Dimethylselenide Research Articles

Effects of growth conditions on production of methyl selenides in cultures of Rhodobacter sphaeroides

2.4.1 exposed to selenate or selenite produced volatile selenium compounds. Total amounts of dimethyl selenide, dimethyl diselenide, dimethyl sulfide and dimethyl disulfide in culture medium and headspace were determined. The highest selenate volatilization occurred in the late stationary phase of growth. However, cultures deprived of light in the stationary phase of growth produced much less of the volatile organo-selenium compounds. Lower culture pHs increased the rate of selenium volatilization. Low sulfate concentration limited biomass production and selenium volatilization; high sulfate concentrations had an enhancing effect on the release of organo-selenium compounds. Cultures of R. sphaeroides reacted very differently to amendments with increasing amounts of selenate and selenite. Only small amounts of selenite were volatilized; meanwhile high amounts of methylated selenides were found in selenate-poisoned cultures.

Crystallographic characterisation of dihalogenodimethylselenium compounds, Me2SeX2 (X = Cl, Br or I) and the dependence of their structures on the nature of the halogen

The reaction of Me 2 Se with I 2 in diethyl ether produced the charge-transfer complex Me 2 Se–I–I, which has a short I–I distance of 2.916(3) A, when compared to the analogous Group 16 compound Me 3 As–I–I, reflecting the weaker donor power of Se compared to As towards diiodine. Dimethyl selenide reacted with Br 2 to produce the regular trigonal-bipyramidal molecule Me 2 SeBr 2 with Se–Br bond lengths of 2.546(4) and 2.551(4) A, i.e. virtually identical. However, the dichloro-compound, Me 2 SeCl 2 , prepared from the reaction of SO 2 Cl 2 with Me 2 Se, shows significant variations in Se–Cl bonds [2.349(5), 2.408(6), 2.351(6) and 2.405(5) A (two inequivalent molecules in the asymmetric unit)]. This is due to significant long Se ··· Cl contacts which lie within the van der Waals radii. These results illustrate the structural changes observed for the Me 2 SeX 2 (X = I, Br or Cl) series in the solid state upon changing the nature of the halogen.

Maritime emission of selenium to the atmosphere in Eastern Mediterranean seas

Results presented in this article report the first assessment of at least 3 volatile selenium species (MeSeH, DMSe, DMDSe) in marine water and air. Dimethyl selenide (DMSe) was the main compound encountered and the total concentration of the volatile selenides was found to be correlated with the marine plankton biomass as measured through chlorophyll a content. Estimation of a net selenium flux from the ocean to the marine atmosphere has been established. This gaseous flux corroborates previous hypotheses on selenium cycling and indicates that maritime emissions are a major source of selenium to the atmosphere in the Mediterranean basin.

Gas-phase reactions of dimethyl selenide with ozone and the hydroxyl and nitrate radicals

Experiments were carried out in a large-volume chamber to investigate the products of the atmospherically important reactions of dimethyl selenide. Dimethyl selenoxide [(CH 3) 2SeO] was observed as the major product of the gas-phase reaction of dimethyl selenide with ozone, with an estimated yield of ∼ 90%. Significant fragmentation via Se-C bond breakage occurred during the reactions of dimethyl selenide with the OH radical and the NO 3 radical as indicated by HCHO formation yields of ∼ 40 and ∼ 60%, respectively. The spectra of the Se-containing products from both the reactions with the OH radical (in the presence of NO x ) and the NO 3 radical are consistent with the formation of nitrate salts, which are postulated to be [CH 3Se(OH) 2] + NO 3 − and [(CH 3) 2SeOH] + NO 3 −, which could arise from the intermediate formation of methaneseleninic acid [CH 3Se(O)OH] and dimethyl selenoxide and their ensuing reactions with HNO 3.

