Selenium Compounds

Surface-modifi ed quantum dots (QDs) are extensively used as fl uorescent labels for sensing and biosensing events. [ 1 , 2 ] Fluorescence resonance energy transfer (FRET) or electron-transfer quenching of the QDs are two fundamental photophysical mechanisms to probe sensing processes at the surface of the QDs. [ 2 , 3 ] Indeed, these photophysical mechanisms were implemented to detect ions, [ 4 ] to follow pH changes, [ 5 ] and to detect molecular substrates, such as saccharides or neurotransmitters. [ 6 ] Similarly, QDs have been widely used for biosensing, and different luminescence sensors that follow the formation of antigen-antibody complexes, [ 7 ] DNA hybridization [ 8 , 9 ] and aptamer-substrate complexes [ 10 ] were reported. Also, QDs have been extensively used to follow biocatalytic transformations and to quantitatively probe the substrates of enzymes. [ 9 , 11 ] Here we wish to report on the use of chemically modifi ed CdSe/ZnS QDs as fl uorescent probes for the analysis of explosives, and specifi cally, the detection of trinitrotoluene (TNT) or trinitrotriazine (RDX). The QDs are functionalized with electron donating ligands that bind nitro-containing explosives, exhibiting electron acceptor properties, to the QDs surfaces, via supramolecular donor-acceptor interactions. The concentration of the explosive substrates at the QDs via the donor-acceptor complexes leads to the quenching of the luminescence of the QDs, thus allowing the quantitative analysis of the substrates. The sensitivities of the QDs sensors are controlled by the electron donating properties of the capping layer that modifi es the particles. The rapid and sensitive analysis of nitroaromatic explosives attracts substantial recent efforts, and different optical [ 12 ] or electrochemical [ 13 ] TNT or RDX sensors were reported. Other sensors for explosives include surface acoustic wave (SAW) systems, where piezoelectric crystal coated with absorbing materials such as carbowax [ 14 ] or cyclodextrin polymers, [ 15 ] were

Selenophosphate is the active selenium-donor compound required by bacteria and mammals for the specific synthesis of Secys-tRNA, the precursor of selenocysteine in selenoenzymes. Although free selenide can be used in vitro for the synthesis of selenophosphate, the actual physiological selenium substrate has not been identified. Rhodanese (EC 2.3.1.1) normally occurs as a persulfide of a critical cysteine residue and is believed to function as a sulfurdelivery protein. Also, it has been demonstrated that a seleniumsubstituted rhodanese (E-Se form) can exist in vitro. In this study, we have prepared and characterized an E-Se rhodanese. Persulfidefree bovine-liver rhodanese (E form) did not react with SeO 3 2؊ directly, but in the presence of reduced glutathione (GSH) and SeO 3 2؊ E-Se rhodanese was generated. These results indicate that the intermediates produced from the reaction of GSH with SeO 3 2؊ are required for the formation of a selenium-substituted rhodanese. E-Se rhodanese was stable in the presence of excess GSH at neutral pH at 37°C. E-Se rhodanese could effectively replace the high concentrations of selenide normally used in the selenophosphate synthetase in vitro assay in which the selenium-dependent hydrolysis of ATP is measured. These results show that a seleniumbound rhodanese could be used as the selenium donor in the in vitro selenophosphate synthetase assay.

Composite polymer particles consisting of a solid poly(acrolein-co-styrene) core and a poly (N-vinylcaprolactam) (PVCL) polymer shell doped with CdSe/ZnS semiconductor quantum dots (QDs) were fabricated. The temperature response of the composite particles was observed as a decrease in their hydrodynamic diameter upon heating above the lower critical solution temperature of the thermosensitive PVCL polymer. Embedding QDs in the PVCL shell yields particles whose fluorescence is sensitive to temperature changes. This sensitivity was determined by the dependence of the QD fluorescence intensity on the distances between them in the PVCL shell, which reversibly change as a result of the temperature-driven conformational changes in the polymer. The QD-containing thermosensitive particles were assembled with protein molecules in such a way that they retained their thermosensitive properties, including the completely reversible temperature dependence of their fluorescence response. The composite particles developed can be used as local temperature sensors, as carriers for biomolecules, as well as in biosensing and various bioassays employing optical detection schemes.

The accumulated organic form of selenium previously detected by X-ray absorption near-edge structure (XANES) analyses in Cupriavidus metallidurans CH34 exposed to selenite or selenate was identified as seleno-L-methionine by coupling high-performance liquid chromatography to inductively coupled plasma-mass spectrometry.

