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An analysis of the tail feathers of 104 osprey nestlings (Pandion haliaetus L.) from Lake Asnen, southern Sweden, was undertaken for total mercury and selenium content. Results indicate that the bioaccumulated quantity of selenium that is thought to be protective for the organisms against the toxic effects of mercury is somewhat insufficient to bind all body mercury.

Research describes the formation and interconversions of the thallium chalcogenide anions using NMR spectroscopy, X-ray crystallography, and ab initio methods. Data reveal that the anions are ordered in cubic structural arrangement of thallium and selenide atoms.

Research presents new findings about an exceptional compound belonging to silicon chalcogenide class of compounds. Data reveal that the quaternary compound containing divalent barium ions and stabilized by the other three metals forms silverlike crystals.

Research describes a unique regio- and stereoselective carbonylation reaction of acetylene selenides catalyzed by palladium(II). Data show that the synthetic approach employed results in high yield of 2-seleno-3-chloroacrylates under mild conditions.

Research demonstrates that the reactivity of 3H-azepine with selenium dioxide is dependent on the position of tert-butyl groups in azepine compounds. Data indicate that selenium dioxide catalyzed oxidation of 2,5-di-tert-butyl-3H-azepine results in a 3H-azepine ring cleavage reaction.

Results demonstrate the synthesis and characterization of five ternary rare-earth selenides conforming to U(sub)3ScS(sub)6 structural configuration. Data on magnetic measurements reveal that the new compounds exhibit paramagnetic properties down to 5 K.

A study on the reactivities of organic selenium compounds was conducted to interpret uniformly the observed delta Se values of para-substituted phenyl selenides in relation to their structures in solution, based on the calculated delta Se values. It also presents the results of the calculation for the calculated delta Se values based on the GIAO theory and underscores their usefulness in explaining the observed delta Se values and understanding the organic selenium chemistry based on 77Se nuclear magnetic resonance spectroscopy.

Simulations were performed on 138-molecule SeF6 clusters freezing isothermally at 130, 120 and 80 K. At 120 K, the nucleation rate was the same as in previous simulations done adiabatically but the final product was different. During the nanosecond period of the runs, clusters transforming adiabatically had frozen to bcc crystals while warming from 120 K to about 130 K. On the other hand, isothermal clusters at 120 and 130 K changed to monoclinic clusters after passing through the bcc phase. Clusters cooled to 80 K froze to a variety of structures.

The crystal structure of the tetrameric DNA-binding domain of the single-stranded DNA binding protein from Escherichia coli was determined at a resolution of 2.9 [Angstrom] using multiwavelength anomalous dispersion. Each monomer in the tetramer is topologically similar to an oligomer-binding fold. Two monomers each contribute three [Beta]-strands to a single six-stranded [Beta]-sheet to form a dimer. Two dimer-dimer interfaces are observed within the crystal. One of these stabilizes the tetramer in solution. The other interface promotes a superhelical structure within the crystal that may reflect tetramer-tetramer interactions involved in the positive cooperative binding of the single-stranded DNA-binding protein to single-stranded DNA.

A series of 1,2-benzisoselenazol-3(2H)-ones was synthesized from the irradiation of pyridine-2-thioneoxycarbonyl (PTOC) imidate esters in a water-cooled benzene solution. The synthetic process for the formation of ebselen and its analogues involved the photochemical decomposition of PROC imidate esters and homolytic intramolecular substitutions which led to the formation of amidyl radical. Furthermore, the target compounds were also synthesized from the reaction of 2,2'-diselenobis(N-alkylbenzamides) with benzoyl or tert-butyl peroxides.

The novel method for the synthesis of mixed six-membered SexS4-xN2 (x = 0-4) chalcogen nitrides was developed based on the utilization of [(Me3Si)2N]S, SCl2 and S2Cl2 as starting materials. The synthetic process was characterized by the introduction of selenium into the six-membered ring during the reaction of [(Me3Si)2N]2S with mixtures of sulfur and selenium chlorides. The heterocyclic chalcogen-nitrogen reaction products exhibited molecular stabilities that were dependent on the selenium content.

Homoleptic vanadium complex ((3,5-Me2Ph)AdN)3V was synthesized and characterized by X-ray crystallography and nuclear magnetic resonance spectroscopy. The complex was made to react with chalcogens to yield diamagnetic terminal chalcogenide derivatives of formula ((3,5-Me2Ph)AdN)3V=E, where E is either S or Se. The derivatives were similarly characterized.

