Excess Se Research Articles

Synthesis and Electrical Properties of a New Compound (BiSe)0.97(Bi2Se3)1.26(BiSe)0.97(MoSe2) Containing Metallic 1T-MoSe2

The synthesis and electrical properties of a new misfit compound containing BiSe, Bi2Se3, and MoSe2 constituent layers are reported. The reaction pathway involves competition between the formation of (BiSe)1+x(Bi2Se3)1+y(BiSe)1+x(MoSe2) and [(Bi2Se3)1+y]2(MoSe2). Excess Bi and Se are required in the precursor to synthesize (BiSe)1+x(Bi2Se3)1+y(BiSe)1+x(MoSe2). High-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) confirm the stacking sequence of the heterostructure. Small grains of both 2H- and 1T-MoSe2 are observed in the MoSe2 layers. X-ray photoelectron spectroscopy (XPS) indicates that there is a significantly higher percentage of 1T-MoSe2 in (BiSe)1+x(Bi2Se3)1+y(BiSe)1+x(MoSe2) than in (BiSe)0.97(MoSe2), suggesting that more charge transfer to MoSe2 occurs due to the additional BiSe layer. The additional charge transfer results in (BiSe)1+x(Bi2Se3)1+y(BiSe)1+x(MoSe2) having a low resistivity (14–19 μΩ m) with metallic temperature dependence. The heterogeneous mix of MoSe2 polytypes observed in the XPS complicates the interpretation of the Hall data as two bands contribute to the electrical continuity.

Differential protein expression due to Se deficiency and Se toxicity in rat liver

There is a U-shaped dose-response between selenium (Se) status and health outcomes, but underlying metabolic processes are unclear. This study aims to identify candidate proteins in liver regulated by dietary Se, ranging from deficiency to toxic. Male rats (n=4) were fed graded Se concentrations as selenite for 28 days. Bulk Se analysis was performed by ICP-MS on both soluble and insoluble fractions. Soluble fraction samples were chromatographically separated for identification of selenocompounds by SEC-ICP-MS and protein quantification by LC-MS/MS. Bioinformatics analysis compared low-Se (0 and 0.08 µg Se g−1) and high-Se (0.8, 2 and 5 µg Se g−1) with adequate-Se (0.24 µg Se g−1) diets. Major breakpoints for Se were seen at 0.8 and 2 µg Se g−1 in the insoluble and soluble fractions, respectively. Glutathione peroxidase 1 protein abundance reached a plateau at ≥0.08 µg Se g−1diet; Se bound to selenium binding protein 2 was observed with 2 and 5 µg Se g−1 Se. The extreme diets presented the highest number of differentially expressed (P value <0.05, FC ≥1.2) proteins in comparison to the adequate-Se diet (0 µg Se g−1: 45 proteins; 5 µg Se g−1: 59 proteins); 13 proteins were commonly affected in 0 and 5 µg Se g−1 treatments. Network analysis revealed that the metabolism of glutathione, xenobiotics and amino acids were enriched in both 0 and 5 µg Se g−1 diets, indicating a U-shape effect of Se. This similarity is likely due to down-stream effects of lack of essential selenoproteins in Se deficiency and due to toxic effects of Se that exceeds the capacity to cope with excess Se.

The Dynamics of Selenium Uptake by Maize (Zea mays L.)

The dynamics of selenium (Se) uptake by two maize varieties (Zea mays L.) were assessed under two selenium doses (0.1 and 0.2 mg kg−1 of soil) applied to the soil. The addition of Se increased the biomass yield of the Se-susceptible variety (Bielik), while significantly decreasing the yield of the Se-resistant variety (Lober), and this suppression was stronger at the higher Se dose. The content and uptake of selenium by maize also increased with the Se dose, and the Bielik variety proved to be more effective. In terms of crop quality for animal nutrition, the optimal Se content (330–365 µg kg−1) was reached after 81 days of vegetation under the lower Se dose only, while the higher treatment led to excessive Se accumulation in maize biomass.

Substituent Effects in the Synthesis of Heterostructures.