Amending soils with Se-hyperaccumulator plant derived sources of selenium (Se) may be useful for increasing the Se content in food crops in Se-deficient regions of the world. In this study we evaluated total Se and the different chemical species of Se in broccoli and carrots grown in soils amended with ground shoots of the Se-hyperaccumulator Stanleya pinnata. With increasing application rates of S. pinnata, total plant Se concentrations increased to nutritionally ideal levels inside edible parts. Selenium compounds in aqueous extracts were analyzed by SAX-HPLC-ICPMS and identified as a variety of mainly organic-Se forms. Together with bulk Se K-edge X-ray absorption near-edge structure (XANES) analysis performed on broccoli florets, carrot roots and shoots, dried ground S. pinnata, and the amended soil at post-plant, we demonstrate that Se-enriched S. pinnata is valuable as a soil amendment for enriching broccoli and carrots with healthful forms of organic-Se.

Using amino-acid histidine as chelating agent, CdS nanoparticles have been synthesized by sonochemical method. It is found that by varying the ultrasonic irradiation time, we can tune the band gap and particle size of CdS nanoparticles. The imidazole ring of histidine captures the Cd ions from the solution, and prevents the growth of the CdS nanoparticles. The deviation in the linear relation in between cube of radius of nanoparticles and ultrasonic irradiation time confirms the growth of CdS nanoparticles occur via two process; one is the diffusion process of the reactants as well as reaction at the surface of the crystallite. CdS nanoparticles synthesized using histidine as organic chelating agent have band edge emission at ∼481 nm and have greater photoluminescence intensity with blue-shift to higher energy due to typical quantum confinement effect.

ZnO nanowires (NWs) with a ZnS coating are synthesized in order to modify the surface without changing the diameter of the NWs. They have the wurtzite ZnO at the core and a cubic ZnS at the outer layer. The NWs show a sharp ultraviolet and a broad visible emission of the photoluminescence spectra. Surface modification has led to a change in the position of the maxima of the visible emission in ZnO-ZnS NWs. The photocarrier relaxation under steady UV illumination occurs in ZnO NW arrays but is absent in ZnO-ZnS NW arrays. The dark current value for both type of NWs are similar, whereas the photocurrent value is much higher in the surface-modified NWs. Higher photocurrent value indicates a transport of the photogenerated carriers from the ZnS layer to ZnO during UV illumination. The carrier transport mechanism is proposed through a model.

Selenium is a set of different programming apparatuses each with an alternate way to deal with supporting test automation. Most Selenium online training QA Engineers center around a couple of apparatuses that must address the issues of their venture, anyway adapting every one of the instruments will give you various different for moving toward various test automation issues.

We describe six patients who developed orange to redbrown scalp discoloration after application of selenium sulfide-containing shampoos. This phenomenon has been described only once previously. In all of the cases, the discoloration resolved shortly after discontinuing the selenium sulfide. Lightly swabbing with isopropyl alcohol facilitated removal of the discoloration. This simple technique serves as a painless diagnostic method, which may prevent unnecessary evaluation with a biopsy.

We present in this work a novel application of constant pressure molecular dynamics method (MD) that allows shape variation of MD cells. The new pressostat method, based on metric-tensor flexiblecell algorithm that has patched the drawbacks of the original P-R algorithm, is extended to address the long range charge-charge interaction in ionic systems by combining its usage with the Ewald summation method. It can reflect the underlying oscillation of the MD cells by releasing the constraint of fixed shape of the simulation box, which was not resolved successfully by other methods previously. We also show that when equipped with the Nose-Poincare thermostat algorithm, the new method can properly describe the evolution of the system in isothermal-isobaric (NPT) ensemble. The reliability of the new method is verified by the results from its application on solid NaCl at given temperatures and pressures. Other applications on the phase transition of ZrO 2 from tetragonal to cubic reveals that the effective axial ratio of a + b /2c changes from 0.922 to 1, showing a good match to that from experimental measurement. The new algorithm has potential applications to other ionic systems to obtain various material properties.

Quantum dots (QDs) are one of the first nanotechnologies to be integrated with the biological sciences that used for imaging or tracking macromolecules/cells in cell/tissue. Because of QDs are important in biomedical and biological applications, identify a variety of synthesis methods to produce QDs with different characteristics also is particularly important. Hence, in this review the authors discussed three methods for synthesis of heavy metal chalcogenide-based QDs for use in biomedical field: (i) Organometallic method for synthesis of QDs consists of three components: precursors, organic surfactants and solvents. The authors also discussed water-solubilisation strategies of synthesised QDs including encapsulation and ligand exchange. (ii) Aqueous synthesis technique using short-chain thiols as stabilising agents is a useful alternative to organometallic synthesis of CdSe, CdS and CdTe QDs. (iii) The third method discussed in this article for QDs synthesis involves the utilise of microorganisms to prepare QDs with controlled size, shape, chemical composition and functionality. The authors also discussed recently new methods for the synthesis of the appropriate QDs for use in biology. In addition, attachment of biomolecules such as antibodies, oligonucleotides on the surface of QDs for specific targeting and different opinions about toxicity of QD have been studied.