X-ray crystallography was done to elucidate the structural characteristics of ((CO)3Mn(mu-SePh)3Co(mu-SePh)3Mn(CO)3)-, (CO)4Mn(mu-SeMe)2Co(CO)(mu-SeMe)3Mn(CO)3, and ((CO)3Mn(mu-SePh)3Mn(CO)3)-. The data provided evidences that the stability of the neutral Mn(I)-Co(III)-Mn(I)-selenolate complexes is determined by the distinct electronic effects between methaneselenolate and benzeneselenolate.

A method for the synthesis of 2',3'-didehydro-2'-deoxythymidine (D4T) from 2-deoxyribose was developed based on reactions mediated by nucleophilic PhSeH and electrophilic PhSeCl selenium reagents. The synthetic strategy involved the oxidative elimination of selenium by nucleophilic PhSeH and electrophilic PhSeCl to form a double bond of glycal and D4T. The electrophilic selenium reagents provided excellent yields of the target compound with high stereoselectivities in the glycosylation step.

Thermospray is a high-temperature and high-pressure process compared with pneumatic nebulization. In this study, these characteristics of thermospray were exploited for selenium speciation with inductively coupled plasma atomic emission spectrometric (ICP-AES) detection. In aqueous solution, the sensitivity for Se(IV) was found to be lower than that for Se(VI). Addition of methanol into the solution further depressed the sensitivity for Se(IV) to a negligible level compared to that for Se(VI). The low sensitivity for Se(IV) arises from its reduction to Se(0) within the thermospray process, after which selenium metal was trapped on the vaporizer. This loss of Se(IV) can be counteracted by addition of an oxidant ([K.sub.2][S.sub.2][O.sub.8] or [K.sub.2][Cr.sub.2][O.sub.7]) into the selenium solution, which prevents Se(IV) from being reduced within the vaporizer. Based on these results, a method for speciation of Se(IV) and Se(VI) was developed. The concentration of Se(VI) is selectively determined in a sample aliquot with 20% (v/v) methanol added. In another sample aliquot with an addition of 5 mmol/L [K.sub.2][S.sub.2][O.sub.8] or 2 mmol/L [K.sub.2][Cr.sub.2][O.sub.7], the total selenium concentration is determined. The selenite content is calculated by difference. The detection limits for Se(VI) at 196.0 nm were measured to be 2 ng/mL for aqueous solution and 9 ng/mL for 20% (v/v) methanol solution. A concomitant with oxidation or reduction ability, which can obstruct the selenite reduction within the thermospray vaporizer or counteract the function of an oxidant added, will be a potential interferent in the determination of Se(VI) or total selenium, although the tolerance limits of such interferents as Cr(VI) and Sn(II) were determined to be well above their concentrations in many environmental samples such as natural water. The effects of methanol concentration, oxidant concentration, and nitric acid concentration in solution were studied in detail. Good accuracy and precision of the method were demonstrated for the analysis of spiked tap water samples.

The [Sb2Se4]2- chalcogenometalate anion is composed two edge-sharing pyramidal SbSe3 units with a four-membered ring that contains two terminal Se atoms in cis configuration. Furthermore, the bridging Sb-Set bond distances of the chalcogenometalate anion contains Sb2Se4 fragments. The Sb2Se4 fragments produces [PPh4]2[Sb4Se6]6 after electrochemical reduction. The [K(2.2.2-cryptand)]2[As4Se6] chalcogenometalate contains four cations and two anions that are crystallographically independent from each other.

The ternary selenides Rb3Yb7Se12 and CsEr3Se5 have one-dimensional structures that are dependent on the sizes of the metal cations. The structure is composed of ReSe6 octahedral units that exhibit edge-sharing and the size of the channel cross sections range from five by four to six by four. The coordination numbers of the selenium of ternary selenides are five or six compared to three alkali metals and three rare-earth metal cations of ternary sulfides.

Pd(II) complexes of 16Se4[Pd(16Se4)][BF4]2 and [Pd(16Se4)][BF4]Cl have a cis, cis, cis configuration with respect to the coordination plane of the coronand. The [Pd(16Se4)]2+ exhibits a c,c,c diastereomer in tetraflouroborate and chloro, tetrafluoroborate salt crystals. The c,c,c and c,t,c forms are the predominant species of [Pd(16Se4)][BF4]2 in aqueous solutions at room temperature. Configurational interconvertion occurs at elevated temperatures and a 1.6 c,t,c:c,c,c ratio is the observed equilibrium composition at room temperature.

