Incorporation Of Se Research Articles

Voyage of selenium from environment to life: Beneficial or toxic?

Selenium (Se), a naturally occurring metalloid, is an essential micronutrient for life as it is incorporated as selenocysteine in proteins. Although beneficial at low doses, Se is hazardous at high concentrations and poses a serious threat to various ecosystems. Due to this contrasting 'dual' nature, Se has garnered the attention of researchers wishing to unravel its puzzling properties. In this review, we describe the impact of selenium's journey from environment to diverse biological systems, with an emphasis on its chemical advantage. We describe the uneven distribution of Se and how this affects the bioavailability of this element, which, in turn, profoundly affects the habitat of a region. Once taken up, the subsequent incorporation of Se into proteins as selenocysteine and its antioxidant functions are detailed here. The causes of improved protein function due to the incorporation of redox-active Se atom (instead of S) are examined. Subsequently, the reasons for the deleterious effects of Se, which depend on its chemical form (organo-selenium or the inorganic forms) in different organisms are elaborated. AlthoughSe is vital for the function of many antioxidant enzymes, how the pro-oxidant nature of Se can be potentially exploited in different therapies is highlighted. Furthermore, we succinctly explain how the presence of Se in biological systems offsets the toxic effects of heavy metal mercury. Finally, the different avenues of research that are fundamental to expand our understanding of selenium biology are suggested.

Clickable Selenylation - a Paradigm for Seleno-Medicinal Chemistry.

Selenium (Se) is an emerging versatile player in medicinal chemistry. The incorporation of Se into small molecules and natural products could have multiple benefits. However, the lack of efficient methods for the synthesis of Se-containing chemical library has greatly hindered the development of seleno-medicinal chemistry. With the aim to address this issue, we proposed the development of "clickable selenylation" reactions, which can be used in the synthesis of Se-containing in situ library and DNA-encoded library (SeDEL), thereby quickly producing ultra-large collections of Se-containing compounds and boosting the development of seleno-medicinal chemistry. This research paradigm can be concluded as "clickable selenylation chemistry development→in situ library construction/SeDEL synthesis→phenotype- or target-based screening→seleno-hit compound".

Monosaccharide composition and in vivo immuno-stimulatory potential of soluble yam (Dioscorea opposita Thunb.) polysaccharides in response to a covalent Se incorporation

The present study aimed to investigate whether selenylation modification could affect compositional features and in vivo immuno-stimulatory potential of yam polysaccharides. In this study, the soluble yam mucilage polysaccharides (YPS) were prepared and selenylated in the HNO3-Na2SeO3 system, and two selenylated polysaccharide products, namely SeYPS-1 and SeYPS-2 with respective Se contents of 719 and 1585 mg/kg, were thus obtained. GC–MS analysis demonstrated that the compositional features of SeYPS-1 and SeYPS-2 were similar to those of YPS. Meanwhile, the immuno-stimulatory potential of the selenylated products, especially SeYPS-2, in the BALB/c mice model was higher than that of YPS, reflected by the elevated contents of serum immunoglobins and increased percentage of CD4+ splenic lymphocytes. It was thus confirmed that the selenylation did not change the composition of monosaccharides but endowed YPS with greater immuno-stimulation in the mice, while the higher extent of selenylation also caused a much enhanced immuno-stimulatory potential of SeYPS-2.

DFT and experimental investigations on CdTe1-xSex for thermoelectric and optoelectronic applications

The optical and electronic characteristics of CdTe-based semiconductors play an important role in modern optoelectronic devices. In the current study, pure and Se doped CdTe compositions were theoretically investigated through density functional theory within the framework of Wien2k code using a modified Becke–Johnson technique. Experimentally CdTe1−xSex (x = 0, 3.125 %, 6.25 %, and 12.5 %) uniform and evenly distributed thin films were successfully deposited through a chemically derived sol-gel-based spin coating technique. The morphological, electronic, thermoelectric, and optical properties were studied through comparative simulations and experimental investigations. Ab-initio and experimental results reveal the similarities and correlation among the findings. The experimental energy band gap was found to reduce from 1.84 eV for pure CdTe to 1.55 eV by incorporation of Se in the pristine CdTe structure. The thermoelectric response in terms of electrical conductivity, Seebeck coefficient, thermal conductivity, and specific heat was recorded and a significant variation was observed. The optical parameters show an enhanced trend in the visible regime with the incorporation of Se content in structure. Absorption coefficient and real epsilon were shown to a sharp increase with increment of Se content. The outcomes of this work are considered that Se containing CdTe composition are promising candidates for enhanced thermoelectric and optoelectronic applications.