Heat stress is associated with compromised performance and productivity in poultry due to declines in feed intake, nutrient utilization, growth rate, egg production and quality, and feed efficiency. Emerging evidences have shown that acute heat exposure results in increased production of free radicals and causes oxidative damage to lipids, proteins, and DNA. Additionally, heat stress can influence immune response by changing the expression of cytokines and by making the immune cells more susceptible to oxidative stress. Selenium, as a part of specific selenoproteins, can help to maintain antioxidant defenses, thereby preventing damages to tissues. An optimum response with supplementation of selenium in diet has been found to improve feed intake, body weight gain, feed efficiency, egg production and quality, and antioxidant status in heat-stressed poultry. Selenium compounds are also known to improve immune responses by altering the production of certain cytokines secreted by cells of the immune system and by enhancing the resistance of the immune cells to oxidative stress. It was reported that selenium supplementation had inhibitory effects on tumor necrosis factor alpha levels in heat-stressed broiler chicks, but the details are not completely elucidated. In the present review, the effect of selenium on production performance, nutrient utilization, antioxidative status, and immune responses of heat-stressed poultry is summarized.

Background: With cancer cells encompassing consistently higher production of reactive oxygen species (ROS) and with an induced antioxidant defense to counteract the increased basal ROS production, tumors have a limited reserve capacity resulting in an increased vulnerability of some cancer cells to ROS. Based on this, oxidative stress has been recognized as a tumor-specific target for the rational design of new anticancer agents. Among redox modulating compounds, selenium compounds have gained substantial attention due to their promising chemotherapeutic potential. Scope of review: This review aims in summarizing and providing the recent developments of our understanding of the molecular mechanisms that underlie the potential anticancer effects of selenium compounds. Major conclusions: It is well established that selenium at higher doses readily can turn into a prooxidant and thereby exert its potential anticancer properties. However, the biological activity of selenium compounds and the mechanism behind these effects are highly dependent on its speciation and the specific metabolic pathways of cells and tissues. Conversely, the chemical properties and the main molecular mechanisms of the most relevant inorganic and organic selenium compounds as well as selenium-based nanoparticles must be taken into account and are discussed herein. General significance: Elucidating and deepening our mechanistic knowledge of selenium compounds will help in designing and optimizing compounds with more specific antitumor properties for possible future application of selenium compounds in the treatment of cancer. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Selenium (Se) is an essential dietary component for animals including humans and is regarded as a protective agent against cancer. Although the mode of anticancer action of Se is not fully understood yet, several mechanisms, such as antioxidant protection by selenoenzymes, specific inhibition of tumor cell growth by Se metabolites, modulation of cell cycle and apoptosis, and effect on DNA repair have all been proposed. Despite the unsupported results of the last SELECT trial, the cancer-preventing activity of Se was demonstrated in majority of the epidemiological studies. Moreover, recent studies suggest that Se has a potential to be used not only in cancer prevention but also in cancer treatment where in combination with other anticancer drugs or radiation, it can increase efficacy of cancer therapy. In combating cancer cells, Se acts as pro-oxidant rather than antioxidant, inducing apoptosis through the generation of oxidative stress. Thus, the inorganic Se compound, sodium selenite (SeL), due to its prooxidant character, represents a promising alternative for cancer therapy. However, this Se compound is highly toxic compared to organic Se forms. Thus, the unregulated intake of dietary or pharmacological Se supplements mainly in the form of SeL has a potential to expose the body tissues to the toxic levels of Se with subsequent negative consequences on DNA integrity. Hence, due to a broad interest to exploit the positive effects of Se on human health and cancer therapy, studies investigating the negative effects such as toxicity and DNA damage induction resulting from high Se intake are also highly required. Here, we review a role of Se in cancer prevention and cancer therapy, as well as mechanisms underlying Se-induced toxicity and DNA injury. Since Saccharomyces cerevisiae has proven a powerful tool for addressing some important questions regarding Se biology, a part of this review is devoted to this model system.

The biological profile of sodium selenosulfate, Na(2)SeSO(3), is still largely unknown. The present study found that sodium sulfite reacted with elemental selenium at nanoparticle size already at 37 degrees C to yield sodium selenosulfate. Additionally, selenosulfate was obtained by mixing sodium selenite, glutathione, and sodium sulfite at room temperature. In vitro, sodium selenosulfate killed HepG2 or Caco2 cells, in a dose-dependent fashion, and 12.5 microM fully suppressed their proliferation. In addition, sodium selenosulfate showed a consistent cytotoxic effect when added to three kinds of leukemia cell lines (HL60, T lymph adenoma, and Daudi).