There have been a number of surprising reports of unexpected products when preparing heterostructures of Bi2Se3 with other 2D layers. These reports prompted us to explore the formation of metastable heterostructures containing Bi2Se3 using X-ray diffraction techniques to follow the reaction pathway. We discovered that the products formed depend on the electronic properties of the second constituent. Bi|Se layers deposited in a 2:3 ratio with enough atoms to make a single five-plane layer evolved to form thermodynamically stable Bi2Se3 as expected from the phase diagram. When the same Bi|Se layers were sequentially deposited with M|Se layers that form semiconductor layers (PbSe and 2H-MoSe2), Bi2Se3-containing heterostructures formed. When the same Bi|Se layers were deposited with M|Se layers that form metallic layers (TiSe2, VSe2, and 1T-MoSe2), BiSe-containing heterostructures formed. The amount of excess Se in the precursor controls whether [(Bi2Se3)1+δ]1[(MoSe2)]1 or [(BiSe)1+γ]1[(MoSe2)]1 forms. XPS data indicates that a mixture of both metallic 1T and semiconducting 2H-MoSe2 is present in [(BiSe)1+γ]1[(MoSe2)]1, while only semiconducting 2H-MoSe2 is present when layered with Bi2Se3. The electronic structure of adjacent layers impacts the formation of different structures from layers with similar local compositions. This provides an important additional parameter to consider when designing the synthesis of heterostructures, similar to substituent effects in molecular chemistry.

Transgenerational effects of selenomethionine on behaviour, social cognition, and the expression of genes in the serotonergic pathway in zebrafish

Elevated levels of contaminants from human activities have become a major threat to animals, particularly within aquatic ecosystems. Selenium (Se) is a naturally occurring element with a narrow range of safe intake, but excessive Se has toxicological effects, as it can bioaccumulate and cause cognitive and behavioural impairments. In this study, we investigated whether exposure to Se would also have transgenerational effects, causing changes in the descendants of exposed individuals. We exposed adult female zebrafish to either a control diet or environmentally relevant concentrations of dietary Se-Met (3.6, 12.8, 34.1 μg Se/g dry weight) for 90 days. Then, females from each treatment group were bred with untreated males, and the offspring (F1-generation) were raised to adulthood (6 months old) without Se exposure. In behavioural tests, offspring that were maternally exposed to 34.1 μg Se/g showed signs of elevated stress, weaker group preferences, and impaired social learning. Maternal exposure to high levels of Se-Met also led to dysregulation of the serotonergic system via changes in mRNA expression of serotonin receptors, including the 5-HT1A, 5-HT1B, and 5-HT1D subtypes, the serotonin transporter, and monoamine oxidase (MAO). Such perturbations in the serotonergic system, thus, appear to underlie the neurobehavioural deficits that we observed. These findings suggest that Se contamination can have important transgenerational consequences on social behaviour and cognition.

Dietary Selenium Regulates microRNAs in Metabolic Disease: Recent Progress.

Selenium (Se) is an essential element for the maintenance of a healthy physiological state. However, due to environmental and dietary factors and the narrow safety range of Se, diseases caused by Se deficiency or excess have gained considerable traction in recent years. In particular, links have been identified between low Se status, cognitive decline, immune disorders, and increased mortality, whereas excess Se increases metabolic risk. Considerable evidence has suggested microRNAs (miRNAs) regulate interactions between the environment (including the diet) and genes, and play important roles in several diseases, including cancer. MiRNAs target messenger RNAs to induce changes in proteins including selenoprotein expression, ultimately generating disease. While a plethora of data exists on the epigenetic regulation of other dietary factors, nutrient Se epigenetics and especially miRNA regulated mechanisms remain unclear. Thus, this review mainly focuses on Se metabolism, pathogenic mechanisms, and miRNAs as key regulatory factors in Se-related diseases. Finally, we attempt to clarify the regulatory mechanisms underpinning Se, miRNAs, selenoproteins, and Se-related diseases.

Dietary Marginal and Excess Selenium Increased Triglycerides Deposition, Induced Endoplasmic Reticulum Stress and Differentially Influenced Selenoproteins Expression in the Anterior and Middle Intestines of Yellow Catfish Pelteobagrus fulvidraco.

