On line speciation of Se(VI), Se(IV), and trimethylselenium by HPLC-microwave oven-hydride generation-atomic absorption spectrometry

An on-line system is proposed consisting of an anion-exchange chromatographic column, microwave-induced thermooxidation of trimethylselenium in the presence of persulphate, and microwave-induced thermoreduction of Se(VI) to Se(IV) in HCl medium, followed by hydride generation and atomic absorption for the determination of trimethylselenium (TMeSe), Se(IV) and Se(VI). Trimethylselenium is eluted in the dead volume of an anion-exchange column (Hamilton PRP-X-100), before elution of Se(IV) and Se(VI). Optimum chromatographic conditions have been obtained using 100 mmol L^–1 phosphate buffer (pH=6.8) H₂PO ₄ ^– /HPO ₄ ^2– as the mobile phase. Recoveries were around 100%, absolute detection limits were 1.1, 1.4 and 2.2 ng for TMeSe, Se(IV) and Se(VI), respectively. Precision was lower than 10% in all cases. The method has been applied to tap water.     

Gold(I) complexes with selenones and triphenylphosphine as ligands

A number of mixed ligand complexes of gold(I) with various selenones and Ph₃P, [Ph₃PAuSe=C<]Cl have been prepared and characterized by elemental analyses, i.r. and n.m.r. methods. A decrease in the i.r. frequency of the C=Se mode of selenones upon complexation is indicative of gold(I) binding viaa selenone group. An upfield shift in the ¹³ C-n.m.r. for the C=Se resonance of selenones and downfield shifts in ³¹P-n.m.r. for the Ph₃P moiety are consistent with the selenium coordination to gold(I). Available data in the literature suggest that P–Au–Se type complexes are usually linear.     

Perfluoroalkylphosphines and arsines obtained by Pd-catalyzed cross-coupling reaction with organoheteroatom stannanes

Pd-catalyzed cross-coupling reaction of organoheteroatom stannanes containing elements of the groups 15 (P, As) and 16 (Se) with perfluoroalkyl iodides (R_fI) was studied. Herein, a one-pot two-step reaction to form P–R_f, As–R_f and Se–R_f bonds is reported. The stannanes n-Bu₃SnZPh_n (Z = P, As, Se; n = 1–2) were generated in situ by the reaction of the Ph_nZ⁻ anion with n-Bu₃SnCl. The cross-coupling reactions of these stannanes with R_fI afforded C-heteroatom products, new perfluoroalkylarsines and perfluoroalkylselenides in good yields (47–90%) and perfluoroalkylphosphines in moderate yields (15–48%).     

Radiation-induced redox speciation of77Br in aqueous solution as determined by anion chromatography

⁷⁷Br is of potential use in diagnostic nuclear medicine as the parent of ultrashort-lived^77mSe in a radioisotopic generator system. The chemical form(s) of the radiobromine in aqueous solution, and their radiation-induced chemical transformations, are of importance for biomedical generator development. Approximately 150 mCi of radiobromine, initially present as Br^–, was studied over a period of three weeks and analyzed for BrO _x ^– (x=0–4) by anion exchange chromatography. Radiolysis of the solution gave rise to a small quantity of BrO ₃ ^– , but 99.5% of the activity remained as bromide.     

Formation of linkage isomers via the substitution of halides by selenocyanate in ruthenium(III) complexes

Summary Substitution of the halide ion of [Ru(NH₃)₅X]²⁺ (X=Cl^– or Br^–) by SeCN^– was monitored spectrophotometrically between 45 and 60° C in aqueous medium. The pseudo-first order rate constants were evaluated by Guggenheim's procedure, which shows linearity for 2–3 half-lives. The rate increases linearly with [SeCN^–] and all the plots have a positive intercept on the rate axis. The SeCN^–-independent path represents aquation and the SeCN^–-dependent path represents anation of the aqua complex with simultaneous formation of two isomeric (the N bonded and the Se bonded) products. The formation of the isomeric products is entropy controlled.     

On the existence of VXn+ (X = O,S,Se; n = 0,1,2) Ions and their tetrachloro complexes: Semi-empirical molecular orbital calculations

Summary The existence of VXⁿ⁺ (X = O, S, Se; n = 0, 1, 2) ions and their tetrachloro complexes, [VXCl₄]^m– (m = 4, 3, 2), has been probed using iterative extended-Hückel molecular orbital (EHMO) calculations. The EHMO results indicate that all of the species are expected to exist (a few species are already known). Calculated stability decreases in the sequence O > S > Se and with increasing charge on the [VXCl₄]^m– complex ion. Calculated properties and energy level sequences have been compared with those of the known [VOCl₄(H₂O)]^2– ion and related species.     