Altering the high-temperature stability and thermoelectric properties of Cu1.8S thermoelectric materials by Se incorporation

Thermoelectric materials based on Cu 1.8 S are not hampered by electric-field-driven degradation in real applications, but their high-temperature applications are problematic owing to their tendency to oxidize or spontaneously decompose. Here, we reveal that Cu 1.8 S powder is gradually oxidized to form a mixture of Cu 2 O, Cu(SO 4 ), and Cu 2 O(SO 4 ) at high temperatures under air. Although a dense oxide film is formed on the surface of the sintered Cu 1.8 S block at high temperature, hindering the oxidation process, the brittle oxide film fails to inhibit the spontaneous decomposition of the Cu 1.8 S block into the Cu 1.96 S phase and S vapor at high temperatures. Thus, Cu 1.8 S thermoelectric materials are unsuitable for applications above 300 °C in air. To address this issue, we partially replaced S atoms with Se; the sintered Cu 1.8 S 0.8 Se 0.2 blocks exhibited significantly increased anti-oxidation and anti-decomposition capacities in air. In addition, we found that the thermoelectric figure of merit of the sintered Cu 1.8 S 0.8 Se 0.2 block was 47% higher than that of traditionally prepared, pure Cu 1.8 S at 450 °C. • The Cu 1.8 S block cannot function stably at temperatures over 300 °C. • The anti-oxidation and anti-decomposition capacities of the Cu 1.8 S 0.8 Se 0.2 are improved. • The ZT of the Cu 1.8 S 0.8 Se 0.2 is 117% higher than that of pure Cu 1.8 S at 450 °C.

Wide‐Gap Chalcopyrite Solar Cells with Indium Oxide–Based Transparent Back Contacts

Herein, the performance of wide‐gap Cu(In,Ga)Se2 (CIGS) and (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells with In2O3:Sn (ITO) and In2O3:H (IOH) as transparent back contact (TBC) materials is evaluated. Since both TBCs restrict sodium in‐diffusion from the glass substrate, fine‐tuning of a NaF precursor layer is crucial. It is found that the optimum Na supply is lower for ACIGS than for CIGS samples. An excessive sodium amount deteriorates the solar cell performance, presumably by facilitating GaO x growth at the TBC/absorber interface. The efficiency (η) further depends on the absorber stoichiometry, with highest fill factors (and η) reached for close‐stoichiometric compositions. An ACIGS solar cell with η = 12% at a bandgap of 1.44 eV is processed, using IOH as a TBC. The best CIGS device reaches η = 11.2% on ITO. Due to its very high infrared transparency, IOH is judged superior to ITO for implementation in a top cell of a tandem device. However, while ITO layers maintain their conductivity, IOH films show an increased sheet resistance after absorber deposition. Chemical investigations indicate that incorporation of Se during the initial stage of absorber processing may be responsible for the deteriorated conductivity of the IOH back contact in the final device.

Reduced Recombination and Improved Performance of CdSe/CdTe Solar Cells due to Cu Migration Induced by Light Soaking.

