyrite's electrodissolution.
The influence of potential on the species and surface films formed during electrodissolution of chalcopyrite were investigated in 0.5M sulfuric acid solution at 25°C. Cyclic voltammetry, chronoamperometry, potentiostatic and potentiodynamic polarization methods were applied. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to analyze the minerals and product layers on the surface before and after electrodissolution. The chalcopyrite electrode was shown to be passive for potentials up to 0.90VSHE. Above this potential, transpassive dissolution occurs. Results of XPS studies have suggested that a metal-deficient sulfide film (Cu1−xFe1−yS2−z) consisting of cuprous sulfide (Cu–S) and iron sulfide (Fe–S) bonds, is the most plausible copper and iron containing sulfide phase which passivates the surface of chalcopyrite. It is demonstrated that the transpassive dissolution of chalcopyrite is significantly linked to oxidation of sulfur (from sulfide in the passive film to elemental sulfur and maybe sulfur species with higher oxidation states, e.g. thiosulfate). No elemental sulfur or polysulfide species were detected on the surface for potentials below 0.90VSHE.
A New Reagent for Direct Difluoromethylation Fujiwara, Yuta; Dixon, Janice A; Rodriguez, Rodrigo A ...
Journal of the American Chemical Society,
01/2012, Letnik:
134, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Molecular scaffolds containing alkylfluorine substituents are desired in many areas of chemical research from materials to pharmaceuticals. Herein, we report the invention of a new reagent ...(Zn(SO2CF2H)2, DFMS) for the innate difluoromethylation of organic substrates via a radical process. This mild, operationally simple, chemoselective, and scalable difluoromethylation method is compatible with a range of nitrogen-containing heteroarene substrates of varying complexity as well as select classes of conjugated π-systems and thiols. Regiochemical comparisons suggest that the CF2H radical generated from the new reagent possesses nucleophilic character.
The recent outbreak of coronavirus disease 2019 (COVID‐19), caused by the Severe Acute Respiratory Syndrome Coronavirus‐2 (SARS‐CoV‐2) has resulted in a world‐wide pandemic. Disseminated lung injury ...with the development of acute respiratory distress syndrome (ARDS) is the main cause of mortality in COVID‐19. Although liver failure does not seem to occur in the absence of pre‐existing liver disease, hepatic involvement in COVID‐19 may correlate with overall disease severity and serve as a prognostic factor for the development of ARDS. The spectrum of liver injury in COVID‐19 may range from direct infection by SARS‐CoV‐2, indirect involvement by systemic inflammation, hypoxic changes, iatrogenic causes such as drugs and ventilation to exacerbation of underlying liver disease. This concise review discusses the potential pathophysiological mechanisms for SARS‐CoV‐2 hepatic tropism as well as acute and possibly long‐term liver injury in COVID‐19.
Nitrogen-rich heterocyclic compounds have had a profound effect on human health because these chemical motifs are found in a large number of drugs used to combat a broad range of diseases and ...pathophysiological conditions. Advances in transition-metal-mediated cross-coupling have simplified the synthesis of such molecules; however, C-H functionalization of medicinally important heterocycles that does not rely on pre-functionalized starting materials is an underdeveloped area. Unfortunately, the innate properties of heterocycles that make them so desirable for biological applications--such as aqueous solubility and their ability to act as ligands--render them challenging substrates for direct chemical functionalization. Here we report that zinc sulphinate salts can be used to transfer alkyl radicals to heterocycles, allowing for the mild (moderate temperature, 50 °C or less), direct and operationally simple formation of medicinally relevant C-C bonds while reacting in a complementary fashion to other innate C-H functionalization methods (Minisci, borono-Minisci, electrophilic aromatic substitution, transition-metal-mediated C-H insertion and C-H deprotonation). We prepared a toolkit of these reagents and studied their reactivity across a wide range of heterocycles (natural products, drugs and building blocks) without recourse to protecting-group chemistry. The reagents can even be used in tandem fashion in a single pot in the presence of water and air.
The lack of measurements of three‐dimensional (3D) distribution of horizontal wind vectors is a major challenge in atmospheric science. Here, we develop an algorithm to retrieve winds for nine ...pressure levels at 1° grid spacing from 70°N to 70°S. The retrieval is done by tracking water vapor from the hyperspectral Cross‐track Infrared Sounder aboard two polar satellites (NOAA‐20 and Suomi‐NPP) that have overlapped tracks separated by 50 min. We impose a gross error check by flagging retrievals that are too different from ERA‐5 reanalysis. Testing the algorithm for the first week of January and July 2020 indicates that our algorithm yields 104 wind profiles per day and these 3D winds qualitatively agree with ERA‐5. Compared with radiosonde data, the errors are within the range of reported errors of cloud‐tracking winds.
Plain Language Summary
We developed an algorithm to derive winds in the tropics and midlatitudes across nine vertical levels from two polar‐orbiting satellites carrying high‐resolution sounding instruments. Our algorithm yields 104 wind profiles per day. Comparisons with measurements from weather balloons show that our wind retrievals are within the error range of existing satellite wind products (usually at one level at a given time and location) and outperform them in vertical resolution.
