Types Of Oxygen Species Research Articles

Revealing the effects of asymmetric M-O-Ce structure on CO oxidation over M(Cu, Mn, Fe, La and Zr)-doped CeO2 catalysts: Atomic radius and oxygen vacancies

Although CeO2 catalysts doped with different metal ions can significantly enhance CO activity, the intrinsic relationship between these activities and the catalyst structure is still not clearly understood. In this paper, M(Cu, Mn, Fe, La and Zr)-doped CeO2 catalysts prepared by aerosol method are used as research targets for CO oxidation. Cu-CeO2 with the smallest atomic radius ratio has the best redox capacity and more oxygen vacancy content. DFT results show that promoting the interface effect in the presence of Cu-Ov-Ce is conducive to enhancing CO adsorption capacity. Operando TPR-DRIFTS-MS results reveal that different types of oxygen species (including M=O, CeO, M-O-Ce, and M-OH) exhibit different reactivity on the surface of Ce-based catalysts. M(Cu, Mn, Fe, La and Zr)=O is more likely to react with CO above 100°C. CeO, M-O-Ce, and M-OH also react with CO to form oxygen vacancies (such as M-Ov-Ce and CeOv) and CO2 after reaching a certain temperature. Among them, the formation of M-Ov-Ce has a positive role in promoting the decomposition of O₂. Importantly, carbonate is the rate-determining step that affects the activation of M-Ov-Ce. Monodentate carbonates decompose more easily at low temperatures. These findings reveal a novel doping effect and provide a new idea for the design and development of Ce based catalysts with high CO removal ability.

Insight into the roles of superoxide-type (Mn(-O-)2Mn), bridge-type (Mn-O-Mn), and terminal-type (Mn[dbnd]O) oxygen species on MnO2 of different crystal structures in CO oxidation using operando TPR-DRIFTS-MS

MnO2 is a promising catalyst due to its abundant metal valence and good redox ability. Different crystal phases of MnO2 have different oxygen species, but the relationship between their catalytic activity and crystal structures is unclear. In this study, four MnO2 catalysts with crystal structures (α-, β-, γ-, and δ-MnO2) were selected to unveil the roles of terminal-type (MnO), superoxide-type Mn(-O-)2Mn, and bridge-type (Mn-O-Mn) oxygen species in CO oxidation. γ-MnO2 has the best CO oxidation performance. Density functional theory calculation results show that MnO on γ-MnO2 can adsorb CO easier than other two types of oxygen species. Operando TPR-DRIFTS-MS results show that MnO on the surface of γ-MnO2 can react with CO to form terminal-type oxygen vacancies (M2+=□2–) at low temperatures. Meanwhiles, Mn(-□-)(-O-)Mn and Mn-□-Mn can dissociate O2 to form MnO under certain conditions to promote CO oxidation. MnO2 catalysts with more MnO oxygen species are of great significance for CO oxidation at a low temperature.

Elucidating the role of active oxygen species and hydroxyl groups in the furfural base-free oxidation to furoic acid over δ-MnO2

δ-MnO2 shows potential application in furfural base-free oxidation to furoic acid. While, its catalytic mechanism was unclear, which limited the further improvement of the catalytic activity. Therefore, three δ crystal MnO2 with different hydroxyl and active oxygen species concentrations were prepared and applied in the furfural oxidation reaction. IR, Furfural-IR, O2-TPD, H2O-18O2-TPD, and XPS techniques characterized the hydroxyl and active oxygen species. The results show that the hydroxyl group on δ-MnO2 is important in absorbing and attacking furfural to form geminal diol intermediate. Moreover, two types of oxygen species O-OH and Oads originating from the surface hydroxyl and the strongly adsorbed gas-phase O2, respectively, play an essential role in defhydrogenating geminal diol to furoic acid. Most importantly, the hydroxyl, O-OH, and Oads consumed on δ-MnO2 can be reconstructed under reaction conditions. Among the three δ crystal MnO2, δ-MnO2, with the most abundant hydroxyl and active oxygen species, exhibited the best catalytic performance with 99.53% furfural conversion and nearly 100% furoic acid selectivity. This work identifies the function of hydroxyl and active oxygen species on δ-MnO2 in furfural oxidation reaction, guiding the design of a non-noble metal catalyst for furoic acid synthesis under base-free conditions.