The mononuclear and dinuclear nickel(II) complexes, (Et4N)2(Ni2(Se(CH2)3Se)3) (1), (Ph4P)2(Ni2(mu-2,4,6-(Me)3C6H2Se)2(2,4,6-(Me)3C6H2Se)4).8CH3CN (3) and (Ph4P)2(Ni(SePh)4) (2), are synthesized in anhydrous ethanol/acetonitrile media. Compound 1 and 3 contain square planar NiSe4 chromophores, whereas compound 2 exhibits a distorted tetrahedral conformation. All the complexes are sensitive to oxygen, and their synthesis is blocked by the presence of water in the reaction mixture. The average Ni-Se bond length in homoleptic square planar selenolates is shorter than that in the tetrahedral complex.

The salt metathesis or chalcogenolysis of metal chalcogenolates generates group 4 homoleptic tris(trimethylsilyl)silyl selenolates and tellurolates. Salt metathesis between MCl4 (M = Zr, Hf) and (tetrahydrofuran)2LiSeSi(SiMe3)3, or chalcogenolysis reaction between M(CH2Ph)4 and HESi(SiMe3)3 (E = Se, Te) generate M(ESi(SiMe3)3)4. The X-ray crystal structures of M(ESi(SiMe3)3)4 and M(SeSi(SiMe3)3)3- (CH2Ph) (M = Ti, Zr, Hf; E = Se, Te) are determined. The tellurolate ligand readily reacts with Lewis bases, despite steric shielding. The synthesis of 1,2-bis(dimethylphosphino)ethane adducts is discussed.

The Pd2X2(dpmMe)2 (dpm = 1,1-bis(diphenylphosphino)ethane) complexes react with elemental Se to form air stable, isolable A-frame adducts Pd2X2(mu-Se)(P-P)2 (2a-d). The substituents at the methylene C-atom are in anti position in the solid state structure of anti-Pd2Cl2(mu-Se)(mu-dpmMe)2. The Pd atoms exhibit a distorted square planar conformation with bond angles from 84.3-99.1 degrees. The oxidation of mu-Se precursors forms mu-SeO products. The experimental procedure for the synthesis of 2a-d is discussed.

Treatment of W6Cl12 with Na2Se in refulxing pyridine (py) and piperdine (pip) generate W6Se8(py)6 (2) and W(sub 6-)Se8(pip)6 (1). Both the complexes containan octahedron of tungsten atom having eight triply-bridged selenium atoms capping the octahedra faces. The average W-W and W-Se bond distance values for 1 and 2 are 2.691(1) and 2.574(1) angstroms respectively. Photoelectron spectra indicate typical tungsten binding energies at 30.8 eV (W 4f(sub7/2)) and 32.9 eV (W 4f(sub 5/2)). Characteristic IR spectra are obtained at 243-254 per centimeter due to T(sub 1u) W-Se stretching modes.

The reactions between Fe(CO)5 and polysulfides or polyselenides are performed under optimum conditions of chain lengths, countercations and stoichiometry. In the presence of excess Fe(CO)5, Fe3(CO)9(mu3-E)(super 2-) is formed. With the rise in the ratio and chain length of polychalcogenide, the oxidation of the iron centers elevates, resulting in the clusters Fe(CO) 12E6(super 2-) and Fe5(CO 14) mu (sub 3) -e 2 (super 2-) (E = S, Se).

A study of interface microstructure and strain relaxation of CdSe shows that the varying misorientations present along the interface of CdSe epilayer are associated with the proportion of different 60 degree misfit dislocations and stacking faults. The high density of the long stacking faults is due to dimorphic activity of CdSe. CdSe was atomic-epitaxy-grown on ZnSe/GaAs(001) and viewed using transmission and high resolution electron microscopy.

The molten alkali polyselenophosphate flux method helps prepare five isostructural quaternary alkali metal transition metal selenophosphate compounds. Single-crystal X-ray diffraction studies reveal the presence of ethane-like (P2Se6)4- units in these compounds, which have low dimensional extended structures. Optical spectroscopy helps determine the band gaps in these complexes.