Selenium (Se) is an essential micro-mineral and plays important roles in antioxidant responses, and also influences lipid metabolism and selenoprotein expression in vertebrates, but the effects and mechanism remain unknown. The study was undertaken to decipher the insights into dietary Se influencing lipid metabolism and selenoprotein expression in the anterior and middle intestine (AI and MI) of yellow catfish Pelteobagrus fulvidraco. Yellow catfish (weight: 8.27 ± 0.03 g) were fed a 0.03- (M-Se), 0.25- (A-Se), or 6.39- (E-Se) mg Se/kg diet for 12 wk. AI and MI were analyzed for triglycerides (TGs) and Se concentrations, histochemistry and immunofluorescence, enzyme activities, and gene and protein levelsassociated with antioxidant responses, lipid metabolism, endoplasmic reticulum (ER) stress, and selenoproteome. Compared to the A-Se group, M-Se and E-Se diets significantly decreased weight gain (WG) and increased TGs concentration in the AI and MI. In the AI, compared with A-Se group, M-Se and E-Se diets significantly increased activities of fatty acid synthase, expression of lipogenic genes, and suppressed lipolysis. In the MI, compared to the A-Se group, M-Se and E-Se diets significantly increased activities of lipogenesis and expression of lipogenic genes. Compared with A-Se group, E-Se diet significantly increased glutathione peroxidase (GPX) activities in the AI and MI, and M-Se diet did not significantly reduce GPX activities in the AI and MI. Compared with the A- Se group, E-Se diet significantly increased glutathione peroxidase (GPX) activities in the plasma and liver, and M-Se diet significantly reduced GPX activities in the plasma and liver. Compared with the A-Se group, M-Se and E-Se groups also increased glucose-regulated protein 78 (GRP78, ER stress marker) protein expression of the intestine. Dietary Se supplementation also differentially influenced the expression of the 28 selenoproteins in the AI and MI, many of which possessed antioxidant characteristics. Compared with the A-Se group, the M-Se group significantly decreased mRNA levels of txnrd2 and txnrd3, but made no difference on mRNA levels of these seven GPX proteins in the MI. Moreover, we characterized sterol regulatory element binding protein 1c (SREBP1c) binding sites of three ER-resident proteins (selenom, selenon, and selenos) promoters, and found that Se positively controlled selenom, selenon, and selenos expression via SREBP1c binding to the selenom, selenon, and selenos promoter. Thus, dietary marginal and excess Se increased TGs deposition of yellow catfish P. fulvidraco, which might be mediated by ER-resident selenoproteins expression and ER stress.

Hair Se Is a Sensitive Biomarker to Monitor the Effects of Se Supplementation in Elderly.

It is rapidly increasing to have selenium (Se) supplementation for urban elderly population in China since they are facing a widespread deficiency daily Se intake. However, until now, there is no low-cost, non-invasive, rapid, and reliable method to monitor the health improvement or risk for elderly Se-supplemented population in China. The present cross-sectional study (229 participants with older than 55 years old) performed in Beijing, China, revealed that the Se concentrations of non-supplementer users (n = 27) were 55 ± 23 μg/L in urine, 139.9 ± 102.3 μg/L in serum, and 487.6 ± 158.7 μg/kg in hair. But a significant increase on hair Se concentrations (615.4 ± 238.8 μg/kg) was observed for Se supplementer users (n = 202) (p < 0.05); there were no significant statistical differences in serum and urine between the Se-supplemented (n = 202) and Se non-supplemented groups (n = 27). This indicated the hair Se levels could be a more sensitive biomarker for Se-supplemented elderly population. Participants who consumed Se supplements for 7-12 months had the highest Se status based on hair and serum Se concentrations (p < 0.05). The present study also revealed that most elderly adults in Beijing just need to supplement 50 μg Se per day to achieve Se plateau status. Furthermore, hair Se levels were positively related with triglycerides/TG levels (p < 0.05) but not body mass index/BMI, total cholesterol/TC, and low-density lipoprotein cholesterol/LDL, implicating Se supplementation for Se sufficiency baseline in elderly population in Beijing likely posed health risk, especially on TG because of excessive Se oxidation stress. An ongoing monitoring of Se status via hair is still warranted to prevent future Se deficiency or excess in China.

Selenium: widespread yet scarce, essential yet toxic

Selenium (Se) is an essential element for humans and animals, with one of the narrowest ranges between deficiency ( 400 µg day−1). Se is very widespread in all environments (rocks, soils, waters, air, plant and animal tissue) but in very low concentrations. Thus, there are no ores from which Se can be effectively mined. This can create a potential problem in supplying Se for commercial uses or for battling Se deficiency which already affects more than one billion people and is predicted to rise in the future. Besides Se deficiency, there are many incidents where excess Se in water and soil caused deformities in animals and humans. Often high-Se areas are found near past coal mining and burning sites, which have never been remediated and still pose a potential threat to human health. This article aims to inform readers about the general chemical characteristics of Se, environmental cycling of Se, and past incidents of Se deficiency and toxicity. The article also touches on the removal of excess Se from waters and soils, as well as biofortification methods for preventing Se deficiency in humans and animals.

