Free Selenium Research Articles

Glutathione peroxidase (GPX1) - Selenocysteine metabolism preserves the follicular fluid's (FF) redox homeostasis via IGF-1- NMD cascade in follicular ovarian cysts (FOCs)

Follicular ovarian cysts (FOCs) are characterized by follicles in the ovaries that are >20 mm in diameter and persist for >10 days without the corpus luteum, leading to anovulation, dysregulation of folliculogenesis and subfertility in humans and livestock species. Despite their clinical significance, the precise impact of FOCs on oocyte reserve, maturation, and quality still needs to be explored. While FOCs are observed in both human and livestock populations, they are notably prevalent in livestock species. Consequently, livestock species serve as valuable models for investigating the molecular intricacies of FOCs. Thus, in this study, using goat FOCs, we performed integrated proteomic, metabolomic and functional analyses to demonstrate that oocyte maturation is hampered due to increased reactive oxygen species (ROS) in FOCs follicular fluid (FF) via downregulation of glutathione peroxidase (GPX1), a critical antioxidant seleno enzyme required to negate oxidative stress. Notably, GPX1 reduction was positively correlated with the FF's decline of free selenium and selenocysteine metabolic enzymes, O-phosphoryl-tRNA (Sec) selenium transferase (SEPSECS) and selenocysteine lyase (SCLY) levels. Adding GPX1, selenocysteine, or selenium to the culture media rescued the oocyte maturation abnormalities caused by FOCs FF by down-regulating the ROS. Additionally, we demonstrate that substituting GPX1 regulator, Insulin-like growth factor-I (IGF-1) in the in vitro maturation media improved the oocyte maturation in the cystic FF by down-regulating the ROS activity via suppressing Non-sense-mediated decay (NMD) of GPX1. In contrast, inhibition of IGF-1R and the target of rapamycin complex 1 (mTORC1) hampered the oocyte maturation via NMD up-regulation. These findings imply that the GPX1 regulation via selenocysteine metabolism and the IGF-1-mediated NMD may be critical for the redox homeostasis of FF. We propose that GPX1 enhancers hold promise as therapeutics for enhancing the competence of FOCs oocytes. However, further in vivo studies are necessary to validate these findings observed in vitro.

Effect of co-encapsulation of Lactobacillus acidophilus LA5 and selenium in hydrogelated matrix of basil seed mucilage/sodium caseinate on properties of set yogurt

This study aims to prepare and optimize basil seed mucilage and sodium caseinate as a biocomposite wall to co-encapsulate Lactobacillus acidophilus LA5 and selenium. The efficacy of this biocomposite wall in improving the viability of L. acidophilus LA5 under in vitro acidic conditions was investigated. The mixture design method was applied to find optimal ratio of basil seed mucilage/sodium caseinate as components of the capsule wall. The maximum encapsulation efficiency of the selenium and L. acidophilus LA5 and the minimum zeta potential led to the selection of the optimal ratio of basil seed mucilage/sodium caseinate (basil seed mucilage 58.27% and sodium caseinate 41.73%). Possible cross-linking of basil seed mucilage and sodium caseinate, thermal properties, crystal structure, and morphology of the capsule were investigated using FTIR, DSC, XRD, and SEM tests, respectively. The composite wall of basil seed mucilage/sodium caseinate significantly enhanced the viability of encapsulated L. acidophilus LA5 in comparison to the control sample (free L. acidophilus LA5) (p < 0.05). Five yogurt samples were produced, including samples with free probiotic, free probiotic bacterium and selenium, free selenium, control (no probiotic bacterium and selenium), and probiotic yogurt with encapsulated selenium and probiotic bacterium. The physical, chemical, sensorial, and microbial characteristics of yogurt samples were investigated during storage for 21 days at 4 °C. Yoghurt enriched with free selenium and microcapsules (co-encapsulated probiotic and selenium) had minimum and maximum viscosities, respectively (p < 0.05). In addition, the probiotic yogurt sample with encapsulated L. acidophilus LA5 and selenium received a higher overall acceptance score than the other treatments (p < 0.05). As a result, basil seed mucilage and sodium caseinate based composite wall was demonstrated great potential to encapsulate probiotics and selenium for application in yogurt formulation.