Key Points
Horizontal wind vectors are retrieved by tracking water vapor fields from an infrared sounder aboard two polar‐orbiting satellites
Approximately 104 wind profiles are derived per day at nine levels from surface to 100 hPa at 1° resolution from 70°N to 70°S
Compared to radiosonde data, retrieved winds have similar errors to cloud‐tracking winds
The dissolution of a massive chalcopyrite electrode (98.1% chalcopyrite, 1.9% siderite) was studied in 0.5
M sulfuric acid solution. Different anodic potentials were applied and the behavior of the ...electrode was observed by means of EIS, potentiodynamic, and Mott–Schottky techniques. Electrochemical impedance spectroscopy studies at open circuit potential (around −235
mV vs. MSE) proved the existence of a thin surface layer on the electrode. This layer was stable up to 100
mV vs. MSE and was assumed to be Cu
1−
x
Fe
1−
y
S
2 (
y
≫
x
) based on reports from previous studies. By increasing the potential to the range of 100–300
mV vs. MSE, the previously formed layer partially dissolved and a second layer (Cu
1−
x−
z
S
2) formed on the surface. Both of the layers showed the characteristics of passive layers at low potentiodynamic scan rate (0.05
mV
s
−1) while at high scan rates they acted like pseudo-passive layers. However, in the potential range of 300–420
mV vs. MSE, both of these surface layers dissolved and active dissolution of the electrode started. Further increase in potential caused the formation of a CuS layer which hindered the dissolution rate of the electrode. The formation of CuS is concomitant with Fe
2(SO
4)
3 formation and the latter may act as a nucleation precursor for jarosite at higher potentials (around 750
mV vs. MSE). Jarosite precipitation on the electrode surface hindered the dissolution of chalcopyrite at higher potentials. Different equivalent electrochemical circuits were modeled for each potential range and the model regression results compared with the experimental results of EIS to determine the proposed sequence of chalcopyrite dissolution.
Obesity and type 2 diabetes mellitus (T2DM) are metabolic disorders characterized by metabolic inflexibility with multiple pathological organ manifestations, including non-alcoholic fatty liver ...disease (NAFLD). Nuclear receptors are ligand-dependent transcription factors with a multifaceted role in controlling many metabolic activities, such as regulation of genes involved in lipid and glucose metabolism and modulation of inflammatory genes. The activity of nuclear receptors is key in maintaining metabolic flexibility. Their activity depends on the availability of endogenous ligands, like fatty acids or oxysterols, and their derivatives produced by the catabolic action of metabolic lipases, most of which are under the control of nuclear receptors. For example, adipose triglyceride lipase (ATGL) is activated by peroxisome proliferator-activated receptor γ (PPARγ) and conversely releases fatty acids as ligands for PPARα, therefore, demonstrating the interdependency of nuclear receptors and lipases. The diverse biological functions and importance of nuclear receptors in metabolic syndrome and NAFLD has led to substantial effort to target them therapeutically. This review summarizes recent findings on the roles of lipases and selected nuclear receptors, PPARs, and liver X receptor (LXR) in obesity, diabetes, and NAFLD.
► We combine photovoltaic (PV), solar thermal (ST), and phase change material (PCM). ► The simulation uses a 1D energy balance model with thermally linked masses. ► We investigate PCM physical and ...thermal properties and water flow schemes. ► We find an improvement in PV performance with a decrease in ST performance. ► PCMs with tuneable melting points and high thermal conductivity are desired.
In this paper an energy balance model and simulation results are presented for a generic combined photovoltaic (PV) solar thermal (ST) system that incorporates phase change material (PCM). This is a promising integration of technology because the PV converts visible and ultra-violet parts of the solar spectrum, the ST utilises infra-red parts of the spectrum and waste heat from the PV, and the PCM reduces the temperature of the PV which increases PV efficiency. Parameters that are investigated cover PCM physical and thermal properties and water flow schemes. By including an appropriate PCM in an optimised system, the PV output can be increased by typically 9% with an average water temperature rise of 20
°C. Although any increase in PV performance has an associated decrease in ST performance, a practical and worthwhile compromise can still be achieved. This paper demonstrates that there is considerable scope for experimental realisation of the combined PV/ST/PCM system particularly if this is coupled with the development of PCMs with tuneable melting points and high thermal conductivity.
THE AMUNDSEN SEA LOW Raphael, M. N.; Marshall, G. J.; Turner, J. ...
Bulletin of the American Meteorological Society,
01/2016, Letnik:
97, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Amundsen Sea low (ASL) is a climatological low pressure center that exerts considerable influence on the climate of West Antarctica. Its potential to explain important recent changes in Antarctic ...climate, for example, in temperature and sea ice extent, means that it has become the focus of an increasing number of studies. Here, the authors summarize the current understanding of the ASL, using reanalysis datasets to analyze recent variability and trends, as well as ice-core chemistry and climate model projections, to examine past and future changes in the ASL, respectively. The ASL has deepened in recent decades, affecting the climate through its influence on the regional meridional wind field, which controls the advection of moisture and heat into the continent. Deepening of the ASL in spring is consistent with observed West Antarctic warming and greater sea ice extent in the Ross Sea. Climate model simulations for recent decades indicate that this deepening is mediated by tropical variability while climate model projections through the twenty-first century suggest that the ASL will deepen in some seasons in response to greenhouse gas concentration increases.
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