Lipid droplet targeting-guided hypoxic photodynamic therapy with curcumin analogs.

Two photosensitizers (CCOH and CCN) were designed and synthesized by introducing coumarin into the curcumin (CUR) structure. Compared with CUR, more reactive oxygen species (ROS) were generated by CCOH and CCN in type I and II synergy upon light irradiation. Cell experiments indicated that CCN with an excellent LD-targeting effect could be used to monitor the changes in the morphology and number of LDs in tumor cells during PDT.

Highly stable preferential carbon monoxide oxidation by dinuclear heterogeneous catalysts

Atomically dispersed catalysts have been shown highly active for preferential oxidation of carbon monoxide in the presence of excess hydrogen (PROX). However, their stability has been less than ideal. We show here that the introduction of a structural component to minimize diffusion of the active metal center can greatly improve the stability without compromising the activity. Using an Ir dinuclear heterogeneous catalyst (DHC) as a study platform, we identify two types of oxygen species, interfacial and bridge, that work in concert to enable both activity and stability. The work sheds important light on the synergistic effect between the active metal center and the supporting substrate and may find broad applications for the use of atomically dispersed catalysts.

Nanoporous nickel with rich adsorbed oxygen for efficient alkaline hydrogen evolution electrocatalysis

Sluggish water dissociation kinetics severely limits the rate of alkaline electrocatalytic hydrogen evolution reaction (HER). Therefore, finding highly active electrocatalysts and clarifying the mechanism of water dissociation are challenging but important. In this study, we report an integrated nanoporous nickel (np-Ni) catalyst with high alkaline HER performance and the origin of the corresponding enhanced catalytic activity. In 1 mol L−1 KOH solution, this np-Ni electrode shows an HER overpotential of 20 mV at 10 mA cm−2, along with fast water dissociation kinetics. The excellent performance is not only attributed to the large surface area provided by the three-dimensional interconnected conductive network but also from the enhanced intrinsic activity induced by the unique surface properties. Further studies reveal that the types of oxygen species that naturally form on the Ni surface play a key role in water dissociation. Remarkably, when the lattice oxygen almost disappears, the Ni surface terminates with adsorbed oxygen (Oads), exhibiting the fastest water dissociation kinetics. Density functional theory calculation suggests that when Oads acts as the surface termination of Ni metal, the orientation and configuration of polar water molecules are strongly affected by Oads. Finally, the H—OH bond of interfacial water molecules is effectively activated in a manner similar to hydrogen bonding. This work not only identifies a high-performance and low-cost electrocatalyst but also provides new insights into the chemical processes underlying water dissociation, thus benefiting the rational design of electrocatalysts.

Back Cover: Direct Evidence of Subsurface Oxygen Formation in Oxide‐Derived Cu by X‐ray Photoelectron Spectroscopy (Angew. Chem. Int. Ed. 3/2022)

Subsurface oxygen in oxide-derived Cu is evidenced by X-ray photoelectron spectroscopy, as reported by Hsin-Yi Wang et al. in their Research Article (e202111021). The results point out that after reduction of the Cu oxide precursor, two types of oxygen species, (i) oxygen staying at lattice defects and/or vacancies in the surface-most region and (ii) interstitial oxygen intercalated in the metal structure, are embedded between the fully reduced metallic surface and the Cu2O buried beneath. This study adds convincing support for subsurface oxygen formation.

