Se Analogues Research Articles

Origin and occurrence of selenium in some Australian coals

The analyses are reported of six Australian coals for mineral type and content, B, Se speciation (by selective leaching) and S speciation (by selective leaching and XANES) together with XANES data for Se in one coal (from a marine sequence). The results of these analyses and of thermodynamic calculations of thiophenes and Se analogues are used to suggest that selenoprotein structures in coal's precursors (bacteria and algae and possibly higher plants) make Se bonding in coal unique from that of the other trace elements.

Dicoordinate Copper(I) Silanechalcogenolates

The copper silanechalcogenolates tBu3PCuESiPh3 (1, E = O; 2, E = S; 3, E = Se) were prepared from the reaction of [tBu3PCu(CH3CN)3]BF4 with [Ph3SiELi(THF)2]2 in acetonitrile. The compounds were obtained as colorless, crystalline, but thermally labile solids. X-ray crystallography shows that complexes 1-3 are monomeric in the solid state with no Cu...Cu interactions. The Cu atoms have either a linear or a near-linear coordination geometry in all three complexes. Interestingly, the O atom in complex 1 is also linear, which is in contrast to the highly bent S (2) and Se analogues (3). Density functional theory calculations suggest that both the linear geometry of 1 and an associated extremely short Cu-O distance [1.769(4) A] are not the result of pi delocalization but are the result of a fine balance of electrostatic interaction and Pauli repulsion.

Synthesis and Structures of Se Analogues of the Antithyroid Drug 6‐n‐Propyl‐2‐thiouracil and Its Alkyl Derivatives: Formation of Dimeric Se–Se Compounds and Deselenation Reactions of Charge‐Transfer Adducts of Diiodine

Four selenium analogues of the antithyroid drug 6-n-propyl-2-thiouracil (PTU), of formulae RSeU, (R = methyl (Me) (1), ethyl (Et) (2), n-propyl (nPr) (3), and isopropyl (iPr) 4), have been synthesized. Reaction of 1-4 with diiodine in a 1:1 molar ratio in dichloromethane results in the formation of [(RSeU)I(2)] (R = methyl (5), ethyl (6), n-propyl (7) and isopropyl (8)). All compounds have been characterized by elemental analysis, FT-Raman, FT-IR, UV/Vis, (1)H-, (13)C-, (77)Se-1D and -2D NMR spectroscopy, and ESI-MS spectrometric techniques. Recrystallization of 4 from dichloromethane afforded (4CH(2)Cl(2)). Crystals of [(nPrSeU)I(2)] (7), a charge-transfer complex, were obtained from chloroform solutions, while crystallization of 6 and 7 from acetone afforded the diselenides [N-(6-Et-4-pyrimidone)(6-EtSeU)(2)] (92 H(2)O) and [N-(6-nPr-4-pyrimidone)(6-nPrSeU)(2)] (10) as oxidation products. Recrystallization of 7 from methanol/acetonitrile solutions led to deselenation with the formation of 6-n-propyl-2-uracil (nPrU) (11). [(nPrSeU)I(2)] (7) was found to be a charge-transfer complex with a Se--I bond. These results are discussed in relation to the mechanism of action of antithyroid drugs.

Preparation of chalcogenolato-bridged dinuclear Tp*Rh–Cp*Ru complexes (Tp*= hydrotris(3,5-dimethylpyrazol-1-yl)borate, Cp*=η5-pentamethylcyclopentadienyl) and binding of dioxygen to their Ru sites

