Confusion between dimethyl selenenyl sulfide and dimethyl selenone released by bacteria

Dimethyl selenone [(CH₃)₂SeO₂] has been reported in the literature as a metabolite released by bacteria in contact with selenium metal or selenium salts. In this study, mass spectral, chromatographic, and boiling-point data are presented that show that dimethyl selenone has been confused with dimethyl selenenyl sulfide (CH₃SeSCH₃). In addition, the headspaces above monocultures of selenium-resistant bacteria were examined using gas chromatography followed by fluorine-induced chemiluminescence detection. A number of alkyl sulfur and selenium species were detected, along with dimethyl selenenyl sulfide. A pathway from oxidized selenium salts to reduced methylated selenides and dimethyl selenenyl sulfide is also presented.     

The First Selenonium Azides and a Selenonium Selenocyanate

The reaction of [R₃Se]I (R = CH₃, C₆H₅) with silver azide resulted in the formation of [(CH₃)₃Se]N₃ ( 1 ) and [(C₆H₅)₃Se]N₃ ( 2 ); these are the first selenium—azide species to be obtained in pure form. A similar reaction with silver selenocyanate yielded [(CH₃)₃Se]SeCN ( 3 ), an example of a mixed valence selenium compound. Thorough characterization by multinuclear NMR and vibrational spectroscopy and crystal structure determination has been carried out.     

Formation and Reactivity of Organo‐Functionalized Tin Selenide Clusters

Reactions of R¹SnCl₃ (R¹=CMe₂CH₂C(O)Me) with (SiMe₃)₂Se yield a series of organo‐functionalized tin selenide clusters, [(SnR¹)₂SeCl₄] ( 1 ), [(SnR¹)₂Se₂Cl₂] ( 2 ), [(SnR¹)₃Se₄Cl] ( 3 ), and [(SnR¹)₄Se₆] ( 4 ), depending on the solvent and ratio of the reactants used. NMR experiments clearly suggest a stepwise formation of 1 through 4 by subsequent condensation steps with the concomitant release of Me₃SiCl. Furthermore, addition of hydrazines to the keto‐functionalized clusters leads to the formation of hydrazone derivatives, [(Sn₂(μ‐R³)(μ‐Se)Cl₄] ( 5 , R³=[CMe₂CH₂CMe(NH)]₂), [(SnR²)₃Se₄Cl] ( 6 , R²=CMe₂CH₂C(NNH₂)Me), [(SnR⁴)₃Se₄][SnCl₃] ( 7 , R⁴=CMe₂CH₂C(NNHPh)Me), [(SnR²)₄Se₆] ( 8 ), and [(SnR⁴)₄Se₆] ( 9 ). Upon treatment of 4 with [Cu(PPh₃)₃Cl] and excess (SiMe₃)₂Se, the cluster fragments to form [(R¹Sn)₂Se₂(CuPPh₃)₂Se₂] ( 10 ), the first discrete Sn/Se/Cu cluster compound reported in the literature. The derivatization reactions indicate fundamental differences between organotin sulfide and organotin selenide chemistry.     

Simultaneous arsenic‐ and selenium‐specific detection of the dimethyldiselenoarsinate anion by high‐performance liquid chromatography–inductively coupled plasma atomic emission spectrometry