Performance of Zn-Al co-doped La2O3 catalysts in the oxidative coupling of methane

Zn-doped and Zn-Al co-doped La2O3 catalysts were prepared by citric acid sol-gel method and characterized by a series of in situ technologies, to investigate the structure-activity relationship of La2O3-based catalysts in the oxidative coupling of methane (OCM). The in situ XRD results reveal a thermal expansion of the La2O3 crystal along the c-axis at high temperature. The H2-TPR results show two types of oxygen species on the La2O3-based catalysts, viz., the strong-binding oxygen species and weak-binding oxygen species; in addition, the XPS results indicate that the strong-binding oxygen species is probably attributed to anion radical O−. The doping with Zn can significantly increase the number of oxygen vacancies in the Zn-doped La2O3 catalysts, which can promote the activation of oxygen and generate more strong-binding oxygen species; as a result, the Zn-doped La2O3 catalyst shows better performance in OCM in comparison with the unmodified La2O3 catalyst. Moreover, the co-doping with Al can promote the dispersion of Zn in La2O3 and further raise the number of strong-binding oxygen species in the Zn-Al co-doped La2O3 catalysts, which is beneficial to enhance the selectivity to C2+ hydrocarbons in the OCM reaction.

Unveiling the Role of Active Oxygen Species in Oxidative Dehydrogenation of Ethane with CO2 over NiFe/CeO2

AbstractThe oxidative dehydrogenation of ethane (ODH) assisted by CO2 to produce ethylene is inevitably accompanied by the side reaction of dry reforming (DRE) to produce carbon monoxide. However, the key factor determining the dehydrogenation selectivity is still ambiguous. In this paper, four different NiFe/CeO2 catalysts were synthesized via an impregnation method over four types of CeO2. The dehydrogenation selectivity of the four catalysts ranged from 40 % to 83 %. Temperature‐programmed surface reaction and transient response experiments reveal the existence of two types of oxygen species over NiFe/CeO2 catalysts. FeOx layers exist as an oxygen species supply buffer over CeO2 supports. Weakly electrophilic oxygen species supplied by FeOx overlayers could participate in producing C2H4 while strong electrophilic oxygen species supplied by CeO2 supports could participate in producing CO. The content of weakly electrophilic oxygen species is identified to be a rational descriptor of C2H4 selectivity.

Curcumin protects cardiomyopathy damage through inhibiting the production of reactive oxygen species in type 2 diabetic mice

Type 2 diabetes mellitus (DM)-induced cardiomyopathy is a multifactorial and complex disease involving oxidative stress, lipids, and fibrosis. It is based on metabolic disorders and microvascular disease and causes extensive focal necrosis of the heart muscle. Curcumin (CUR) is a natural polyphenol isolated from turmeric rhizomes and plays an important role in the antioxidant, anti-apoptotic and anti-inflammatory effects of diabetes. Therefore, we established a mouse model of diabetic cardiomyopathy (DCM) in type 2 diabetic db/db mice in our study. We divided the experiment into three groups: the control group, DM group and DM + CUR group.We performed cardiac dissection on mice treated in different conditions and conducted special pathological staining on isolated cardiac tissue. We were surprised to find that a high glucose environment can promote cardiomyocyte apoptosis by TUNEL assay. In addition, after detecting dihydroethiidine (DHE), hematoxylin-eosin (H&E) and Oil Red O staining, we unexpectedly found that CUR can inhibit the production of reactive oxygen species (ROS), reduce myocardial apoptosis, and myocardial lipid accumulation. CUR upregulated the expression of Bcl-2, and downstream the expression of Bax and Caspase-3 proteins by immunohistochemical determination and western blotting. Therefore, these results suggest that CUR has a certain protective effect on diabetic cardiomyopathy by inhibiting the production of ROS.

