Selenium Substitution Research Articles

Field effect transistors with layered two-dimensional SnS2−xSex conduction channels: Effects of selenium substitution

A thorough characterization of field effect transistors with conduction channels made of SnS2−xSex nanocrystals having different selenium content is presented. The main effect of increasing the selenium content is a suppression of the drain-source current modulation by the gate voltage. The temperature dependence of SnS2−xSex conductivity for all compositions is characterized by an activation energy that gradually decreases with x. A simple donor model, with parameters of SnS2 and SnSe2 deduced from density functional theory, suggests that the change in the activation energy is mostly due to enhanced dielectric constants that accompany the band gap reduction in SnS2−xSex.

Molecular Weight Effect on the Absorption, Charge Carrier Mobility, and Photovoltaic Performance of an Indacenodiselenophene-Based Ladder-Type Polymer

Selenium substitution on a ladder-type indacenodithiophene-based polymer (PIDT-DFBT) is investigated in order to reduce band gap, improve charge mobilities, and enhance the photovoltaic performance of the material. The new indacenodiselenophene-based polymer (PIDSe-DFBT) possessed improved absorption over its sulfur analogue in films, as well as substantially higher charge mobilities (0.15 and 0.064 cm2/(V s) hole and electron mobility, respectively, compared to 0.002 and 0.008 cm2/(V s) for PIDT-DFBT). The enhanced material properties led to an improved power conversion efficiency of 6.8% in photovoltaic cells, a 13% improvement over PIDT-DFBT-based devices. Furthermore, we examined the effect of molecular weight on the properties of PIDSe-DFBT and found not only a strong molecular weight dependence on mobilities, but also on the absorptivity of polymer films, with each 15 000 g/mol increase in weight, leading to a 25% increase in the absorptivity of the material. The molecular weight dependence of the material’s properties resulted in a significant difference in photovoltaic performance with the high-molecular-weight PIDSe-DFBT providing a higher photocurrent, fill factor, and efficiency due to its improved absorption and hole mobility. These results demonstrate the importance of achieving high molecular weight and the potential that selenium-containing ladder-type polymers have in the design of high-performance semiconducting polymers for organic photovoltaics (OPVs).

Synthesis of 6-Se-Guanosine RNAs for Structural Study

6-Se-guanosine phosphoramidite and RNAs have been synthesized by selenium substitution of the 6-oxygen atom, and it is revealed that the Se-derivatization is relatively stable and that bulge and wobble structures can better accommodate a large Se atom than a duplex. This Se-modification is useful in the structural study of RNAs and their protein complexes.

Anionic depolymerization transition in IrTe2.

Selenium substitution drastically increases the transition temperature of iridium ditelluride (IrTe(2)) to a diamagnetic superstructure from 278 to 560 K. Transmission electron microscopy experiments revealed that this enhancement is accompanied by the evolution of nonsinusoidal structure modulations from q = 1/5(101) to q = 1/6(101) types. These comprehensive results are consistent with the concept of the destabilization of polymeric Te-Te bonds at the transition, the temperature of which is increased by chemical and hydrostatic pressure and by the substitution of Te with the more electronegative Se. This temperature-induced depolymerization transition in IrTe(2) is unique in crystalline inorganic solids.

Dependence of the structural, transport and magnetic properties of Tl1−yFe2−z(Se1−xSx)2 with isovalent substitution of Se by S

The effect of selenium substitution by sulfur in the Tl1−yFe2−zSe2 antiferromagnet was studied by x-ray and electron diffraction, magnetization and transport measurements. Tl0.8Fe1.5(Se1−xSx)2 (nominal composition) solid solution was synthesized in the full x range (0 ≤ x(S) ≤ 1) using the sealed tube technique. No superconductivity was found down to 4.2 K in the series despite the fact that the optimal crystallographic parameters, determined by Rietveld refinements, are reached in the series (i.e. the Fe–(Se, S) interplane height and (Se, S)–Fe–(Se, S) angle for which the critical superconducting transition Tc is usually maximal in pnictides). A quasi-full Tl site (y ∼ 0.05) compared to significant alkaline deficiency (y = 0.2–0.3) in analogous A1−yFe2−zSe2 (A = K, Rb, Cs), and the resulting differences in iron valency, density of states and doping, are suggested as an explanation for this absence of superconductivity. Transmission electron microscopy confirmed the existence of an ordered iron vacancies network in the samples of the Tl0.8Fe1.5(Se1−xSx)2 series in the form of the tetragonal superstructure (I4/m). The Néel temperature (TN) indicating the onset of antiferromagnetism order in this supercell is found to decrease from 450 K in the selenide (x = 0) to 330 K in the sulfide (x = 1). Finally, we demonstrate a direct linear relationship between TN and the Fe–(Se, S) bond length (or Fe–(Se, S) height).