Reactions of [Tp*Rh(coe)(MeCN)](1; Tp*= hydrotris(3,5-dimethylpyrazol-1-yl); coe = cyclooctene) with one equiv of diphenyl dichalcogenides PhEEPh (E = Se, Te) afforded the mononuclear Rh(III) complexes [Tp*Rh(EPh)(2)(MeCN)](2b: E = Se; 2c: E = Te), as reported previously for the formation of [Tp*Rh(SPh)(2)(MeCN)](2a) from the reaction of 1 and PhSSPh. Complexes 2a-2c were treated with the Ru(II) complex [(Cp*Ru)(4)(mu(3)-Cl)(4)](Cp*=eta(5)-C(5)Me(5)) in THF at room temperature, yielding the chalcogenolato-bridged dinuclear complexes [Tp*RhCl(mu-EPh)(2)RuCp*(MeCN)](3). Complex 3a (E = S) in solution was converted slowly into a mixture of 3a and the sterically less encumbered dinuclear complex [Tp*RhCl(SPh)(mu-eta(1)-S-eta(6)-Ph)RuCp*](4a) at room temperature. In 4a, one SPh group binds only to the Rh center as a terminal ligand, while the other SPh group bridges the Rh and Ru atoms by coordinating to the former at the S atom and to the latter with the Ph group in a pi fashion. The Se analogue 3b also underwent a similar transformation under more forcing conditions, e.g. in benzene at reflux, whereas formation of the mu-eta(1)-Te-eta(6)-Ph complex was not observed for the Te analogue 3c even under these forcing conditions. When complexes 3 was dissolved in THF exposed to air, the MeCN ligand bound to Ru was substituted by dioxygen to give the peroxo complexes [Tp*RhCl(mu-EPh)(2)RuCp*(eta(2)-O(2))](5a: E = S; 5b: E = Se; 5c: E = Te). X-Ray analyses have been undertaken to determine the detailed structures for 2c, 3a, 3b, 4a, 5a, 5b, and 5c.

Impressive Structural Diversity and Polymorphism in the Modular Compounds ABi3Q5 (A: Rb, Cs; Q: S, Se Te).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Impressive structural diversity and polymorphism in the modular compounds ABi3Q5 (A = Rb, Cs; Q = S, Se, Te).

An outstanding example of structural diversity and complexity is found in the compounds with the general formula ABi(3)Q(5) (A = alkali metal; Q = chalcogen). gamma-RbBi(3)S(5) (I), alpha-RbBi(3)Se(5) (II), beta-RbBi(3)Se(5) (III), gamma-RbBi(3)Se(5) (IV), CsBi(3)Se(5) (V), RbBi(3)Se(4)Te (VI), and RbBi(3)Se(3)Te(2) (VII) were synthesized from A(2)Q (A = Rb, Cs; Q = S, Se) and Bi(2)Q(3) (Q = S, Se or Te) at temperatures above 650 degrees C using appropriate reaction protocols. gamma-RbBi(3)S(5) and alpha-RbBi(3)Se(5) have three-dimensional tunnel structures while the rest of the compounds have lamellar structures. gamma-RbBi(3)S(5), gamma-RbBi(3)Se(5), and its isostructural analogues RbBi(3)Se(4)Te and RbBi(3)Se(3)Te(2) crystallize in the orthorhombic space group Pnma with a = 11.744(2) A, b = 4.0519(5) A, c = 21.081(3) A, R1 = 2.9%, wR2 = 6.3% for (I), a = 21.956(7) A, b = 4.136(2) A, c = 12.357(4) A, R1 = 6.2%, wR2 = 13.5% for (IV), and a = 22.018(3) A, b = 4.2217(6) A, c = 12.614(2) A, R1 = 6.2%, wR2 = 10.3% for (VI). gamma-RbBi(3)S(5) has a three-dimensional tunnel structure that differs from the Se analogues. alpha-RbBi(3)Se(5) crystallizes in the monoclinic space group C2/m with a = 36.779(4) A, b = 4.1480(5) A, c = 25.363(3) A, beta = 120.403(2) degrees, R1 = 4.9%, wR2 = 9.9%. beta-RbBi(3)Se(5) and isostructural CsBi(3)Se(5) adopt the space group P2(1)/m with a = 13.537(2) A, b = 4.1431(6) A, c = 21.545(3) A, beta = 91.297(3) degrees, R1 = 4.9%, wR2 = 11.0% for (III) and a = 13.603(3) A, b = 4.1502(8) A, c = 21.639(4) A, beta = 91.435(3) degrees, R1 = 6.1%, wR2 = 13.4% for (V). alpha-RbBi(3)Se(5) is also three-dimensional, whereas beta-RbBi(3)Se(5) and CsBi(3)Se(5) have stepped layers with alkali metal ions found disordered in several trigonal prismatic sites between the layers. In gamma-RbBi(3)Se(5) and RbBi(3)Se(4)Te, the layers consist of Bi(2)Te(3)-type fragments, which are connected in a stepwise manner. In the mixed Se/Te analogue, the Te occupies the chalcogen sites that are on the "surface" of the layers. All compounds are narrow band-gap semiconductors with optical band gaps ranging 0.4-1.0 eV. The thermal stability of all phases was studied, and it was determined that gamma-RbBi(3)Se(5) is more stable than the and alpha- and beta-forms. Electronic band calculations at the density functional theory (DFT) level performed on alpha-, beta-, and gamma-RbBi(3)Se(5) support the presence of indirect band gaps and were used to assess their relative thermodynamic stability.