Correlating Oxygen Species with Product Selectivity for Dehydrogenation of Butane over Titanium Mixed Oxide Catalysts

This study investigated the dehydrogenation of butane over TiO2-based catalysts prepared by a co-precipitation method. The catalysts were characterized in detail using various surface techniques, such as XRD, XPS, SEM, and pyridine-FTIR. Their performances towards butane dehydrogenation showed that the product distribution was considerably affected by reaction temperature, as well as the composition of the catalysts. Two different selectivity regions were observed for most of the catalysts. Higher butenes selectivity over butadiene was obtained at relatively low temperatures, while an opposite trend was observed at high temperatures. In-situ DRIFT measurements did not find obvious change of the reaction pathway for butane dehydrogenation over the TiO2-based catalysts. The variation in selectivity with temperature can be well correlated with the different types of oxygen species on the catalysts.

(Invited) Understanding the Oxygen Release at High Potential for Transition Metal Oxides

The design of new materials is a pivotal question for the development of the next generation of electrochemical energy storage and conversion devices. Recently, triggering the redox activity of oxygen ions in transition metal oxides used as positive electrodes for Li-ion batteries was proposed as a promising strategy to develop Li-rich compounds with reversible capacity exceeding those of classical insertion layered compounds. Nevertheless, the science at play must be rationalized in order to control this phenomenon and assess the potential applications of such Li-rich electrodes. Indeed, following this discovery, fundamental questions remain. Among them, the exact nature of the oxygen species formed upon oxidation is critical since it governs not only its redox potential but also the discharge behavior for which sluggish kinetics and hysteresis were observed. Using recent examples, the different types of oxygen species will be discussed and their electrochemical behavior compared. Moreover, while early measurements suggested gaseous oxygen to be produced for these Li-rich at potentials above 4.3 V vs. Li+/Li, recent observations point toward oxygen evolution within a potential range that can span from 3.5 to 4.5 V vs. Li+/Li. This observation asks for 1) the development of new analytical tools in order to accurately detect and quantify these gaseous species and 2) to rationalize the standard potential for the evolution of lattice oxygen from the transition metal oxides. These two points will be discussed and strategies to circumvent this detrimental phenomenon will be proposed.

New Insights into Thermal Chromia Growth on Fe18Cr(10Ni) Model Alloys at 900°C: Scaling Kinetics and Microstructures

Specimen of Fe-18Cr(-10Ni) (wt.-%) were isothermally oxidized in dry and wet high p(O2) gas at 900°C. The morphology and microstructural evolution of the chromia scales formed were analysed by SEM-EBSD. At high pO2 test gas containing O2 and H2O, the pO2 is independent of the H2O content of the test gas. However, both types of oxygen species, i.e. O2 as well as H2O contribute to the chromia scaling reaction. The effect of specimen thickness on chromia scaling allows the change of the concentration of the intrinsic defects and their diffusivities in thermally grown chromia scales independently from the test gas applied. Chromia scales are under pressure during scale growth. For thermodynamic reasons the concentration and diffusivity of the intrinsic, native defects in oxides under hydro-static pressure varies with the amount of pressure applied. Ion beam polished oxide cross-sections were analysed in terms of oxide grain growth and nucleation rates of new oxide at the oxide-gas interface. Chromia scales formed on the various substrates at high p(O2) test gas grew at different rates, and microstructures formed on Fe18Cr(-10Ni) differ in grain shape and size. The chromia growth kinetic was found to be depending on the thickness of the specimens used, the H2O content of the gas, and its Ni content. The scale growth mechanism consists of two interlinked levels. At the meta-level oxide nucleation and oxide grain growth are affected by the cation flux in the oxide scale formed and the nature of the oxygen species in the gas. This fixes the number, size and shape of the oxide grains as well as the number of oxide grain boundaries available as short-circuit diffusion paths. The lattice level denotes the atomic level. Hereby the cation flux in the single grain by lattice diffusion and cation vacancy condensation are linked. The defect structure in the oxide lattice is important. The factors affecting it are the Cr diffusion in the substrate and the presence of Ni in the alloy, local p(O2), H-defects and oxide growth stress. The experimental findings will be discussed with strong focus on the oxide growth mechanism, the chromia microstructure of the scales formed under the various conditions and the concentration and mobility of the native defects in the chromia scales and its interactions with H-containing species originating from water vapour in the test gas. Furthermore, the role of Fe as base and Ni as alloying element in the metal substrate will be discussed. This is done by considering the differences between the Ni-Cr-O and Fe-Cr-O phase diagrams and the consequence of the existence of the Fe3+ ion on the miscibility of the oxides formed by the various cations.