Serum gonadotropins, cortisol, PSA, and micronutrient levels among men with prostate carcinoma

BackgroundProstate cancer (PrCa) is a malignant tumour of the prostate that has many associated risk factors. There is continuous rise in the incidence among adult blacks which is a reflection of racial differences in testosterone concentrations.MethodsThe study involves 50 PrCa patients attending or referred to two tertiary health Institutions and 25 healthy men as controls. Weight and height of participants were measured, and body mass index (BMI) was calculated. Ten millilitres of venous blood sample was collected from each participant, allowed to clot, and then centrifuged at 5000 rpm for 5 min at room temperature (22–28 °C) to obtain the serum. Serum cortisol, testosterone, follicle-stimulating hormone (FSH), luteinizing hormone (LH), total prostate-specific antigen (TPSA), free prostate-specific antigen (FPSA), selenium, copper, magnesium, and zinc were determined. Prostate ultrasonography and biopsy were also done for histopathological studies.ResultFrom this study, a significant increase (p < 0.05) in weight, BMI, serum FPSA, TPSA, and copper; a non-significant increase (p > 0.05) in serum cortisol, testosterone; a significant decrease (p < 0.05) in serum LH, selenium, zinc, and magnesium; and a non-significant decrease (p > 0.05) in serum FSH were observed among people living with PrCa when compared to the controls. However, no significant difference (p > 0.05) was observed in the height between the two groups. Ultrasonography and histology revealed evidence of prostatitis, hypertrophy, and carcinoma among the test group.ConclusionIt can be concluded that PrCa is associated with increase serum cortisol, testosterone, and copper; and decreased serum LH, FSH, selenium, zinc, and magnesium concentrations and combination of biochemical, ultrasonographic, and histologic features are of diagnostic importance.

Inhibition mechanism of SARS-CoV-2 main protease by ebselen and its derivatives

The SARS-CoV-2 pandemic has triggered global efforts to develop therapeutics. The main protease of SARS-CoV-2 (Mpro), critical for viral replication, is a key target for therapeutic development. An organoselenium drug called ebselen has been demonstrated to have potent Mpro inhibition and antiviral activity. We have examined the binding modes of ebselen and its derivative in Mpro via high resolution co-crystallography and investigated their chemical reactivity via mass spectrometry. Stronger Mpro inhibition than ebselen and potent ability to rescue infected cells were observed for a number of derivatives. A free selenium atom bound with cysteine of catalytic dyad has been revealed in crystallographic structures of Mpro with ebselen and MR6-31-2 suggesting hydrolysis of the enzyme bound organoselenium covalent adduct and formation of a phenolic by-product, confirmed by mass spectrometry. The target engagement with selenation mechanism of inhibition suggests wider therapeutic applications of these compounds against SARS-CoV-2 and other zoonotic beta-corona viruses.

Conditions adjustment of polycaprolactone nanofibers scaffolds encapsulated with core shells of Au@Se via laser ablation for wound healing applications

Au@Se core–shell nanoparticles were obtained via laser ablation technique to be incorporated into polycaprolactone (PCL) nanofibrous scaffolds for wound healing applications at different contributions of Se nanoparticles (SeNPs). The synthesized layers were inspected via X-ray diffraction (XRD) and Fourier transformed infrared (FTIR). Additionally, microstructural and surface morphology were followed with different SeNPs contributions before and after fibroblast culturing. Moreover, Selenium dopant is affected Maximum roughness valley depth while it starts from 0.31 µm at Au@0.0Se@PCL reaching 0.457 µm at Au@12Se@PCL; however, after culturing starts from 0.3833 µm reaching 0.41 µm. Besides, the antibacterial activity was screened, showing the absence of inhibition zones in free selenium composition; however, it grows up reaching 8.3 ± 0.8, and 8.0 ± 0.8 for E. coli and S. aureus, respectively at the maximum contribution of selenium. SeNPs contributed composites show higher cell viability than Selenium free composite that it reaches its max in Au@8.0Se@PCL, recording 95.3 ± 2.3%. Composites show an excellent Wound dressing capability that its performance is directly proportional to selenium content. This significant enrichment of antibacterial activity and cell viability could recommend these composites for additional research in medical applications.

