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Tesi sul tema "Selenium compounds"
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1
Bates, C. M. "Pentamethylcyclopentadienyl (Cp*) compounds of selenium and tellurium". Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636056.
Testo completoAbstract (sommario):
Successful preparations were: (1) bis(pentamethylcyclopentadienyl)selenium, prepared by the reaction of selenium diethydithiocarbamate with lithiated pentamethylcyclopentadiene; (2) Cp*SenLi (n = 2,3,4), prepared by the reaction of elemental selenium with lithiated pentamethylcyclopentadiene in THF and its subsequent reaction with iodomethane to produce (3) methyl(pentamethylcyclopentadienyl)selenium or water to produce the polyselenide mixture (4) Cp*2Sen (n = 2,3,4). (4) was also produced by the low temperature reaction of selenium chloride with lithiated pentamethylcyclopentadiene. The compounds were characterised by conventional methods including 77Se NMR spectroscopy. The x-ray structural determination was obtained for compound (1) revealing the largest C-Se-C bond angle recorded for a simple diorganoselenide. The reactivities of the compounds (1) (3) and (4) were investigated in reactions with unsaturated transition metal fragments. In the reactions of (1) with sources of the tungsten and chromium carbonyl compounds [W(CO)5THF], [W(CO)3(CH3CN)3], [Cr(CO)5THF], [Cr(CO)4nbd] and [Cr(CO)3(CH3CN)3] the first example of reduction of a selenide to form a diselenide within the transition metal coordination sphere was observed. These produced the complexes [M(CO)2{Se2Cp*2}] (M = W, Cr). The x-ray structure determinations are included. These complexes contain the longest Se-C bonds recorded. A 1,2 metal shift was observed for the tungsten complex using the technique of two dimensional exchange NMR spectroscopy. (3) reacts with [W(CO5THF] or [Cr(CO)5THF] to produce the complexes [W(CO)5{Se(Me)Cp*}] and [Cr(CO)5{Se(Me)Cp*}]. The first recorded Se-W satellites are reported for the former. The compounds (1), (3) and (4) were reacted with diiron nonacarbonyl to produce the complex [Fe3Se2(CO)5]. Compound (1) was reacted with a half molar equivalent of [PdCl2(PhCN)2] to produce the complex [Pd2Cl4(SeCp*2)].
2
Carroll, Luke Dean. "Modulation of oxidative damage by selenium compounds". Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14124.
Testo completoAbstract (sommario):
Myeloperoxidase (MPO) is the primary enzyme responsible for the production of strong oxidants by neutrophils in response to pathogens. One of the major oxidants produced is hypochlorous acid (HOCl), which can react with amine groups to form the secondary oxidants N-chloramines. These oxidants play a role in the destruction of pathogens, however they also have the potential to damage host cells, and have been implicated in numerous inflammatory diseases. This Thesis explores the potential for selenium containing compounds and enzymes to act as catalytic oxidant scavengers. Reaction rates between MPO-derived oxidants and selenium compounds were determined product characterization of products performed. The reduction of the oxidised products, selenoxides, was examined and the rate constant for the thiol reduction of selenoxides determined. It is demonstrated that selenium and sulfur containing enzymes are capable of scavenging these oxidants, as well as reversing the formation of selenoxides. The ability of selenium compounds to protect against damage induced by treatment of cells with HOCl and N-chloramines was also assessed. Overall, selenium containing compounds and enzymes show potential in scavenging these oxidants with endogenous thiols capable of reversing the oxidised selenium products, making them a potential therapeutic intervention in inflammatory conditions.
3
Meng, Shuang. "Heteroepitaxial growth of gallium selenium compounds on silicon /". Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/9749.
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4
Braude, Jeremy. "Organic Selenium Compounds as Oxidants in Cancer Therapy". Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3424584.
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5
Chiu, Winnie Wai Hang. "Metal complexes with sulfur and selenium donor ligands /". View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202009%20CHIU.
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6
Cooney, Rita A. "Speciation and identification of selenium compounds in biological matrices". Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/30258.
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7
Tan, Thatt Yang Timothy School of Chemical Engineering & Industrial Chemistry UNSW. "Photocatalytic reduction of selenate and selenite : water/wastewater treatment and the formation of nano-selenium compounds". Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2003. http://handle.unsw.edu.au/1959.4/20448.
Testo completoAbstract (sommario):
The current work investigates the photocatalytic reduction of selenium (Se) ions, selenate Se(VI) and selenite Se(IV), from two perspectives: Se ion removal from water and wastewater and the formation of nano-Se compounds. Se ion pollution has become an environmental issue in recent years, and hence there is an urgent need for an efficient removal technique. In addition, there is increasing interest in the formation of nano-size semiconductors for niche applications. Since Se is a semiconductor, its formation onto the semiconductor TiO2 could lead to the discovery of new composite materials. The current study has successfully elucidated the mechanism of Se ions reduction by photocatalysis. Factors such as the simultaneous adsorption of the Se ions (the electron scavenger in this case) and a suitable organic compound (the hole scavenger), and the chemical properties of the hole scavenger were crucial for effective and efficient Se ions photoreduction. Optimum conditions in relation to pH, concentrations and types of hole scavenger were reported and discussed. It was also found that stoichiometric adsorption ratio of formate and selenate resulted to optimum photoreduction rate. A modified Langmuir-Hinshelwood kinetic model that considered the simultaneous adsorption of both solutes was derived. The current investigation has also seen the successful formation Se deposits of different morphologies onto the TiO2 particles. Discrete Se particles of various sizes in the nano-size range as well as a Se film were deposited onto the TiO2 particles under different initial experimental conditions. The Se-TiO2 composite semiconductor was explored for the removal of cadmium Cd2+ ions, which resulted in the formation of CdSe-TiO2 systems. The photoreduction of Se ions using silver-modified TiO2 showed the enhanced reduction of Se ions to Se2- in the form of H2Se gas. It is suggested that the H2Se gas generated from the current photoreduction process could be used as a safer and cheaper technique in the formation of Se-compounds such copper selenide, cadmium selenide and zinc selenide. All these compounds were widely used in optical and semiconducting devices.
8
Du, Junyi. "X-ray crystallographic studies of sulfur/selenium heteroatom compounds". Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/8984.
Testo completoAbstract (sommario):
The major aim of research reported on this thesis uses X-ray crystallography to investigate the structural features of a series of pentafluorosulfuranyl (SF₅) containing aromatic compounds, chalcogen amides, 2,4-diaryl-1,3-selenazoles and 2,4-diaryl-1,3-chalcogen azoles bearing SF₅ group and organo phosphorus-chalcogen macrocycles incorporationg double OP(S)SC[sub]n or OP(Se)SeC[sub]n scaffolds. The basic theory of crystallography is introduced in Chapter 1, followed by a general discussion on pentafluorosulfuranyl (SF₅) containing heteroatom compounds and sulfur/selenium heterocycles in Chapter 2. Ten pentafluorosulfuranyl (SF₅)-containing aromatic compounds have been studied crystallographically in Chapter 3. All S-F bond lengths in these compounds are very similar [1.571(3) to 1.618(3) Å and 178.5(3) to 180.0° for the C-S-F(ax) bond] and the angles of two adjacent F(eq) is approximate to 90°. The intramolecular C[sub](aryl)-H···F(eq) and intermolecular C[sub](aryl)-H···O/N/F/Cl interactions, and π-stacking interactions are observed in the packing frameworks. X-ray crystal structure analysis reveals that in the structures of 2,4-diaryl-1,3-selenazoles in Chapter 4, the five-membered N-C-Se-C-C rings have either planar or near-planar conformations, and exhibit a series of the intramolecular and intermolecular C-H∙∙∙O/N/Se/Br/Cl) interactions and π-stacking interactions. The crystal structures of 2,4-diaryl-1,3-chalcogen azoles with both a pentafluorosulfuranyl (SF₅) group and a five-membered N-C-Se-C-C ring have been investigated in Chapter 5. A diverse picture of molecular configuration and intramolecular/intermolecular C-H∙∙∙N/Se/S and π-stacking interactions information are disclosed in selenamide, thiamides, 1,3-selenazoles and 1,3-thiazoles. Nine organo phosphorus-chalcogen macrocycles with nine- to fifteen-membered ring incorporating double OP(S)SC[sub]n or OP(Se)SeC[sub]n scaffolds have been discussed crystallographically in Chapter 6. The similar intramolecular and intermolecular C-H∙∙∙O, C-H∙∙∙S or C-H∙∙∙Se interactions are observed to lead to the similar packing networks.
9
Robey, Stephanie. "Reactions of Platinum(II) Compounds with Selenium Containing Amino Acids". TopSCHOLAR®, 2013. http://digitalcommons.wku.edu/theses/1252.
Testo completoAbstract (sommario):
Platinum(II) anticancer medications essentially react with DNA forming kinks inthe double helix of DNA and causing apoptosis. It has also been noted that theseanticancer medications react with methionine and cysteine in the body. With the new discoveries of selenium containing amino acids including selenomethionine and selenocysteine, new research is ongoing to see what types of products can be formed from these amino acids. Our research reacts [Pt(Met-S,N)Cl2] 2+ with selenomethionine to determine what types of products are produced. Monochelates including [Pt(SeMet-Se,N)Cl2] 2+ have formed two isomers, as well as other products that insinuate both selenomethionine and methionine binding with the platinum to form various [Pt(SeMet- Se,N)(Met-S,N)]2+ products. When initially reacting 6 mM [Pt(Met-S,N)Cl2] 2+ with 3 mM SeMet, the monochelates of both are produced without forming any free methionine which would suggest that there is free platinum in our solution creating the SeMet monochelate. When adding additional SeMet to the solution the same products are formed that are created when reacting 6 mM [Pt(Met-S,N)Cl2] 2+ and 6 mM SeMet. The 1H NMR spectrum for these products imply a product of [Pt(SeMet-Se,N)(Met-S,N)] 2+. Also, reactions with [Pt(en)(ox)] 2+ and SeMet were conducted and produced various products at two different pH’s. A [Pt(SeMet-Se,N2] 2+ product was formed at lower pH and produced free ethylenediamine, however at a higher pH only [Pt(en)(SeMet-Se,N)]2+ was produced.