Selenium (Se) is an essential trace element involved in different physiological functions of the human body and plays a role in cancer prevention and treatment. Induction of apoptosis is considered an important cellular event that can account for the cancer preventive effects of Se. The mechanisms of Se-induced apoptosis are associated with the chemical forms of Se and their metabolism as well as the type of cancer studied. So, some selenocompounds, such as SeO 2 involve the activation of caspase-3 while sodium selenite induces apoptosis in the absence of the activation of caspases. Modulation of mitochondrial functions has been reported to play a key role in the regulation of apoptosis and also to be one of the targets of Se compounds. Other mechanisms for apoptosis induction are the modulation of glutathione and reactive oxygen species levels, which may function as intracellular messengers to regulate signaling pathways, or the regulation of kinase, among others. Emerging evidence indicates the overlaps between the apoptosis and other types of cell death such as autophagy. In this review we report different processes of cell death induced by Se compounds in cancer treatment and prevention.

Quantum dots (QDs) coupled into disordered arrays have exhibited the intriguing property of bulk-like transport while maintaining discrete excitonic optical transitions. We have utilized ultrafast cross-polarized transient grating (CPTG) spectroscopy to measure electron−hole wave function overlap in CdSe QD films with chemically modified surfaces for tuning inter-QD electronic coupling. By comparing the CPTG decays with those of isolated QDs, we find that excitons coherently delocalize to form excited states more than 200% larger than the QD diameter.

The uptake of selenite, selenate and selenomethionine (SeMet) was performed with brush border membrane vesicles (BBMV) prepared from rats fed selenium-deficient and supplemented diets. At equilibrium (60 min), the uptake of 75Se from [TSSe]selenite ranged from 16.5 to 18.9 nmoimg-1 protein. There was a curvilinear relationship in the uptake of selenite over a concentration range of 10-1000/~. About 2 nmoi mg-1 protein was obtained with selenomethionine (SeMet) which occurred between 90 and 180 s. In contrast to selenite, there was a linear relationship in the initial uptake of SeMet over a concentration range of 10-1000/t~. The uptake of selenate was approximately 50-fold lower than selenite, reaching 350 pmol mg-1 protein. Dietary selenium level had no effect on the rate of 75Se accumulation by BBMV. Dramatic differences are found in the uptake and binding of selenium by BBMV incubated with different selenocompounds.

The main theme of this chapter concerns the precise biochemical mechanisms involved in stages up to, and including, gastrointestinal absorption of vitamins and certain selected minerals. Essential data regarding sequential events, immediately following absorption of these micronutrients, are also included. There is reference to water-soluble vitamins that are, in general, either coenzymes in various metabolic reactions or carriers of certain biochemical groupings. In contrast, fat-soluble vitamins frequently function as integral components of cell membranes; they, too, receive ample attention. It is appropriate, nevertheless, to recognize that some minerals required in very small amounts are closely allied biochemically with particular vitamins; these specific associations are apportioned emphasis at relevant places in the text. Although predominant discussion centres on the physiological state, clinical reference is necessarily made to gastrointestinal disorders in which imbalance of vitamins and minerals consequently results in an additional detrimental impact on health. the vitamins, together with a select group of inorganic elements and the factors that, in turn, modify them.

A simple, efficient, and eco-friendly synthetic protocol has been developed for the preparation of diaryl selenium compounds. To the best of our knowledge, this is the first Letter on the use of selenium dioxide as selenium source for the synthesis of diaryl selenides. Compared with other selenium sources the new source SeO 2 gives an environment-friendly and low-cost synthetic route, which may be useful for large-scale synthesis.

Hydrophobic-interaction chromatography coupled on-line with chemical-vapor-generation atomicfluorescence spectrometry (HIC-CVGAFS), optimized recently for the analysis of thiol-containing proteins under denaturing conditions, has been used to study the chemical reduction of denatured proteins. Four proteins chosen as models (human serum albumin (HSA), bovine serum albumin (BSA), a-lactalbumin (a-Lac) from bovine milk, and lysozyme from chicken egg (Lys)) were denatured with urea and reduced with dithiothreitol (DTT), with selenol as catalyst. The method is based on derivatization of the -SH groups of proteins with p-hydroxymercurybenzoate (PHMB), followed by HIC separation and post-column on-line reaction of the derivatized reduced, denatured proteins with bromine generated in situ. Hg II , derived from rapid conversion of uncomplexed and protein-complexed PHMB, is selectively detected by AFS in an Ar/H 2 miniaturized flame after sodium borohydride (NaBH 4 ) reduction to Hg°. The yield of the reduction was studied as a function of reductant concentration, reduction time (t red ), and urea concentration. Results showed that the optimum values for DTT and selenol concentrations and for t red were between 1 and 100 mmol L À1 and between 1 and 20 min, respectively, depending on the protein studied. The percentage disulfide bond reduction increases as the urea concentration used for protein denaturation increases, giving a single-step sigmoid increment for single-domain, low-MW proteins (a-Lac and Lys), and a two-step sigmoid increment for multi-domain, high MW proteins (HSA and BSA). The shapes of plots of percentage reduced disulfide against urea concentration are characteristic of each protein and are correlated with the location of S-S in the protein. Under the adopted conditions complete protein denaturation is the conditio sine qua non for obtaining 100% S-S reduction. The detection limit for denatured, reduced proteins examined under the optimized conditions was found to be in the range 1-5·10 À12 mol L À1 (10-30 pg), depending on the protein considered.