Transition of Blast Furnace Slag from Silicate Based to Aluminate Based: Density and Surface Tension

The effects of the Al2O3 concentration and Al2O3/SiO2 ratio on the density and surface tension of molten aluminosilicate CaO-SiO2-Al2O3-9 mass pct MgO-1 mass pct TiO2 slag were investigated at temperatures from 1723 K to 1823 K (1450 °C to 1550 °C) using the Archimedean method and the maximum bubble pressure (MBP) technique, respectively. The mechanism of the changes in density and surface tension with composition was analyzed from the viewpoint of the degree of polymerization in the structure and the types of oxygen species in the melts. At a fixed CaO/SiO2 ratio of 1.20, the density decreased with increasing Al2O3 content up to 25 mass pct, subsequently increasing. Increasing the Al2O3/SiO2 ratio from 0.47 to 0.92 caused an increase in the density at a fixed CaO content, and the density decreased slightly when the Al2O3/SiO2 ratio was greater than 0.92. Based on the structural information, the density decreased when the Al2O3 content enhanced the network structure and increased when the (Q2 + Q3)/(Q0 + Q1) ratio and structural complexity decreased. The surface tension increased with increasing Al2O3 content and Al2O3/SiO2 ratio. On the one hand, the surface-active component of SiO2 decreased; on the other hand, the concentration of [AlO4]5− tetrahedra and metal cations that act as charge compensators increased at the melt surface. A model based on the anionic and cationic radii and the Butler equation was employed to predict the surface tension, and an iso-surface tension diagram was obtained at 1773 K (1500 °C).

Analysis of the Surface Oxidation Process on Pt Nanoparticles on a Glassy Carbon Electrode by Angle-Resolved, Grazing-Incidence X-ray Photoelectron Spectroscopy.

We have analyzed the surface oxidation process of Pt nanoparticles that were uniformly dispersed on a glassy carbon electrode (Pt/GC), which was adopted as a model of a practical Pt/C catalyst for fuel cells, in N2-purged 0.1 M HF solution by using angle-resolved, grazing-incidence X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-ARGIXPS). Positive shifts in the binding energies of Pt 4f spectra were clearly observed for the surface oxidation of Pt nanoparticles at potentials E > 0.7 V vs RHE, followed by a bulk oxidation of Pt to form Pt(II) at E > 1.1 V. Three types of oxygen species (H2Oad, OHad, and Oad) were identified in the O 1s spectra. It was found for the first time that the surface oxidation process of the Pt/GC electrode at E < ca. 0.8 V (OHad formation) is similar to that of a Pt(111) single-crystal electrode, whereas that in the high potential region (Oad formation) resembles that of a Pt(110) surface or polycrystalline Pt film.

Increased monocyte-derived reactive oxygen species in type 2 diabetes: role of endoplasmic reticulum stress.