Influence of pH, salinity, and selenium on the growth of Aeromonas veronii in evaporation agricultural drainage water

Aeromonas veronii was isolated from seleniferous agricultural drainage water and characterized in terms of growth kinetics under changing environmental parameters [i.e. pH, selenium (Se) and salinity (electrical conductivity, EC)] that simulated evaporation. Aeromonas veronii metabolized peptone and was active in volatilizing Se, principally as dimethyl selenide (DMSe). Other volatile products produced included dimethyl disulfide, methyl selenol, dimethyl selenosulfide and dimethyl diselenide. The rate of Se volatilization correlated with the growth of A. veronii, with the highest levels of DMSe released during the exponential phase of growth. The C assimilated was primarily respired as CO 2 or incorporated into cell biomass with a small fraction used in the alkylation of Se. The maximum growth rate ( μ max) for A. veronii was 0.23 h −1 at pH 7.94, 10 μg Se 1 −1, and EC of 3.9 dS m −1 and decreased to 0.06 h −1 with increasing salt content (40.2 dS m −1), pH (8.53) and Se (500 μg l −1). Salinity appeared to be the dominant inhibitory factor as observed by a decrease in growth rate and mass of cells. The range in salt content that was most inhibitory to the growth rate of A. veronii was from EC 11.7 to 40.2 dS m −1. As drainage waters evaporate in holding facilities, salinity tends to increase having serious ecological effects on the growth of A. veronii.

Effects of annealing atmosphere and temperature on acceptor activation in ZnSe:N grown by photoassisted MOVPE

Effects of annealing atmosphere and temperature on acceptor activation in nitrogen-doped ZnSe layers grown by photoassisted metalorganic vapor-phase epitaxy (MOVPE) have been investigated. It is shown that as-grown high resistive layers are converted to p-type by thermal annealing in N2 atmosphere in the temperature range from 500 to 550°C, while they do not if annealed in atmospheres of H2, diethylzinc (DEZn), and dimethylselenide (DMSe) in which hydrogen is contained. The net acceptor concentration NA − ND has reached up to 4 × 1017cm−3 by the thermal annealing at 500°C, but it is lower when annealed at 550°C. By exposing to H2 atmosphere at 350°C, NA − ND decreases with the exposure time. However, it almost recovers to the value obtained by the first annealing in N2, if the layer is annealed again in N2 atmosphere at 500°C. These results are discussed based on the hydrogen passivation model, i.e. the dehydrogenation and hydrogenation occur reversibly and result in activation and passivation of nitrogen acceptors, respectively.

Behavior of Methylated Metabolites of Selenium in Rats Orally Administered with Various Dose Levels of Sodium Selenite.

The behavior of methylated selenium metabolites in the urine and in the expiration of rats which administered orally at various dosages (0, 0.31, 1.25 and 5.00 mg Se/kg diet) of selenite, was investigated. The contents of selenium in organs depended on the dose levels. Using Sephadex gel chromatograms of rat liver cytosols it was shown that at the toxic levels the amount of selenium more than that physiologically required for the active site of GSH-Px may bind to the other site. Excretions of trimethylselenonium ion (TMSe) in the urine and dimethyl selenide (DMSe) in exhaust gas increased with increasing accumulative levels of selenium. The excretion behaviors of TMSe and DMSe for 30 d after administration showed the same content level only at toxic dosage (average selenium intake level : 95μg Se/d). The present study suggested that as exposed by deficient to nutrient levels, selenium levels and GSH-Px activity in organs may be used to evaluate selenium level in the body, and the amount of TMSe in the urine and DMSe in exhaust gas may be utilized as indicators to predict the toxic selenium exposure level.

Vapor Phase Electronic Absorption and MCD Spectra for Dimethyl Sulfide, Dimethyl Selenide, and Dimethyl Telluride in the UV Region

Electronic absorption and magnetic circular dichroism spectra for (CH3)2X, X = S, Se, and Te, in the vapor phase were measured in the range 2.5−5.3 μm-1 with a spectral bandwidth of ≤0.003 μm-1. The spectra show well-resolved vibrational structure for the nX → (n + 1)p Rydberg system with positive MCD B terms for (CH3)2Se and (CH3)2Te, but a negative B term for (CH3)2S. The difference in the MCD spectra is interpreted in terms of the influence of magnetic coupling with the broad nX → σ* valence transition, which lies rather close in energy to the Rydberg system for X = S, but is separated to lower energy for X = Se or Te. The interpretation requires a nX → σ* transition assignment of 1A1 → 1B1 and provides support for the most recent 1A1 symmetry assignment of the nX → (n + 1)p Rydberg excited state. The assignment of several weak, previously unreported, bands for X = Se and Te is also given.