Inhibition of intestinal a-glucosidases and pancreatic a-amylases is an approach to controlling blood glucose and serum insulin levels in individuals with Type II diabetes. The two human intestinal glucosidases are maltase-glucoamylase and sucrase-isomaltase. Each incorporates two family 31 glycoside hydrolases responsible for the final step of starch hydrolysis. Here we compare the inhibition profiles of the individual N-and C-terminal catalytic subunits of both glucosidases by clinical glucosidase inhibitors, acarbose and miglitol, and newly discovered glucosidase inhibitors from an Ayurvedic remedy used for the treatment of Type II diabetes. We show that features of the compounds introduce selectivity towards the subunits. Together with structural data, the results enhance the understanding of the role of each catalytic subunit in starch digestion, helping to guide the development of new compounds with subunit specific antidiabetic activity. The results may also have relevance to other metabolic diseases such as obesity and cardiovascular disease.

We present in this work a novel application of constant pressure molecular dynamics method (MD) that allows shape variation of MD cells. The new pressostat method, based on metric-tensor flexiblecell algorithm that has patched the drawbacks of the original P-R algorithm, is extended to address the long range charge-charge interaction in ionic systems by combining its usage with the Ewald summation method. It can reflect the underlying oscillation of the MD cells by releasing the constraint of fixed shape of the simulation box, which was not resolved successfully by other methods previously. We also show that when equipped with the Nose-Poincare thermostat algorithm, the new method can properly describe the evolution of the system in isothermal-isobaric (NPT) ensemble. The reliability of the new method is verified by the results from its application on solid NaCl at given temperatures and pressures. Other applications on the phase transition of ZrO 2 from tetragonal to cubic reveals that the effective axial ratio of a + b /2c changes from 0.922 to 1, showing a good match to that from experimental measurement. The new algorithm has potential applications to other ionic systems to obtain various material properties.

Interest in taking advantage of the unique spectral properties of semiconductor quantum dots (QDs) has driven their widespread use in biological applications such as in vitro cellular labeling/imaging and sensing. Despite their demonstrated utility, concerns over the potential toxic effects of QD core materials on cellular proliferation and homeostasis have persisted, leaving in question the suitability of QDs as alternatives for more traditional fluorescent materials (e.g., organic dyes, fluorescent proteins) for in vitro cellular applications. Surprisingly, direct comparative studies examining the cytotoxic potential of QDs versus these more traditional cellular labeling fluorophores remain limited. Here, using CdSe/ZnS (core/shell) QDs as a prototypical assay material, we present a comprehensive study in which we characterize the influence of QD dose (concentration and incubation time), QD surface capping ligand and delivery modality (peptide or cationic amphiphile transfection r...

The electronic structure of CdSe/CdS core/shell seeded nanorods of experimentally relevant size is studied using a combination of molecular dynamics and semiempirical pseudopotential techniques, with the aim to address the transition from type-I to a quasi-type-II band alignment. The hole is found to be localized in the core region regardless of its size. The overlap of the electron density with the core region depends markedly on the size of the CdSe core: For small cores, we observe little overlap, consistent with type-II behavior. For large cores, significant core-overlap of a number of excitonic states can lead to type-I behavior. When electron-hole interactions are taken into account, the core-overlap is further increased. Our calculations indicate that the observed transition from type-II to type-I is largely due to simple volume effects, and not to band alignment.