The influence of selenium supplementation of animal feed on human selenium intake in Serbia

The use of selenium as animal feed supplement in Serbia was approved in 1989 for some categories of pigs, sheep and poultry. From 2000 selenium in animal feed became a requirement for all categories of farm animals. The aim of this study was to determine the consumption of selenium by Serbian livestock and in poultry production between 1990-1991 and 2000-2008 and to analyze the selenium content of meat, milk and eggs sold on Serbian markets to gain insight into human selenium intake. Data indicate a low level of selenium inclusion in animal feed during 1990-1991 compared to during 2000-2008. These results coincide with Serbian regulations. From 2001 an organic form of selenium (selenized yeast) was introduced in small quantities (less than 8% of the total consumed selenium). Analysis of meat, milk and eggs from Serbian markets shows increased selenium levels compared to 1991. However, the estimated total human daily intake in Serbia is 40.9 ?g, which is under the recommended quantity. Increasing the quantity of selenium included in animal feed and the substitution of inorganic selenium with selenized yeast could be beneficial for animal health and farm productivity. As a consequence a further improvement in the human selenium status in Serbia should be possible.

Esicon 2012,Kolkata: The best of Indian Endocrinology

It has been 42 years since the first ESICON was held. Over the years, ESICON has grown from strength to strength in becoming the largest national forum for endocrinologists in India. Amongst all the sub-specialties of medicine, endocrinology has the strongest association with global health, be it diabetes, thyroid disorders or osteoporosis. It covers the entire gamut of medical science and is one of the fastest developing fields in medical research, worldwide. This annual program is designed to update endocrinologists on recent advances and practices in the field of endocrinology, as well as encourage research in endocrinology. ESICON 2012 has invited eminent national speakers and speakers from across the globe, in order to create a platform for academic interaction between researchers, clinicians and trainees. To establish ESICON as one of the premier endocrine meetings we need to collaborate and exchange ideas with other renowned societies across the world. Thyroid ultrasonography is a well established diagnostic tool in the hands of practicing clinical endocrinologists in the west especially USA. For the first time in an ESICON meeting, we have arranged for a hands-on thyroid ultrasound training mainly focusing on trainees. The Endocrine Society has agreed to conduct this program. Moreover, we have also arranged for a short training in medical statistics, which will enable young researchers to develop their analytical skills and facilitate international publications. Workshops on clinical genetics and insulin pumps are also been organized. Another key feature of ESICON is the oral communications and poster presentations by researchers in the field of endocrinology. This year, more than hundred abstracts will be presented in the meeting. The topics of research papers cover the entire spectrum of endocrinology from diabetes, thyroid, adrenal, pituitary, bone to reproductive and pediatric endocrinology. For the first time since its inception, we are publishing a special conference edition of Indian Journal of Endocrinology and Metabolism. The main focus of this edition is the brief communications of the papers to be presented as abstracts in the meeting. The objective of this supplement is to give a fillip to research activity in India. We have received brief communications from all over India that gives a perspective on varied endocrine researches covering all fields of endocrinology. We have epidemiological research papers ranging from dyshormonogenetic goiter, hypothyroidism after external beam radiation, empty sella syndrome to hyperparathyroidism, cardiovascular risk (CV) risk in PCOS. We have basic research papers like association of severity of diabetic neuropathy with serum sFasL level, characterization of GH1 gene in isolated growth hormone deficiency (GHD) and use of urinary cortisol creatinine ratio as a novel diagnostic tool in Cushing's syndrome. In the area of intervention, we have a huge variety from effect of vitamin D fortification in school children, selenium substitution in autoimmune thyroid disease and also effect of ileal interposition and sleeve gastrectomy in diabetes treatment, to name a few. Numerous interesting case reports with learning issues like De Morseir syndrome, gigantism and pachydermoperiostosis have also been illustrated. Endocrinology cuts across different disciplines of medicine and requires integrated inputs from fields like genetics, biochemistry, physiology, immunology, molecular biology just like the hormones that act like chemical messengers influencing the whole of our systems biology. This supplement aims to provide the most up-to-date information in various aspects of endocrinology to practicing endocrinologists, trainees and researchers alike. Basic science topics like calcium sensing receptors, molecular pathology of pituitary tumors have been given due importance as has diagnostic issues like FRAX, vitamin D assay, clinical management concerns like management of diabetes insipidus, osteoporosis, neonatal hypoglycemia and futuristic topics like stem cell therapy in diabetes, thyromimetics. It is a great honor for the organizing committee to have eminent experts in the field of endocrinology from India and across the world to deliver lectures in ESICON 2012. The recent advances and clinical practice guidelines from experts in different fields of endocrinology have been incorporated as mini reviews in this edition. We wish to thank all authors including the young researchers and eminent speakers for their time and effort in providing up to date information and concise review relating to all fields of endocrinology. Without their valuable inputs, this edition would not have seen the light of the day. We would like to express our sincere gratitude to the editor of the journal who has given us this opportunity.