Specificity of Biogenic Selenium Nanoparticles for Prostate Cancer Therapy With Reduced Risk of Toxicity: An in vitro and in vivo Study.

Selenium deficiency is associated with many physiological disorders including the high risk of cancer. The rehabilitation of selenium with different selenium supplements, however, fails due to their low therapeutic index. Therefore, it is advantageous to have a less toxic form of selenium for supplementation with potentially high anticancer activity. Here we show Bacillus licheniformis derived biogenic selenium nanoparticles at a minimal concentration of 2 μg Se/ml induce necroptosis in LNCaP-FGC cells, without affecting the RBC integrity. Real-time gene expression analysis indicated the overexpression of tumor necrotic factor (TNF) and interferon regulatory factor (IRF1) and decreased expression of androgen receptor (AR) and prostate-specific antigen (PSA). Furthermore, histopathological analysis showed the subsequent oral administrations of 10 times higher concentration of these endotoxin free selenium nanoparticles in C3H/HeJ mice (50 mg Se/kg of body weight), induce significantly lower toxicity compared to the L-selenomethionine (5 mg Se/kg). Our study suggested that the biogenic SeNP could emerge as the safest form of selenium supplementation with potent anticancer activity.

In-vitro cytotoxicity of java tea mediated selenium nanoballs against L6 cell lines

The emergence of Nanotechnology has provided a catholic research in recent years by intersecting with assorted branches of science and forming collision on all forms of life. At present there has been a prodigious excitement in the field of Nano pharmacology to seek the role of Nano selenium in individual healthcare and explains how selenium is a double edged sword in the pathologies of chronic diseases like Diabetes mellitus because of their inferior toxicity and ability to gradually release the bioactive principle and free selenium after ingestion. Thus the present study is an embryonic attempt and was aimed at the adroitful synthesis of selenium nanoballs from the aqueous extract of well known herbal tea leaves namely Java tea (Orthosiphon stamineus) using selenious acid solution. The synthesized Selenium nanoparticles were then subjected to various characterization techniques such as UV, FTIR, FESEM, EDAX and Zeta potential respectively. Finally the green synthesized SeNps were tested for their cytotoxic effect against L6 rat skeletal muscle cell lines. The pre clinical studies are underway to prove the insulin mimic activity of the selenium nanoparticles.&#x0D; Keywords: Selenium Nanoparticles, Java tea, L6 cell lines.

Electrodeposition of Cobalt Selenide Thin Films Using Combined Voltammetry and Electrochemical Quartz Crystal Microgravimetry

Electrodeposition and composition of CoSe thin films have been studied using electrochemical quartz crystal microgravimetry and stripping voltammetry. CoSe thin films were synthesized using 0.1 M KNO3 solution containing SeO2 and Co(NO3)2 at room temperature. During the electrodeposition, selenium was electrodeposited first, followed by the induced under potential deposition of cobalt to result in CoSe films. Photocurrent transients proved that as synthesized Se and CoSe are p-type semiconductors and their band gaps have been determined with reflectance spectrometry. Deposition mechanism and effect of electrolyte composition on the film composition were studied in detail using electrolyte containing different ratio. Composition of CoSe thins films has been determined by combining EQCM and stripping voltammetry. First, free selenium in the electrodeposited film was reduced to soluble Se2- at –0.8 V in 0.1 M Na2SO4 solution and frequency change was used to determine the content of free selenium. The film was again subjected to –1.5 V in the same blank electrolyte to reduce CoSe to Co+Se2- and accompanied frequency change was used to determine selenium in CoSe based on the 1:1 stoichiometry. Finally, the content of free cobalt in the electrodeposited film was determined from the frequency change during the oxidation of Co to Co2+ and difference between total cobalt and cobalt in CoSe thin film. Compositional analysis indicated that film composition is sensitive to electrodeposition potential as well as composition of electrolyte.