The synthesis and cytotoxic activity of a series of twenty six aroyl and heteroaroyl selenylacetic acid derivatives of general formula Ar-CO-Se-CH 2 -COOH or Heterar-CO-Se-CH 2 -COOH are reported. The synthesis was carried out by reaction of acyl chlorides with sodium hydrogen selenide, prepared in situ, and this led to the formation of sodium aroylselenides that subsequently reacted with α-bromoacetic acid to produce the corresponding selenylacetic acid derivatives. All of the compounds were tested against a prostate cancer cell line (PC-3) and some of the more active compounds were assessed against a panel of four human cancer cell lines (CCRF-CEM, HTB-54, HT-29, MCF-7) and one mammary gland-derived non-malignant cell line (184B5). Some of the compounds exhibited remarkable cytotoxic and antiproliferative activities against MCF-7 and PC-3 that were higher than those of the reference compounds doxorubicin and etoposide, respectively. For example, in MCF-7 when Ar = phenyl, 3,5-dimethoxyphenyl or benzyl OPEN ACCESS Molecules 2009, 14 3314

The use of a separation step, such as liquid chromatography, prior to inductively coupled plasma mass spectrometry (ICP-MS) has become a common tool for highly selective and sensitive analyses. This type of coupling has several benefits including the ability to perform speciation analysis or to remove isobaric interferences. Several limitations of conventional instruments result from the necessity to scan or pulse the mass spectrometer to obtain a complete mass spectrum. When the instrument is operated in such a non-continuous manner, duty cycle is reduced, resulting in poorer absolute limits of detection. Additionally, with scanning instruments, spectral skew can be introduced into the measurement, limiting quantitation accuracy. To address these shortcomings, a high-performance liquid chromatograph has been coupled to an ICP-MS capable of continuous sample introduction and simultaneous multimass detection. These features have been realized with a novel detector array, the focal plane camera. Instrument performance has been tested for both speciation analysis and for the elimination of isobaric interferences. Absolute limits of detection in the sub picogram to tens of picograms regime are obtainable, while the added mass dimension introduced by simultaneous detection dramatically increases chromatographic peak capacity.

BACKGROUND: We investigated the effects of the foliar and fruit application of sodium selenate on selenium (Se) accumulation, fruit growth and ripening in peach and pear. Trials were conducted in two growing seasons. In 2008 selenate was applied at a rate of 0.1 and 1.0 mg Se L −1 to the leaves of peach. In 2009 selenate was applied at a rate of 1 mg Se L −1 via foliar (LT) or fruit (FT) application to peach and pear.

Batch experiments were conducted to investigate the removal of selenocyanate (SeCN À ) from oil refinery wastewater and artificial wastewater with elemental iron [Fe ]. The chemical forms of selenium in the reacted solids were determined with X-ray photoelectron spectroscopy (XPS) and a sulfite extraction procedure. SeCN À was effectively removed from the wastewater with Fe(0) filings when the water pH was controlled at approximately 6. SeCN À was removed by Fe(0) through the formation of elemental selenium [Se(0)] and ferrous selenide. The possible chemical reactions between SeCN À and Fe(0) included deselenation of SeCN À and electrochemical reduction of Se(0) to selenide. A cost-effective process may be developed for the treatment of SeCN À in wastewater using Fe(0). r

We developed a new peptide, natural phytochelatin (PC), which tightly binds to CdSe/ZnS quantum dots' (QDs) surfaces and renders them water-soluble. Coating QDs with this flexible and all-hydrophilic peptide offers high colloidal stability, adds only 0.8−0.9 nm to the radius of the particles (as compared to their original inorganic radius), preserves very high quantum yield (QY) in water, and affords facile bioconjugation with various functional groups. We demonstrate specific targeting (with minimal nonspecific binding) of such fluorescein-conjugated QDs to ScFv-fused mouse prion protein expressed in live N2A cells. We also demonstrated homogeneous in vivo biodistribution with no significant toxicity in live zebrafish.

Naturally occurring selenium compounds like selenite and selenodiglutathione are metabolized to selenide in plants and animals. This highly reactive form of selenium can undergo methylation and form monomethylated and multimethylated species. These redox active selenium metabolites are of particular biological and pharmacological interest since they are potent inducers of apoptosis in cancer cells. The mammalian thioredoxin and glutaredoxin systems efficiently reduce selenite and selenodiglutathione to selenide. The reactions are non-stoichiometric aerobically due to redox cycling of selenide with oxygen and thiols. Using LDI-MS, we identified that the addition of S-adenosylmethionine (SAM) to the reactions formed methylselenol. This metabolite was a superior substrate to both the thioredoxin and glutaredoxin systems increasing the velocities of the nonstoichiometric redox cycles three-fold. In vitro cell experiments demonstrated that the presence of SAM increased the cytotoxicity of selenite and selenodiglutathione, which could neither be explained by altered selenium uptake nor impaired extra-cellular redox environment, previously shown to be highly important to selenite uptake and cytotoxicity. Our data suggest that selenide and SAM react spontaneously forming methylselenol, a highly nucleophilic and cytotoxic agent, with important physiological and pharmacological implications for the highly interesting anticancer effects of selenium.