Comparison of recoveries of inogranic and organic incorporated75Se by four mineralization methods of biological material

The recovery of selenium⁷⁵Se added as selenite to human blood and to mixed food, and the recovery of biologically incorporated⁷⁵Se from different rat tissues were determined by using four mineralization methods. The recoveries of⁷⁵Se after dry ashing /HNO₃, Mg/NO₃/₂/ and after three wet digestion methods — 1. HNO₃, HClO₄ 2. HNO₃, HClO₄, H₂SO₄ 3. HNO₃, HClO₄, MgCl₂ were as follows: 50–106%, 96–99%, 92–99% and 97–100%, resp. Losses of⁷⁵Se in wet digestion /HNO₃, HClO₄/ were observed at the end of the procedure, when an excess of acids was evaporated. The addition of MgCl₂ to the digestion mixture prevented the escape of⁷⁵Se and thus permitted the total evaporation of the digest without any loss of selenium.     

Analytical methods for the speciation of selenium compounds: a review

Selenium, like sulphur, exists in the environment in several oxidation states and as a variety of inorganic and organic compounds. Dissolved inorganic selenium can be found in natural waters as selenide Se (–II), as colloidal elemental selenium Se (0), as selenite anions HSeO ₃ ^– and SeO ₃ ^2– i.e. Se (+IV) and as the selenate anion (SeO ₄ ^2– ) i.e. Se (+VI). Organic forms of selenium that may be found in organisms, air or in the aqueous environment, are volatile (methylselenides) or non volatile (trimethylselenonium ion, selenoamino acids and their derivatives). Knowledge of the different chemical forms and their environmental and biomedical distribution is important because of the dependence of bioavailability and toxicity on speciation. This paper reviews the different analytical methods used for the speciation of selenium compounds, with special attention to inorganic selenium and organoselenium species.     

Effect of selenium on the Hg,Zn, Fe and Co content of yeast cells

The yeast cells, Saccharomyces cerevisiae, were exposed to Hg²⁺ ions (10^–4M) and SeO₂ (2·10^–4–10^–2M) or Se- methionine (2·10^–4M). Instrumental neutron activation analysis (INAA) was used to analyze changes in the Hg, Zn, Fe and Co levels in these cells. When the yeast was incubated in a medium containing 10^–3M and 10^–2M SeO₂, the Hg content of the yeast markedly increased. It was also found that the uptake of Se and Hg influenced the levels of Zn, Fe and Co found in the cells. While the presence of Se-methionine (Se-Met), SeO₂ or Hg²⁺ ions caused increases in the intracellular Zn levels, the combined presence of Hg²⁺ and SeO₂ and their assumed interaction, reduced the efficiency of Se for increasing the Zn content of yeast.     

Use of INAA to study the effect of selenium on uranium accumulation in cells of saccharomyces cerevisiae

Differences in the effects of seleno-cystine (CySe)₂ and inorganic Se(IV) and Se(VI) compounds on uranium(VI) uptake by yeast cells, Saccharomyces cerevisiae have been studied. The Se, U, Zn and Co levels of the yeast cells were measured by neutron activation analysis. An increase in the concentration of U cells within the first 2 hours of incubation was produced by the presence of SeO₂ (2·10^–4–5·10^–4M) and (CySe)₂ (1·10^–4M) in the yeast medium. Moreover, the highest SeO₂ concentration (5·10^–4M) and (CySe)₂ more efficiently enhanced the U content of the cells than SeO₂ at the low concentration end (2·10^–4M). However, the effect of SeO₂ and (CySe)₂ on U uptake diminishes with incubation time (from 2 to 48 hours). Se(VI) [as (NH₄)₂SeO₄] leads to a marked decrease in the content of uranium in Saccharomyces cerevisiae (an antagonistic interaction). As expected, uranium uptake by the yeast influence the retention of selenium in the cells. Uranium significantly increased the uptake yield of Se by Saccharomyces cerevisiae when the yeast was incubated in the medium containing (CySe)₂. Furthermore, during the initial 24 hours of the incubation an increase of the Se content of the cells in the presence of U was observed when Se(VI) was in the culture medium. Selenium and uranium dosages affected the Zn and Co contents of cells.     