The performance of CdTe solar cells has advanced impressively in recent years with the incorporation of Se. Instabilities associated with light soaking and copper reorganization have been extensively examined for the previous generation of CdS/CdTe solar cells, but instabilities in Cu-doped Se-alloyed CdTe devices remain relatively unexplored. In this work, we fabricated a range of CdSe/CdTe solar cells by sputtering CdSe layers with thicknesses of 100, 120, 150, 180, and 200 nm on transparent oxide-coated glass and then depositing CdTe by close-spaced sublimation. After CdCl2 annealing, Cu-doping, and back metal deposition, a variety of analyses were performed both before and after light soaking to understand the changes in device performance. The device efficiency was degraded with light soaking in most cases, but devices fabricated with a CdSe layer thickness of 120 nm showed reasonably good efficiency initially (13.5%) and a dramatic improvement with light soaking (16.5%). The efficiency improvement is examined within the context of Cu ion reorganization that is well known for CdS/CdTe devices. Low-temperature photoluminescence data and Voc versus temperature measurements indicate a reduction in nonradiative recombination due to the passivation of defects and defect complexes in the graded CdSexTe1-x layer.

Unraveling the Conversion Evolution on Solid-State Na-SeS2 Battery via In Situ TEM.

All‐solid‐state (ASS) Na–S batteries are promising for a large‐scale energy‐storage system owing to numerous merits. However, the high conversion reaction barrier impedes their practical application. In this work, the basic mechanism on how Se catalyzes the conversion reaction in the Na–S batteries is unraveled. The sodiation/desodiation of Na–SeS2 nanobatteries are systematically evaluated via in situ transmission electron microscopy (in situ TEM) with a microheating device. The real‐time analyses reveal an amorphous Na–Se x S y intermediate phase appears during the direct conversion from SeS2 to Na2S, and a reverse reaction succeeds at 100 °C with a prior formation of Se. The absence of polysulfides and a much lower desodiation temperature in contrast to Na–S nanobatteries demonstrate that the Se incorporation significantly lowers the conversion reaction barrier. According to these findings, the ASS SeS2 batteries using a Na3SbS4 solid electrolyte (SE) are assembled using various SE:C ratios in the composite cathodes to investigate the effect of the ion and electron transport on the electrochemical properties, including the effective transport properties, MacMullin number, and the tortuosity factor. The obtained results in turn confirm the findings from the in situ TEM. These findings are applicable to optimize other S‐based active materials and improve their utilization.

Isotopic constraints on selenium degassing from basaltic magma and near-surface capture by fumarolic deposits: Implications for Se redistribution onto the Earth's surface

Volcanic emanations from cooling basaltic lava represent a diffuse and relatively poorly constrained source of metallic and non-metallic compounds to the Earth's surface. These compounds become incorporated in fumarolic minerals and redeposit at the surface of lava flows before entering the environmental cycle. The semi-volatile and chalcophile element selenium (Se) can be either vital or toxic to animals and humans. Thus, understanding the pathways of Se capture and relative concentrations in fumaroles is imperative for estimating their contributions to soils and aquifers in volcanically active regions, with implications for animal and human health. In this study, we report Se concentrations and Se stable isotope composition in a sample suite comprising degassed and undegassed basaltic rocks and various fumarolic deposits (thenardite, Na-K sulfate, gypsum, fluoride, and native sulfur) fed from degassing lava flows at Piton de la Fournaise volcano, Réunion Island. Erupted basaltic lavas (136–58 ng·g−1 Se) lost up to more than half of their pre-eruptive Se due to subaerial degassing and retained a heavier isotope composition (δ82/76Se = 0.11 ± 0.17‰, 2 s.d.) compared to less undegassed volcanic glass (138 ng·g−1 Se and δ82/76Se = −0.19 ± 0.04‰, 2 s.e.). Fumarolic deposits that formed over a temperature range of ~800–100 °C and captured Se from the degassing lava show higher to very high Se concentrations ranging from 0.54 μg·g−1 to 1578 μg·g−1 and significant Se isotope fractionation (δ82/76Se = +0.6 to −2.08‰). We propose two separate models that can explain the relative concentration and Se isotope composition of the deposits: 1) A compound oxidation state-dependent Se incorporation into the various fumarolic minerals, or 2) Temperature-dependent Rayleigh condensation from a cooling gas triggered by compound saturation. The Rayleigh condensation model can entirely explain the Se concentration and isotope composition of the fumaroles and predicts that up to 80% of the Se released from the lava is likely to be captured by precipitation to form solid phases within the lava pile, most dramatically in the coldest deposits below the sublimation temperature of SeO2 (< 315 °C). In contrast, mineral-dependent isotope pathways cannot fully explain our data, including the lighter Se isotope compositions in the more oxidized compounds compared to more reduced ones. Such a mineralogical effect cannot be excluded but further investigations and experimental studies are required in order to scrutinize and invoke its role. Finally, the environmental impact of these degassing-induced secondary products will be dependent on the relative compound water solubilities resulting in either Se mobilization towards aquifers or accumulation onto developing soils and plants. Such studies could prove useful for developing risk assessments in volcanically active regions on our planet, and for reaching a better understanding of the global continent-ocean Se isotope budget and signature.