10
Wong, Donald Chun Kit. "Toxic effects of selenite and selenate on marine microalgae : a physiological and ultrastructural study". Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29341.
Testo completoAbstract (sommario):
Seven species of marine phytoplankters assigned to different taxonomic divisions were tested for toxic responses to two different molecular species of selenium known to be prevalent in seawater, selenite and selenate. Selenate proved to be more toxic than selenite, although severe toxicity was only observed at high concentrations
(10⁻² and 10⁻³ M) of both selenate and selenite. At these concentrations, growth was completely or severely inhibited in most species tested. In some of the species that remained viable, both the percentage of motile cells and their swimming speed were drastically reduced. Scanning electron microscopy revealed that, under these circumstances, Dunaliella tertiolecta cells possessed much shorter flagella compared to the controls, while those that became non-motile lacked flagella altogether. Despite these striking alterations in both growth and morphology, cells of Amphidinium carterae, Dunaliella tertiolecta and Pavlova lutheri showed, after prolonged exposures, signs of adaptation to high selenium concentrations. Lower concentrations of selenium were generally non-toxic and frequently even stimulatory to growth. These observations suggest that for meaningful inferences on selenium toxicity
both the concentration range and the length of the studies must be considered and the potential for adaptation to high selenium concentrations taken into consideration.
The main ultrastructural and physiological changes in cells of Dunaliella tertiolecta, Pavlova lutheri and Amphidinium carterae treated with selenite or selenate involved the cell coat, mitochondria, chloroplasts as well as the respiratory and photosynthetic rates. Other changes were observed in the nucleus, lipids, vacuoles, nitrogen and carbon contents, but these showed greater variability among the microalgae studied. The major alterations suggested that energy transducing systems were severely affected by selenium toxicity. These led to significant decreases or even elimination of storage products which were indicative of severe shortage in energy and produced major reductions in growth. These occurred later upon exposure to the toxicant and coincided with the loss of cell coat material, suggesting that the shedding of cell surface material might play a major role in the detoxification and adaptation of the microalgae to toxic concentrations of selenium.Science, Faculty of
Botany, Department of
Graduate
11
Zhou, Jiamin, e University of Lethbridge Faculty of Arts and Science. "Synthesis of 1-chloro-1,2,4,6-selenatriazines and some products of reduction". Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2005, 2005. http://hdl.handle.net/10133/295.
Testo completoAbstract (sommario):
A general route to 1-chloro-1,2,4,6-selenatriazines with substuents on 3,5 positions has been developed by the reactions of N-imidoylamidines with selenium tetrachloride. The mechanism for these reactions is discussed according to the observed intermediates. At least two intermediates exist. One of the intermediates, 1,1-dichloro-3-trichloromethyl-4H-5-diisopropylphenyl-1,2,4,6-selenatriazine, was identified by 1HNMR, Mass spectroscopy and X-ray crystallography. 1-Chloro-1,2,4,6-selenatriazines were synthesized in high yield and fully characterized. Five 1-chloro-1,2,4,6-selenatriazine crystal structures were obtained. Reduction of 1-chloro-1,2,4,6-selenatriazines with triphenylamtimony immediately produced the corresponding selenatriazinyl radicals in hot acetonitrile. Pure radicals were obtained by in-situ crystallization as their dimers from reaction. Two crystal structures were obtained for 3-trifluoromethyl-5-p-tolyl-1,2,4,6-selenatriazinyl dimer and 3-trifluoromethyl-5-p-methyloxyphenyl-1,2,4,6-selenatriazinyl dimer. EPR spectroscopy measured all radicals coupling to three unique nitrogen atoms with 7 broad lines. There is no resolvable hyperfine coupling to 77Se, 37Cl/19F and phenyl protons.xv, 172 leaves : ill. ; 29 cm.
12
Khan, Rana. "Structural studies of halogen, interhalogen and pseudohalogen compounds of phosphorus, selenium and tellurium". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/structural-studies-of-halogen-interhalogen-and-pseudohalogen-compounds-of-phosphorus-selenium-and-tellurium(b1ba6ec9-198c-4de5-be73-f136a4db3ee0).html.
Testo completoAbstract (sommario):
A series of compounds with the general formula R3PX2 and R3PX4 (where R = o-tolyl, m-tolyl, p-tolyl, o-anisyl, m-anisyl, p-anisyl, o-thioanisyl, p-thioanisyl, p-fluorophenyl, p-chlorophenyl, mesityl and X = Cl, Br, I) have been synthesised and studied by X-ray crystallography, multinuclear NMR spectroscopy and Raman spectroscopy. A study of the conformational features of the aryl groups in these structures was undertaken in order to investigate the role of steric effects and crystal packing on P-X and X-X bond lengths. Compounds with the general formula RSeX / RSeX3 (where R = p-fluorophenyl, p-chlorophenyl, p-bromophenyl, p-iodophenyl and X = Cl, Br, I) have been synthesised by reacting the diselenides with halogens in the stoichiometric ratios. The X-ray crystal structure of p-ClC₆H₄SeI.I₂ is the first crystallographically characterised example of a compound of stoichiometry RSeI₃, although it is better represented as an I₂ adduct of a Se(II) iodide than a Se(IV) compound. In contrast, (p-FC₆H₄)Se-Se(I)₂(p-FC₆H₄) is an I₂ adduct where the Se-Se bond has not been cleaved by iodine. Both structures are stabilised by weak Se...I and I...I interactions. p-FC₆H₄SeCl₃ is an example of a dimeric structure with bridging chlorines. [Ph₄PX] and Ph₃PX₂ were reacted with PhEX (where E = Se, Te and X = I, Br, Cl) to produce salts containing [PhEX₂]- and [PhEX₄] anions. Where possible all the products were then analysed via NMR and Raman spectroscopy and X-ray crystallography. The reactions of the ligand tris-p-fluorophenyl phosphine with sulfur and selenium are presented along with the subsequent reactions of these compounds with diiodine. All of the compounds are characterised via X-ray crystallography.
13
Ghose, Aurnab. "Molecular mechanisms mediating the induction of apoptosis by chemopreventive selenium compounds". Thesis, University of Glasgow, 2001. http://theses.gla.ac.uk/1154/.
Testo completoAbstract (sommario):
Using the cervical carcinoma cell line, HeLa, molecular mediators of selenium-induced apoptosis were investigated. These studies were later extended to biopsies of normal human oral mucosa cells (NOMCs) and human oral carcinoma cells (SCCs), using a primary culture system. Two selenium compounds were tested: selenodiglutathione (SDG), the primary metabolite of selenite, the most commonly used cancer-protective selenium compound in animal models, and the synthetic compound, 1,4-phenylenebis (methylene)selenocyanate (pXSC), one of the most potent chemopreventive selenium compounds. Both compounds induced apoptosis in the cells tested and this was associated with a strong induction of Fas ligand (Fasl). Blocking Fas activation resulted in inhibition of apoptosis. Activities of stress kinases INK (c-jun N-terminal kinase) and p38 were also induced on selenium treatment and intervention studies using specific chemical inhibitors and/or dominant negative mutants suggested that INK, but not p38, was functionally important for the induction of apoptosis and Fasl. The relative levels of induction of INK activity and Fasl also correlated with the extent of apoptosis observed. On treatment with SDG, but not pXSC, SCCs were found to preferentially activate the JNK/Fasl pathway compared to NOMCs and this correlated with enhanced sensitivity of SCCs to SDG-induced apoptosis. Both SDG and pXSC also appeared to modulate activities of other signalling proteins like extracellular regulated kinases (ERKs) 1,2 & 5 and Akt. However, functional interference with these pathways using specific chemical inhibitors or constitutively activated mutants revealed either none or a small effect on apoptosis-induction. One exception was the activation of Akt by SDG in SCCs: inhibiting its activity sensitised the cells to apoptosis significantly. Finally, preliminary xenograft studies have confirmed the induction of apoptosis in vivo, using chemopreventive dietary levels of selenium.
14
Ryan, M. Dominic (Michael Dominic). "Organopolychalcogenides, new bond energy results and synthesis via the first selenium transfer reagent". Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75753.
Testo completoAbstract (sommario):
Reevaluation of organosulfur heats of formation resulted in the conclusion that the sulfur-sulfur bond of aliphatic disulfides is nearly 15 Kcal/mole stronger than the disulfide carbon-sulfur bond energy. Semi-empirical calculations using AM1, MNDO and MINDO/3 from the AMPAC program package confirmed these results and clarified their relative impact on organosulfide and disulfide properties.Existing organoselenium bond energy data were also reevaluated and erroneous assumptions discovered. New bond energy estimates were made via a new procedure. It was concluded that the selenium-selenium bond is also stronger than the selenium-carbon of aliphatic diselenides.
The above results led to the conclusion that loss of molecular dichalcogen from molecules such as disulfides or diselenides is favored over the stepwise loss of a single chalcogen by about 40 Kcal/mol. Loss of molecular diselenium from dibenzyl diselenide is reported. The average carbon-selenium bond energy of the latter is calculated to be only 27 Kcal/mol.