Synthesis and conformational studies of palladium(II) complexes containing [PhP(O)NP(E)Ph]− (E=S or Se)

The ligands [Ph₂P(O)NP(E)Ph₂]⁻ (E=S I; E=Se II) can readily be complexed to a range of palladium(II) starting materials affording new six-membered Pd–O–P–N–P–E palladacycles. Hence ligand substitution reaction of the chloride complexes [PdCl₂(bipy)] (bipy=2,2′-bipyridine), [{Pd(μ-Cl)(L–L)}₂] (HL–L=C₉H₁₃N or C₁₂H₁₃N), [{Pd(μ-Cl)Cl(PMe₂Ph)}₂] or [PdCl₂(PR₃)₂] [PR₃=PPh₃; 2PR₃=Ph₂PCH₂CH₂PPh₂or cis-Ph₂PCH=CHPPh₂] with either I (or II) in thf or CH₃OH gave [Pd{Ph₂P(O)NP(E)Ph₂-O,E}(bipy)]PF₆, [Pd{Ph₂P(O)NP(E)Ph₂-O,E}(L–L)], [Pd{Ph₂P(O)NP(E)Ph₂-O,E}Cl(PMe₂Ph)] or [Pd{Ph₂P(O)NP(E)Ph₂-O,E} (PR₃)₂]PF₆ in good yields. All compounds described have been characterised by a combination of multinuclear NMR [31 P{1 H} and 1 H] and IR spectroscopy and microanalysis. The molecular structures of five complexes containing the selenium ligand II have been determined by single-crystal X-ray crystallography. Three different ring conformations were observed, a pseudo-butterfly, hinge and in the case of all three PR₃ complexes, pseudo-boat conformations. Within the Pd–O–P–N–P–Se rings there is evidence for π-electron delocalisation.     

Application of tertiary amines for arsenic and selenium signal enhancement and polyatomic interference reduction in ICP-MS analysis of biological samples

Water soluble tertiary amines enhance signals and decrease polyatomic chloride interferences in the direct inductively coupled plasma – mass spectrometric (ICP-MS) determination of As and Se in biological samples. Preliminary experiments with amine concentrations and nebulizer flow rates produced element and interference signal intensity changes. Arsenic and Se ICP-MS determination parameters have been optimized by a simplex procedure with amines in an argon plasma or without amines but with addition of N₂ to the Ar. Variables include RF (radio frequency) power, nebulizer gas flow rate, intermediate gas flow rate, and amine concentration or nitrogen gas flow rate. Detection limit, minimization of polyatomic ion intensities, and reproducibility have been evaluated as reponse factors. The signal enhancement and element-to-molecular interference ratios differ to some extent with analyte intensity optimum operating conditions. The detection limits with addition of nitrogen (16 pg mL^–1 for As and 180 pg mL^–1 for Se) or of amines (8 pg mL^–1 for As and 120 pg mL^–1 for Se) and the extent of chloride interference minimization were compared. Amines addition was more beneficial. Biological standard reference materials and food and fecal samples were analyzed following different sample dissolution procedures.     

Oxygen reduction in acid media at the amorphous Mo–Os–Se carbonyl cluster coated glassy carbon electrodes

An amorphous Mo–Os–Se carbonyl cluster compound has been synthesized in 1,2-dichlorobenzene (b.p.≈180°C) to be tested as an electrocatalyst for molecular oxygen reduction in 0.5 M H₂SO₄. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) performed for the powder supported on pyrolytic carbon show a distribution of nanometer-scale amorphous particles with agglomerations in cluster forms. The catalytic activity was studied by the rotating disc electrode technique. Kinetic studies show a first-order reaction with a Tafel slope of −0.118 V dec⁻¹ and dα/dT=1.55×10⁻³ K⁻¹. In the temperature range 298–343 K, an activation energy of 32 kJ mol⁻¹ was determined.     

The effect of high pressure on the ion pair equilibrium constant of alkali metal fluorides: A spectrophotometric study