Electrochromic second-order NLO chromophores based on MII (M = Ni, Pd, Pt) complexes with diselenolato–dithione (donor–acceptor) ligands

The donor-acceptor type mixed-ligand complexes [M(Bz(2)pipdt)(dsit)]; dsit = 2-thioxo-1,3-dithiole-4,5-diselenolato (donor); Bz(2)pipdt = 1,4-dibenzyl-piperazine-2,3-dithione (acceptor); M(II) = Ni (1), Pd (2), and Pt (3) were prepared and characterized to investigate the variation of the properties by substituting selenium for sulfur in the donor ligand dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato of the corresponding known complexes. Both these classes of complexes exhibit large negative second-order polarizabilities, amongst the highest values determined so far for metal-complexes, and are potential candidates for redox switchability of the molecular first hyperpolarizability due to the bleaching/restoring of the solvatochromic peak for mono-reduction/oxidation. DFT and TD-DFT calculations on 1-3 allow one to correlate geometries and electronic structures and are in agreement with the observed minor changes following the substitution of selenium for sulfur atoms in the dichalcogenolato ligand. The observed differences can be ascribed to the increased size of the selenium atom leading to increased M-X distances and dipolar moments of the ground state, which are highest for the Pd-derivative in the triad.

Spin glass and semiconducting behavior in one-dimensional BaFe2−δSe3(δ≈0.2)crystals

We investigate the physical properties and electronic structure of BaFe${}_{1.79(2)}$Se${}_{3}$ crystals, which were grown out of tellurium flux. The crystal structure of the compound, an iron-deficient derivative of the ThCr${}_{2}$Si${}_{2}$-type, is built upon edge-shared FeSe${}_{4}$ tetrahedra fused into double chains. The semiconducting BaFe${}_{1.79(2)}$Se${}_{3}$ (${\ensuremath{\rho}}_{295\mathrm{K}}$ $=$ 0.18 \ensuremath{\Omega}\ifmmode\cdot\else\textperiodcentered\fi{}cm and ${E}_{g}$ = 0.30 eV) does not order magnetically; however, there is evidence for short-range magnetic correlations of spin glass type (${T}_{f}$ \ensuremath{\approx} 50 K) in magnetization, heat capacity, and neutron diffraction results. A one-third substitution of selenium with sulfur leads to a slightly higher electrical conductivity (${\ensuremath{\rho}}_{295\mathrm{K}}$ $=$ 0.11 \ensuremath{\Omega}\ifmmode\cdot\else\textperiodcentered\fi{}cm and ${E}_{g}$ = 0.22 eV) and a lower spin glass freezing temperature (${T}_{f}$ \ensuremath{\approx} 15 K), corroborating with higher electrical conductivity reported for BaFe${}_{2}$S${}_{3}$. According to the electronic structure calculations, BaFe${}_{2}$Se${}_{3}$ can be considered as a one-dimensional ladder structure with a weak interchain coupling.

Origin of structural instability in TlInS2(1−x)Se2x solid solutions

The influence of the isovalent substitution of selenium for sulfur in the anion sublattice of mixed TlInS2(1−x)Se2x crystals has been studied by means of dielectric measurements. It is shown that transformations in the In4(SxSe1−x)10 structural unit must be taken into account considering the nature of possible phase transitions in TlInS2(1−x)Se2 solid solutions. Possible mechanisms of the phase transition including instabilities in the electronic subsystem of pure TlInSe2 crystals are discussed.