Complex effects of selenium-arabinogalactan nanocomposite on both phytopathogen Clavibacter michiganensis subsp. sepedonicus and potato plants

A novel selenium nanobiocomposite consisting of X-ray amorphous nanoparticles of red elemental selenium (average size ∼67 nm) uniformly encapsulated into arabinogalactan macromolecules has been synthesized. The effect of this nanobiocomposite and its precursors (pure arabinogalactan and selenium dioxide) on the viability of a phytopathogenic bacterium Clavibacter michiganensis subsp. sepedonicus (Spieck et Kotth.) Skapt et Burkh (C. michiganensis) and potato plants has been investigated in vitro. The bactericidal effects of free selenium dioxide and the nanocomposite obtained from the former (normalized selenium concentration 0.000625%) have been demonstrated. The targeted metabolic (trophic) delivery of antimicrobial selenium nanoparticles to the bacterial cells by the arabinogalactan matrix incorporating the particles was detected in the latter case. The treatment of potato plants with selenium dioxide was found to have a negative effect on peroxidase activity and plant growth. On the contrary, treating the plants with the selenium nanocomposite had no negative effects. Thus, the nanocomposite of elemental selenium and arabinogalactan produced in the present work can be considered a new antimicrobial agent for plant sanitation with minimal side effects.

Ni3Se4 hollow architectures as catalytic materials for the counter electrodes of dye-sensitized solar cells

Nanoparticles of nickel selenides (Ni3Se4) were synthesized with various hollow architectures by a simple, one-step, low temperature hydrothermal process. Using three organic solvents having different alkyl chains, precisely methanol (MeOH), ethanol (EtOH), and propan-1-ol (n-PrOH), the Ni3Se4 nanoparticles showed three kinds of morphologies: sea urchins-like, rice-balls-like and strawberry-fruits-like hollow nanostructures, respectively. The solvent polarity shows a trend of MeOH>EtOH>n-PrOH, and the same trend on the surface area and roughness of the corresponding Ni3Se4 nanoparticles can be observed. Therefore, we propose a three-step mechanism for Ni3Se4 growth: (1) the nucleation based on a selenium core surrounded by free selenium ions; (2) the Ni3Se4 formation; (3) the dissolution of selenium core to form the hollow nanoparticles. Accordingly, the first-step is the key state because the higher solvent polarity would cause the more free selenium ions and thereby the larger surface area on Ni3Se4 nanoparticles. For the dye-sensitized solar cells (DSSCs), the films of nickel selenide can be utilized as the electrocatalytic counter electrodes (CE) for the redox of I−/I3−. The nickel selenide film obtained using methanol (hereafter urchins-like Ni3Se4@MeOH) shows extremely large effective surface area (5.63 times larger than traditional Pt film) and fast redox ability (1.08 times higher than traditional Pt film). The urchins-like Ni3Se4@MeOH CE rendered for its DSSC a power conversion efficiency (η) of 8.31%, while the expensive platinum counter electrode (Pt-CE) could bestow for its DSSC only an η of 8.03%. It may be said that nickel selenide is a promising catalytic material to replace the expensive platinum in a DSSC.