Behavioral patterns of heterometallic cuboidal derivatives of [M3Q4(H2O)9]4+ (M = Mo, W; Q = S, Se).

This Account reports recent progress in the study of some approximately 20 heterometal derivatives of [Mo3S4(H2O)9]4+ with reference also to W and Se analogues. Single cubes (3:1) and corner-shared double cubes (6:1), as well as dimers of the 3:1 single cubes, are considered. A classification of the heterometals as subtypes A, B, and C is introduced.

Selenium speciation in human milk with special respect to quality control.

Selenium- (SE) organo compounds of pooled human milk (7th-14th d after delivery) were separated by centrifugation and subsequent size-exclusion chromatography (SEC) as described in ref. (1). The SEC fractions were used for Se determinations by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) in parallel to identification procedures of the organic ligands by two different capillary zone electrophoresis (CZE) methods. Further, the combination of isotachophoresis- (ITP) CZE with ETV-ICP-MS was used for final identifications. Mass balances were carried out at each analytical step for quality assurance. Reinjection experiments were performed to check the stability of Se-organo compounds during the analytical procedure. These quality-control experiments showed that no species transformations took place during the analytical procedure, and the Se species were native in human milk. The identification and quantification of organic ligands were clear and resulted in values of 2 (+/- 0.2) mg/L GSH/GSeH, 2 (+/- 0.22) mg/L cystamine/Se-cystamine, 4 (+/- 0.4) mg/L cystine/ Se-cystine, and 1 (+/- 0.18) mg/L methionine/Se-methionine. Unfortunately, a differentiation between sulfur (S) and Se analogs was not possible with the applied CE methods. The Se values per organic ligand were determined as 2.5 (+/- 0.23) mg/L associated with GSH (as GSeH), 3.1 (+/- 0.31) mg/L associated with cystamine (as Se-cystamine), 5.2 (+/- 0.4) mg/L associated with cystine (as Se-cystine), and 1 (+/- 0.1) mg/L associated with methionine (as Se-methionine).

Oxidation reactions of 4H-chalcogenopyrans

We have studied the oxidation of 4H-chalcogenopyrans and chalcogenopyrylium salts by lead tetraacetate. We have established that the major reaction products on oxidation of 2,6-diphenyl-4H-thiopyran and selenopyran are 2,6-diphenyl-4H-thio(seleno)pyran-4-ones, while 2-benzoyl-5-phenyl(seleno)thiophenes are formed as impurities. The major product on oxidation of 2,6-diphenyl-4H-pyran is 2-benzoyl-5-phenylfuran. We have shown that 2,4,6-triphenyl-4H-pyran does not undergo oxidation by hydrogen peroxide in neutral medium, in contrast to its S and Se analogs. This supports the hypothesis that the heteroatom participates in the oxidation process.

The 1,2,3,5-ditelluradiazolyl [HCN2Te2] species. Theoretical characterizations of the cation, radical, and radical dimers

Dithia- and diselena-diazolyl radicals (HCN2E2 E = S, Se) and dimers are important building blocks in the design of low-dimensional molecular conductors. Research on the tellurium-based analogues is much rarer. This work reports the molecular and electronic structures of the cation, radical, and radical dimers of 1,2,3,5-ditelluradiazolyl using ab initio theory including electron correlation by Møller–Plesset perturbation theory up to partial fourth order (MP4SDQ). A face-to-face C2v dimer is predicted to be bound with respect to two radicals by approximately 18 kcal/mol. A C2h, dimer also has been studied and is ca. 2 kcal/mol less stable than the C2v conformer. Relaxing symmetry constraints on the dimers led to more energetically stable structures at the Hartree–Fock level but the C2v structure remains the most stable at a level of theory including electron correlation effects. The results for the Te compounds along with our earlier research on the S and Se analogues provide predictions for the geometries, vibrational frequencies, and ionization potentials for the Te species to assist in future experiments. Key words: tellurium, ab initio, ditelluradiazolyl, dimers, binding.