Simultaneous Kinetics of Selenite Oxidation and Sorption on δ-MnO2 in Stirred-Flow Reactors.

Selenium (Se) is an essential and crucial micronutrient for humans and animals, but excessive Se brings negativity and toxicity. The adsorption and oxidation of Se(IV) on Mn-oxide surfaces are important processes for understanding the geochemical fate of Se and developing engineered remediation strategies. In this study, the characterization of simultaneous adsorption, oxidation, and desorption of Se(IV) on δ-MnO2 mineral was carried out using stirred-flow reactors. About 9.5% to 25.3% of Se(IV) was oxidized to Se(VI) in the stirred-flow system in a continuous and slow process, with the kinetic rate constant k of 0.032 h−1, which was significantly higher than the apparent rate constant of 0.0014 h−1 obtained by the quasi-level kinetic fit of the batch method. The oxidation reaction was driven by proton concentration, and its rate also depended on the Se(IV) influent concentration, flow rate, and δ-MnO2 dosage. During the reaction of Se(IV) and δ-MnO2, Mn(II) was produced and adsorbed strongly on Mn oxide surfaces, which was evidenced by the total reflectance Fourier transform infrared (ATR-FTIR) results. The X-ray photoelectron spectroscopy (XPS) data indicated that the reaction of Se(VI) on δ-MnO2 produced Mn(III) as the main product. These results contribute to a deeper understanding of the interface chemical process of Se(IV) with δ-MnO2 in the environment.

Mercury interactions with selenium and sulfur and the relevance of the Se:Hg molar ratio to fish consumption advice.

Eating fish is often recommended as part of a healthful diet. However, fish, particularly large predatory fish, can contain significant levels of the highly toxic methylmercury (MeHg). Ocean fish in general also contain high levels of selenium (Se), which is reported to confer protection against toxicity of various metals including mercury (Hg). Se and Hg have a high mutual binding affinity, and each can reduce the toxicity of the other. This is an evolving area of extensive research and controversy with variable results in the animal and epidemiologic literature. MeHg is toxic to many organ systems through high affinity for -SH (thiol) ligands on enzymes and microtubules. Hg toxicity also causes oxidative damage particularly to neurons in the brain. Hg is a potent and apparently irreversible inhibitor of the selenoenzymes, glutathione peroxidases (GPX), and thioredoxin reductases (TXNRD) that are important antioxidants, each with a selenocysteine (SeCys) at the active site. Hg binding to the SeCys inhibits these enzymes, accounting in part for the oxidative damage that is an important manifestation of Hg toxicity, particularly if there is not a pool of excess Se to synthesize new enzymes. A molar excess of Se reflected in an Se:Hg molar ratio > 1 is often invoked as evidence that the Hg content can be discounted. Some recent papers now suggest that if the Se:Hg molar ratio exceeds 1:1, the fish is safe and the mercury concentration can be ignored. Such papers suggested that the molar ratio rather than the Hg concentration should be emphasized in fish advisories. This paper examines some of the limitations of current understanding of the Se:Hg molar ratio in guiding fish consumption advice; Se is certainly an important part of the Hg toxicity story, but it is not the whole story. We examine how Hg toxicity relates also to thiol binding. We suggest that a 1:1 molar ratio cannot be relied on because not all of the Se in fish or in the fish eater is available to interact with Hg. Moreover, in some fish, Se levels are sufficiently high to warrant concern about Se toxicity.

In Vivo Formation of HgSe Nanoparticles and Hg-Tetraselenolate Complex from Methylmercury in Seabirds-Implications for the Hg-Se Antagonism.