The preparation of 2-thiatriselenides (RSeSSeR) and 2,3-dithiatetraselenides (RSeSSSeR) has been achieved from selenosilanes. The products were characterized by $ sp{77}$Se NMR and the trends of chemical shifts were analyzed.
The preparation of the first selenium transfer reagents, including the first unsymmetrical chalcogen transfer reagent, is reported. Their use to effect the synthesis of 2-selenatrisulfides (RSSeSR) is also reported. Low temperature $ sp{77}$Se NMR was used to elucidate the reaction mechanism and characterize several intermediates such as selenuranes, selenonium ions and azole selenides. In addition, 2,3-diselenatetrasulfides (RSSeSeSR) were characterized by $ sp{77}$Se NMR.
15
Thomas, Paul Matthew. "Structural chemistry of organically templated materials". Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670194.
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16
Zhang, Shu. "Effect of chitosan on the induction of DNA damage response by selenium compounds". College Park, Md.: University of Maryland, 2009. http://hdl.handle.net/1903/10019.
Testo completoAbstract (sommario):
Thesis (M.S.) -- University of Maryland, College Park, 2009.Thesis research directed by: Dept. of Nutrition and Food Science. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
17
Majeed, Zulfiqar. "The reactions of directly related tellurium and selenium heterocyclic compounds with triiron dodecacarbonyl". Thesis, Aston University, 1999. http://publications.aston.ac.uk/9622/.
Testo completoAbstract (sommario):
The reactions of directly related tellurium and selenium heterocyclic compounds with triiron dodecacarbonyl are described. The reaction of 2-telluraphthalide, C8H8OTe with [Fe3(CO)12 gave [Fe{C6H4(CH2)Te}(CO)3]2, (1). An iron atom has inserted into the telluracyclic ring, and it is probable that one co-ordinated CO ligand arises from the initially organic carbonyl group. X-ray analysis of compound (1) showed that the compound has a Fe2Te2 core, which is achieved by dimerisation. The reaction of telluraphthalic anhydride, C8H402Te with [Fe3(CO)12] gave a known, but unexpected, organic phthalide product, C8H602, which was confirmed by X-ray crystallography. Selenaphthalic anhydride, C8H4O2Se gave intractable products on reaction with [Fe3(CO)12], 2-selenaphthalide, C8H6OSe, on reaction with [Fe3(CO)12] gave a major product [Fe2{C6H4(CH2)Se}(CO)6], (2) and a minor product [Fe3{C6H4(CH2)Se}(CO)8], (3) which is an intermediate in the formation of (2). X-ray analysis of (2) shows that compound (2) is very similar to (1) except that the 18 electron rule is satisfied by co-ordination of a Fe(CO)3 moiety, rather than dimerisation. Compound (3), also studied by X-ray crystallography, differs from (2) mainly in the addition of an Fe(CO)2 moiety. Telluraphtbalic anhydride, C8H402Te, and selenaphthalic anhydride, C8H402Se, are both monoclinic and crystallise in space group P21/n. 2-Selenaphthalide, C8H402Se, is also monoclinic, space group P21/C. The reactions of the following compounds (l,3-dihydrobenzo[c]selenophene, 1,3,7,9-tetrahydrobenzo[1,2c; 4,5c'] ditellurophene, dibenzoselenophene, phenoxselenine, 3, 5-naphtho-1-telluracyclohexane and 3,5-naphtho-1-selenacyclohexane) with [Fe3lCO)12] are reported. It is unfortunate that the above compounds do not react under the conditions employed; this may be due to differing degrees of ring strain. 1,8-bis(bromomethyl)naphthalene, C12H10Br2 is monoclinic and crystallises in space group C2/c. 1,1-diiodo-3,5-naphthotelluracyclohexane, C12H10TeI2 and 3,5-naphtho-l-telluracyclohexane, C12H10Te are monoclinic and crystallise in space group P21/c. 3,5-naphtho-l-selenacyclohexane, C12H10Se and 2,2,8,8-tetraiodo-1,3,7,9-tetrahydrobenzo[1,2c;4,5c']ditellurophene are also monoclinic, space group P21/a. The syntheses of intramolecular stabilised organo-tellurium and selenium compounds are reported, having a general formula of REX (where R = phenylazophenyl; E = Se, Te; X = electronegative group, for example C1, Br or I). The crystal structures of R'TeBr, RTeI, RSeCI, RSeCI/I and RSeI (where R = phenylazophenyl) are reported. The tellurium containing X-ray structures are triclinic and have a space group P-1. The selenium containing X-ray structures are monoclinic with space group P21/n. The inclusion of nitrogen in selenium heterocycles provides access to an entirely new area of organometallic chemistry. The reaction of 2-methylbenzoselenazole with [Fe3(CO)12] gave [Fe2{C6H4(NCH2CH3)Se}(CO)6]. The reactions of 2-(methyltelluro)benzanilide or 2-(methylseleno)benzanilide with [Fe3(CO)12] gave reaction products [Fe2(μTeMe)2(CO)6] and [Fe2 (μ-SeMe)2(CO)6] respectively, which were confmned by X-ray crystallography. The use of Mossbauer spectroscopy on the products obtained from the reactions of heterocyclic compounds with [Fe3(CO)12] can give useful information, for example the number of iron sites and the environments of these iron sites within the products.
18
Björk, Malin. "Synthesis of sulfur and seleniumn heterocycles, including derivatives of imidazopyridine and benzimidazole /". Stockholm, 2005. http://diss.kib.ki.se/2005/91-7140-597-6/.
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Burriss, Daniel. "INTERACTIONS OF COMPOUNDS CONTAINING GROUP 12 AND 16 ELEMENTS". UKnowledge, 2017. https://uknowledge.uky.edu/chemistry_etds/89.
Testo completoAbstract (sommario):
The focus of this dissertation is on the interactions of compounds containing group 12 and 16 elements. This work is presented in three major parts. First, the interaction of the synthetic dithiol N,N’-bis(2-mercaptoethyl)isophthalamide), abbreviated BDTH2, with selenite. Second, the interaction of cysteine with Cd(II) and the biologically relevant Cd-Cysteine crystal structure. Third, the green synthesis of CdSe quantum dots (QDs).
The interaction of BDTH2 with selenite is different from the interactions with other metals and metalloids previously studied. Under ambient conditions, BDTH2 is oxidized to the disulfide, BDT(S-S), while selenite is reduced to elemental selenium. However, under carefully controlled conditions, the reaction of BDTH2 with selenite produces a mixture of BDT(S-S) and the covalently bound Se(II) species, BDT(S-Se-S). While the mixture could not be separated, experimental 77Se NMR combined with computational analysis confirmed the presence of BDT(S-Se-S).
The interaction of the amino acid cysteine with Cd(II) was studied as a means to sequester, and potentially recycle, Cd(II) from bulk CdS waste. Single crystals of Cd(Cys)Cl·H2O were grown, and the crystal structure determined. Surprisingly, this is only the second structure to be determined by X-ray crystallography of a compound containing the Cd-Cysteine unit. Not only does this structure have biological relevance, but it also corrects a structure proposed in 1965.
Using the knowledge gained from studying the interaction of BDTH2 with selenite, a green synthesis of water-soluble CdSe QDs by the reaction of selenite with Cd(Cys)Cl·H2O in water at room temperature was developed. This green method for the synthesis of CdSe QDs was extended to ZnSe and HgSe QDs. The mechanism of CdSe formation was investigated using Cd(II) combined with various thiols.
20
Malik, Muhammad Shahid. "Chiral discrimination of selenium containing compounds through multinuclear NMR spectroscopy in the presence of a chiral dirhodium complex". [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=968000215.
Testo completo
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Wang, Ziyan, e 王子砚. "MBE growth of AlInN and Bi2Se3 thin films and hetero-structures". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47163483.
Testo completoAbstract (sommario):
Molecular Beam Epitaxy is an advanced method for the synthesis of single-crystal thin-film structures. However, the growth behavior varies case by case due to the complicated kinetic process. In this thesis, the epitaxial growth processes of AlxIn1-xN alloy and Bi2Se3 thin-films are studied.
Heteroepitaxial growth of AlxIn1-xN alloy on GaN(0001) substrate is carried out in the Nitrogen-rich flux conditions. A series of transient growth stages are identified from the initiation of the deposition. A significant effect of source beam-flux on the incorporation rate of Indium atoms is observed and measured. A correlation between the incorporation rate and the growth conditions (flux ratio and growth temperature) is revealed by the dependence of the growth-rate of the film on beam fluxes. A mathematic model is then suggested to explain the effect, through which the measured results indicating a surface diffusing and trapping process is indicated. Unexpected behavior of the lattice-parameter evolution of the growth front during deposition is also observed, indicating a complex strain-relaxation process of the epilayers.
For three-dimensional (3D) topological insulator of Bi2Se3, growths are attempted on various substrate surfaces, including clean Si(111)-(7x7), Hydrogen terminated Si(111), Bismuth induced Si(111) reconstructed surfaces, GaN(0001), and some selenide “psudo-substrates”. The specific formation process of this quintuple-layered material in MBE is investigated, from which the Van der Waals epitaxy growth characteristics inherent to deposition of Bi2Se3 is determined, and the mechanism of the “two-step growth” technique for this material is further clarified. Among the various substrates, those that are inert to chemical reaction with Bi/Se are important for the growth. The epilayers’ lattice-misfit with the substrate is also a crucial factor to the structural quality of the Bi2Se3 epifilms, such as the defects density and the single-crystalline domain size. The effect of a vicinal substrate on suppressing the twin-defects in film is also addressed. Using a suitable substrate and adapting an optimal condition, ultra-thin films of Bi2Se3 with a superior structural quality have been achieved. Multilayered Bi2Se3 structures with ZnSe and In2Se3 spacers are attempted. Finally the high-quality superlattices of Bi2Se3/In2Se3 are successfully synthesized. The hetero-interfaces in the superlattice structure of Bi2Se3/In2Se3 are sharp, and the individual layers are uniform with thicknesses being strictly controlled.