The seleno‐bis (S‐glutathionyl) arsinium ion, [(GS)₂AsSe]^?, which can be synthesized from arsenite, selenite and glutathione (GSH) at physiological pH, fundamentally links the mammalian metabolism of arsenite with that of selenite and is potentially involved in the chronic toxicity/carcinogenicity of inorganic arsenic. A mammalian metabolite of inorganic arsenic, dimethylarsinic acid, reacts with selenite and GSH in a similar manner to form the dimethyldiselenoarsinate anion, [(CH₃)₂As(Se)₂]^?. Since dimethylarsinic acid is an environmentally abundant arsenic compound that could interfere with the mammalian metabolism of the essential trace element selenium via the in vivo formation of [(CH₃)₂As(Se)₂]^?, a chromatographic method was developed to rapidly identify this compound in aqueous samples. Using an inductively coupled plasma atomic emission spectrometer (ICP‐AES) as the simultaneous arsenic‐ and selenium‐specific detector, the chromatographic retention behaviour of [(CH₃)₂As(Se)₂]^? was investigated on styrene–divinylbenzene‐based high‐performance liquid chromatography (HPLC) columns. With a Hamilton PRP‐1 column as the stationary phase (250 × 4.1 mm ID, equipped with a guard column) and a phosphate‐buffered saline buffer (0.01 mol dm^?3, pH 7.4) as the mobile phase, [(CH₃)₂As(Se)₂]^? was identified in the column effluent according to its arsenic:selenium molar ratio of 1 : 2. With this stationary phase/mobile phase combination, [(CH₃)₂As(Se)₂]^? was baseline‐separated from arsenite, selenite, dimethylarsinate, methylarsonate and low molecular weight thiols (GSH, oxidized GSH) that are frequently encountered in biological samples. Thus, the HPLC–ICP‐AES method developed should be useful for rapid identification and quantification of [(CH₃)₂As(Se)₂]^? in biological fluids. Copyright © 2003 John Wiley & Sons, Ltd.     

Cyclic and stripping voltammetry of Se(+4) and Se(−2) at the HMDE in acidic media

Electroreduction of Se(+4) and electrooxidation of Se(?2) were studied at mercury electrodes in acidic media and an improved mechanism of the reduction process was proposed. This mechanism takes into account the fact that the reduction path is concentration-dependent. At lower concentrations of Se(+4), mercury selenide and hydrogen selenide are formed at various potentials. At higher Se(+4) concentrations the electrode quickly becomes covered by a rigid deposit of mercury selenide and then the reduction starts to proceed to elemental selenium. Another form of selenium was formed in the vicinity of the mercury surface due to a chemical reaction between H₂SeO₃ and H₂Se. Oxidation of hydrogen selenide proceeds similarly, in the sense that after coverage of the electrode surface by a deposit of mercury selenide the oxidation starts to proceed to elemental selenium. The cathodic stripping peak of mercury selenide can be obtained down to 2 × 10^?8M of Se(+4), but this peak is often split and therefore the determination of traces of Se(+4) by the cathodic stripping technique is cumbersome.     

Bridge Cleavage Reactions of Dinuclear Diselenolenes: Preparation of Palladium Complexes of Novel Chelating Selenolato/Selenide Ligands, [PdX(Se{R′}CnH2n−4Se)(PR3)](n = 6, 7, 8; R = Ph,Bu; X = Br,I; R′ = Me,Et, etc.)

Abstract

The dinuclear palladium diselenolenes [Pd₂(Se₂C_nH_2n?4)₂(PR₃)₂] react with haloalkanes, via electrophilic attack at the bridging selenium atoms, to yield the neutral mononuclear square planar palladium(II) complexes [PdX(Se{R′}C_nH_2n?4Se)(PR₃)] (n = 6, 7, 8; R = Ph, Bu; X = Br, I; R′ = Me, Et, etc.), containing a novel chelating selenolato/selenide ligand, in which the alkylated selenium and halogen donor atoms occupy cis-positions. The products have been characterised by mass spectrometry and multinuclear NMR spectroscopy; the molecular structure of the compound with n = 8, R = Ph, R′ = Et has been determined by X-ray crystallography.     