Electrochemically stable, cost-effective and facile produced selenium@activated carbon composite counter electrodes for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs), as third generation photovoltaic technology, have been extensively investigated due to their numerous advantages, such as inexpensive and simple/fast preparation methods. As known, DSSCs are composed of different components. Counter electrode, which is one of the components, is an indispensable part of high-performance DSSCs. Designing new counter electrodes (CEs) with low cost and desired physical and electrochemical properties are important to achieve higher performance/stable DSSCs. In this sense, in this current report, new selenium@activated carbon (Se@AC) composites as alternative to expensive platinum (Pt) were produced by cost-effective and facile applied ball milling method, and used as CE in the DSSC architecture. Here, firstly, porous activated carbon (AC) was prepared from fruit peel wastes via chemical activation technique. Then the Se was incorporated into the structure of porous AC with different ratios to improve different physical and electrochemical properties of pristine AC. After Se incorporation strategy, the electro-catalytic activity and charge transfer parameters (RCT value decreased from 27.41 to 12.09 Ω cm2) of Se@AC composite CEs were significantly enhanced. The fabricated DSSC with a CE using Se@AC:3@5 showed a power conversion efficiency (PCE) value of 5.67% with current density (Jsc) of 13.26 mA/cm2, open-circuit voltage (Voc) of 648 mV and fill factor (FF) of 66%, which can acceptable close to the performance of the fabricated DSSC with the Pt-based CE (6.86%). The improvement electro-catalytic activity and charge transfer properties obtained with the low cost and facile production process could render the Se@AC composite CE standing out as an effective alternative to the precious/expensive Pt reference CE.

Controlling the Anionic Ratio and Gradient in Kesterite Technology.

Accurate anionic control during the formation of chalcogenide solid solutions is fundamental for tuning the physicochemical properties of this class of materials. Compositional grading is the key aspect of band gap engineering and is especially valuable at the device interfaces for an optimum band alignment, for controlling interface defects and recombination and for optimizing the formation of carrier-selective contacts. However, a simple and reliable technique that allows standardizing anionic compositional profiles is currently missing for kesterites and the feasibility of achieving a compositional gradient remains a challenging task. This work aims at addressing these issues by a simple and innovative technique. It basically consists of first preparing a pure sulfide absorber with a specific thickness followed by the synthesis of a pure selenide part of complementary thickness on top of it. Specifically, the technique is applied to the synthesis of Cu2ZnSn(S,Se)4 and Cu2ZnGe(S,Se)4 kesterite absorbers, and a series of characterizations are performed to understand the anionic redistribution within the absorbers. For identical processing conditions, different Se incorporation dynamics is identified for Sn- and Ge-based kesterites, leading to a homogeneous or graded composition in depth. It is first demonstrated that for Sn-based kesterite the anionic composition can be perfectly controlled through the thicknesses ratio of the sulfide and selenide absorber parts. Then, it is demonstrated that for Ge-based kesterite an anionic (Se–S) gradient is obtained and that by adjusting the processing conditions the composition at the back side can be finely tuned. This technique represents an innovative approach that will help to improve the compositional reproducibility and determine a band gap grading strategy pathway for kesterites. Furthermore, due to its simplicity and reliability, the proposed methodology could be extended to other chalcogenide materials.