Effect of fasting on lipid metabolism and oxidative stability in fattening chicken fed a diet supplemented with organic selenium

Abstract. The aim of the study was to assess the effect of organic selenium dietary supplementation on serum and tissue lipid composition after fattening period and after 48 h fasting in fattening chicken. The study was performed in the Ross hybrid line chicken divided into two groups: control group fed standard diet and Sel Plex group fed standard diet supplemented with 0.3 ppm organic selenium. Blood, liver, intestine and adipose tissue samples were taken upon fattening completion and after 48 h fasting. Total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triacylglycerol and lipoprotein concentrations were determined in serum, whereas total and free cholesterol, triacylglycerol, lipid peroxide and selenium concentrations and glutathione peroxidase activity (GSH-Px) were determined in tissue samples. During fattening period, the correlation of organic selenium with lipid metabolism manifested as decreased concentrations of serum triacylglycerols and very-low-density lipoprotein (VLDL) (P&lt;0.05), liver triacylglycerols (P&lt;0.05), adipose tissue cholesterol (P&lt;0.05) and small intestine cholesterol (P&lt;0.05), and reduced lipid peroxidation (P&lt;0.05). Upon chicken exposure to 48 h fasting, organic selenium supplementation resulted in increased free cholesterol concentration in adipose tissue (P&lt;0.05), GSH-Px activity in the liver (P&lt;0.05), and selenium (P&lt;0.05) accumulation in the liver.

Solution NMR Structure of Selenium-binding Protein from Methanococcus vannielii

Selenium is an important nutrient. The lack of selenium will suppress expression of various enzymes that will lead to cell abnormality and diseases. However, high concentrations of free selenium are toxic to the cell because it adversely affects numerous cell metabolic pathways. In Methanococcus vannielii, selenium transport in the cell is established by the selenium-binding protein, SeBP. SeBP sequesters selenium during transport, thus regulating the level of free selenium in the cell, and delivers it specifically to the selenophosphate synthase enzyme. In solution, SeBP is an oligomer of 8.8-kDa subunits. It is a symmetric pentamer. The solution structure of SeBP was determined by NMR spectroscopy. Each subunit of SeBP is composed of an alpha-helix on top of a 4-stranded twisted beta-sheet. The stability of the five subunits stems mainly from hydrophobic interactions and supplemented by hydrogen bond interactions. The loop containing Cys(59) has been shown to be important for selenium binding, is flexible, and adopts multiple conformations. However, the cysteine accessibility is restricted in the structure, reducing the possibility of the binding of free selenium readily. Therefore, a different selenium precursor or other factors might be needed to facilitate opening of this loop to expose Cys(59) for selenium binding.

(337) Effect of Selenium Supply by Trunk Injection on Fruit Quality of `Niitaka' Asian Pear

Many trials to supply selenium to fruit have been carried out since tests have confirmed selenium's role as a medical substance. Supplying selenium in orchards by soil and foliar application was not effective because of loss from rainfall. In order to increase selenium absorption by fruit, this study carried out tree trunk injections during the growing season. Selenium solutions in concentrations of 5, 10, 25, and 50 mg·L–1 were supplied to `Niitaka' pear (Pyruspyrifolia) trees by trunk injection (1.5 L/tree) four times at 15-day intervals from June 2004. The treatment with 50 mg·L–1 selenium showed necrosis symptoms at leaf-margins after secondary treatment and toxicity as abnormally red fruit skin color. Fruit weight and leaf area were decreased by selenium treatments, while severe symptoms appeared with higher selenium concentrations. Hunter values `a' and `b' in fruit skin color were increased by selenium treatment in comparison to the control. The selenium treatment showed lower soluble solids by as much as 1.2%, and higher fruit firmness. Selenium concentration in pear fruit was increased by trunk injection with a 5 mg·L–1 solution. The bound selenium in pear fruit after 3 months of storage in cold room conditions was very high, but free selenium was low.

Inactivation of the selB gene in Methanococcus maripaludis: effect on synthesis of selenoproteins and their sulfur-containing homologs.