Potentiation of the cytotoxicity of chloroethylnitrosourea by O6-arylmethylguanines.

It was reported recently that monomeric O6-benzylguanine (1) acts as an alternative substrate for a DNA repair enzyme, O6-alkylguanine-DNA alkyltransferase (AGT), and that therefore pretreatment of cells with 1 induces depletion of AGT resulting in an enhanced cytotoxic response to alkylating antitumor agents. In order to study the interaction of O6-benzylguanine derivatives with AGT and to obtain greater AGT depletion, we synthesized the following O6-arylmethylguanine derivatives and related compounds: O6-(4-, 3- and 2-fluorobenzyl)guanines (2, 3, 4), O6-(4-, 3- and 2-trifluoromethylbenzyl)guanines (5, 6, 7), O6-(4-, 3- and 2-pyridylmethyl)guanines (8, 9, 10), O6-(2- and 1-naphthylmethyl)guanines (11, 12), O6-biphenylmethylguanine (13), S and Se analogues of O6-benzylguanine (14, 15) and O6-phenylguanine (16). Ten of these are new compounds. All these compounds were tested for their potentiation of N'-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-N-(2-chloroethyl)-N-nitrosou rea (ACNU) cytotoxicity using HeLa S3 and C6-1 cells. Compounds 2, 3, 5, 8, 9, 11 and 13 were active, as was 1. Compounds 7 and 12, with a substituent at the alpha position of the benzyl group, and compound 10, the alpha-nitrogen analogue of 1, were almost completely devoid of potentiating activity. These results suggest that the alpha-position of the O6-benzyl group plays an important role in the interaction of O6-benzylguanines with AGT. Of the other compounds, 4 and 6 exhibited very weak activity and 14, 15 and 16 were inactive. Possible reasons for these differences in activity are discussed in relation to the biomimetic dealkylation rates of O6-benzylguanine derivatives and the chemical characteristics of their substituents.

Cyclic aryleneazachalcogens: Synthesis, vibrational spectra, and ?-electron structures

It is shown that a convenient general method for the synthesis of benzo-2,1,3-thiadiazole, its Se analog, their 4,5,6,7-tetrafluoro derivatives, and naphtho[1,8-c,d][1.2.6]thiadiazine is the reaction of the corresponding arylenediamines with chalcogen tetrahalides. A complete interpretation of the vibrational spectra of the synthesized compounds was obtained using the experimental shifts of the bands caused by the introduction of the 15N and 77Se isotopes into the compositions of the molecules and calculations of the frequencies and forms of the normal vibrations within the stretching-force field approximation. The peculiarities of the π-electron structures of the molecules of these substances were established by means of an analysis of the force constants of the CC, CN, NS, and NSe bonds and quantum-chemical calculations by the MNDO method: 1) The group π orbitals of the NXN fragments (X=S, Se) interact effectively with the group π orbitals of the carbocycles; 2) the p AO of nitrogen and sulfur make the principal contribution to the π MO of different symmetries (a2 and b1, respectively), as a consequence of which their π overlapping with one another is small, and the chemical bond within the limits of the NSN group is best described in the form of $$( - \mathop {\rm N}\limits^ - - \mathop {\text{S}}\limits^{\text{ + }} - {\text{N}} - {\text{)}}\begin{array}{*{20}c} \leftarrow & \to \\ \end{array} ( - {\text{N}} = \mathop {\text{S}}\limits^{\text{ + }} - \mathop {\rm N}\limits^ - - {\text{)}}$$ ; resonance; the same is also valid for the NSeN group; 3) on the whole, the π MO display a tendency for localization in individual molecular fragments. All of these factors decrease the aromatic character of the molecules.