Reaction of MCl2 (M = Pd, Pt) with 1 molar equiv of (16)aneSe4 in refluxing MeCN solution, in the presence of T1PF6, produces the complexes (M(16)aneSe4)(PF6)2. Crystals of (Pd(16)aneSe4)(PF6)2.2MeCN belong to a monoclinic space group, with Pd(II) having a perfect square planar geometry. NMR studies at various temperatures indicate a dynamic interconversion of invertomers for (M(16)aneSe4)2+ ions in solution. A similar synthetic technique enables the preparation of bis-bidentate complexes of the type (M(MeSeCH2CH2CH2SeMe)2)(PF6)2.

Synthesis of a series of novel selenidohexacobalt carbonyl clusters involves a reaction of Co2(CO)8 with CSe2 and or with red selenium. X-ray studies of ((mu 3-Se)Co3(CO)7)2mu 4-(Se)2 reveal that a Se2 bridge connects two (mu 3-Se)CO3 pyramids exhibiting anti configuration. A cuboctahedron geometry is observed for the complex Co6(mu 3-Se)8(CO)6.2C6H6. Reaction of Co2(CO)8 with CSe2 produces a new complex Co6(mu 4-Se)(mu 6-C2)(CO)14.

Elemental selenium vapor is used in the plasma-assisted two-stage selenization process that facilitates formation of copper selenide semiconductor thin films. The presence of the Se(x) species in the gas phase is unaffected by the kinetics of its interaction with the precursor. Highly crystalline CuSe films are produced within 2 to 5 minutes at low temperatures. The CuSe growth phase is hexagonal in accordance with the copper selenium vapor reaction thermodynamics.

Analysis of photoconductive power switching in polycrystalline zinc selenide switches using transparent liquid electrolytic electrodes shows that switch optical transmission is nonlinear at a laser energy of 100 micro Joules and a medium applied field. High internal electric fields cause nonlinear optical transmission in the switches. Switch geometry and suitable pulse forming circuits in the switch enable the switch to emit sub-nanosecond electrical pulses and cause electric field compression and initiate electroabsorption in the switch. Computer simulation data indicate that impact ionization is not seen in the switches even at internal fields of 160 kilo volts per cm and field compression ratios of 4.

Low pressure organometallic chemical vapor deposition (CVD) under selenium-rich growth conditions yields high quality nitrogen-doped p-type ZnSe epilayer on (100) GaAs substrate. Hall measurements performed on these epilayers provide the free carrier concentration and resistivity of ZnSe. ZnSe assimilates nitrogen as a shallow level in a molar ratio combination.

Longitudinal geometrical analysis of photoconductivity in polycrystalline ZnSe switches reveals nonlinear characteristics at high voltage electric fields. Perforated metal film electrodes, plasma, liquid electrolyte and ultraviolet-light-produced carriers operate as the experimental parameters. The occurrence of nonlinear properties near band edge illumination eliminates the 'lock-on' process in the switch to increase the voltage gain.

A study of the Hall effect and deep hole level in indium selenide crystals doped with lead reveal that homopolar optical phonons and ionized impurity scattering affect hole mobility at higher temperatures. Two hole trapping levels above the valence band are observed using the deep level transient spectroscopy.

Se solid-state NMR spectra with cross-polarization and magic-angle spinning on (M(Se4)(sub 2))(super 2-) complexes with (Me(sub 4)N)+ and (Et(sub 4)N)+ facilitate the calculation of main constituents of Se77 shielding tensor from spinning sideband intensities. Structural changes in the (M(Se4)(sub 2))(super 2) geometry with cations between (Et4N)+ and (Me4N)+ complexes manifest in Se(77) isotropic chemical shifts.

Two new six-membered ring species containing selenium (Se) are synthesized, and spectroscopy studies show that the crystal structure of the first complex (Zn(CH2SiMe3)SCMes)3 has a distorted nonplanar, hexagonal arrangement with alternating Zn and Se atoms. The second complex (Li(THF)SeMes)3 has a six-membered Li3Se3 ring containing lithium and selenium atoms with nonplanar coordination. Six-membered ring species undergo delocalization of nonbonded electron pairs into pi-orbitals.