Confirmation of the Biomethylation of Antimony Compounds

We have evidence that an organic and an inorganic salt of antimony were reduced and methylated biologically by microorganisms in laboratory experiments. The organoantimony compound produced was trimethylstibine [(CH₃)₃Sb] and was detected in a culture headspace. This was confirmed by matching the compound's retention time in capillary gas chromatography, as detected by fluorine-induced chemiluminescence, with a com- mercial standard and by its mass spectrum determined with gas chromatography/ mass spectrometry (GC–MS). (CH₃)₃Sb was detected in the headspace of soil samples amended with either potassium antimonyltartrate or potassium hexahydroxyantimonate and augmented with any one of three different nitrate-containing growth media. The identity of the microorganisms in soil that accomplished this are as yet unknown. Of 48 soil samples amended with these two compounds, 24 produced trimethylstibine. Bioreduction of trimethyldibromoantimony was also detected in a liquid monoculture of Pseudomonas fluorescens K27 which also produced tri- methylstibine. This headspace production of (CH₃)₃Sb was determined to be linked to the culture's cell population as measured by optical density. This microbe, however, did not biomethylate either potassium antimonyltartrate or potassium hexahydroxyantimonate in any experiments we performed. © 1997 John Wiley & Sons, Ltd.     

Magnetic dispersive solid phase extraction using modified magnetic multi-walled carbon nanotubes combined with electrothermal atomic absorption spectrometry for the determination of selenium

A novel magnetic dispersive solid phase extraction method using magnetic multi-walled carbon nanotubes modified with 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione potassium salt (bismuthiol II) (MMWCNTs@Bis) as the sorbent was developed for the separation and preconcentration of inorganic selenium (IV) prior to its determination by electrothermal atomic absorption spectrometry. The prepared MMWCNTs@Bis sorbent was characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer and X-ray diffraction. Total selenium was determined after reduction of Se(VI) to Se(IV) by addition of hydrochloric acid and heating the mixture in a boiling water bath. Se(VI) concentration was determined from the difference between the amounts of total selenium and Se(IV). Under the optimised experimental conditions, an enhancement factor of 196 and a detection limit (based on 3S_b/m) of 0.003 µg L^?1 was obtained for aqueous samples. The relative standard deviation at 0.1 µg L^?1 concentration level of Se(IV) (n = 6) was found to be 5.2 and 7.7% for intra- and inter-day analysis, respectively. The method was successfully applied to the determination of inorganic selenium species in water and total selenium in food samples.     

Theoretical Investigation on the Effect of Different Nitrogen Donors on Intramolecular Se⋅⋅⋅N Interactions

The effect of different donor nitrogen atoms on the strength and nature of intramolecular Se ??? N interactions is evaluated for organoselenium compounds having N,N‐dimethylaminomethyl (dime), oxazoline (oxa) and pyridyl (py) substituents. Quantum chemical calculations on three series of compounds [2‐(dime)C₆H₄SeX ( 1 a – g ), 2‐(oxa)C₆H₄SeX ( 2 a – g ), 2‐(py)C₆H₄SeX ( 3 a – g ); X=Cl, Br, OH, CN, SPh, SePh, CH₃] at the B3LYP/6‐31G(d) level show that the stability of different conformers depends on the strength of intramolecular nonbonded Se ??? N interactions. Natural bond orbital (NBO), NBO deletion and atoms in molecules (AIM) analyses suggest that the nature of the Se ??? N interaction is predominantly covalent and involves nN→σ*_{Se? X} orbital interaction. In the three series of compounds, the strength of the Se ??? N interaction decreases in the order 3 > 2 > 1 for a particular X, and it decreases in the order Cl>Br>OH>SPh≈CN≈SePh>CH₃ for all the three series 1 – 3 . However, further analyses suggest that the differences in strength of Se ??? N interaction in 1 – 3 is predominantly determined by the distance between the Se and N atoms, which in turn is an outcome of specific structures of 1 , 2 and 3 , and the nature of the donor nitrogen atoms involved has very little effect on the strength of Se ??? N interaction. It is also observed that Se ??? N interaction becomes stronger in polar solvents such as CHCl₃, as indicated by the shorter r_{Se ??? N} and higher E_{Se ??? N} values in CHCl₃ compared to those observed in the gas phase.     