Selenium substitution during radiotherapy of solid tumors

Selenium substitution during radiotherapy of solid tumors

Influence of the chalcogen substitution on the character of magnetic ordering in Fe0.5TiS2 − x Se x intercalated compounds

The crystal structure and magnetic properties of layered Fe0.5TiS2 − x Se x (0 ≤ x ≤ 2) compounds intercalated by iron atoms have been investigated. It has been shown that the substitution of selenium for sulfur is accompanied by an increase in the unit cell volume, a transition from the ferromagnetic to antiferromagnetic behavior, and a nonmonotonic variation in the paramagnetic Curie temperature. The intercalated iron atoms are characterized by lower values of the effective moment (3.4–4.0μB) as compared to the predicted value (4.89μB) for the Fe2+ ion at g = 2. The results obtained have been discussed under the assumption that there are the hybridization of 3d electronic states of intercalated Fe atoms with the electronic states of the TiS2 − x Se x host compounds and the competition of exchange interactions of different types.

Enhanced performances of melt spun Bi 2(Te,Se) 3 for n-type thermoelectric legs

In this article, a rapid and cost-effective melt spinning (MS) subsequently combined with a spark plasma sintering (SPS) process was utilized to prepared n-type Bi 2(Te 1− x Se x ) 3 ( x = 0.0–1.0) solid solutions from high purity single elemental chunks. The substitution of tellurium by selenium has significant impacts on the electrical and thermal transport properties of the Bi 2(Se x Te 1− x ) 3 compounds in a manner which can be well understood using a valence bond rule and the corresponding change in band gap. Furthermore, the selenium substitution effectively adjusts the carrier density allowing an optimum value of ∼5 × 10 −19 cm −3. As a result, a maximum ZT of 1.05 at 420 K was achieved for the Bi 2(Se 0.2Te 0.8) 3 sample which also shows an improved average ZT of ∼0.97 in the entire measurement temperature range. By adopting the same p-type legs, the module fabricated by the MS-SPS Bi 2(Se 0.2Te 0.8) 3 material which acts as n-type legs shows ∼10% enhancement in thermoelectric conversion efficiency compared with the module fabricated by n-type zone melted ingots.

High-dose selenium substitution in sepsis: a prospective randomized clinical trial

Systemic inflammatory response syndrome (SIRS) and sepsis remain the leading cause of death in the critically ill. A reduction in the antioxidant capacity, including selenoenzymes that are dependent on selenium (Se), could be a contributing factor. Se supplementation in septic patients have yielded conflicting results. We hypothesized that a high-dose Se supplementation would (1) improve markers of inflammation, nutrition and antioxidant defence, and (2) decrease mortality. This prospective, randomized, open-label, single-centre clinical trial included 150 patients with SIRS/sepsis and a SOFA score of >5. Patients in the Se+ group (n = 75) received Se for 14 days (1,000 μg on day 1,500 μg/day on days 2-14). Patients in both the control (Se-) group (n = 75) and the Se+ group received a standard Se dose (<75 μg/day). Plasma Se, whole-blood glutathione peroxidase (GPx) activity, C-reactive protein (CRP), procalcitonin (PCT), albumin, prealbumin and cholesterol levels, along with APACHE II and SOFA scores, were determined at baseline and on days 1-7 and day 14. Mortality was assessed at day 28. Plasma Se and GPx activity were increased in the Se+ group from day 1 onwards. Negative correlations were demonstrated between plasma Se, CRP (P = 0.035), PCT (P = 0.022) and SOFA (P = 0.001) at admission but not on days 7 or 14. Prealbumin and cholesterol increased in the Se+ group versus the respective baselines. Mortality was similar between groups, with no gender differences. High-dose Se substitution in patients with SIRS/sepsis increased plasma Se and GPx levels, but did not reduce mortality. Markers of inflammation were reduced similarly in both groups.

Selenium substitution during radiotherapy in head and neck cancer

Selenium substitution during radiotherapy in head and neck cancer

ChemInform Abstract: Substitution of Selenium in Diallylselenide by Sulfur Upon Treatment with H2S-DMSO.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Theoretical Studies of the Structural, Electronic, and Optical Properties of Phosphafluorenes

Phosphafluorenes have drawn increasing attention recently in the applications of organic electronic devices due to their particular optoelectronic properties. To reveal their molecular structures, optoelectronic properties, and structure-property relationships of the newly emerged functional materials, an in-depth theoretical investigation was elaborated via quantum chemical calculations. The optimized geometric and electronic structures in both ground and exited states, the mobility of the hole and electron, the absorption and emission spectra, and the singlet exciton generation fraction of these novel phosphors-containing materials have been studied by density functional theory (DFT), single excitation configuration interaction (CIS), time-dependent density functional theory (TDDFT) methods, and the polarizable continuum model (PCM). The results show that the highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), triplet energies ((3)E(g)), energy gaps (E(g)), as well as some other electronic properties including ionization potentials (IPs), electron affinities (EAs), reorganization energies (lambda), the singlet exciton generation fraction, radiative lifetime, and absorption and emission spectra can be easily tuned by chemical modifications of the phosphorus atom via methyl, phenyl, oxygen, sulfur, or selenium substitution, indicating that the phosphafluorenes are interesting optoelectronic functional materials, which have great potential in the applications of OLEDs, organic solar cells, organic storage, and sensors.