High quantities of selenophenes and benzoselenophenes are produced due to the smooth interaction between replaced and unreplaced 1-(benzylseleno)-4-iodobut-3-en-2-ols and 2-(benzylseleno)-1-(2-iodophenyl)ethanols. The selenium atom serves as the site for the intramolecular homolytic replacement by two aryl and vinyl radicals, which participate in the interaction. An aromatic selenophene ring system is formed in both instances when easy dehydration is preceded by the elimination of the benzyl radical. A rate constant for the ring closure is obtained by the experiments on the ring closure of a phenyl radical when tri-n-butyltin hydride yields a phenylethane.

Numerous methods are adopted to synthesize two selenium-nitrogen halides, Se3N2Cl2 and (Se3N2Cl)2. ((Me3Si)2N)Se interacts with a combination of SeCl4 and Se2Cl2 to yield pure derivatives, which reveal the suitable ratio between Se and Cl. Basic Se-N compounds can be synthesized by this reagent due to its high adaptability. The occurrence of the Se3N2Cl+ cation in Se3N2Cl2 is revealed by force-yield measurements. The employment of Se3N2Cl2 as a reagent in S-N chemistry is restricted due to its explosive characteristic and its insolubility. A thermally unsteady Se-N chloride is formed when Se3N2Cl2 is chlorinated.

The reduction of alpha-(PPh4)2(Pt(Se4)3) DMF with Li2BEt3H in DMF results in the isolation of the (PPh4)2(Pt(Se4)2). The reaction of the appropriate metal xanthate with Li2Se and Se in DMF is used in the production of the compounds (NEt4)5(2Pd(Se4)(sub 2.)1/2Pd(Se5)2), alpha-(PPh4)2(Pt(Se4)3).DMF and beta-(PPh4)2(Pt(Se4)3).

The reaction of Ni(super 0) with triethylphosphine selenide was examined. It was shown that Ni(COD)2 (COD = cyclooctadiene) reacts with Et3PSe at elevated temperature to give a mixture of Ni3Se2 and Ni, that the two combine at lower temperature to give the cluster compound Ni23Se12(PEt3)13, and that this compound gives a similar mixture of Ni3Se2 and Ni on heating. The structure of the cluster is a molecular example of an intergrowth of NiSe and Ni.

The Se-77 exchange kinetics of S2Cl2 mixtures with Se2X2 (X = Br, Cl) is determined using two-dimensional NMR exchange spectroscopy. The results show that the Se-77 magnetization transfer in S2Cl2/SeBr2 mixtures follows an ex ionic exhange mechanism involving the dissociation of SeX bonds. This observation is supported by the pattern of cross-peaks obtained in the two-dimensional spectra and the dependence of the magnetization transfer rate on the concentration of halide ions.

Cell death and mutation caused by oxidative DNA damage are implicated in neurodegenerative and cardiovascular diseases, cancer, and aging. Selenocystine inhibited all DNA damage at low micromolar concentrations, whereas selenomethionine showed similar inhibition at 40 times these concentrations, and 2-aminophenyl diselenide showed no effect.

Reaction between WCl6 and selenium generate a novel member of selenium polycation family, Se(sub 17)(super 2+)(WCl(sub 6)(super -))2 (1). The crystal structure of 1 contains Se(sub 17)(super 2-) having two seven-membered selenium rings in chair conformation and WCl(sub 6)(super -) in a distorted octahedra. The seven membered selenium rings are attached by a Se3 chain. The structure of Se(sub 17)(super 2-) is consistent with S(sub 19)(super 2+).

Two polyselenide complexes, (Mo2Se2(mu-Se)2(eta-2-Se2)2)2- and the oxa analog of the earlier complex, are synthesized, and their structure and properties are studied. The two complexes possess polysulfide analogs. The trans-Tellurium analog of (Mo2O2(mu-Se)2(eta-2-Se2)2)2-, which is the oxo analog, is also synthesized. The study of these analogs indicates that the structural and spectroscopic features exhibit pi-bonding effects.

A solvothermal method is used to synthesize and crystallize two dimeric vanadium polyselenides, (V2O2Se10)4- and (V2O2Se8)4-, which have the same core structure V2O2Se2. Methanol is used to avoid oxovanadate formation during the reaction since water is not a suitable solvent. The V2O2Se2 core structure has a bent rhombus with two cis terminal oxygen atoms which may be present due to methanol. Solvothermal methods negate the use of classical complex compound solution techniques.