The behaviors of strain evolution during the hetero-growth process are finally investigated. An exponential relaxation of misfit strain is observed. And the correlation between the residual strain and the starting surface in the initial growth stage is also identified.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
22
Ramoutar, Ria R. "Understanding the antioxidant mechanism of inorganic selenium, oxo-sulfur, and polyphenol compounds, and the biological implications of functionalized nanoparticles". Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1252937986/.
Testo completo
23
Viswanathan, Uma Maheswari [Verfasser], e Claus [Akademischer Betreuer] Jacob. "Study of antimicrobial, biochemical and nanotechnological aspects of novel sulfur, selenium and tellurium compounds / Uma Maheswari Viswanathan. Betreuer: Claus Jacob". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2014. http://d-nb.info/1058360779/34.
Testo completo
24
Hassan, Mohammad Rokib, e University of Lethbridge Faculty of Arts and Science. "Self-assembled molecular rods and squares with chalcogenadiazole framework ligands". Thesis, Lethbridge, Alta. : University of Lethbridge, Dept. of Chemistry and Biochemistry, c2010, 2010. http://hdl.handle.net/10133/2639.
Testo completoAbstract (sommario):
During the attempts to carry out Suzuki coupling reactions, the σ-bonded Pd−Caryl
benzochalcogenadiazolyl complexes trans-[ClPd(PPh3)2(C6H2BrN2E)] (E = S, Se) were
isolated. The corresponding bromo derivatives were also synthesized on purpose to
investigate their activity in Stille coupling reactions. A head-to-tail dimer trans-
[{ClPd(PPh3)(μ-C6H2BrN2Se)}2] was synthesized from the thermolysis of trans-
[ClPd(PPh3)2(C6H2BrN2Se)] in the presence of SeO2. The reduction potentials of the
mononuclear and dinuclear complexes were measured by cyclic voltammetry (CV) and
square wave voltammetry (SWV).
4,7-bis(2/4-pyridyl)benzochalcogenadiazole ligands were synthesized by Stille coupling
reactions and the 1,5-bis(4-pyridyl)naphthalene ligand was prepared by a Suzuki
coupling reaction. Reactions of the labile complex [BrRe(CO)4(NCMe)] with 4,7-bis(4-
pyridyl)benzochalcogenadiazole ligands in a 2:1 ratio afforded self-assembled molecular
rods [{ReBr(CO)4}2(μ-4,7-bis(4-pyridyl)benzochalcogenadiazoles)]. Palladium directed
molecular squares [(enPd)(μ-4,7-bis(4-pyridyl)benzochalcogenadiazole)]4[PF6]8 were
prepared by reactions of enPd(PF6)2 and 4,7-bis(4-pyridyl)benzochalco-genadiazoles in a
1:1 ratio. The optoelectronic properties of the ligands and the molecular rods were
investigated by CV and SWV, and by luminescence spectroscopy. The optical properties
of the square complexes were also studied by luminescence spectroscopy.xvii, 152 leaves : ill. (some col.) ; 29 cm
25
Kruger, John Scott. "Synthesis and characterization of several novel aluminum and gallium phosphates templated by cobalt complexes". Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/30553.
Testo completo
26
Kullberg, Martin. "Studies on nucleoside H-phosphonoselenoate chemistry and chalcogen exchange reaction between P(V) and P(III) compounds". Doctoral thesis, Stockholm : Institutionen för organisk kemi, Stockholms universitet, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-736.
Testo completo
27
Karimi, Farhad. "[11C]Carbon Monoxide in Palladium- / Selenium-Promoted Carbonylation Reactions : Synthesis of 11C-Imides, Hydrazides, Amides, Carboxylic Acids, Carboxylic Esters, Carbothioates, Ketones and Carbamoyl Compounds". Doctoral thesis, Uppsala universitet, Avdelningen för organisk kemi, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2931.
Testo completoAbstract (sommario):
[11C]Carbon monoxide in low concentrations has been used in palladium- or seleniummediated carbonylation reactions such as the synthesis of 11C-imides, hydrazides, amides, carboxylic acids, esters, carbothioates, ketones and carbamoyl compounds. In these reactions aryl iodides have been used in most cases. However, less reactive aryl triflate, chloride and bromides were activated using tetrabutylammonium iodide. The reactivities of nucleophiles may have influence on the radiochemical yield of the 11Clabelled compounds. Carboxyamination of aryl halides using aniline derivatives yielded 10% of the corresponding 11C-amide. However, the radiochemical yields increased significantly when the aniline derivatives were treated with lithium bis(trimethylsilyl)amide. In contrast, this reagent did not improve the radiochemical yields when primary amines such as methylamine and benzylamine were used. In these cases the radiochemical yields were improved by using pempidine. 11C-Esterification usually gave low yields. However, the radiochemical yields of 11C-esters could be improved by using magnesium bromide and pempidine. An excess of ligand may have a significant impact on palladium-promoted carbonylation reaction. The radiochemical yields of 11C-ketones were improved when using excess amounts of tri-o-tolylphosphine. (13C)Carbon monoxide may be utilized for the synthesis of 13C-substituated compounds in order to confirm the position of 11C-labelling.
28
Costa, Carlos Eduardo da. "Biotransformações na obtenção de hidróxi-selenetos e hidróxi-teluretos quirais". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/46/46135/tde-20062016-125006/.
Testo completoAbstract (sommario):
Neste trabalho foi estudado o comportamento de hidróxi-calcogenetos (Se e Te) frente a biotransformações, empregando enzimas isoladas em meio orgânico ou aquoso e empregando microorganismos (fungos). Estudos comparativos sobre a influência de diversas variáveis, como solvente, temperatura, imobilização enzimática e estrutura do hidróxi-calcogeneto, foram realizados. Inicialmente os compostos foram sintetizados utilizando métodos descritos na literatura, em seguida foi estudada a resolução de hidróxiselenetos em meio orgânico empregando lipases isoladas (Esquema 1), (ver arquivo), incluindo um estudo de imobilização da PSL em diversos suportes, além do estudo da influência da variação do solvente, da temperatura, da lipase, etc. Na resolução em meio aquoso empregando enzimas isoladas, primeiramente os hidróxi-selenetos foram acetilados quimicamente e depois realizado uma triagem (com dez enzimas de diferentes fontes) empregando indicador de pH colori métrico. Posteriormente os acetatos dos hidróxi-selenetos (Esquema 2) (ver arquivo) foram submetidos à resolução enzimática em meio aquoso empregando as enzimas que foram selecionadas na triagem enzimática. As biotransformações utilizando fungos foram realizadas empregando células inteiras de algumas linhagens de Aspergillus terreus. Na seqüência foi realizada a resolução de hidróxi-teluretos em meio orgânico utilizando lipases isoladas (Esquema 3)(ver arquivo). Nessas resoluções também foi estudada a influência da variação do solvente, da lipase, do tempo, etc. De forma a demonstrar a importância dos compostos resolvidos, um hidróxi-seleneto quiral e dois hidróxi-teluretos quirais foram usados para preparar compostos pertencentes a classes de unidades estruturais de vasta ocorrência em produtos naturais: um álcool alílico e duas lactonas (Esquema 4)(ver arquivo).In this work, the behavior of hydroxy chalcogenides (Se and Te) towards the biotransformations using isolated enzymes in organic media or aqueous media and using microorganisms (fungi) was studied. A comparative study of the effect of temperature, solvent, enzyme immobilization and structure of the substrates on the resolution was performed. Initially, the compounds had been synthesized using described methods in the literature, after, the resolution of hydroxy selenides in organic media using isolated lipases was carried out (Scheme 1)(see PDF), including a study on the immobilization of PPL on some supports, as well studies on the influence of the variation of the solvent, the temperature, lipase, etc. In the resolution in aqueous media using isolated lipases, initially the hydroxy selenides were transformed into their acetates by convertional chemical methods, and then, a screening with ten enzymes from different sources was carried out using pH indicator. In the following, the enzymatic resolution of the selanyl acetates in aqueous media using the enzymes selected in the screening step was performed (Scheme 2)(see file). The biotransformations by fungi were performed using whole cells of some Aspergillus terreus strains. In the sequence, the resolution of hydroxy tellurides in organic media using isolated lipases was carried out (Scheme 3) (see file). In these resolutions, the influence of the variation of the solvent, lipase and the reaction time was also studied. In order to demonstrate the potencial of the resolved compounds, one chiral hydroxy selenide and one chiral hydroxy telluride were used to prepare compounds belonging to classes of building blocks of wide occurrence in natural products: an allylic alcohol and a lactone (Scheme 4)(see file).
29
Hsu, Chih-An. "Absorber and Window Study – CdSexTe1-x/CdTe Thin Film Solar Cells". Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7813.
Testo completoAbstract (sommario):
CdTe an II-VI semiconductor has been a leading thin film photovoltaic material due to its near ideal bandgap and high absorption coefficient [1]. The typical thin film CdTe solar cells have been of the superstrate configuration with CdS (Eg-2.42eV) as the n-type heterojunction partner. Due to the relatively narrow bandgap of CdS, a wider bandgap n-type window layer has recently emerged as a promising substitute: alloys of MgyZn1-yO have been successfully used as the emitter or window layer. The benefits in the usage of MgyZn1-yO (MZO) are its tunable bandgap and wide optical spectrum on optoelectronic devices. Due to an increasing bandgap of the window layer, the carrier collection can be improved in the short wavelength range (<500 nm). In addition alloys of CdSexTe1-x (CST) have also been used in the absorber layer (i.e., CST/CdTe) for the fabrication of CdTe devices to improve the carrier collection and lifetime [2]. The lower bandgap of the CST alloy can lead to higher short-circuit current (JSC), but it can also result in lower open circuit voltage (VOC). Another critical aspect of the CdTe solar cell is the use of copper as a p-type dopant, which is typically incorporated in the cell during the fabrication of the back contact. The most challenging issue related to further advancing the CdTe solar cell efficiency is the relatively low level of p-type doping, which limits the VOC. Efforts to dope CdTe with group V dopants are yet to produce the desired results.