What is the central question of this study? Patients with type 2 diabetes exhibit increased oxidative stress in peripheral blood mononuclear cells, including monocytes; however, the mechanisms remain unknown. What is the main finding and its importance? The main finding of this study is that factors contained within the plasma of patients with type 2 diabetes can contribute to increased oxidative stress in monocytes, making them more adherent to endothelial cells. We show that these effects are largely mediated by the interaction between endoplasmic reticulum stress and NADPH oxidase activity. Recent evidence suggests that exposure of human monocytes to glucolipotoxic media to mimic the composition of plasma of patients with type 2 diabetes (T2D) results in the induction of endoplasmic reticulum (ER) stress markers and formation of reactive oxygen species (ROS). The extent to which these findings translate to patients with T2D remains unclear. Thus, we first measured ROS (dihydroethidium fluorescence) in peripheral blood mononuclear cells (PBMCs) from whole blood of T2D patients (n=8) and compared the values with age-matched healthy control subjects (n=8). The T2D patients exhibited greater basal intracellular ROS (mean±SD, +3.4±1.4-fold; P<0.05) compared with control subjects. Next, the increase in ROS in PBMCs isolated from T2D patients was partly recapitulated in cultured human monocytes (THP-1 cells) exposed to plasma from T2D patients for 36h (+1.3±0.08-fold versus plasma from control subjects; P<0.05). In addition, we found that increased ROS formation in THP-1 cells treated with T2D plasma was NADPH oxidase derived and led to increased endothelial cell adhesion (+1.8±0.5-fold; P<0.05) and lipid uptake (+1.3±0.3-fold; P<0.05). Notably, we found that T2D plasma-induced monocyte ROS and downstream functional effects were abolished by treating cells with tauroursodeoxycholic acid, a chemical chaperone known to inhibit ER stress. Collectively, these data indicate that monocyte ROS production with T2D can be attributed, in part, to signals from the circulating environment. Furthermore, an interplay between ER stress and NADPH oxidase activity contributes to ROS production and may be a mechanism mediating endothelial cell adhesion and foam cell formation in T2D.

Effects of Combustion Catalyst Dispersed by a Novel Microemulsion Method as Fuel Additive on Diesel Engine Emissions, Performance, and Characteristics

The effects of oxygen storage properties of combustion catalysts on pollutant emissions and engine performance, using an automated diesel engine, were studied. A novel microemulsion-based protocol was utilized to disperse the catalysts in the diesel fuel. The catalyst-microemulsion (catalyst-μE) system remains stable upon its addition to the diesel fuel. Different concentrations of iron doped cerium oxide (0, 5, 10, and 20 mol %) were synthesized in microemulsion systems and characterized by dynamic light scattering (DLS) and UV–visible spectrometry. Various characterization techniques were employed. X-ray diffraction (XRD) was used to show the effect of iron presence on crystallites structure of the catalysts. Hydrogen temperature programed reduction (H2-TPR) and oxygen temperature programed desorption (O2-TPD) were utilized to quantify the total oxygen storage capacity (OSC) and types of oxygen species, respectively. The effects of oxygen storage capacity and oxygen types of the samples on emission of the pollutants and performance of engine were studied afterward. Regarding the emissions, it is shown that Ce0.95Fe0.05O2-α catalyst decreased the soot, unburned-hydrocarbons (HC), and carbon monoxide (CO) by 20.0, 57.7, and 26.6%, respectively. It is also shown that the catalyst with more OSC and more mobile oxygen (the so-called α-oxygen) was more influential in decreasing the mentioned pollutants. The results of in-cylinder pressure and heat release rate analyses indicate that the oxygen storage/release capacity of the catalysts can improve the burning process by decreasing the ignition delay with no significant change in the combustion duration. The results also reveal that addition of the catalysts decreases the brake specific fuel consumption (BSFC) by 3–4% on average and, therefore, improving the fuel economy.

Role of perivascular adipose tissue on vascular reactive oxygen species in type 2 diabetes: a give-and-take relationship.

