Physiological and behavioral effects of exposure of fathead minnows (Pimephales promelas) and channel catfish (Ictalurus punctatus) to selenate-selenium (Se) and nitrite were investigated.

Enterococcus faecalis is a well known nosocomial drug resistant pathogen that is responsible for urinary tract infections, bacteremia, wound infections and endocarditis through the formation of biofilms. It has been shown that 68 genes present within the core genome of E. faecalis are upregulated in biofilm formation. One of those 68 genes is a putative seleniumdependent molybdenum hydroxylase (SDMH). Adjacent to this gene are a series of open reading frames that have been postulated to play a role in the maturation of a labile selenium cofactor. The biosynthesis of this labile cofactor has yet to be studied at either the genetic or biochemical level. The addition of selenium to growth medium caused a significant increase in biofilm density and extracellular hydrogen peroxide by wild type E. faecalis. By site-directed mutagenesis gene products encoded in the SDMH operon were shown to be necessary for the selenium-dependent biofilm formation as well as extracellular hydrogen peroxide production. This biofilm and peroxide phenotype is inhibited both by tungsten or auranofin in wild type E. faecalis suggesting the SDMH is a necessary enzyme for selenium-dependent biofilm and peroxide formation. These results show that the gene products encoded within the SDMH operon are necessary for a selenium-dependent biofilm formation as well as extracellular hydrogen peroxide production. These mutants will provide the basis for defining the synthesis of the labile selenium cofactor and allow for an expanded understanding of the biological use of selenium.

<p> A continuation of studies of main group compounds carried out in this laboratory has led to the investigation of the structural and oxidative chemistry of several compounds and mixtures of the elements phosphorus, arsenic, sulfur and selenium. A number of questions and a lack of data regarding known compounds of these elements lead to an examination of the series P4-X^AsX^S3-Y^SeY, X = 0-4, Y = 0-3. Raman spectra of several members of the series have been recorded. The 31P and natural abundance 77Se nmr spectra of these compounds were also recorded, including a reinvestigation and complete assignment of the 31P nmr spectrum of P4Se3 . Several trends in the coupling constants and chemical shifts were noted and an empirical equation was devised for the 31P nmr spectral assignments for quaternary members of the series. The compound formerly believed to be P2As2S3 was shown to be PAs3S3. The crystal structure of an occupationally disordered crystal of stoichiometry P2As2S3 is also reported in this thesis.</p> <p> The compound As4S4 and 1:1 As:Se fused mixtures were separately oxidized with the Lewis acids AsF5 and SbF5 to produce the new cations As3S4+ and As3Se4+. The cations were characterized as the salts As3S4 (AsF6), As3S4 (SbF6), As3Se4 (AsF6 ) and As3Se4 (SbF6) by Raman spectroscopy and infrared spectroscopy. The determination of the crystal structures of the first three salts is also reported.</p> <p> Reactions of As4S4 with PF5, PCl5, BCl3, SO3, NbF5 , TaF5 and WF6 were shown to not proceed or, in the case of PF5, to not produce a stable adduct. The action of AsF5 on compounds and mixtures of heavy main group elements (e.g., Sb2Te3) of groups V and VI produced no new compounds that were identified and generally just gave known homo-polyatomic cations of the chalcogens.</p> <p> Oxidation of As4S4 with the halogens (X) chlorine and bromine produced AsX3 and S2X2 while the reaction of SbCl5 with As4S4 or 1:1 As:Se fused mixtures produced SbCl3, AsCl3 and the salts SCl3 (SbCl6) and SeCl3 (SbCl6),respectively. The crystal structure of SCl3 (SbCl6) is reported here along with unit cell data for SeCl3 (SbCl6) and SBr1.2Cl1.8 (SbCl6) and the Raman data for all three compounds. Only AsSI was produced by the oxidation of As4S4 by I2 in SO2 while a reaction between molten P4Se3 and I2 gave the new compound αP4Se3I2. Raman spectra for both AsSI and αP4Se3I2 were recorded as well as the 31P nmr spectrum for the latter.</p> / Thesis / Doctor of Philosophy (PhD)

<p> A procedure was established for instrumental radioactivation analysis of selenium in biological materials using se77m, and used to determine selenium bound to plasma and cells of blood from 254 normal individuals. Variations with time, age, sex and hematocrit were investigated. Analysis of subfractions of plasma and cells indicated the highest selenium concentration in the plasma alpha and beta globulins. The selenium content of other tissues was determined for two individuals.</p> <p> A method was devised for instrumental radioactivation analysis of sulphur in dialyzed biological material using s37. The bound sulphur content of samples of plasma and cells from normal human blood was determined. The method would appear to have application in the instrumental activation analysis for other elements in various matrices.</p> / Thesis / Doctor of Philosophy (PhD)

<p> The mass spectra of disubstituted 1,4-dithiane, 1,4-oxathiane, and 1,4-oxaselenane, as well as the mass spectra of some disubstituted bicyclic and tricyclic sulfur and selenium compounds, were studied. The exact composition of the major ions of many of these compounds was determined. Fragmentation mechanisms are proposed to account for the major peaks in their spectra.</p> / Thesis / Master of Science (MSc)

<p> The nature of the coloured solutions of selenium and tellurium in sulfuric acid has been investigated using mainly cryoscopic, conductimetric, and spectrophotometric techniques. Evidence has been obtained for the new species Se₈²⁺ and Se₄²⁺ in the green and yellow solutions of selenium respectively. Evidence on red solutions of tellurium seems consistent with the formulation Te₄²⁺. Solid compounds analysing as Se₄S₄O₁₃, Se₄(HS₂O₇)₂ and TeO(HS₂O₇)₂ have been prepared and characterised. </p> <P> Solutions of some selenium(IV) and selenium(VI) compounds have been examined. It is shown that a number of phosphates and arsenates ionise in sulfuric acid to give the P(OH)₄⁺ and As(OH)₄⁺ ions respectively. Ammonium metavanadate and vanadium pentoxide ionise to give the complex acid H[VO(HSO₄)₄]. Potassium chromate and dichromate ionise to give the compound CrO₂(HSO₄)₂ and potassium permanganate ionises to give the non-electrolyte MnO₃∙SO₄H. </p> / Thesis / Doctor of Philosophy (PhD)

<p> The preparation of compounds containing polyatomic cations of sulphur, selenium and tellurium has been investigated by using oxidising agents such as AsF5, SbF5, S2O6F2 and SO3. New compounds, containing polyatomic cations Se8 2+, Se4 2+, Te3n n+, Te4 2+ Ten n+, S16 2+, S8 2+ and S4 2+, and anions of very strong acids such as Sb2F11- and AsF6- were isolated and characterised by a combination of the stoichiometry of the preparation reactions, UV-visible spectrophotometry, Infrared and Raman spectroscopy and magnetic susceptibility measurements.</p> <p> Solutions of sulphur in various concentrations of oleum were investigated in detail by UV-visible spectrophotometry and e.s.r. spectroscopy. Evidence is presented for the formation of the sulphur cations S16 2+, S8 2+ and S4 2+ in these media, and for the presence of low concentrations of the radical cations S8+ and S4+.</p> / Thesis / Doctor of Philosophy (PhD)

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