ZnO has been used as an effective high resistivity transparent. When CdTe is deposited directly on sputtered ZnO, VOC of typically 500-600 mV is produced. Band alignment measurements indicate that a negative conduction band offset with CdS exists; alloying with MgO to produce MgyZn1-yO with a composition of y = 0.15 can produce a flat conduction band alignment with CdS. This material has an additional benefit for improving the energy bandgap of the MZO for better UV light transmission in the short wavelengths. By changing the magnesium content from y = 0 to 0.30 allowed researchers to make the tunable conduction band offset from a “cliff” to a “spike,” with both increased open-circuit voltage and fill factor as increasing magnesium compositions [3] — the bandgap gains as expected with increased magnesium composition. The large compositions (y > 0.30) of MgyZn1-yO cause the enormous spike result in S-kink in the IV measurement so that the FF decreases. Besides, due to the instability of MZO material, the fabrication process has to proceed carefully.
The properties of CST films and cells were investigated as a function of Se composition (x), substrate temperature (TSUB), and ambient used during the CSS deposition. The higher ratio of Se in CST alloy causes the smaller grain structures and lower bandgap, which profoundly detrimental to the device performance (VOC). However, the CST can be deposited in various substrate temperatures and different inert ambient gas to improve the grain structure by utilizing the especial Close Space Sublimation (CSS) deposition system. Therefore, despite the fact that the CST (25% Se) has the optical bandgap (1.37eV), the improvement of grain structure can slightly increase the doping concentration and decrease the grain boundary (GBs) due to increased alloys grain size 3X larger, which is contributed to improving the VOC [4]. The study of higher ratio Se of CST alloy is significant to achieve the high efficiency polycrystalline CST/CdTe photovoltaic devices.
The effect of Cu doping back contact in CdSexTe1-x (CST)/CdTe solar cells with varying amounts of Se (x) has been investigated. The Cu-based back contact was annealed at different thermal temperatures in order to vary the amount of Cu in-diffusion. Net p-type doping was found to increase as the back-contact annealing temperature increased. All cells exhibited a decrease in VOC with increased annealing temperature (i.e., higher Cu concertation), presumably due to a degradation of the lifetime with increased amounts of Cu [5]. However, cells with the highest Se composition appeared to exhibit a higher degree of tolerance to the amount of Cu – i.e., they exhibited a smaller loss in VOC with the increased amount of Cu.
Extrinsic p-type doping of CdSeTe can be fabricated using two different experimental processes. Firstly, by using group I elements such as, Cu to substitute Cd, which is promising during the back contact process. Secondly, using group V (P, As, Sb) elements to substitute Te, and this is suitable for Cd-rich of intrinsic CdTe. Intrinsic CST alloy has lower hole density concentration as higher Se composition with limitation of the VOC. Thus, in order to increase the p-type net doping up to 1016 cm-3 the extrinsic P or As doping have been widely investigated recently. The research studies show the CST/CdTe devices lead to improve VOC up to 850 mV with higher hole density in higher Se compositions of As doped CST alloys. Nevertheless, the group V doped CdTe still cause the formation of compensating defects limits the upper boundary of dupability on the CdTe thin film solar cells. Even if a high hole density concentration is achieved for intrinsically-doped p-type CST/CdTe, it is believed the poor carrier lifetime in the CdTe side would still limit the VOC.
30
Sarfraz, Muhammad [Verfasser]. "Evaluation of antimicrobial and nematicidal properties of nanosized materials, and investigation of the mode of action of redox-active sulfur and selenium compounds / Muhammad Sarfraz". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1222513471/34.
Testo completo
31
Waddell, Paul G. "Metal-chalcogen-nitrogen ring complexes and crystallographic studies". Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/987.
Testo completoAbstract (sommario):
A series of Pt(S₂N₂)(P(OR)[subscript n]R′[subscript(3-n)])₂ complexes were prepared and analysed using ³¹P NMR and IR spectroscopy, elemental analysis and X-ray crystallography. Similarly, a series of Pt(SeSN₂)(P(OR)[subscript n]R′[subscript(3-n)])₂ complexes were also prepared and analysed. The ¹J[subscript(Pt-P)] coupling constants and Pt-P bond lengths for these complexes are influenced by the oxygen content of their phosphorus ligands. The ³¹P NMR spectra for a series of [Pt(S3N)(P(OR)[subscript n]R′[subscript(3-n)])₂][BF₄] complexes are also reported. Planar [S₂N₂H]⁻ complexes were prepared and the X-ray crystal structure of [Pd(S₂N₂H)(bipy)][Cl] is reported. The X-ray structures of MX₂(P(OR)[subscript n]R′[subscript(3-n)])₂ are reported and compared with the previously reported analogues. The magnitude of the ¹J[subscript(Pt-P)] varies linearly with the Pt-P bond length (l[subscript(Pt-P)] = 2.421 – J/24255) for the 12 platinum-containing complexes. This correlation is compared to that of a larger series of complexes. A series of M(ndsdsd₂ (ndsdsd = bis[(nitrilo(diphenyl)-λ⁶-sulfanyl)](diphenyl)-λ⁶-sulfanediimide (Ph₂S(=N-(Ph₂)S≡N)₂)) complexes were prepared and characterised using elemental analysis and multinuclear NMR and IR spectroscopy where appropriate. The X-ray crystal structures of five examples are reported.
32
Colakoglu, Tahir. "The Effects Of Post-annealing Process On The Physical Properties Of Silver-indium-selenium Ternary Semiconductor Thin Films Deposited By Electron Beam Technique". Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12610974/index.pdf.
Testo completoAbstract (sommario):
Ternary chalcopyrite compounds are the semiconductors with suitable properties
to be used as absorber materials in thin film solar cells. AgInSe2 is a promising
candidate with its several advantages over the widely used CuInSe2. The purpose of this study was to optimize the physical properties of the Ag-In-Se (AIS)
thin films that were deposited by e-beam evaporation of Ag3In5Se9 single crystal powder for solar cell applications by means of post-annealing process under
nitrogen atmosphere. The as-grown AIS thin films were annealed at 200, 300 and 400oC and their structural, optical, electrical and photoelectrical properties were examined to
observe the effects of post-annealing process. Structural characterization of the films was performed by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses. Optical properties of the films were investigated by optical transmittance measurements. Electrical and photoelectrical properties of the films were examined by temperature dependent conductivity, photoconductivity under different illumination intensities and spectral photoresponse measurements.
It was discovered that the annealing of AIS thin films at 200oC resulted in the best physical properties for solar cell applications. The obtained films were polycrystalline with mixed binary and ternary crystalline phases, such as
Ag3In5Se9, AgInSe2 and InSe, and showed n-type conductivity with room temperature conductivity value of 2.3x10-6 (Ohmcm)-1. The band gap energy of the 200oC-annealed films was determined as 1.68 eV from spectral photoresponse measurements. The results of the study revealed that the inadequate Ag incorporation and segregation and/or reevaporation of Se atoms at high annealing temperatures were the major problems encountered in producing single phase polycrystalline AgInSe2 thin films. The required stoichiometry of thin films should be maintained during the growth of the films by means of an alternative deposition procedure and the films should be selenized during post-annealing process.
33
Karimi, Farhad. "[11C]Carbon Monoxide in Palladium- / Selenium-Promoted Carbonylation Reactions : Synthesis of 11C-Imides, Hydrazides, Amides, Carboxylic Acids, Carboxylic Esters, Carbothioates, Ketones and Carbamoyl Compounds". Doctoral thesis, Uppsala University, Organic Chemistry, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2931.
Testo completoAbstract (sommario):
[11C]Carbon monoxide in low concentrations has been used in palladium- or seleniummediated carbonylation reactions such as the synthesis of 11C-imides, hydrazides, amides, carboxylic acids, esters, carbothioates, ketones and carbamoyl compounds.
In these reactions aryl iodides have been used in most cases. However, less reactive aryl triflate, chloride and bromides were activated using tetrabutylammonium iodide.
The reactivities of nucleophiles may have influence on the radiochemical yield of the 11Clabelled compounds. Carboxyamination of aryl halides using aniline derivatives yielded 10% of the corresponding 11C-amide. However, the radiochemical yields increased significantly when the aniline derivatives were treated with lithium bis(trimethylsilyl)amide. In contrast, this reagent did not improve the radiochemical yields when primary amines such as methylamine and benzylamine were used. In these cases the radiochemical yields were improved by using pempidine.
11C-Esterification usually gave low yields. However, the radiochemical yields of 11C-esters could be improved by using magnesium bromide and pempidine.
An excess of ligand may have a significant impact on palladium-promoted carbonylation reaction. The radiochemical yields of 11C-ketones were improved when using excess amounts of tri-o-tolylphosphine.
(13C)Carbon monoxide may be utilized for the synthesis of 13C-substituated compounds in order to confirm the position of 11C-labelling.
34
Braga, Hugo de Campos. "Seleno-carboidratos: síntese e avaliação preliminar da atividade biológica". Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/9/9138/tde-01082011-145204/.