Study of the lipophilicity of selenium species

In this work the lipophilicity of different selenium species occurring in environmental matrices and food, Se(IV), Se(VI), selenomethionine (Se-Met), selenocystamine (Se-CM), selenocystine (Se-Cyst), and dimethyl diselenide (CH₃)₂Se₂, was investigated in the octanol–water system, using the shaking flask method and detection with inductively coupled plasma–atomic emission spectrometry (ICP–AES), in order to assess their environmental fate and tendency to bioaccumulate. Polarography was also used for the electrochemically active Se species, Se(IV), Se-Cyst, Se-CM and (CH₃)₂Se₂, and the results were compared with those measured by ICP–AES. Furthermore, the influence of pH was studied by determining the logarithm of the distribution coefficient, log D, at three pH values, 5, 7, and 9, as was the impact of the marine environment on the lipophilicity profile of the six investigated Se species. The results were compared with those estimated approximately by use of PrologD software, based on the Ghose-Crippen log P (P: partition coefficient) calculation system, the only system which incorporates values—even though approximate—for the atom type of Se. Finally, from our experimental data an indicative value of the Se–Se fragment for log P prediction, for use in drug design, was estimated.     

A novel simple synthesis of bis(diorganoselenophosphoryl)selenides (R2PSe)2Se from secondary phosphines and elemental selenium

Secondary phosphines R₂PH [R = Ph(CH₂)₂, 4-t-BuC₆H₄(CH₂)₂, 4-MeOC₆H₄(CH₂)₂, 2-Naphth(CH₂)₂] react with two equivalents of elemental selenium under mild conditions (85 °C, 3 h, toluene) to afford bis(diorganoselenophosphoryl)selenides (R₂PSe)₂Se in high yields (75-92%).     

Reaction of trimethylaluminum with selenium tetrachloride. Synthesis of [(CH3)3 Se][ClAl(CH3)2(Cl)Al(CH3)3]. The first selenium-based liquid clathrate

Selenium tetrachloride reacts with an excess of trimethylaluminum in the presence of aromatic solvents to afford a non-stoichiometric organoaluminum-selenonium based inclusion compound of the formula [(CH₃)₃Se][ClAl(CH₃)₂(Cl)Al(CH₃)₃]·(aromatic solvent) _n . The cation of the parent compound of the inclusion complex results from the alkylation of SeCl₄ producing the (CH₃)₃Se⁺ selenonium ion while the anion consists of a dimethylaluminum chloride unit and a trimethylaluminum unit bridged by a chlorine atom. This liquid inclusion complex, liquid clathrate, can accommodate 8.5 benzene molecules or 8.3 guest toluene molecules per anionic moiety.     

A Series of Low-Coordinate Iron Selenido Complexes: Reactivity of a Linear Iron(I) Silylamide towards Selenium

A variety of different low-coordinate iron selenide complexes is reported. These are obtained by reaction of the linear iron(I) silylamide K{18c6}[Fe(N(Dipp)SiMe₃)₂] (Dipp=2,6-diisopropylphenyl) with red selenium. Careful adjustment of the reaction conditions results in the formation of unique low-coordinate selenido iron complexes, namely a monoselenide bridged [2Fe−1Se]²⁺ complex, as well as mononuclear iron per- and triselenides. Further, C−H bond activation of one of the silylamide ligands by a putative terminal iron monoselenide is observed.     