Photoassisted organometallic vapor-phase epitaxy of ZnSe: An ab initio molecular orbital study

Surface reactions of photoassisted organometallic vapor-phase epitaxy (OMVPE) of ZnSe using dimethyl selenide (DMSe) and dimethylzinc (DMZn) as source gases were studied by ab initio molecular orbital methods. The (001) face of zinc-blende-type ZnSe was simulated by a Zn4Se4 cluster, and the corresponding surface having a hole generated by photon irradiation was simulated by the Zn4Se4 cluster cation. In the Se-layer growing step, electron transfer occurs from the nonbonding Se orbital of DMSe to the Zn4Se4 cluster in both neutral and cation forms with simultaneous back-donation from the cluster part to the antibonding Se-C orbitals, resulting in the weakening of the Se—C bond of DMSe. In the Zn-layer growing step, electron transfer occurs from the Zn-C σ orbital of the adsorbed DMZn to the Zn4Se4 cation resulting in the weakening of the Zn—C bond, while such electron transfer does not occur to the neutral Zn4Se4. Thus, while the Se layer can grow even under nonirradiation, the Zn layer can grow only under irradiation. These results explain the enhancement of the growth rate observed in the photoassisted OMVPE of ZnSe.

Oxidation of Dimethylselenide by .delta.-MnO2: Oxidation Product and Factors Affecting Oxidation Rate

Volatile dimethylselenide (DMSe) was transformed to a nonvolatile Se compound in a δ-Mn0 2 suspension. The nonvolatile product was a single compound identified as dimethylselenoxide based on its mass spectra pattern. After 24 h, 100% of the DMSe added to a δ-MnO 2 suspension was converted to nonpurgable Se as opposed to 20%, 18%, and 4% conversion for chromate, permanganate, and the filtrate from the suspension, respectively. Manganese was found in solution after reaction. These results imply that the reaction between manganese oxide and DMSe was a heterogeneous redox reaction involving solid phase δ-MnD 2 and solution phase DMSe. Oxidation of DMSe to dimethylselenoxide [OSe(CH 3 ) 2 ] by a δ-MnO 2 suspension appears to be first order with respect to δ-MnO 2 , to DMSe, and to hydrogen ion with an overall rate law of d[OSe(CH 3 ) 2 ]/dt = 95 M -2 min -1 [MnO 2 ] 1 [DMSe] 1 [H + ] 1 for the MnD 2 concentration range of 0.89 x 10 -3 - 2.46 x 10 -3 M, the DMSe concentration range of 3.9 x 10 -7 - 15.5 x 10 -7 M Se, and a hydrogen ion concentation range of 7.4 x 10 -6 - 9.5 x 10 -8 M. A general surface site adsorption model is consistent with this rate equation if the uncharged OMnOH is the surface adsorption site. DMSe acts as a Lewis base, and the manganese oxide surface acts as a Lewis acid. DMSe adsorption to OMnOH can be viewed as a Lewis acid/base complex between the largely p orbitals of the DMSe lone pair and the unoccupied e g orbitals on manganese oxide. For such a complex, frontier molecular orbital theory predicts electron transfer to occur via an inner-sphere complex between the DMSe and the manganese oxide.

Indirect detection of selenium‐77 in nuclear magnetic resonance spectra of organoselenium compounds

Abstract77Se was measured by inverse proton detection using multiple‐quantum 1H‐{77Se} correlation spectroscopy. One‐and two‐dimensional heteronuclear multiple quantum coherence (HMQC) experiments are reported for selenophene, benzeneselenol, dimethyl selenide, dimethyl diselenide, and D,L‐selenomethionine with a range of 77Se1H coupling constants from 9.5 to 54.2 Hz. In these compounds having protons with different 77Se1H coupling constants the different correlations can be selectively enhanced by varying the mixing time. The enhancement for indirect versus direct 77Se detection was estimated for dimethyl selenide yielding a value close to the theoretical enhancement.