Testo completoAbstract (sommario):
No presente trabalho foram desenvolvidas duas rotas sintéticas: uma para a preparação de uma série de seleno-carboidratos quirais, derivados da D-xilose e D-galactose, e outra aplicada à obtenção de glicoconjugados e dissacarídeos, onde as duas unidades básicas encontram-se ligadas por um átomo de selênio. Através de estratégias sintéticas simples e eficientes, obteve-se uma série de compostos heterocíclicos com elevado potencial para aplicação biológica. Para a síntese dos derivados xilofuranosídeos, a D-xilose 1 foi inicialmente convertida no diol 3, passando por um intermediário bis-acetonídeo 2. Tosilação seletiva da hidroxila primária, seguida da reação com nucleófilos de selênio resultou na síntese dos seleno-carboidratos 5a-j. Adicionalmente, o composto 5a foi convertido no derivado metilglicosilado 6, mediante desproteção do acetonídeo e reação com metanol em meio ácido. A reação do tosilato 4 com Li2Se2 e Li2Se resultou na formação do disseleneto 7 e do seleneto 8. Posteriormente, uma série de seleno-carboidratos funcionalizados foi preparada pela clivagem redutiva de 7 e reação do selenolato formado com eletrófilos selecionados. A expansão do escopo do trabalho para síntese de derivados galactopiranosídeos contendo selênio seguiu estratégia à anterior. Assim, a D-galactose 12 foi convertida ao bis-acetonídeo e em seguida, a hidroxila primária foi convertida no correspondente tosilato 13 e mesilato 14. Foi utilizado o mesilato 14 para fornecer os seleno-carboidratos 15a-e e 16. Ainda, o disseleneto 17 foi preparado a partir do tosilato 13, e quando clivado com NaBH4, o selenolato gerado reagiu com eletrófilos selecionados, levando a seleno-piranosídeos funcionalizados. Entre os compostos preparados, o disseleneto 7 reduziu significativamente a atividade in vitro da enzima δ-aminolevulinato desidratase, enquanto o fenilseleneto 5a levou à aumento da atividade enzimática, o que aponta para uma atividade antioxidante promissora. Na segunda parte do trabalho, a reatividade dos seleno-carboidratos foi explorada na síntese de glicoconjugados 22 a partir da abertura regiosseletiva de N-Boc aziridinas quirais 23 (A). Numa segunda estratégia utilizou-se β-amino-disselenetos 24 como fonte de selenolato que reagiu com o tosilato 4 com menor eficiência (B). Adicionalmente, foi desenvolvida uma estratégia para a síntese de dissacarídeos conectados por um átomo de selênio, mediante reação de um selenolato glicosídico com outra unidade glicosídica adequadamente funcionalizada.In the present work two different synthetic routes for the synthesis of seleno-carbohydrates were developed starting from the readily available carbohydrates D-xylose and D-galactose. Furthermore, we developed a strategy for the synthesis of glycoconjugates and disaccharides, with the two basic units linked by a selenium atom. Through simple and efficient synthetic strategies, we obtained a series of heterocyclic compounds with high potential for biological application. For the synthesis of xilofuranosides derivatives, D-xylose 1 was initially converted into diol 3, through an intermediate bis-acetonide 2. Selective tosylation of the primary hydroxyl, followed by reaction with selenium nucleophiles resulted in the synthesis of seleno-carbohydrate 5a-j. Additionally, the compound 5a was converted into methylglycosyl derivatived 6 by deprotection of the acetonide and reaction with methanol in acidic medium. The reaction of tosylate 4 with Li2Se2 and Li2Se resulted in the formation of the diselenide and selenide 7 and 8. Subsequently, a series of functionalized seleno-carbohydrates were prepared by reductive cleavage of 7 and reaction of the resulting selenide anion with selected electrophiles. In order to expand the scope of the work, the synthesis of galacto-pyranosides containing selenium was pursued, according to the previous strategy. Thus, D-galactose 12 was converted to bis-acetonide and then the primary hydroxyl was converted into the corresponding tosylate and mesylate 13 and 14. Mesylate 14 was used to provide the seleno-carbohydrate 15a-e and 16. Moreover, the diselenide 17 was prepared from tosylate 13, and when cleaved with NaBH4, the resulting selenide anion was trapped with selected electrophiles, leading to functionalized seleno-pyranosides. Among the compounds prepared, the diselenide 7 significantly reduced the in vitro activity of the enzyme δ-aminolevulinate dehydratase, while the phenylselenide 5a increased enzyme activity, which points to a promising antioxidant activity. In the second part of the work, the reactivity of seleno-carbohydrates has been exploited in the synthesis of glycoconjugates 22 from the regioselective opening of chiral N-Boc aziridines 23 (A). In a second strategy β-amino-diselenides 24 were used as a source of the selenium nucleophile, reacting with tosylate 4 with lower efficiency (B). Additionally, we developed a strategy for the synthesis of disaccharides linked by a selenium atom by a reaction glycosylselenolate with another functionalized glycosyl unit.
35
Griffin, Ivan John. "Optical and magneto-optical studies of wide-bandgap semiconductors". Thesis, University of Bath, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341172.
Testo completo
36
Stolze, Karoline. "Synthese und Charakterisierung niedervalenter Actinoidphosphidtelluride und ternärer Selen-Halogenid-Komplexe des Iridiums". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-202233.
Testo completoAbstract (sommario):
Metallpniktide und -chalkogenide erfahren zunehmend mehr Aufmerksamkeit in Chemie und Festkörperphysik. Dieses Interesse liegt unter anderem in der ungewöhnlichen Strukturchemie der Verbindungen begründet. In den Pniktogen(Pn)- bzw. Chalkogen(Q)-reichen Verbindungen dieser Systeme ist besonders häufig die Bildung der jeweiligen Oligo- oder Polyanionen bzw. Moleküle zu beobachten. Einerseits können die homoatomaren Pn–Pn- bzw. Q–Q-Bindungen zur Ausbildung niederdimensionaler Strukturmotive mit anisotropen Eigenschaften, wie bspw. Supraleitung und Metall-Halbleiter-Übergänge, führen; andererseits ergeben sich aus dem sterischen Raumanspruch der Struktureinheiten in Kombination mit den hohen Koordinationszahlen schwerer Übergangs- oder Actinoidmetalle komplexe Strukturen. Die Pn- bzw. Q-Atome treten häufig gemischtvalent auf, was zusammen mit den beschriebenen Strukturmerkmalen die enorme Variabilität und Anpassungsfähigkeit dieser Stoffsysteme widerspiegelt.
Im Rahmen des ersten Teils der vorliegenden Dissertation wurde die potentielle Oligoanionenbildung in den bisher als quadratisch-planar beschriebenen Phosphidschichten von Actinoidphosphidtelluriden diskutiert. Über eine chemische Transportreaktion mit Iod ist es gelungen Kristalle des Uranphosphidtellurids UPTe und des verwandten, bisher unbekannten Diuranphosphidditelluridoxids U2PTe2O zu züchten und die Kristallstrukturen durch Einkristallröntgendiffraktometrie aufzuklären. Die Strukturen beider Verbindungen können durch eine Abfolge von [U2P2]- und [Te2]-Schichten, bzw. [U2P2]-, [U2O2]- und [Te2]-Schichten entlang [001] beschrieben werden. Die Phosphoratome in den [U2P2]-Abschnitten bilden eine Schicht parallel ausgerichteter P2-Anionen. Die Zusammenlagerung der Phosphoratome sowie die geordnete Ausrichtung der Hanteln bedingt eine Symmetriereduktion der ursprünglich tetragonal angenommenen Struktur mit fehlgeordneten Phosphoratomen hin zu einem Strukturmodell in der monoklinen Raumgruppe I11m. Bindungsanalysen im Realraum mit Hilfe des Elektronen-Lokalisierbarkeits-Indikator (ELI D) ergaben für UPTe in der monoklin verzerrten Struktur ein zusätzliches Doppelmaximum auf der gedachten Linie zwischen den Phosphoratomen P1 und P2, welches als homoatomare P–P-Bindungen interpretiert werden kann.
Zudem konnte über eine Festkörpersynthese die ternäre Verbindung Thoriumphosphidtellurid ThPTe erhalten werden, deren Pulverröntgendaten ein zu UPTe analoges Strukturbild zeigt. Wenngleich die Fehlordnung in der Phosphorschicht von ThPTe experimentell nicht aufgelöst werden konnte, war es durch Raman-Spektroskopie möglich, die Existenz der P2 Hanteln sowohl in ThPTe als auch in UPTe zu belegen. Beide isotype Verbindungen können in ionischer Grenzschreibweise als A4+ + ½ P24– + Te2– (A = Th, U) formuliert werden.
Im zweiten Teil der vorliegenden Dissertation wurde die vielfältige Strukturchemie neuer Selen-Halogenid-Komplexe des Iridiums insbesondere hinsichtlich ihrer Oligoselenidliganden sowie koordinativ gebundener Selenmoleküle dargelegt. Durch die Aktivierung von elementarem Iridium in Selentetrahalogenid-Schmelzen konnten erstmalig Verbindungen im System Ir–Se–Br dargestellt und die Strukturvielfalt im System Ir–Se–Cl signifikant erweitert werden. Die synthetisierten ein- bis achtkernigen Iridium(III)-Komplexe zeichnen sich durch eine bemerkenswerte Diversität ihrer Liganden aus, die von Halogenidionen, Selenmono- und Selendihalogenid-Einheiten über zyklische Selenmoleküle bis zu Oligoselenidketten reicht. Die variablen Verknüpfungsmoden dieser Liganden erweitern zusätzlich das Spektrum möglicher Komplexformen und -größen.