The genome of Methanococcus maripaludis harbors genes for at least six selenocysteine-containing proteins and also for homologs that contain a cysteine codon in the position of the UGA selenocysteine codon. To investigate the synthesis and function of both the Se and the S forms, a mutant with an inactivated selB gene was constructed and analyzed. The mutant was unable to synthesize any of the selenoproteins, thus proving that the gene product is the archaeal translation factor (aSelB) specialized for selenocysteine insertion. The wild-type form of M. maripaludis repressed the synthesis of the S forms of selenoproteins, i.e., the selenium-independent alternative system, in selenium-enriched medium, but the mutant did not. We concluded that free selenium is not involved in regulation but rather a successional compound such as selenocysteyl-tRNA or some selenoprotein. Apart from the S forms, several enzymes from the general methanogenic route were affected by selenium supplementation of the wild type or by the selB mutation. Although the growth of M. maripaludis on H(2)/CO(2) is only marginally affected by the selB lesion, the gene is indispensable for growth on formate because M. maripaludis possesses only a selenocysteine-containing formate dehydrogenase.

Determination of selenium concentration and its chemical forms in the milk of Kuwaiti and non-Kuwaiti lactating mothers

The objectives of the present study were to compare the selenium status in the milk and plasma of Kuwaiti mothers with that of non-Kuwaiti mothers during 0–18 months of lactation and to identify and compare the chemical forms of selenium in human milk and cow milk. Thirty-four donors between 25 to 40 years of age (Kuwaitis, n = 17; non-Kuwaitis, n = 17) were studied. Milk samples were obtained prior to the first feeding of the infant and blood samples were collected shortly after. Milk fractionation was performed by ultracentrifugation, gel-column chromatography, and thin-layer chromatography. Concentrations of selenium were analyzed using atomic absorption spectrophotometry and glutathione-peroxidase by spectrophotometry. Concentrations of selenium in milk and plasma and content of proteins in milk were significantly higher in the Kuwaiti group than those of the non-Kuwaitis during the first 12 months of lactation. The selenium profile in milk was parallel with those of total proteins, casein, and whey. In general, these parameters including the activity of glutathione-peroxidase, were decreased as lactation was prolonged. The major chemical form of selenium in human milk was found to be selenomethionine. Cow milk did not appear to contain this compound, but might have a free selenium form that is neither selenite nor selenate. In conclusion, 1) the higher level of selenium in the milk of Kuwaiti mothers may reflect the high protein content of regional diets and traditional treatment with herbal medicines during post-parturition and 2) selenomethionine is the major selenium-containing compound located in the whey protein fraction of human milk, and this may enhance the bio-availability of selenium. J. Trace Elem. Exp. Med. 14:57–67, 2001. © 2001 Wiley-Liss, Inc.

Utilization of selenocysteine as a source of selenium for selenophosphate biosynthesis.

Selenophosphate synthetase (SPS), the selD gene product from Escherichia coli, catalyzes the biosynthesis of monoselenophosphate from selenide and ATP. Characterization of selenophosphate synthetase revealed the determined K(m) value for selenide is far above the optimal concentration needed for growth and approached levels which are toxic. Selenocysteine lyase enzymes, which decompose selenocysteine to elemental selenium (Se(0)) and alanine, were considered as candidates for the control of free selenium levels in vivo. The ability of a lyase protein to generate Se(0) in the proximity of SPS maybe an attractive solution to selenium toxicity as well as the high K(m) value for selenide. Recently, three E. coli NifS-like proteins, CsdB, CSD, and IscS, were characterized. All three proteins exhibit lyase activity on L-cysteine and L-selenocysteine and produce sulfane sulfur, S(0), or Se(0) respectively. Each lyase can effectively mobilize Se(0) from L-selenocysteine for selenophosphate biosynthesis.

