Search for: Copper oxidation

Formate (HCOO–) is the most dominant intermediate identified during carbon dioxide electrochemical reduction (CO2ER). While previous studies showed that copper (Cu)-based materials that include Cu(0), Cu2O, and CuO are ideal catalysts for CO2ER, challenges to scalability stem from low selectivity and undesirable products in the −1.0–1.0 V range. There are few studies on the binding mechanism of intermediates and products for these systems as well as on changes to surface sites upon applying potential. Here, we use an in situ approach to study the redox surface chemistry of formate on Cu thin films deposited on Si wafers using a VeeMAX III spectroelectrochemical (SEC) cell compatible with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Spectra for surface species were collected in real time as a function of applied potential during cyclic voltammetry (CV) experiments. Results showed the reproducibility of CV curves on freshly prepared Cu/Si wafers with relatively high signal-to-noise ATR-FTIR absorbance features of surface species during these electrochemical experiments. The oxidation reaction of HCOO– to bicarbonate (HCO3–) was observed using ATR-FTIR at a voltage of 0.27 V. Samples were then subjected to reduction in the CV, and the aqueous phase products below the detection limit of the SEC-ATR-FTIR were identified using ion chromatography (IC). We report the formation of glycolate (H3C2O3–) and glyoxylate (HC2O3–) with trace amounts of oxalate (C2O42–), indicating that C–C coupling reactions proceed in these systems. Changes to the oxidation state of surface Cu were measured using X-ray photoelectron spectroscopy, which showed a reduction in Cu(0) and an increase in Cu(OH)2, indicating surface oxidation. 

The development of bioluminescence‐based tools has seen steady growth in the field of chemical biology over the past few decades ranging in uses from reporter genes to assay development and targeted imaging. More recently, coelenterazine‐utilizing luciferases such asGaussia,Renilla, and the engineered nano‐luciferases have been utilized due to their intense luminescence relative to firefly luciferin/luciferase. The emerging importance of these systems warrants investigations into the components that affect their light production. Previous work has reported that one marine luciferase, Gaussia, is potently inhibited by copper salt. The mechanism for inhibition was not elucidated but was hypothesized to occur via binding to the enzyme. In this study, we provide the first report of a group of nonhomologous marine luciferases also exhibiting marked decreases in light emission in the presence of copper (II). We investigate the mechanism of action behind this inhibition and demonstrate that the observed copper inhibition does not stem from a luciferase interaction but rather the chemical oxidation of imidazopyrazinone luciferins generating inert, dehydrated luciferins.

 

Chemical modifications such as intercalation can be used to modify surface properties or to further functionalize the surface states of topological insulators (TIs). Using ambient pressure x-ray photoelectron spectroscopy, we report copper migration in${\mathrm{C}\mathrm{u}}_x{\mathrm{B}\mathrm{i}}_2{\mathrm{S}\mathrm{e}}_3$, which occurs on a timescale of hours to days after initial surface cleaving. The increase in near-surface copper proceeds along with the oxidation of the sample surface and large changes in the selenium content. These complex changes are further modeled with core-level spectroscopy simulations, which suggest a composition gradient near the surface which develops with oxygen exposure. Our results shed light on a new phenomenon that must be considered for intercalated TIs—and intercalated materials in general—that surface chemical composition can change when specimens are exposed to ambient conditions.

 

Histatin-5 (Hist-5) is an antimicrobial peptide found in human saliva that functions to defend the oral cavity from microbial infections, such as those caused by the fungal pathogen Candida albicans (C. albicans). Hist-5 can bind Cu in multiple oxidation states, Cu2+ and Cu+  in vitro, and supplemental Cu2+ has been shown to improve the fungicidal activity of the peptide against C. albicans in culture. However, the exact role of Cu on the antifungal activity of Hist-5 and whether direct peptide–Cu interactions occur intracellularly has yet to be fully determined. Here, we used a combination of fluorescence spectroscopy and confocal microscopy experiments to show reversible Cu-dependent quenching of a fluorescent Hist-5 analogue, Hist-5*, indicating a direct interaction between Hist-5 and intracellular Cu. X-ray fluorescence microscopy images revealed peptide-induced changes to cellular Cu distribution and cell-associated Cu content. These data support a model in which Hist-5 can facilitate the hyperaccumulation of Cu in C. albicans and directly interact with Cu intracellularly to increase the fungicidal activity of Hist-5.