A major complication of type 2 diabetes (T2D) is atherosclerotic vascular disease, which develops earlier and more rapidly in patients with T2D than in subjects without diabetes (1). One of the characteristic features of T2D is excessive generation of reactive oxygen species (ROS) in the artery wall and the resultant oxidative stress, which contributes to the development of endothelial dysfunction and atherosclerosis (2–5). Moreover, activity of NADPH oxidase, the primary ROS-generating enzyme in vascular cells, has been shown to be increased in T2D (2–5). Notably, behavioral and pharmacological interventions that reduce vascular NADPH oxidase expression and activity demonstrate improvements in endothelial function and reduced atherogenesis (6–8). Furthermore, mice lacking components of the NADPH oxidase subunits are protected against hypertension, and when crossed to the apoE−/− background, they have a marked reduction in vascular ROS production, enhanced nitric oxide bioavailability, and reduced atherosclerotic lesion formation (9,10), thus demonstrating that excessive NADPH oxidase–derived ROS is detrimental to vascular health. Although the recognition that increased vascular NADPH oxidase is an important contributor to vascular complications in T2D, the mechanisms regulating its enzyme activity remain poorly understood. Recent studies implicate adipose tissue adjacent to the artery wall (i.e., perivascular adipose tissue [PVAT]) as playing an important role in the pathogenesis of vascular diseases (11–13). The PVAT serves not …

X-ray photoelectron spectroscopy of Sm-doped layered perovskite for intermediate temperature-operating solid oxide fuel cell

Chemical states of Sm doped layered perovksite, SmBa1−xSrxCo2O5+d (x=0 and 0.5), have been investigated by X-ray Photoelectron Spectroscopy (XPS). Substitution of Sr in SmBa1−xSrxCo2O5+d oxide system shifts the binding energy of Sm 3d5/2 to the more positive side and the charge state of Sm remained Sm3+. Therefore, the substitution of Sr into the SmBa1–xSrxCo2O5+d oxide system does not change the charge state of Sm. Three types of oxygen species were observed in SmBa0.5Sr0.5Co2O5+d (SBSCO) and SBCO from the O 1s spectra comprised of lattice oxygen, carbonated species and adsorbed oxygen species with respect to the measured binding energy ranges. The more Sr was substituted into the Sm doped layered perovskite, the larger the binding energy values became. In case of the Co spectra of SBSCO, two satellite peaks were observed at the range of 786.0–789.0eV and at 804.93eV. The evidence of Co3+ and Co4+ indicated that Co is existing in the chemical form of mixed valence state including Co3+ and Co4+ in SBCO and SBSCO oxide systems.

Coronary endothelial dysfunction and mitochondrial reactive oxygen species in type 2 diabetic mice

Endothelial cell (EC) dysfunction is implicated in cardiovascular diseases, including diabetes. The decrease in nitric oxide (NO) bioavailability is the hallmark of endothelial dysfunction, and it leads to attenuated vascular relaxation and atherosclerosis followed by a decrease in blood flow. In the heart, decreased coronary blood flow is responsible for insufficient oxygen supply to cardiomyocytes and, subsequently, increases the incidence of cardiac ischemia. In this study we investigate whether and how reactive oxygen species (ROS) in mitochondria contribute to coronary endothelial dysfunction in type 2 diabetic (T2D) mice. T2D was induced in mice by a high-fat diet combined with a single injection of low-dose streptozotocin. ACh-induced vascular relaxation was significantly attenuated in coronary arteries (CAs) from T2D mice compared with controls. The pharmacological approach reveals that NO-dependent, but not hyperpolarization- or prostacyclin-dependent, relaxation was decreased in CAs from T2D mice. Attenuated ACh-induced relaxation in CAs from T2D mice was restored toward control level by treatment with mitoTempol (a mitochondria-specific O2(-) scavenger). Coronary ECs isolated from T2D mice exhibited a significant increase in mitochondrial ROS concentration and decrease in SOD2 protein expression compared with coronary ECs isolated from control mice. Furthermore, protein ubiquitination of SOD2 was significantly increased in coronary ECs isolated from T2D mice. These results suggest that augmented SOD2 ubiquitination leads to the increase in mitochondrial ROS concentration in coronary ECs from T2D mice and attenuates coronary vascular relaxation in T2D mice.