Effect of the “negative chemical” pressure on the temperatures of phase transitions in the TlInS2 layered crystal

The temperature dependences of the permittivity of TlInS2(1 −x)Se2x solid solutions have been experimentally investigated in the temperature range including the points of structural phase transitions in the solid solutions. It has been established that the isovalent substitution of selenium for sulfur in the anion sublattice of the TlInS2(1 − x)Se2x solid solutions shifts the phase transition temperatures Ti and Tc toward the low-temperature range with a simultaneous decrease in the temperature interval of the existence of the incommensurate phase. The T-x phase diagram is constructed for the solid solutions under study and the coordinates are determined for a critical point (of the Lifshitz type) at which the lines Ti(x) and Tc(x) converge in the phase diagram. The pattern of the T-x phase diagram for the TlInS2(1 − x)Se2x solid solutions has been analyzed within the phenomenological model of a virtual crystal.

Evaluation of the effect of selenium on radiation-induced toxicities in head neck cancer patients

e20698 Background: The substitution of selenium effects in activation of the selenium dependent enzyme glutathione peroxidase which is important for scavenging free radicals. Until today only limited data are available about the clinical impact of selenium regarding the toxicities due to free radical producing therapies, e.g. irradiation or chemotherapy. Methods: 39 patients (8 female, 31 male) with advanced head neck cancer were included to a randomized phase II study. All patients had shown a reduced concentration of selenium in the blood and serum (main inclusion criterium). The mean age was 63.52 ± 9.31 years. Tumour localizations: oral cancer 15 patients, oropharynx 19 patients, hypopharynx 5 patients, CUP 1 patient. Group A (n=22) received 500 μg sodium selenite at the days of radiotherapy and 300 μg sodium selenite at holidays or weekend. Group B (17) was irradiated without any selenium substitution. Both groups were well balanced according age, gender, localization and stage of the tumour. We evaluated the RTOG grade of radiation-associated toxicities once per week. Following statistical methods were used: Mantel-Haenssel-χ2-test, Fisher's exact Test. SPSS. Results: We observed the following serious toxicities (group A versus group B): dysphagia 22.7% vs. 35.3%, loss of taste 22.7% vs. 47.1%, dry mouth 22.7% vs. 23.5%, and stomatitis 36.4% vs. 23.5%. A statistical trend (Fisher's exact test) is only seen in the area of loss of taste (p=0.172). The analysis per week had only shown a significant reduction of dysphagia in the selenium group at the last week of irradiation (p=0.04). Conclusions: The small randomized trial has shown limited effects of selenium in the prevention of ageusia (loss of taste) and dysphagia due to radiotherapy because of head and neck cancer. A clinical relevant radioprotection was not observed. [Table: see text]

A study of sulfur/selenium substitution effects on physical and mechanical properties of vacuum-grown ZnS 1− xSe x compounds using Boubaker polynomials expansion scheme (BPES)

In this study, the effects of the sulfur–selenium substitution inside sprayed ZnS compounds are discussed. First, the spray pyrolysis method has been used to grow the ZnS layers on glass substrates at relatively low temperatures. After an appropriate cooling phase, the substrate-layer set was introduced inside a sealed tube. Consecutively, selenium supply was introduced and vaporized under vacuum conditions inside the sealed tube containing the formerly ZnS prepared layers. The annealing time was varied from 1 to 48 h. Precisely, the tube arrangement was heated to about 350 °C in order to vaporize the selenium. On heating supply withdrawal, the selenium reacts with the existing layer. To prevent revaporization and minimize undesirable zinc oxides formation during crystal growth, a small amount of nitrogen was introduced into the tube. AFM technique and Vickers microhardness protocol subjected to the Boubaker polynomials expansion Scheme (BPES), have been carried out in order to evaluate the obtained ZnS 1− x Se x | 0≤ x<0.5 layers performance and properties.