In vivo and in vitro evidence for detoxification of methylmercury (MeHg) as insoluble mercury selenide (HgSe) underlies the central paradigm that mercury exposure is not or little hazardous when tissue Se is in molar excess (Se:Hg > 1). However, this hypothesis overlooks the binding of Hg to selenoproteins, which lowers the amount of bioavailable Se that acts as a detoxification reservoir for MeHg, thereby underestimating the toxicity of mercury. This question was addressed by determining the chemical forms of Hg in various tissues of giant petrels Macronectes spp. using a combination of high energy-resolution X-ray absorption near edge structure and extended X-ray absorption fine structure spectroscopy, and transmission electron microscopy coupled to elemental mapping. Three main Hg species were identified, a MeHg-cysteinate complex, a four-coordinate selenocysteinate complex (Hg(Sec)4), and a HgSe precipitate, together with a minor dicysteinate complex Hg(Cys)2. The amount of HgSe decreases in the order liver > kidneys > brain = muscle, and the amount of Hg(Sec)4 in the order muscle > kidneys > brain > liver. On the basis of biochemical considerations and structural modeling, we hypothesize that Hg(Sec)4 is bound to the carboxy-terminus domain of selenoprotein P (SelP) which contains 12 Sec residues. Structural flexibility allows SelP to form multinuclear Hgx(Se,Sec)y complexes, which can be biomineralized to HgSe by protein self-assembly. Because Hg(Sec)4 has a Se:Hg molar ratio of 4:1, this species severely depletes the stock of bioavailable Se for selenoprotein synthesis and activity to one μg Se/g dry wet in the muscle of several birds. This concentration is still relatively high because selenium is naturally abundant in seawater, therefore it probably does not fall below the metabolic need for essential selenium. However, this study shows that this may not be the case for terrestrial animals, and that muscle may be the first tissue potentially injured by Hg toxicity.

Controllable fabrication and photocatalytic performance of nanoscale single-layer MoSe2 islands with substantial edges on an Ag(111) substrate.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging as new electrocatalysts and photocatalysts. The edge sites of 2D TMDs show high catalytic activity and are thus favored at the catalyst surface over TMD inert basal planes. However, 2D TMDs that predominantly expose edges are thermodynamically unfavorable, limiting the number of edge sites at the surface. Herein, we demonstrate a controllable synthesis strategy of single-layer 2D MoSe2 islands with a lateral size of approximately 5-12 nm on an Ag(111) substrate by pre-deposition of excess Se atoms. The surplus Se atoms react with the Ag(111) substrate and form silver selenide compounds to separate MoSe2 islands and further prevent MoSe2 islands from growing up. The nanoscale MoSe2 islands greatly increase the ratio of exposed edge sites relative to the basal plane sites, which leads to excellent photocatalytic activity for the degradation of a methylene blue (MB) organic pollutant. This work paves the way to limit the size of 2D TMDs at the nanoscale and enables new opportunities for enhancing the catalytic activity of 2D TMD materials.

Selenium Toxicity in Plants and Environment: Biogeochemistry and Remediation Possibilities.

Selenium (Se) is a widely distributed trace element with dual (beneficial or toxic) effects for humans, animals, and plants. The availability of Se in the soil is reliant on the structure of the parental material and the procedures succeeding to soil formation. Anthropogenic activities affect the content of Se in the environment. Although plants are the core source of Se in animal and human diet, the role of Se in plants is still debatable. A low concentration of Se can be beneficial for plant growth, development, and ecophysiology both under optimum and unfavorable environmental conditions. However, excess Se results in toxic effects, especially in Se sensitive plants, due to changing structure and function of proteins and induce oxidative/nitrosative stress, which disrupts several metabolic processes. Contrary, Se hyperaccumulators absorb and tolerate exceedingly large amounts of Se, could be potentially used to remediate, i.e., remove, transfer, stabilize, and/or detoxify Se-contaminants in the soil and groundwater. Thereby, Se-hyperaccumulators can play a dynamic role in overcoming global problem Se-inadequacy and toxicity. However, the knowledge of Se uptake and metabolism is essential for the effective phytoremediation to remove this element. Moreover, selecting the most efficient species accumulating Se is crucial for successful phytoremediation of a particular Se-contaminated area. This review emphasizes Se toxicity in plants and the environment with regards to Se biogeochemistry and phytoremediation aspects. This review follows a critical approach and stimulates thought for future research avenues.

Revisiting the Effects of Different Dietary Sources of Selenium on the Health and Performance of Dairy Animals: a Review.