Coordination of (CH 3) 2X (X  O, S, and Se) to borane: an ab initio molecular orbital study

The mechanism of coordination of (CH 3) 2X (X = O, S, and Se), i.e. dimethyl ether, dimethyl sulfide, and dimethyl selenide, to BH 3 as well as free (CH 3) 2X itself has been studied by ab initio molecular orbital methods. In all cases coordination occurs through σ-donation from (CH 3) 2X to BH 3. Both (CH 3) 2Se and (CH 3) 2S coordinate to BH 3 with their local C 2-like axis tilting largely from the local C 3-like axis of BH 3 while (CH 3) 2O coordinates to BH 3 with moderate tilting. These trends can be rationalized in terms of orbital interaction stabilization energy. The orbital interaction stabilization energy term is large for (CH 3) 2Se and (CH 3) 2S while the electrostatic energy term is almost the same for the three complexes. All these features support the general idea that both (CH 3) 2Se and (CH 3) 2S are soft Lewis bases and (CH 3) 2O is a hard Lewis base.

In situ optical monitoring of the movpe growth of ZnSe on GaAs

AbstractIn situ optical reflection measurement was employed to study surface processes during the MOVPE growth of ZnSe films under an alternate supply of diethylzinc (DEZn) and dimethylselenide (DMSe) using H2 and/or N2 as carrier gases. We have found that the time‐dependent reflection signal exhibits a unique saw‐toothed pattern during the DEZn supply, which is attributed to the adsorption and structural change of the DEZn. In contrast, the influence of DMSe on the time‐dependent signal appears to be rather marginal. A growth mechanism is proposed based on these experimental results, through which the important role of ambient hydrogen is discussed.

Soil management factors affecting volatilization of selenium from dewatered sediments

Microbial volatilization of selenium (Se) may be an effective bioremediation technique to remove Se from dewatered sediments. In this laboratory study, soil management parameters (wetting and drying cycles, aeration, mixing, aggregate size, and water quality) were assessed for their influence upon Se volatilization. Selenium volatilization rates were higher under continuously moist conditions (—33 kPa) compared with wetting and drying cycles. After 6 months of incubation, a continuously moist seleniferous soil had lost approximately 21% of the Se inventory, whereas the same soil incubated under wetting and drying cycles had dissipated 7% of the total Se. Incubation under anoxia (N2 atmosphere) increased evolution of dimethyl selenide (DMSe) 1.4‐fold compared with aerated conditions. When soil samples were incubated under static versus continuously mixed conditions, the latter treatment enhanced volatilization 1.8‐fold. This was attributed to increased availability of the Se to the methylating soil microbi...

Physicochemical properties of dimethyl selenide and dimethyl diselenide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhysicochemical properties of dimethyl selenide and dimethyl diselenideU. Karlson, W. T. Frankenberger Jr., and W. F. SpencerCite this: J. Chem. Eng. Data 1994, 39, 3, 608–610Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://doi.org/10.1021/je00015a049RIGHTS & PERMISSIONSArticle Views747Altmetric-Citations50LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (356 KB) Get e-Alerts Get e-Alerts

Surface reactions in photoassisted MOVPE growth of ZnSe as studied by in-situ optical reflection measurements

Optical reflection measurements were performed during metalorganic vapor phase epitaxy (MOVPE) growth of ZnSe at a variety of source supply modes, i.e., simultaneous and alternate supplies of diethylzinc (DEZn) and dimethylselenide (DMSe), and with and without above-bandgap photoirradiation. Reflection change took place at an interval of the DEZn supply in an alternate source supply mode, while it did not at an interval of the DMSe supply. On the other hand, the reflection signal induced by the DEZn supply tended to fall off unless the DMSe supply followed immediately. The observed results suggest that the formation of a precursor in the simultaneous presence of DEZn and DMSe on the surface is responsible for photoassisted growth rate enhancement.

Effect of photo-irradiation on the growth of ZnSe in metalorganic molecular beam epitaxy

The photo-irradiation effect on the growth of ZnSe in metalorganic molecular beam epitaxy (MOMBE) using dimethylzinc (DMZn) and dimethylselenide (DMSe) as source gases has been investigated. It was revealed that a Se-stabilized (2×1) reconstruction changed to Zn-stabilized c(2×2) by irradiating a high-pressure Hg lamp to the surface under simultaneous supply of MO gases. In the case of growth under alternate gas supply mode, the I d 1 emission, which originates from an exciton bound to deep acceptor, was much reduced in intensity if the lamp was irradiated during the DMZn gas supply, while the Y emission, which is reported to originate from an exciton bound to a structural defect, newly appeared by the irradiation during the DMSe gas supply. It was found that photo-irradiation not only enhances desorption of Se atoms from the surface during the DMSe supply, but is also effective for the perfection of Zn-stabilized surface during the DMZn supply.