We report a facile production of an up-converted surface-emitting DFB laser, performed by exploiting the versatility of sol-gel chemistry, the intriguing properties of well designed graded CdSe-CdS-Cd 0.5 Zn 0.5 S-ZnS colloidal quantum dots, and the scalability of nanoimprinting. Our laser prototype operates in the visible region following efficient optical pumping by either direct one-photon excitation or through the up-conversion of near infrared (NIR) light. By achieving cavity mode Q-factors in excess of 650 and retaining high lasing stabilities in air, this work highlights the feasibility of creating integrated lasing devices through solution based methods.

A slow growth in size at the early stages of reaction, together with a period of zero growth in size and size distribution is observed via monitoring the temporal evolution of the optical properties of the growing CdSe nanocrystals from reaction media consisting of tri-n-octylphosphine (TOP). The synthetic approach is as simple as a swift injection of a TOPSe/TOP solution into a Cd-source/TOP solution at 300 1C with subsequent growth at 250 1C. The various Cd sources investigated are cadmium acetate (Cd(Ac) 2 ), cadmium oxide (CdO)/tetradecylphosphonic acid (TDPA), CdO, and CdO/oleylamine (OLA). With these various Cd sources studied, CdO with a 4Cd-to-1Se stoichiometry demonstrates its suitability for high-quality and large-scale production, due to a slow growth in size (less than 17 nm redshift of bandgap absorption and emission) and size distribution, as well as fairly constant photoluminescent properties of the growing nanocrystals during the 0.5-60 min growth time. r 2005 Published by Elsevier B.V.

We present results of the studies relating to preparation of Langmuir−Blodgett (LB) monolayers of tri-n-octylphosphine oxide-capped cadmium selenide quantum dots (QCdSe) onto indium−tin oxide (ITO) coated glass substrate. The monolayer behavior has been studied at the air−water interface under various subphase conditions. This nanopatterned platform has been explored to fabricate an electrochemical DNA biosensor for detection of chronic myelogenous leukemia (CML) by covalently immobilizing the thiolterminated oligonucleotide probe sequence via a displacement reaction. The results of electrochemical response studies reveal that this biosensor can detect target DNA in the range of 10 −6 to 10 −14 M within 120 s, has a shelf life of 2 months, and can be used about 8 times. Further, this nucleic acid sensor has been found to distinguish the CML-positive and the control negative clinical patient samples.

Neurological disorders are common, costly, and can cause enduring disability. Although mostly unknown, a few environmental toxicants are recognized causes of neurological disorders and subclinical brain dysfunction. One of the best known neurotoxins is methylmercury (MeHg), a ubiquitous environmental toxicant that leads to long-lasting neurological and developmental deficits in animals and humans. In the aquatic environment, MeHg is accumulated in fish, which represent a major source of human exposure. Although several episodes of MeHg poisoning have contributed to the understanding of the clinical symptoms and histological changes elicited by this neurotoxicant in humans, experimental studies have been pivotal in elucidating the molecular mechanisms that mediate MeHg-induced neurotoxicity. The objective of this mini-review is to summarize data from experimental studies on molecular mechanisms of MeHg-induced neurotoxicity. While the full picture has yet to be unmasked, in vitro approaches based on cultured cells, isolated mitochondria and tissue slices, as well as in vivo studies based mainly on the use of rodents, point to impairment in intracellular calcium homeostasis, alteration of glutamate homeostasis and oxidative stress as important events in MeHg-induced neurotoxicity. The potential relationship among these events is discussed, with particular emphasis on the neurotoxic cycle triggered by MeHg-induced excitotoxicity and oxidative stress. The particular sensitivity of the developing brain to MeHg toxicity, the critical role of selenoproteins and the potential protective role of selenocompounds are also discussed. These concepts provide the biochemical bases to the understanding of MeHg neurotoxicity, contributing to the discovery of endogenous and exogenous molecules that counteract such toxicity and provide efficacious means for ablating this vicious cycle.

The rational design and synthesis of CdSe/CdTe/ZnTe (core-shell-shell) type-II quantum dots are reported. Their photophysical properties are investigated via the interband CdSe!ZnTe emission and its associated relaxation dynamics. In comparison to the strong CdSe (core only) emission (l max % 550 nm, F f % 0.28), a moderate CdSe!CdTe emission (l max % 1026 nm, F f % 1.2 10 À3 ) and rather weak CdSe!ZnTe interband emission (l max % 1415 nm, F f % 1.1 10 À5 ) are resolved for the CdSe/CdTe/ ZnTe structure (3.4/1.8/1.3 nm). Capping CdSe/CdTe with ZnTe results in a distant electron-hole separation between CdSe (electron) and ZnTe (hole) via an intermediate CdTe layer. In the case of the CdSe/CdTe/ ZnTe structure, a lifetime as long as 150 ns is observed for the CdSe! ZnTe (1415 nm) emission. This result further indicates an enormously long radiative lifetime of % 10 ms. Upon excitation of the CdSe/CdTe/ ZnTe structure, the long-lived charge separation may further serve as an excellent hole carrier for catalyzing the redox oxidation reaction.