Die kleinsten, dargestellten ternären Iridiumkomplexe a-fac-[IrBr3(SeBr2)3], m-fac-[IrBr3(SeBr2)3] und mer-[IrBr3(SeBr2)3] besitzen ausschließlich endständige Selendibromid- und Bromidliganden, die sich in ihrer Konfiguration unterscheiden.
In den isotypen, zweikernigen Iridiumkomplexen [Se9(IrX3)2] (X = Cl, Br, Cl/Br) wird ein ungeladener, unter den Allotropen des Selens unbekannter Se9-Ring in Kronen-Konformation durch zwei IrX3-Moleküle stabilisiert. Der cyclo-Nonaselenligand ist der erste seiner Art, der mittels Röntgenbeugung am Einkristall charakterisiert werden konnte. Se9(IrCl1.66(1)Br1.34(1))2 repräsentiert zudem die erste quaternäre Verbindung in den Systemen M–Se–Cl–Br (M = Platinmetalle).
Die ringförmigen, vier- und sechskernigen Komplexe [Ir4Se10Br16] sowie [Ir6Se8Cl30] und [Ir6Se6Cl30] zählen zu den größten Ringstrukturen unter den Chalkogen-Halogeniden der Platinmetalle. Ihre intramolekulare Verknüpfung wird unter anderem durch µ-verbrückende X–-Anionen und sehr seltene (SeX)–-Einheiten realisiert. Die verwandten [Ir6Se8Cl30]- und [Ir6Se6Cl30]-Ringe können als molekularer Ausschnitt der aus [IrCl6/2]-Oktaedern bestehenden Honigwabenstruktur von alpha-IrCl3 beschrieben werden.
Die achtkernigen Iridiumkomplexe [Ir8Se28Br14] und [Ir8Se40Br10] bilden über die sechsfach-verbrückenden Se22–-Hanteln und die vierfach-verbrückenden Se42–-Ketten sehr große, ellipsoide Moleküle aus, die stark einem Ausschnitt aus der Netzwerkstruktur von Ir3Se8 ähneln. Beide Komplexe unterscheiden sich lediglich in ihren apikal koordinierenden Liganden: SeBr2-Einheiten im Fall von [Ir8Se28Br14] und ungeladene Heptaselenringe im Fall von [Ir8Se40Br10]. Die Se7-Moleküle repräsentieren ihrerseits die ersten cyclo-Heptaseleneinheiten in Boot-Konformation. An den [Ir8Se28Br14] Komplex koordinieren über Wasserstoffbrückenbindungen zusätzlich zwei Wassermoleküle. Die räumliche Anordnung der Moleküle im Festkörper von Ir8Se28Br14·2H2O stellt eine hervorragende Näherung der dichtesten Ellipsoidpackung dar.
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Zamberlan, Daniele Coradini. "Avaliação do efeito do disseleneto de difenila em modelo de doença de Alzheimer no nematódeo Caernorhabditis elegans". Universidade Federal de Santa Maria, 2014. http://repositorio.ufsm.br/handle/1/11253.
Testo completoAbstract (sommario):
Alzheimer s (DA) is a neurodegenerative disease evidenced by cognitive disorders and attention deficit and learning, and is the main cause of dementia in the elderly. The amyloid hypothesis posits that extracellular amyloid-β (Aβ) deposits are the fundamental etiological factor of the disease. However, the AD etiology has yet to be fully understood and common treatments remain largely non-efficacious. Caernorhabditis elegans transgenic strains expressing toxic Aβ has been employed as AD in vivo model in order to elucidate mechanisms and verifying the effectiveness of pharmacological compounds. The organoselenium compound tested in this study, Diphenyl-diselenide (PhSe)2, has shown efficacy in ameliorate several parametres in neurodegenerative disease models. In the present study, we analyzed the effects of (PhSe)2 chronic treatment on Aβ peptide-induced toxicity in C. elegans. This data shows that chronic exposure to (PhSe)2 attenuated oxidative stress induced by Aβ with concomitant recovery of associative learning memory in worms. In addition, (PhSe)2 decreased Aβ transgene expression, suppressing the Aβ peptide and down-regulating hsp-16.2 by reducing the need of this chaperone under Aβ toxicity. This observations suggest that (PhSe)2 plays an important role in protection against oxidative stress-induced toxicity, this representing a promising potential pharmaceutical modality by attenuating Aβ expression.A Doença de Alzheimer (DA) é uma doença neurodegenerativa evidenciada por distúrbios cognitivos e déficit de atenção e aprendizagem, sendo a principal causa de demência em idosos. A Hipótese Amilóide postula o acúmulo de depósitos extracelulares do peptídio β-amilóide (Aβ) no cérebro como o principal fator da doença. Entretanto, sua etiologia ainda não está completamente elucidada e seu tratamento visa apenas a melhora dos sintomas. Cepas transgênicas do nematódeo Caernorhabditis elegans que expressam as espécies tóxicas Aβ, têm sido utilizadas como modelos in vivo de DA para elucidar mecanismos e verificar a eficácia de novas moleculas. O disseleneto de difenila ((PhSe)2), composto orgânico de selênio utilizado nesse estudo, tem demonstrado eficácia em melhorar diversos parâmetros em modelos de doenças neurodegenerativas. No presente estudo foram analisados os efeitos do tratamento crônico com (PhSe)2 na toxicidade induzida pela Aβ em C. elegans. Os resultados mostraram que a exposição crônica ao (PhSe)2 atenuou o estresse oxidativo induzido pela Aβ, além de recuperar a memória associativa no nematódeo. Além disso, o (PhSe)2 diminuiu a expressão do gene Aβ, levando a supressão do peptídio Aβ e reduzindo a expressão do gene hsp-16.2, por diminuir a necessidade desta chaperona frente a toxicidade Aβ. Estes dados sugerem que o (PhSe)2 desempenha um importante papel na proteção contra a toxicidade induzida por estresse oxidativo, além de representar um promissor agente farmacológico por atenuar a expressão do Aβ.
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Chapple, Charles E. "Finding a needle in haystack: the Eukaryotic selenoproteome". Doctoral thesis, Universitat Pompeu Fabra, 2009. http://hdl.handle.net/10803/7184.
Testo completoAbstract (sommario):
Les selenoproteïnes constitueixen una família diversa de proteïnes, caracteritzada per la presència del Seleni (Se), en forma de l'amino àcid atípic, la selenocisteïna (Sec). La selenocisteïna, coneguda com l'amino àcid 21, és similar a la cisteïna (Cys) amb un àtom de seleni en lloc de sofre (S). Les selenoproteïnes són els responsables majoritaris dels efectes biològics del seleni i s'ha observat que poden estar implicades en la infertilitat masculina, el càncer, algunes malalties coronàries,l'activació de virus latents i l'envelliment. La selenocisteïna es codifica pel codó UGA, normalment codó de parada (STOP). Per a la recodificació correcta del UGA són necessaris diversos factors. A la part 3' de la regió no traduïda (UTR) dels transcrits dels gens de selenoproteïnes en organismes eucariotes s'hi troba una estructura de "stem-loop" anomenada SECIS. La proteïna SBP2 interactua amb el SECIS, així com amb el ribosoma, i forma un complex amb el factor d'elongació EFsec i el tRNA de la selenocisteïna, el tRNASec. Donat que el codó TGA normalment significa fi de la traducció, les formes tradicionals de cerca de gens no el reconeixen com a codó codificant. Per aquesta raó ha estat necessari desenvolupar una metodologia específica per a la predicció de gens de selenoproteïnes. En els últims anys, hem contribuït a la descripció del selenoproteoma eucariota amb el descobriment de noves famílies (Castellano et al., 2005), amb l'elaboració de nous mètodes (Taskov et al., 2005; Chapple et al., 2009) i l'anotació de diferents genomes (Jaillon et al., 2004; Drosophila 12 genomes Consortium, 2007; Bovine Genome Sequencing and Analysis Consortium, 2009). Finalment, hem identificat el primer animal que no té selenoproteïnes (Drosophila 12 genomes Consortium, 2007; Chapple and Guigó, 2008), un descobriment soprenent donat que, fins el moment, es creia que les selenoproteïnes eren essencials per la vida animal.Selenoproteins are a diverse family of proteins containing the trace element Selenium (Se)in the form of the non-canonical amino acid selenocysteine (Sec). Selenocysteine, the 21st amino acid, is similar to cysteine (Cys)but with Se replacing Sulphur. In many cases the homologous gene of a known selenoprotein is present with cysteine in the place of Sec in a different genome. Selenoproteins are believed to be the effectors of the biological functions of Selenium and have been implicated in male infertility, cancer and heart diseases, viral expression and ageing. Selenocysteine is coded by the opal STOP codon (TGA). A number of factors combine to achieve the co-translational recoding of TGA to Sec. The 3' Untranslated regions (UTRs) of eukaryotic selenoprotein transcripts contain a stem-loop structure called a Sec Insertion Sequence (SECIS) element. This is recognised by the Secis Binding Protein 2 (SBP2), which binds to both the SECIS element and the ribosome. SBP2, in turn, recruits the Sec-specific Elongation Factor EFsec, and the selenocysteine transfer RNA, tRNASec. The dual meaning of the TGA codon means that selenoprotein genes are often mispredicted by the standard annotation pipelines. The correct prediction of these genes, therefore, requires the development of specific methods. In the past few years we have contributed significally to the description of the eukaryotic selenoproteome2 with the discovery of novel families (Castellano et al., 2005), the elaboration of novel methods (Taskov et al., 2005; Chapple et al., 2009) and the annotation of different genomes (Jaillon et al., 2004; Drosophila 12 genomes Consortium, 2007; Bovine Genome Sequencing and Analysis Consortium, 2009). Finally, and perhaps most importantly, we have identified the first animal to lack selenoprotein genes (Drosophila 12 genomes Consortium, 2007; Chapple and Guigó, 2008). This last finding is particularly surprising because it had previously been believed that selenoproteins were essential for animal life.