Mössbauer study of the inactive Fe3S4 and Fe3Se4 and the active Fe4Se4 forms of beef heart aconitase.

Active beef heart aconitase contains an iron-sulfur cluster with an [Fe4S4]2+ core. This cluster can be converted into Fe3S4 with concomitant loss of enzymatic activity. We have reconstituted apo-aconitase with iron and selenide to obtain Fe4Se4 aconitase. The Se analog has higher catalytic activity than the native S-containing enzyme when isocitrate is the substrate. Oxidation of [Fe4Se4]2+ with ferricyanide yields the inactive [Fe3Se4]1+ form. The Se-containing 3-Fe cluster can be reduced to [Fe3Se4]0. We have studied the [Fe3S4]1+,0, [Fe3Se4]1+,0, and [Fe4Se4]2+ states with Mössbauer spectroscopy from 1.3 K to 200 K in magnetic fields up to 6.0 T. The spectra of the S- and Se-containing enzymes were found to be remarkably similar. The spectra of the 3-Fe clusters were analyzed and the salient features of the electronic structure are discussed.

4 K crystallographic and electronic structures of (TMTTF) 2X salts (X −: PF 6−, AsF 6−

The 4 K crystallographic and electronic structures of (TMTTF) 2PF 6 and (TMTTF) 2AsF 6 are presented. The structural investigation was performed by neutron diffraction. Thermal expansion and structural data are compared to those of the Se analogues. The tight-binding band electronic structures are based on calculations of the transfer integrals within the dimer splitting approximation. The results are discussed and compared to the room-temperature values. The trasfer integrals of the two salts, which are very similar at 300 K, tend to differ markedly at low temperature. The observed differences in the transfer integrals are related to the changes of the orientation of two neighbouring organic chains. The variations of the electronic parameters appear to depend on the anion.

ChemInform Abstract: (Os(η2‐PHS)(CO)2(PPh3)2), a Stable η2‐Thioxophosphine (H‐P=S) Metal Complex.

AbstractThe title complex (IIa) and its Se analogue (IIb) are prepared by treating the acetato(phosphine sulfide and selenide) complex (I) with one equiv. CF3SO3H followed by DBU.

Thin-layer chromatography of some organic selenium compounds and their oxygen and sulfur analogs

The Chromatographic behavior of some series of organic selenium compounds and their oxygen and sulfur analogs (urea, thiourea, selenourea; xanthene, thioxanthene, selenoxanthene; xanthone, thioxanthone, selenoxanthone) has been examined by thin-layer chromatography (TLC) on silica gel. The experimental results show the possibility of attaining fast separations on very small amounts of substance (at the microgram level) by simple monodimensional TLC techniques. Urea and its S and Se analogs as well as xanthones are well separated by two- or three-component eluting solvents; xanthenes are not easily screened even by solvent mixtures. The separation of xanthenes from xanthones by the two-dimensional TLC technique is also described. A further result is the possibility of detecting species in trace amounts in the matrix being examined.

Nonlinear transport at low temperatures in peierls-distorted quasi one-dimensional conductors

The carrier mobility deduced from the experimental low-field conductivity σ and the carrier concentration (calculated from the known gap) is ∼ 10 4 cm 2/Vsec in TTF-TCNQ (tetrathiafulvalene tetracyanoquinodimethane) and its Se analog TSeF-TCNQ. The observed low temperature increase in σ with field arises from heating of the carriers. This results in several nonlinear effects, e.g., increase in the mobility, surmounting of barriers (arising from charge density wave accommodation to defects) and creation of electron-hole pairs.

Synthèse et études spectroscopiques des tellurolesters

A general procedure for Te-alkylated tellurolesters synthesis is reported. The carbonyl i.r. frequencies and 13C chemical shifts of these compounds are compared to the O, S and Se analogs. The origin of the electronic interaction between the carbonyl group and the heteroatom is shown to depend on this latter nature: whereas a combination of both inductive and mesomeric effects is to be taken into account for O. This effect is mainly inductive for Se and Te. In the case of S-compounds, no such a simple model can be involved. The reason of which might be the participation of the 3d-orbitals to the electronic system. Moreover, the previously reported Te heavy atom effect has been detected on the α methylene groups exclusively.