Rice (Oryza sativa) is the staple food for half of the world's population, but the selenium (Se) concentrations in rice grain are low in many rice-growing regions. This study investigated the effects of water management on the Se speciation dynamics in the soil solution and Se uptake and speciation in rice in a pot experiment. A control containing no Se or 0.5 mg kg -1 of soil of selenite or selenate was added to the soil, and plants were grown under aerobic or flooded conditions. Flooding soil increased soluble Se concentration when no Se or selenite was added to the soil, but decreased it markedly when selenate was added. Selenate was the main species in the þselenate treatment, whereas selenite and selenomethionine selenium oxide were detected in the flooded soil solutions of the control and þselenite treatments. Grain Se concentration was 49% higher in the flooded than in the aerobic treatments without Se addition. In contrast, when selenate or selenite was added, the aerobically grown rice contained 25-and 2-fold, respectively, more Se in grain than the anaerobically grown rice. Analysis of Se in rice grain using enzymatic hydrolysis followed by HPLC-ICP-MS and in situ X-ray absorption near-edge structure (XANES) showed selenomethionine to be the predominant Se species. The study showed that selenate addition to aerobic soil was the most effective way to increase Se concentration in rice grain.

A triple responsive nanogel was prepared by the crosslinking of poly (ethylene glycol)-b-poly(l-glutamic acid-co-γ-2-chloroethyl-l-glutamate) (mPEG-b-P(LG-co-CELG)) micelle using the dual redox responsive diselenide bond. Preliminary MTT assay and doxorubicin (DOX) release studies revealed that the nanogel was biocompatible and the DOX release could be accelerated by glutathione (GSH), rendering this nanogel's potential application as intracellular drug carrier.

Background/Purpose: Selenium is a required micronutrient in mammals, needed for the activity of enzymes that contain selenocysteine at their active site. Several isoenzymes of glutathione peroxidase and thioredoxin reductase contain selenocysteine and thus the nutritional status of selenium in tissues can have significant impact on the steady state level of reactive oxygen species. The aims of this study were to evaluate the bioavailability of selenium derived from the selenotrisulfide derivative of lipoic acid (LASe) and determine the ability of this compound to be absorbed into skin. Methods: Bioavailability of selenium derived from LASe was determined using a keratinocyte cell model (HaCat). Efficiency of utilization of selenium was assessed by following the decrease in the incorporation of radiolabeled selenite ( 75 Se) in the presence of increasing concentration of selenium compounds. Percutaneous absorption of LASe was measured by de-termining selenium levels in full thickness biopsy of skin using a Yorkshire pig model. Results: LASe was efficiently absorbed topically into pig skin, a good model of human skin. In a keratinocyte cell line LASe was an efficient source of selenium for selenoprotein synthesis, demonstrating that LASe is a good candidate as a topical selenium micronutrient. Both L-selenomethionine and selenate were found to be poor sources of selenium for selenoprotein synthesis in the skin cell model and L-selenomethionine was poorly absorbed into pig skin. Conclusion: These results indicate that stable selenotrisulfides, such as LASe, are good candidates for testing as topical selenium supplements.

Wet chemical methods such as sequential extraction procedures are commonly used to assess selenium fractionation in anoxic environments, allowing an estimation of the mobility and bioavailability of selenium. However, the interpretation can be biased by unselective extraction of targeted species and artifacts introduced during the extraction. Here, the selectivity of the single extraction steps to gain reliable selenium speciation information are scrutinized for the first time by direct, nondestructive X-ray absorption near edge structure (XANES) spectroscopy at the selenium K-edge. The sequential extraction procedures seriously overestimated the elemental selenium fraction, as major parts (58%) of the total selenium were present as metal selenides and organic selenium compounds, although extracted in the elemental fraction. Spectral fitting of the XANES spectra by the least-squares linear combinations utilizing a large set of model compounds, including previously neglected Se(-I) selenides, showed a novel degree of complexity in the speciation of selenium treating anaerobic biofilms, with up to 4 modeled selenium species contributing to the speciation, i.e., different elemental, organic, and metalbound selenium species. Furthermore, a short exposure (10 min) to ambient air during the sequential extraction procedure induced the oxidation of organic selenium compounds, revealing the fragility of selenium speciation in anaerobic biofilms.