The Influence of Aqueous Se(IV) on the Stability of Different CaCO3 Polymorphs Precipitated under Ambient Conditions

Selenium is an essential bio-element, but because of its bioaccumulation potential, it can become toxic and is an important pollutant. The ubiquitous mineral calcite (CaCO3) has the ability to immobilize anions as SeO32− by different sorption or coprecipitation processes. Experimental studies have found that SeO32− can incorporate in the crystal structure of calcite by substituting CO32−. The presence of foreign ions in aqueous solution strongly affects CaCO3 precipitation, helping stabilize less stable polymorphs such as vaterite and aragonite or hydrated phases. In this work, we studied the aging process of calcium carbonates precipitated from aqueous solutions highly supersaturated with respect to CaCO3 and slightly supersaturated with respect to CaSeO3·H2O under ambient conditions, for times up to 30 days in which solids were kept in the remaining aqueous solution. Under these conditions, CaCO3 precipitated mainly as low crystallinity vaterite aggregates that hosted up to 16% atomic ratio Se:C. Vaterite purified and increased its crystallinity with aging time, but the vaterite–calcite transformation was strongly inhibited. The incorporation of Se(IV) in vaterite did not significantly affect the cell parameters or the external morphology of the aggregates. The precipitation of selenite as CaSeO3·H2O was conditioned by the availability of free Ca2+ and SeO32− that was not previously incorporated into precipitated carbonates.

WSe2 growth on hafnium zirconium oxide by molecular beam epitaxy: the effect of the WSe2 growth conditions on the ferroelectric properties of HZO

Direct integration of transition metal dichalcogenides on a ferroelectric such as hafnium zirconium oxide (HZO) using an industrially scalable technique is important for realizing various ferroelectric-based device architectures. The interface formed due to the processing conditions during direct deposition is the focus of the current study. In this work, molecular beam epitaxy (MBE) is used to directly deposit WSe2 on HZO substrates, and the effects of the MBE growth conditions, specifically high temperature and a high Se flux, are examined. Anneals of HZO under a Se flux, which serve to replicate the conditions during actual WSe2 deposition, result in the crystallization of amorphous as-deposited HZO substrates and incorporation of Se into the HZO. The crystallinity and composition of the HZO substrates affect the degree of Se incorporation. Some of the Se found in the HZO is an adsorbed layer that can be thermally desorbed, but it also has a chemisorbed component fully incorporated within the HZO lattice. Measurement of the electrical properties of the HZO films did not provide evidence that the incorporated Se was detrimental to the functionality of the HZO as a ferroelectric layer.

A newly-explored Pd-based nanocrystal for the pH-universal electrosynthesis of H2O2

For the generation of hydrogen peroxide (H2O2), a robust electrocatalyst with high activity, selectivity and stability under pH-universal conditions is a formidable challenge. Herein, Pd4Se nanoparticles (NPs) have been proposed as a highly active, selective and durable electrocatalyst for H2O2 production over a wide pH range for the first time. In particular, the Pd4Se NPs show superior H2O2 production selectivities of 93.5%, 89.7%, and 86.7% in 0.1 M HClO4, 0.1 M KCl and 0.1 M KOH electrolytes, respectively. Density functional theory (DFT) calculations reveal that Se incorporation prevents the OO early-cleavage issue by suppressing the excessive electronegativity of the Pd sites. In addition, a strong p-d repulsive correlation shifts the Pd-4d band towards the electron-depleting centre, allowing near-barrier-free electron transfer and facilitating [OOH-] stabilization. Owing to a high energy barrier of the dissociation of [OOH-], the four-electrons oxygen reduction pathway is significantly suppressed for high H2O2 selectivity. The Pd4Se NPs are also highly stable, with only a 2.4%, 9.6% and 3.4% decrease for H2O2 selectivity in 0.1 M HClO4, 0.1 M KCl and 0.1 M KOH electrolytes, respectively, after 5000 cycles, which shows that these NPs are a unique and robust Pd-based electrocatalyst for H2O2 generation under pH-universal conditions.