 

Pathogenesis of COVID-19 by SARS-CoV-2 resulted in a global pandemic and public health emergency in 2020. Viral infection can induce oxidative stress through reactive oxygen species (ROS). Inflammation and environmental stress are major sources of oxidative stress after infection. Micronutrients such as iron, copper, zinc, and manganese play various roles in human tissues and their imbalance in blood can impact immune responses against pathogens including SARS CoV-2. We hypothesized that alteration of free metal ions during infection and metal-catalyzed oxidation plays a critical role towards pathogenesis after infection. We analyzed convalescent and hospitalized COVID-19 patient plasma using orthogonal analytical techniques to determine redox active metal concentrations, overall protein oxidation, oxidative modifications, and protein levels via proteomics to understand the consequences of metal-induced oxidative stress in COVID-19 plasma proteins. Metal analysis using ICP-MS showed significantly greater concentrations of copper in COVID-19 plasma compared to healthy controls. We demonstrate significantly greater total protein carbonylation, other oxidative modifications, and deamidation of plasma proteins in COVID-19 plasma compared to healthy controls. Proteomics analysis showed that levels of redox active proteins including hemoglobulin were elevated in COVID-19 plasma. Molecular modeling concurred with potential interactions between iron binding proteins and SARS CoV-2 surface proteins. Overall, increased levels of redox active metals and protein oxidation indicate that oxidative stress-induced protein oxidation in COVID-19 may be a consequence of the interactions of SARS-CoV-2 proteins with host cell metal binding proteins resulting in altered cellular homeostasis.

 

Abstract Selective conversion of methane (CH 4 ) into value-added chemicals represents a grand challenge for the efficient utilization of rising hydrocarbon sources. We report here dimeric copper centers supported on graphitic carbon nitride (denoted as Cu 2 @C 3 N 4 ) as advanced catalysts for CH 4 partial oxidation. The copper-dimer catalysts demonstrate high selectivity for partial oxidation of methane under both thermo- and photocatalytic reaction conditions, with hydrogen peroxide (H 2 O 2 ) and oxygen (O 2 ) being used as the oxidizer, respectively. In particular, the photocatalytic oxidation of CH 4 with O 2 achieves >10% conversion, and >98% selectivity toward methyl oxygenates and a mass-specific activity of 1399.3 mmol g Cu −1 h −1 . Mechanistic studies reveal that the high reactivity of Cu 2 @C 3 N 4 can be ascribed to symphonic mechanisms among the bridging oxygen, the two copper sites and the semiconducting C 3 N 4 substrate, which do not only facilitate the heterolytic scission of C-H bond, but also promotes H 2 O 2 and O 2 activation in thermo- and photocatalysis, respectively. 

Plasmonic metal nanostructures are essential for plasmon‐mediated chemical reactions (PMCRs) and surface‐enhanced Raman spectroscopy (SERS). The nanostructures are commonly made from the coinage metals gold and silver. Copper (Cu) is less used mainly due to the difficulties in fabricating stable nanostructures. However, Cu is an attractive option with its strong plasmonic properties, high catalytic activities, and relatively cheap price. Herein, we fabricated tunable, reliable, and efficient Cu nanoelectrodes (CuNEs). Using time‐resolved electrochemical SERS, we have comprehensively studied the reversible chemical transformations between aromatic amine and nitro groups modified on the CuNE surface. Their PMCRs are well‐controlled by changing the surface roughness, the oxidation states of Cu, and the applied electrode potential. We thus demonstrate that the Cu nanostructures enable better investigations in the interplays between PMCR, electrochemistry, and Cu catalysis.

 

Plasmonic metal nanostructures are essential for plasmon‐mediated chemical reactions (PMCRs) and surface‐enhanced Raman spectroscopy (SERS). The nanostructures are commonly made from the coinage metals gold and silver. Copper (Cu) is less used mainly due to the difficulties in fabricating stable nanostructures. However, Cu is an attractive option with its strong plasmonic properties, high catalytic activities, and relatively cheap price. Herein, we fabricated tunable, reliable, and efficient Cu nanoelectrodes (CuNEs). Using time‐resolved electrochemical SERS, we have comprehensively studied the reversible chemical transformations between aromatic amine and nitro groups modified on the CuNE surface. Their PMCRs are well‐controlled by changing the surface roughness, the oxidation states of Cu, and the applied electrode potential. We thus demonstrate that the Cu nanostructures enable better investigations in the interplays between PMCR, electrochemistry, and Cu catalysis.

 

Understanding the electronic structures of high‐valent metal complexes aids the advancement of metal‐catalyzed cross coupling methodologies. A prototypical complex with formally high valency is [Cu(CF₃)₄]⁻(1), which has a formal Cu(III) oxidation state but whose physical analysis has led some to a Cu(I) assignment in an inverted ligand field model. Recent examinations of1by X‐ray spectroscopies have led previous authors to contradictory conclusions, motivating the re‐examination of its X‐ray absorption profile here by a complementary method, resonant diffraction anomalous fine structure (DAFS). From analysis of DAFS measurements for a series of seven mononuclear Cu complexes including1, here it is shown that there is a systematic trifluoromethyl effect on X‐ray absorption that blue shifts the resonant Cu K‐edge energy by 2–3 eV per CF₃, completely accounting for observed changes in DAFS profiles between formally Cu(III) complexes like1and formally Cu(I) complexes like (Ph₃P)₃CuCF₃(3). Thus, in agreement with the inverted ligand field model, the data presented herein imply that1is best described as containing a Cu(I) ion with dⁿcount approaching 10.