Polyselenide mit langkettigen Tetraalkylammoniumionen Die Kristallstruktur von Trimethyl-tetradecyl-ammonium-hexaselenid

Polyselenides with Long-chain Tetraalkylammonium Ions. Crystal Structure of Trimethyltetradecyl-ammonium Hexaselenide Na₂Se₂ and Na₂Se react with various tetraalkylammonium halides in ethanol and in presence of grey selenium and catalytic quantities of iodine forming different polyselenides Se_n^2? (n = 3, 5—9). In the solutions equilibria of polyselenides seem to occur; cooling of saturated solutions causes crystallization of polyselenides with a composition depending on the cation. Tri- and pentaselenide are dark green. The higher members form black crystals, all compounds are sensitive to oxygen. The i.r. spectra are reported. [(CH₃)₃N(CH₂)₁₃CH₃]₂Se₆ is characterized by a crystallographic structure determination with X-ray data: space group P2₁2₁2, Z = 4, a = 5043, b = 734.2, c = 600.3 pm (986 observed independent reflexions. R = 0.072). The compound consists of trimethyl tetradecylammonium ions and angular Se₆^2? chains of symmetry C₂ with Se? Se bond lengths of 227 and 235 pm.     

Interaction of arsenic and selenium on the metabolism of these elements in hamsters

The interaction of arsenic and selenium compounds on the metabolism of these elements in golden hamsters was studied. Golden hamsters were divided into three groups and administered sodium selenite (Na₂SeO₃), sodium arsenite (NaAsO₂) and Na₂SeO₃ with NaAsO₂, respectively, by a single Subcutaneous injection of 25 m?mol kg^?1 body weight as As or Se (arsenic and selenium were calculated as weight of elemental arsenic and selenium). Selenium and arsenic metabolites were determined by high-performance liquid chromatography–graphite furnace atomic absorption spectrometry (HPLC–GFA AA) and gas chromatography (GC). The results show (1): About 10% by weight of the given dose of selenium was excreted in expiration air as dimethylselenide (Me₂Se) during 12 h after administration of Na₂SeO₃. Excretion of dimethylselenide with the respiratory air was inhibited by administration of Na₂SeO₃ simultaneously with NaAsO₂. (2) Giving Na₂SeO₃ plus NaAsO₂ had no appreciable effect on the excretion of the trimethylselenonium ion (Me₃Se⁺) into the urine and the feces. (3) Giving Na₂SeO₃ plus NaAsO₂ increaed the excretion into the feces of an insoluble unknown-structure selenium compound, the proportion of which was 10.9% by weight of the given dose of selenium. (4) Giving NaAsO₂ plus Na₂SeO₃ decreased the excretion of dimethylarsinic acid (Me₂AsOOH) and inorganic arsenic into the urine during 120 h after the administration of the reagents, the decreased amount being 5.3% (dimethylarsinic acid) and 7.7% (inorganic arsenic) of the given dose of arsenic, respectively. (5) Giving NaAsO₂ plus Na₂SeO₃ increased the excretion into feces of insoluble unknown-structure arsenic compound and inorganic arsenic, the increased amounts being 10.6% and 7.0% of the given dose of arsenic, respectively. (6) Giving NaAsO₂ plus Na₂SeO₃ decreased the excretion into feces of extractable unknown-structure arsenic compound, and the decreased amount was 4.9% of the given dose of arsenic. (7) It made little difference to the excretion of monomethylarsonic acid [MeAsO(OH)₂] into urine and feces and of dimethylarsinic acid (Me₂AsOOH) into feces whether NaAsO₂ was administered alone or with Na₂SeO₃.     

Solubility of carbon dioxide,methane, and propane in silicone polymers. Effect of polymer backbone chains

The solubility of carbon dioxide, methane, and propane in poly(dimethyl silmethylene) [(CH₃)₂SiCH₂]_x and poly(tetramethyl silhexylene siloxane) [(CH₃)₂Si (CH₂)₆Si (CH₃)₂O]_x was measured in the temperature range from 10.0 to 55.0°C and at elevated pressures. The present results are compared with similar measurements made with other silicone polymers. At a given temperature and pressure, the solubility of the above three gases is highest in poly(dimethyl siloxane) (Me₂SiO)_x. The gas solubility is decreased by either backbone-chain or side-chain substitutions of functional groups in (Me₂SiO)_x which increase the stiffness of the polymer chains and decrease the specific or fractional free volume of the polymers. It is conjectured that a decrease in the free volume of silicone polymers has a greater effect in decreasing the gas solubility than differences in gas/polymer interactions [with the exception of specific interactions (e.g., between CO₂ and polar groups in the polymer)]. © 1993 John Wiley & Sons, Inc.     