Biofortification with selenium increases bioactive compounds and antioxidant capacity in tomato fruits

The objective of biofortification is the human consumption of high nutritional quality food, rich in micronutrients. Selenium (Se) is an essential micronutrient in human nutrition, and its essentiality has not been evidenced in plants. However, its application in crops and subsequent consumption can mitigate the deficiency of this micronutrient in the diet of human populations. This work analyzes the capacity of sodium selenite (Na2SeO3) to increase yield, biosynthesis of bioactive compounds and their accumulation in tomato fruits. For this, five treatments were applied via nutrient solution: 0, 2, 4, 6, and 8 mg L-1. At harvest, the nutraceutical quality and the accumulation of Se in fruits were quantified, as well as the productivity of tomato plant. Biofortification was positively affected by the biosynthesis of phytochemical compounds and their concentration in fruit, although tomato yield decreased. The incorporation of Se in nutritive solution is an alternative to increase both the biosynthesis of phytochemical compounds and the concentration of this element in tomato fruits with the possibility of improving public health through its consumption.

Metabolism of Tracer 75Se Selenium From Inorganic and Organic Selenocompounds Into Selenoproteins in Rats, and the Missing 75Se Metabolites.

We now know much about selenium (Se) incorporation into selenoproteins, and there is considerable interest in the optimum form of Se for supplementation and prevention of cancer. To study the flux of 75Se into selenoprotein, rats were fed 0 to 5 μg Se/g diet as selenite for 50–80 d and injected iv with 50 μCi of 75Se-labeled selenite, selenate, selenodiglutathione, selenomethionine, or selenobetaine at tracer levels (~0.5 μg Se). The rats were killed at various times and 75Se incorporation into selenoproteins was assessed by SDS/PAGE. These studies found that there is very rapid Se metabolism from this diverse set of selenocompounds to the common intermediate used for synthesis and incorporation of 75Se into the major selenoproteins in a variety of tissues. No selenocompound was uniquely or preferentially metabolized to provide Se for selenoprotein incorporation. Examination of the SDS/PAGE selenoprotein profiles, however, reveals that synthesis of selenoproteins is only part of the full Se metabolism story. The 75Se missing from the selenoprotein profiles, especially at early timepoints, is likely to be both low-MW and high-MW selenosugars and related precursors, as we recently found in livers of turkeys fed Se-adequate and high-Se diets. Differential metabolism of different selenocompounds into different selenosugar species may occur; these species may be involved in prevention of cancer or other diseases linked to Se status and may be associated with Se toxicity. Additional studies using HPLC-mass spectroscopy will likely be needed to fully flesh out the complete metabolism of selenium.

Importance of Fine Control of Se Flux for Improving Performances of Sb2Se3 Solar Cells Prepared by Vapor Transport Deposition

Sb2Se3 possesses a quasi‐1D (Q1D) structure, which creates an anisotropic charge transporting behavior in which the carrier transport is very efficient along the Q1D direction, which is beneficial for solar cells as long as the absorber is properly aligned along the preferred orientation. However, Sb2Se3 is prone to form donor‐like defects, such as VSe, that are detrimental to the performance. Therefore, both growth of Sb2Se3 along the preferred orientations and the suppression of the formation of VSe are crucial in achieving Sb2Se3 solar cells with a high efficiency. Herein, the importance of fine control of the extra supply of Se during the deposition of Sb2Se3 in controlling crystallographic orientations and the population of VSe in the Sb2Se3 films is described. This control determines the performance of the resulting solar cells in a superstrate configuration with a CdS buffer. Incorporation of Se during the growth resulted in a larger open‐circuit voltage due to the passivation of VSe. However, an excess supply of Se disrupts the favorable orientation by selenizing the top region of the CdS, and therefore degraded the short‐circuit current. Through the optimization of the extra supply of Se vapor, the power conversion efficiency is improved from 3.7% to 5.2%.