Bromophenol blue indicator was used in UV-visible spectrophotometric measurements to study ion association constants of alkali metal fluorides. The equilibrium constants for the ion pair formation of the alkali metal fluorides were determined as a function of ionic strength at one atmosphere pressure and 25°C. The effect of pressure on these association constants was measured at a constant total ionic strength of 1.0 mol-kg^–1 over a pressure range of 1 to 2000 atmospheres at 25°C. The pressure dependences of the stoichiometric association constants of the alkali metal fluorides are given by: lnK _LiF ^* =0.77–2.47×10^–4P–2.12×10^–8P²; lnK _NaF ^* =0.53–1.08×10^–4P–1.66×10^–8P²; lnK _KF ^* =0.24–4.41×10^–5P–7.15×10^–8P²; lnK _RbF ^* =–0.17–8.65×10^–5P–4.51×10^–8P²; and lnK _CsF ^* = –0.37–1.14×10^–4P–6.82×10^–8P², where P is the pressure in atmospheres. The stoichiometric molar volume and compressibility changes for ion pair formation of the alkali metal fluorides were evaluated from the pressure dependence of K _MF ^* data. The thermodynamic association constants were also calculated making use of activity coefficient data from the Pitzer equations. The partial molal volume and compressibility changes for ion pair formation of each alkali metal fluoride are reported.     

Spectroscopic studies of the behaviour of the AgNO3−HNO3 — Tetrabutyl dithiopyrophosphate extraction system

A very efficient extraction of silver with tetrabutyl dithiopyrophosphate (TBDTPP) is followed by dramatic changes in the structure of the extractant molecule. The IR and NMR spectroscopic studies have revealed that in the presence of Ag⁺ and NO ₃ ^– ions the TBDTPP molecule rearranges first into a molecule containing a P–S–P bridge and one P=O group instead of P–O–P and P=S, respectively, and then into a molecule containing two P–S–C and two P=O groups at a P–O–P bridge.     

Structure of 2-chloromethyl-2-oxo-3H-1,4,2-benzoxazaphosphorine

The compressed bicyclic structure of 2-chloromethyl-2-oxo-3H-1,4,2-benzoxaza-phosphorine features a sixmembered heterocycle with P ²,C³ -half-chair with axial equatorial orientation of the P=O group and axial orientation of the CH₂Clgroup. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2355–2357, October, 1989.     

Activation analysis of Se in biological samples through75Se and77mSe

A method is described to separate trace amounts of selenium in biological samples without using a carrier. This method is based on the adsorption on active carbon of the complex ion formed with APDC /ammonium salt of l-pyrrolidine carbodithioic acid/ at pH 1. The efficiency of the radiochemical separation described is measured by using carrier-free⁷⁵Se labelled solutions of sodium selenite at selenium concentrations from 3.5×10^–8 to 3.5×10^–11 g ml^–1. The results were between 95% and 98% with statistical variations from 2% to 10%. The determination of selenium can be made following this separation either through⁷⁵Se in the traditional way, or through^77mSe if the separation is performed prior to irradiation. The detection limits on the available conditions were 0.01 ppm for⁷⁵Se and 0.1 ppm for^77mSe. When the analysis is performed through⁷⁵Se /t=120 d/, the statistical error is notably smaller because the counting time may be considerable, whereas through^77mSe/t=17.5 s/it is higher than 20%, depending on the concentration and the available neutron flux. However, the advantages of gaining time and the fact of performing the trace separation from a non radioactive material, make both procedures competitive as useful tools for the research on the function of Se in vertebrates.     

Zinc(II), cadmium(II) and mercury(II) halide pyrrolidine-2-selone complexes

Summary Reaction of zinc(II), cadmium(II) and mercury(II) halides with Pyrrolidine-2-selone yields complexes of general formula ML₂X₂ (X = Cl, Br or I) which are monomeric, tetrahedral and Se-bonded to the metals. The comparison of their i.r. spectra with the spectrum of the free ligand confirms that the band at 1005 cm^–1 in Pyrrolidine-2-selone arises predominantly from the C=Se stretching vibration. The metalhalogen absorptions above 200 cm^–1 are identified.This work was supported by the National Research Council (C.N.R.) of Italy.     

[RhCl(CO)(PPh3)]2. A precursor for the synthesis of cationic rhodium complexes with nitrogen donor ligands

Summary The use of [RhCl(CO)(PPh₃)]₂ as a precursor for the synthesis of complexes of the types [Rh(CO)L₂(PPh₃)]A (A = [ClO₄]^– or [BPh₄]^–; L = pyridine type ligand) and [Rh(CO)(L-L)(PPh₃)]A (A = [ClO₄]^– or [BPh₄]^–; L-L = bidentate nitrogen donor) and the preparation of several complexes of the types [Rh(CO)L(PPh₃){P(p-RC₆H₄)₃}]BPh₄ and [Rh(CO)(phen)(PPh₃){P(p-RC₆H₄)₃}]A (A = [ClO₄]^– or [BPh₄]^–; R = H or Me) is described.Author to whom all correspondence should be directed.