Fate of free selenium atoms in externally heated quartz tube atomizers for hydride generation atomic absorption spectrometry and their reatomization at tube ends studied by means of the determination of longitudinal free atom distribution

The longitudinal distribution of Se free atoms in externally heated quartz tube hydride atomizers was studied under analytical conditions, i.e. selenium concentrations of 10–100 μg l −1 and argon flow rates of 25–400 ml min −1. The selenium signal was measured through the walls of the optical tube with the tube perpendicular to the radiation beam at various positions along the tube length. The highest concentration of free atoms was found near the middle of the optical tube, where atomization proceeds. Under typical analytical conditions, all free atoms disappear before they reach the ends of the atomizer. The free atom decay rate is greatly enhanced at higher analyte concentrations. This is a major source of calibration graph curvature. The atomization efficiency was influenced much less. The presence of zones where once reacted free atoms are reatomized at the optical tube ends was proven by the spatially resolved observation. Using the measures originally meant to prevent flame ignition on the tube ends, such as quartz windows or prolonged unheated parts of the tube, no reatomization takes place. The effect of reatomization on the analytical performance of the atomizer was shown: the sensitivity is improved and the non-linearity of the calibration graph is substantially reduced, while the baseline noise remains at the same level. Recommendations concerning the quartz tube atomizer design and dimensions are given.

Growth phases during electrochemical selenization of vacuum deposited CuIn metal layers for the formation of semiconducting CuInSe2 films

A new two-stage process for electrochemical selenization of vacuum deposited Cu–In precursor films is demonstrated as an alternative to toxic and hazardous H2Se or Se vapour phase selenization techniques for the formation of semiconducting CuInSe2 thin films. The growth phases and microstructure of films are sensitive to Cu to In thickness ratios in the precursor, selenization current densities and time. Electrochemically selenized films show multiphase and polymorphic behaviour which strongly depends on the precursor structure and composition. The crystalline state of the film varies from a sphalerite to chalcopyrite CuInSe2 phase along with Cu and In binary compounds which are also observed. With In in excess in Cu+In mixed precursor films, use of low selenization currents (1mA/cm2) and longer periods (3h) yield the chalcopyrite CuInSe2 phase. Copper excess in bilayer precursor likewise favours chalcopyrite CuInSe2 growth after a post-selenization annealing. Single-phase chalcopyrite CIS film formation requires full selenization of the precursor and proper adjustment of the Cu/In thin film ratio in the precursor. Absence of free selenium at the post-selenization annealing stage led to secondary reactions and inclusion of binary phases.

Correlation of Mercury and Selenium in the Human Kidney

The total mercury (Hg) and selenium (Se) concentrations were determined in kidney cortex samples of 195 deceased, non-occupationally burdened individuals. Mercury was determined by means of Cold-vapour Atomic Absorption Spectrometry (CV-AAS) and selenium by Graphite-Furnace Atomic Absorption Spectrometry (GF-AAS). The molar Se/Hg ratio is high (up to (a) 300) in cases with relatively low mercury concentrations [Hg]. The ratio decreases with increasing [Hg]. At [Hg] of 700-1000 ng/g it reaches unity, where it remains constant even at larger [Hg]. Since in vitro mercury and selenium form relatively stable adducts, our results suggest the formation of a 1:1 Hg-Se compound that may explain mercury detoxification by selenium. This effect also results in the trapping of available selenium by mercury, too. Decreasing the reserve of free (i.e. not Hg-bound) selenium. The effect of this decrease of free selenium is under further investigation.

Vacuum sublimation of GaSe: a molecular source for deposition of GaSe

The layered structure of GaSe makes it suitable for the technique of Van der Waals epitaxy, a molecular beam deposition technique where heterostructures are fabricated based on a property of interest and are not limited by lattice and thermal expansion mismatch. Single crystal GaSe has been grown on GaAs(111)A by vacuum sublimation from a single GaSe source without terminating the GaAs surface dangling bonds prior to deposition. Mass spectroscopy was used to determine the composition of the molecular source. It was found that GaSe sublimates stoichiometrically to form Ga 2Se and Se 2. This results in free selenium (Se 2) in the molecular beam which can terminate the dangling bonds at the GaAs surface prior to bulk GaSe growth. X-ray photoelectron spectroscopy and reflection high energy electron diffraction studies of the deposition confirm this termination process and the structure of subsequent GaSe growth.