Effect of Se incorporation on thermoelectric properties of Bi2(Se x Te1-x )3 alloys

We used first-principles calculations based on density functional theory and the Boltzmann transport equation with an empirical relaxation time scheme to investigate the thermoelectric (TE) properties of Bi2(Se x Te1-x )3 alloys. We examined various TE indicators and found that Bi2SeTe2 shows relatively highest TE performance in Bi2(Se x Te1-x )3 alloys than bulk Bi2Te3. The result indicated that it is difficult to find the favorable Se composition for Bi2(Se x Te1-x )3 via power factor. The findings suggested that our computational framework provides a useful guide for the effect of Se incorporation on TE performance of Bi2(Se x Te1-x )3 alloys.

A dramatic improvement in the efficiency of TiO2-based DSSCs by simultaneous incorporation of Cu and Se into its lattice

Abstract Humans are great consumers of energy, and solar energy is a great renewable energy source that can address their energy requirements. Dye-sensitized solar cells (DSSCs) are among the photovoltaic devices with an excellent energy generation prospect if their minor shortfalls are addressed. Recently, co-doping of the photoanode material with different elements are the subject of many studies. In this paper, we simultaneously dope Cu and Se into TiO2 photoanode lattice and investigate a fixed ratio of Cu with different Se ratios on the performance of DSSC. We show that this co-doping method allows us to control the crystallinity, porosity, conductivity, dye-loading, and optical properties of the photoanode. Our best cell showed an efficiency of 7.60% with a short circuit current of 16.42 mA/cm2, an open-circuit voltage of 746 mV, and a fill factor of 62%, which is a 64% improvement in comparison with our bare TiO2 cell with 4.63% efficiency.

Analysis of Bioavailability and Induction of Glutathione Peroxidase by Dietary Nanoelemental, Organic and Inorganic Selenium.

Dietary organic selenium (Se) is commonly utilized to increase formation of selenoproteins, including the major antioxidant protein, glutathione peroxidase (GPx). Inorganic Se salts, such as sodium selenite, are also incorporated into selenoproteins, and there is evidence that nanoelemental Se added to the diet may also be effective. We conducted two trials, the first investigated inorganic Se (selenite), organic Se (L-selenomethionine) and nanoelemental Se, in conventional mice. Their bioavailability and effectiveness to increase GPx activity were examined. The second trial focused on determining the mechanism by which dietary Se is incorporated into tissue, utilising both conventional and germ-free (GF) mice. Mice were fed a diet with minimal Se, 0.018 parts per million (ppm), and diets with Se supplementation, to achieve 0.07, 0.15, 0.3 and 1.7 ppm Se, for 5 weeks (first trial). Mass spectrometry, Western blotting and enzymatic assays were used to investigate bioavailability, protein levels and GPx activity in fresh frozen tissue (liver, ileum, plasma, muscle and feces) from the Se fed animals. Inorganic, organic and nanoelemental Se were all effectively incorporated into tissues. The high Se diet (1.7 ppm) resulted in the highest Se levels in all tissues and plasma, independent of the Se source. Interestingly, despite being ~11 to ~25 times less concentrated than the high Se, the lower Se diets (0.07; 0.15) resulted in comparably high Se levels in liver, ileum and plasma for all Se sources. GPx protein levels and enzyme activity were significantly increased by each diet, relative to control. We hypothesised that bacteria may be a vector for the conversion of nanoelemental Se, perhaps in exchange for S in sulphate metabolising bacteria. We therefore investigated Se incorporation from low sulphate diets and in GF mice. All forms of selenium were bioavailable and similarly significantly increased the antioxidant capability of GPx in the intestine and liver of GF mice and mice with sulphate free diets. Se from nanoelemental Se resulted in similar tissue levels to inorganic and organic sources in germ free mice. Thus, endogenous mechanisms, not dependent on bacteria, reduce nanoelemental Se to the metabolite selenide that is then converted to selenophosphate, synthesised to selenocysteine, and incorporated into selenoproteins. In particular, the similar efficacy of nanoelemental Se in comparison to organic Se in both trials is important in the view of the currently limited cheap sources of Se.