Selenium (Se) is one of the most important essential trace elements in livestock production. It is a structural component in at least 25 selenoproteins such as the iodothyronine deiodinases and thioredoxin reductases as selenocysteine at critical positions in the active sites of these enzymes. It is also involved in the synthesis of the thyroid hormone and influences overall body metabolism. Selenium being a component of the glutathione peroxidase enzyme also plays a key role in the antioxidant defense system of animals. Dietary requirements of Se in dairy animals depend on physiological status, endogenous Se content, Se source, and route of administration. Most of the dietary Se is absorbed through the duodenum in ruminants and also some portion through the rumen wall. Inorganic Se salts such as Na-selenate and Na-selenite have shown lower bioavailability than organic and nano-Se. Selenium deficiency has been associated with reproductive disorders such as retained placenta, abortion, early embryonic death, and infertility, together with muscular diseases (like white muscle disease and skeletal and cardiac muscle necrosis). The deficiency of Se can also affect the udder health particularly favoring clinical and subclinical mastitis, along with an increase of milk somatic cell counts in dairy animals. However, excessive Se supplementation (5 to 8 mg/kg DM) can lead to acute toxicity including chronic and acute selenosis. Se is the most vital trace element for the optimum performance of dairy animals. This review focuses to provide insights into the comparative efficacy of different forms of dietary Se (inorganic, organic, and nano-Se) on the health and production of dairy animals and milk Se content.

Production of a Urinary Selenium Metabolite, Trimethylselenonium, by Thiopurine S-Methyltransferase and Indolethylamine N-Methyltransferase

Selenium (Se) is an essential trace element in animals; however, the element can become highly toxic in excess amounts beyond the nutritional level. Although Se is mainly excreted into urine as a selenosugar within the nutritional level, excess amounts of Se are transformed as an alternative urinary metabolite, trimethylselenonium ion (TMSe). Se methylation appears to be an important metabolic process for the detoxification of excess Se; however, the biochemical mechanisms underlying the Se methylation have not been elucidated. In this study, we evaluated biochemical characteristics of two human methyltransferases for Se methylation, thiopurine S-methyltransferase (TPMT) and indolethylamine N-methyltransferase (INMT). The first methylation of Se, i.e., a nonmethylated to a monomethylated form, was specifically driven by TPMT, and INMT specifically mediated the third methylation, i.e., dimethylated to trimethylated form. The second methylation, i.e., a monomethylated to dimethylated form, was driven by either TPMT or INMT. Exogenous expression of TPMT, but not INMT, ameliorated the cytotoxicity of inorganic nonmethylated selenium salt, suggesting that only TPMT gave the cellular resistance against selenite exposure. TPMT was ubiquitously expressed in most mouse tissues and preferably expressed in the liver and kidneys, while INMT was specifically expressed in the lung and supplementally expressed in the liver and kidneys. Our results revealed that both TPMT and INMT cooperatively contributed to the TMSe production, enabling urinary excretion of Se and maintenance of homeostasis of this essential yet highly toxic trace element. Thus, TPMT and INMT can be recognized as selenium methyltransferases as a synonym.

Risk Assessment of Selenium and Boron Pollutants in Environment

According to the literature, there are increasingly more scientific data regarding the environmental pollution of selenium(Se) and the boron(B). The purpose of this review is to give an overview of environmental pollutants for Se andB and the use of plants to alleviate worldwide problems associated with Se and B toxicity. Selenium is an essential element for many species, plant, as well as humans, but it is toxic at higher levels. Boron is relatively soluble in water and commonly causes environmental problems, especially for surface waters where most of the discarded B will end up. Using phytoremediation plants can address this problem. To prevent Se and B toxicity due to excess environmental Se or B, plants may be used to phytoremediate to take up Se and B from soil or water. Research in the past decades had provided a riches ofknowledge regarding the mechanisms by which plants uptake, metabolize, and accumulate Se or B. Moreover, environment studies have revealed the important effects for plantsuptake of Se or B and interactions with herbivores, pollinators, neighbouring vegetation.

Excess Se-doped MoSe2 and nitrogen-doped reduced graphene oxide composite as electrocatalyst for hydrogen evolution and oxygen reduction reaction

Noble metal catalysts (e.g., Pt, Ru, and Ir) are expensive and scarce and cannot be synthesized at a large scale. The cheap and stable chalcogenides seem to be an attractive alternative and are most likely to replace the precious metal catalysts. However, the poor conductivity, limited number of active sites, and other properties of the chalcogenides limit their applications. In this work, we synthesized defect-rich MoSe2 with nitrogen-doped reduced graphene oxide (MoSe2/NG) in a simple hydrothermal process by introducing excess Se precursor. The catalyst with optimal performance (MoSe2/NG-4) exhibits good bifunctional properties in the oxygen reduction reaction and hydrogen evolution reaction (HER). It exhibits a small overpotential of 120 mV at a current density of 10 mA cm −2 in the HER, with a smaller Tafel slope of 69 mV dec−1, which is much lower than the values of most reported most reported Mo-based catalysts. Besides, it behaves as an effective catalyst in the ORR and adopts a four-electron reaction pathway. This excellent bifunctional catalytic property is mainly due to the rich heterostructure of MoSe2/NG-4 and synergistic effect of nitrogen doping, excellent conductivity of graphene, and the rich active sites. This work provides a new approach for the synthesis and application of chalcogenides and their complexes in the field of catalysis.