Mononuclear and Terminal Zirconium and Hafnium Methylidenes

The dimethyl aryloxide complexes [(PNP)M(CH₃)₂(OAr)] (M=Zr or Hf; PNP^?=N[2‐P(CHMe₂)₂‐4‐methylphenyl]₂); Ar=2,6‐iPr₂C₆H₃), which were readily prepared from [(PNP)M(CH₃)₃] by alcoholysis with HOAr, undergo photolytically induced α‐hydrogen abstraction to cleanly produce complexes [(PNP)M=CH₂(OAr)] with terminal methylidene ligands. These unique systems have been fully characterized, including the determination of a solid‐state structure in the case of M=Zr.     

Formation of Metal Selenide and Metal–Selenium Nanoparticles using Distinct Reactivity between Selenium and Noble Metals

Small Se nanoparticles with a diameter of ≈20 nm were generated by the reduction of selenium chloride with NaBH₄ at ?10 °C. The reaction with Ag at 60 °C yielded stable Ag₂Se nanoparticles, which subsequently were transformed into M–Se nanoparticles (M=Cd, Zn, Pb) through cation exchange reactions with corresponding ions. The reaction with Pt formed Pt layers that were evenly coated on the surface of the Se nanoparticles, and the dissolution of the Se cores with hydrazine generated uniform Pt hollow nanoparticles. The reaction with Au generated tiny Au clusters on the Se surface, and eventually formed acorn‐shaped Au–Se nanoparticles through heat treatment. These results indicate that small Se nanoparticles with diameters of ≈20 nm can be used as a versatile platform for the synthesis of metal selenide and metal–selenium hybrid nanoparticles with complex structures.     

Enhancement of Sensitivity for Selenium Determination in Atomic Absorption Spectrophotometry by Introducting Hydrogen Selenide into an Argon-Hydrogen Flame

Abstract

The sensitivity for selenium determination with atomic absorption spectrophotometry is enhanced to a large extent by introducing hydrogen selenide gas into an argon-hydrogen flame. As a reducing agent, zinc granular and stannous chloride is successfully used for quantitative and rapid productions of hydrogen selenide from selenium(IV) solution. The sensitivity for 1 % absorption of the signal is estimated to be about 0.02 ppm of selenium.     

Exploring the elution mechanism of selenium species on liquid chromatography

In the present work, the chromatographic behavior of eight selenium species, namely selenites (Se(IV)), selenates (Se(VI)), seleno‐DL ‐methionine (Se‐Met), selenocystine (Se‐Cyst), selenocystamine (Se‐CM), selenourea (Se‐U), dimethylselenide ((CH₃)₂Se) and dimethyldiselenide ((CH₃)₂Se₂), was investigated under different stationary and mobile phase conditions, in an effort to unravel secondary interferences in their underlying elution mechanism. For this purpose, two end‐capped and a polar‐embedded reversed‐phase stationary phases were employed using different mobile phase conditions. Retention factors (log k_w) were compared with octanol–water distribution coefficients (log D) as well as with log k_w values on two immobilized artificial membrane (IAM) columns and two immobilized artificial plasma proteins stationary phases, obtained in our previous work. The role of electrostatic interactions was confirmed by introducing the net charge of the investigated Se species as an additional term in the log k_w/log D interrelation, which in most cases proved to be statistically significant. Principal component analysis of retention factors on all stationary phases and octanol–water log D values, however, showed that the elution of the investigated selenium species is mainly governed by partitioning mechanism under all different chromatographic conditions, while the pH of the mobile phase and the special column characteristics have only a minor effect.