Studies on the breakdown of organoselenium compounds in a hydrobromic acid–bromine digestion system

The chemical role played by bromine in HBr solution was investigated in the breakdown of both the trimethylselenonium ion and selenomethionine. Hydride generation and gas chromatography, both coupled with atomic fluorescence detection, polarography, and 1H and 77Se nuclear magnetic resonance spectrometry, were employed in order to collect information on the intermediate and final selenium compounds. Trimethylselenonium and selenomethionine were quantitatively converted into inorganic SeIV in hot concentrated HBr, but only in the presence of a large excess of bromine with respect to organoselenium. In the absence of additional bromine and under a stream of inert gas, the digestion of trimethylselenonium resulted in a 95% loss of selenium from the solution. Dimethyl diselenide and dimethyl selenide were detected in the headspace gases of the digestion apparatus. Under the same conditions, selenomethionine gave a result of about 70% of selenium caught in the solution. In this instance experimental evidence indicated that the major selenium component in the headspace gases of the digestion apparatus was methaneselenol. The roles played by bromine and HBr in the conversion of organoselenium into inorganic SeIV were identified as (i) the oxidative addition of bromine to divalent selenium to form bromoselenonium intermediates and (ii) the dealkylation of selenonium compounds by the bromide ion.

Selenium in Plants: Uptake, Functions, and Environmental Toxicity

AbstractSelenium (Se) has chemical properties similar to sulfur, but slight differences can lead to altered tertiary structure and dysfunction of proteins and enzymes, if selenocysteine is incorporated into proteins in place of cysteine.In some areas of California with irrigation agriculture elevated Se concentration in drainage and shallow groundwaters caused bioaccumulation of Se in wetlands and Se toxicity to wildlife. Among higher plants Se accumulators are tolerant to high Se concentrations whereas non‐accumulators are Se‐sensitive. Algae show a requirement of Se for growth and development, but no Se essentiality has been demonstrated for higher plants, possibly with the exception of Se accumulators. Higher plants take up Se preferentially as selenate via the high affinity sulfate permease. Contents of Se in agricultural crops are usually below 1 mg kg−1 DW, and hence such crops are considered safe for human and animal consumption even when grown on moderately high Se soils. Sulfate salinity inhibits uptake of selenate by many plant species.Assimilation of selenate by non‐accumulators leads to synthesis of selenocysteine and selenomethionine; Se‐cysteine is readily incorporated into proteins. High Se can interfere with S and N metabolism in non‐accumulators. In contrast, Se accumulators sequester Se mainly in non‐protein selenoamino acids. Among several selenoenzymes identified in bacteria and mammals, Se‐dependent glutathione peroxidase which catalyses the reduction of organic peroxides and H2O2 has been demonstrated convincingly in algae; in higher plants, however, the experimental evidence regarding its occurrence is controversial. All organisms including higher plants contain Se‐cysteyl‐tRNAs that decode UGA. Selenocysteine is proposed to function as 21st proteinaceous amino acid and thus is suggested to have a biological role in higher plants.Biogeochemical cycling of Se involves significant volatilization of methylated selenides such as dimethyl selenide to the atmosphere from higher plants as well as freshwater algae, but Se exchange between oceans and the atmosphere appears to proceed as net flux to the oceans.

Chemical shift references for 77Se NMR spectroscopy. Selenous acid

AbstractThe temperature and concentration dépendences of the chemical shift of aqueous selenous acid were studied in order to establish a precise relationship between the shift of this convenient reference and that of dimethyl selenide. The chemical shift of saturated H2SeO3 in H2O on the Me2Se shift scale at 20°C is 1300.0 ppm and its temperature coefficient is 0.094 ppm K−1. The relationships to the chemical shifts of Me2Se in CDCl3 and SeO2 in D2O are also discussed. The results permit the correlation of 77Se NMR shifts from several sources.