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Blais, Jean-Simon. "HPLC-AAS interfaces for the determination of ionic alkyllead, arsonium and selenonium compounds". Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74637.
Testo completoAbstract (sommario):
Three direct interfaces for coupling high performance liquid chromatography (HPLC) with atomic absorption spectrometry (AAS) were developed and optimized for the determination of ionic organolead, organoselenium and organoarsenic compounds. The first all-quartz interface consisted of a thermospray nebulizer and a flame microatomizer in which ionic alkyllead analytes (R$ sb{ rm n}$Pb$ sp{ rm (4-n)+};$ R = CH$ sb3,$ C$ sb2$H$ sb5)$ were atomized by a methanol (from HPLC eluent)-oxygen kinetic flame, and channeled in a quartz tube (atom keeper) mounted into the AAS optical beam. Alternately, the classical electrothermal atomization technique for organolead species (quartz furnace under hydrogen atmosphere) was coupled with a post-column derivatization-volatilization apparatus based on the ethylation of ionic alkylleads by sodium tetraethylborate. The limits of detection provided by these two approaches were 1.0-3.4 ng and 0.10-0.15 ng, respectively. Arsonium ((CH$ sb3) sb3$RAs$ sp+;$ R = CH$ sb3,$ CH$ sb2$CH$ sb2$OH, CH$ sb2$COOH) and selenonium ((CH$ sb3) sb2$RSe$ sp+;$ R = CH$ sb3,$ CH$ sb2$CH$ sb2$OH) species were quantified using a novel HPLC-AAS approach based on a direct coupling of three processes: thermospray nebulization, thermochemical hydride generation using hydrogen gas, and diffuse flame atomization. Direct evidences for the thermochemical hydride generation process was obtained by injecting (CH$ sb3) sb3$SeI and SeO$ sb2$ into the interface and capturing the gaseous end products in liquid chemical traps specific for SeH$ sb2$ and Se(IV). Both analytes were derivatized to SeH$ sb2$ only in the presence of hydrogen in the interface. Reverse- and normal-phase high pressure liquid chromatographic methods were also developed and adapted for the HPLC-AAS analyses of alkyllead, arsonium and selenonium compounds in real samples. The limit of detection of the arsonium and selenonium cations were 7.6-13.3 ng and 31.0-43.9 ng, respectively.
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Rickman, Sarah. "Growth and characterization of molybdenum disulfide, molybdenum diselenide, and molybdenum(sulfide, selenide) formed between molybdenum and copper indium(sulfide, selenide) during growth". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 0.94 Mb., 85 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435848.
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Varanasi, Mohan R. "Geometries of small cadmium selenide (CdSe) clusters". Virtual Press, 2006. http://liblink.bsu.edu/uhtbin/catkey/1349770.
Testo completoAbstract (sommario):
The sizes, shapes, relaxed atomic positions, eigenvalues, and total energies are calculated for selected ultra-small CdSe clusters using SIESTA, a software package for electronic structure calculations and molecular dynamics simulations of molecules and solids. The properties of these bare clusters with small numbers of constituent atoms are studied using density functional theory (DFT) for energy calculations and the conjugate gradient approximation as well as simulated annealing type of molecular dynamics techniques in relaxing the structure to find the lowest energy configurations.The ab-initio norm-conserving pseudopotentials, the exchange-correlation approximation, and parameters used in the computations by Siesta software is verified using FHI98PP, a package used to generate and test the ab-initio norm-conserving pseudopotentials. The initial position of the atomic co-ordinates is determined using ancillary software written in Matlab.Department of Physics and Astronomy
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SILVA, LARISSA de S. "Avaliação da concentração de metais e elementos terras raras em amostras de sedimentos dos reservatórios dos sistemas Billings e Guarapiranga". reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/28040.
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O excessivo processo de urbanização da Região Metropolitana de São Paulo resultou na perda das características naturais dos seus cursos d\'água ocasionando profundas alterações nos regimes de vazão e de qualidade. O objetivo desse estudo foi avaliar a concentração de metais tóxicos, os semi-metais As, Sb e Se e os elementos terras raras, presentes em amostras de sedimento superficiais coletadas nos Reservatórios Billings, Guarapiranga e Rio Grande. Os elementos Ag, Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Sb, Se e Zn foram determinados pela técnica de Espectrometria de Emissão Ótica com Plasma Indutivamente Acoplado (ICP OES). Alguns elementos maiores, traço e elementos terras raras (Ce, Eu, La, Lu, Nd, Sm, Tb e Yb) foram determinados pela técnica de Análise por Ativação Neutrônica Instrumental (INAA). A concentração de Hg total foi determinada pela técnica Espectrometria de Absorção Atômica com Geração de Vapor Frio (CVAAS). A validação das metodologias foi realizada por meio da análise de materiais de referência certificados. Para avaliar as possíveis fontes de contaminação antrópicas foram utilizadas as ferramentas de fator de enriquecimento (FE) e o índice de geoacumulação (IGeo). Os resultados obtidos pelas técnicas foram comparados com os valores orientadores TEL e PEL estabelecidos pelo CCME (Canadian Council of Ministers of the Environment) e adotados pela CETESB. Todos os pontos analisados apresentaram valores > TEL para todos os metais e dois pontos da represa Billings (BILL02100 e 02030), valores > PEL para As, Cr, Cu, Hg, Ni, Pb e Zn, provavelmente em decorrência do recebimento das águas do Rio Pinheiros e das bacias de drenagem do ribeirão Cocaia e Bororé. Os valores de FE e IGeo calculados apontaram possíveis contaminações antrópicas para Sb e Se para os elementos determinados por ICP OES e de As, Cr, Sb e Zn, por INAA. O reservatório Billings apresentou, em geral, as maiores concentrações para os elementos analisados, indicando uma má qualidade de seus sedimentos. Este estudo confirma a necessidade de um monitoramento frequente da qualidade do sedimento nos reservatórios estudados como procedimento indispensável para avaliação periódica da qualidade das bacias, considerando sua importância no fornecimento de água para a Região Metropolitana de São Paulo.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
43
Cooke, Sharon A. "Alternative chalcogen sources for the growth of cadmium sulfide and cadmium selenide by metal organic chemical vapour deposition". Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284186.
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Gaul, David Allen. "Synthetic, mechanistic, structural, and dynamic NMR investigations of zinc bis(amide) compounds". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/30741.
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Beer, Michael P. "A study of volatile precursors for the growth of cadmium sulphide and cadmium selenide by Metal Organic Vapour Deposition". Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303986.
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Leung, Yee-pan. "A study on the fabrication and applications of quasi-one-dimensional zinc selenide nanostructures". Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39848942.
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Safoula, Gabriel. "Caracterisation des couches minces polycristallines de selenium dope par un halogene (cl, i) et etude des interfaces metal-selenium (m = cr, bi, te)". Nantes, 1988. http://www.theses.fr/1988NANT2018.
Testo completoAbstract (sommario):
L'effet du dopage a ete analyse par diffraction rx, microscopie electronique a balayage, spectrometrie de masse des ions secondaires, diffusion raman, emission photoelectronique rx, emission electronique auger. On effectue des mesures de conductivite electrique, d'effet hall et de pouvoir thermoelectrique en fonction de la temperature, de la concentration initiale en halogene et du vieillissement. On en deduit que, seule une fraction d'halogene, non uniformement reparti, a un role electriquement actif
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Woznichak, Michelle Marie Gill. "Investigation of the biochemical activity of phenylaminoethyl selenide compounds, synthetic substrate analogs for dopamine beta-monooxygenase". Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/26211.
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Britel, Mohamed Reda. "Etude des propriétés élastiques du système unidimensionnel à onde de densité de charge (TaSe4)2I". Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10087.
Testo completoAbstract (sommario):
L'etude des proprietes elastiques du systeme unidimensionnel a onde de densite de charge (tase4)2i, par la technique ultrasonore a conduit a la mise en evidence, dans un intervalle de temperatures de 1 a 300 k et de frequences de 10 a 100 mhz, des proprietes tres importantes, par la mesure de l'attenuation et de la vitesse d'ondes longitudinales et transverses ultra-sonores: ramollissement critique de la constante c#4#4 a la transition de peierls. Cette anomalie elastique, en accord avec les proprietes electriques, peut etre relie au deplacement atomiques perpendiculaires a l'axe c, mis en evidence dans les experiences de diffraction aux rayons x aux neutrons. Un processus de relaxation existant dans l'intervalle de temperature situe au voisinage de la transition de peierls, en accord avec les experiences de diffusion de neutrons. L'activation thermique du mecanisme est du type vogel-fulcher et non pas arrhenius comme l'ont confirme les mesures, dans un grand intervalle de frequences, entre 1 hz et 100 mhz. Il semble que ce processus active thermiquement puisse etre associe aux fluctuations de la structure en domaine qui existent au voisinage de la transition de peierls. Il y a gel de ces fluctuations a une temperature voisine de 200 k. Une forte diminution de la constante transverse c#4#4 est observee au dessous de 50 k. Elle s'explique par le fait que ce mode est fortement dispersif (mode plat). La diminution de c#4#4 et l'augmentation de l'attenuation sont analysees en considerant que la frequence de la branche acoustique est constante, egale a 0,15 thz, pour les grandes valeurs du vecteur d'onde
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Adams, Jonathan A. "A surface and interface study of aluminum selenide on silicon : growth and characterization of thin films /". Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9797.
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