Selenium toxicity stress-induced phenotypical, biochemical and physiological responses in rice plants: Characterization of symptoms and plant metabolic adjustment

Selenium (Se) at low concentration is considered benefit element to plants. The range between optimal and toxic concentration of Se is narrow and varies among plant species. This study aimed to evaluate the phenotypic, physiological and biochemical responses of four rice genotypes (BRS Esmeralda, BRSMG Relâmpago, BRS Bonança and Bico Ganga) grown hydroponically treated with sodium selenate (1.5 mM L−1). Selenium treated plants showed a dramatically decrease of soluble proteins, chlorophylls, and carotenoids concentration, resulting in the visual symptoms of toxicity characterized as leaf chlorosis and necrosis. Selenium toxicity caused a decrease on shoot and root dry weight of rice plants. Excess Se increased the oxidative stress monitored by the levels of hydrogen peroxide and lipid peroxidation. The enzymatic antioxidant system (catalase, superoxide dismutase, and ascorbate peroxidase) increased in response to Se supply. Interestingly, primary metabolism compounds such as sucrose, total sugars, nitrate, ammonia and amino acids increased in Se-treated plants. The increase in these metabolites may indicate a defense mechanism for the osmotic readjustment of rice plants to mitigate the toxicity caused by Se. However, these metabolites were not effective to minimize the damages on phenotypic traits such as leaf chlorosis and reduced shoot and root dry weight in response to excess Se. Increased sugars profile combined with antioxidant enzymes activities can be an effective biomarkers to indicate stress induced by Se in rice plants. This study shows the physiological attributes that must be taken into account for success in the sustainable cultivation of rice in environments containing excess Se.

1981-P: Impaired Exercise Lipid Oxidation Is Associated with Poor Metabolic Health, Not Excess Body Fat Per Se

Introduction: It is not clear whether impaired exercise lipid oxidation is associated with excess body-fat or changes in metabolic health often associated with the overweight/obese state. Mixed findings may reflect lack of control for key variables including: 1) acute energy balance and macronutrient composition of the diet; 2) intensity and duration of exercise; and 3) subject characteristics including fat-free mass (FFM), fitness and, perhaps most importantly, metabolic health (e.g., insulin resistance). Purpose: To determine whether excess body-fat or loss of metabolic health is associated with altered fuel metabolism during exercise. Methods: Eight metabolically healthy (FH- and ≤1 MetSyn) normal-weight (BMI, 19-24 kg∙m-2) (MHNW) and 8 overweight/obese (26-35 kg∙m-2) (MHO) sedentary adults, and 7 metabolically unhealthy (FH+ and ≥ 2 MetSyn) normal-weight (MUNW) and 7 overweight/obese (MUO) sedentary adults, controlled for age (18-45 yr), sex, and fitness level (≤ “average”), completed a 10-day weight-stable (controlled feeding) testing protocol that included measurement of V?O2peak, RMR, body-fat %, OGTT and lipid oxidation during 45 min of moderate-intensity cycling. ANCOVA with adjustment for rate of O2 consumption (ml∙min-1∙kgBW-1) was used with contrasts to compare indices of lipid oxidation among the four groups. Results: Adjusted means over both sexes for lipid oxidation during exercise, expressed as rate (mg∙min-1∙kgFFM-1), RER and percent total energy expenditure were significantly different between groups (p&amp;lt;0.05). There was a significant difference between MHNW vs. MUO for all indices (p&amp;lt;0.05), and between MUNW vs. MHO for rate (p&amp;lt;0.025). Tukey post-hoc also revealed a significant difference between MHNW vs. MUNW for all indices. Conclusion: We found that impaired exercise lipid oxidation previously ascribed to the overweight/obese state was specifically associated with the loss of metabolic health as opposed to the overweight/obese state per se. Disclosure A.D. Arad: None. F.J. DiMenna: None. H.D. Kittrell: None. H.R. Kissileff: None. J. Albu: None.