Molybdenum-catalyzed episulfidation of (E)-cycloalkenes with elemental sulfur

Episulfidation of (E)-cyclooctene and (E)-cyclononene was achieved with elemental sulfur by using a catalytic amount of a molybdenum oxo complex.     

Organophosphine transition metal complexes as selective surfaces for the reversible detection of sulfur dioxide with piezoelectric crystal sensors

Some organotransition metal complexes, bis (sulfur dioxide)tetrakis (triphenylphosphine oxide) manganese(II)dioxide [Mn(OPPh₃)₄I₂(SO₂)₂] and bis(tribenzylphosphine)copper(II) thiophenolate [Cu(PBz₃)₂SPh], were identified as candidate coatings for the detection of sulfur dioxide on piezoelectric crystal sensors. After treatment to form the mono (sulfur dioxide) adduct, the first complex binds sulfur dioxide to reform the bis adduct, and can be used as a coating for an integrating piezoelectric sensor. The initial complex can be regenerated by placing the coated piezoelectric sensor under vacuum for 4 h. The specified copper complex was found to act as a reversible coating for the detection sulfur dioxide in the range 10–1000 mg l^?1.     

Direct episulfidation of alkenes and allenes with elemental sulfur and thiiranes as sulfur sources,catalyzed by molybdenum oxo complexes

The molybdenum oxo complexes 1a and 1b catalyze efficiently the sulfur transfer to a series of alkenes 4 and allenes 6, for which elemental sulfur, phenylthiirane, or methylthiirane have been employed as sulfur sources to afford the corresponding episulfides 5 and 7. The most effective catalytic episulfidation system to date is the combination of the dithiophosphate-ligated oxo complex 1b and phenylthiirane (Ibeta). This metathesis process is efficient enough to convert usually reluctant alkenes (cyclopentene, cycloheptene, Z-cyclooctene, Z-cyclononene, E-cyclodecene, norbornene, and even bicyclopropylidene) to their episulfides in good yields under mild conditions. The direct catalytic sulfuration of allenes (cyclonona-1,2-diene, cyclonona-1,2,5-triene, cyclodeca-1,2-diene, and 2,4-dimethylpenta-2,3-diene) to their labile methylenethiiranes is unprecedented.     

Unusual sulfur chemistry in the thermal reaction of sultene and thiophene endoperoxide sulfur donors with cyclic alkynes: reversible formation of a persistent thiirenium ion and trapping of a thiirene by [4 + 2] cycloaddition

The highly reactive cyclooctyne 2b serves as sulfur acceptor for both sulfur donors, namely the sultene 1A and thiophene endoperoxide 1B to afford sulfur-transfer products. With the acid-activated sultene 1A, the persistent thiirenium ion 3Ab is formed, which has allowed the direct observation of the initial sulfur-transfer adduct. On treatment with base, the thiirenium ion 3Ab reverts quantitatively to the cyclooctyne and sultene, whereas in neutral media it rearranges to the diene 6Ab. The rearrangement to the diene 6Ab, as well as the formation of spirocyclic adduct 6Ac in the reaction with dithiocyclononyne 2c, is proposed to proceed through a carbene mechanism. In the reaction of the cyclooctyne 2b with thiophene endoperoxide 1B, a thiirene is formed through sulfur transfer by an intermediary oxathiirane derived from the thiophene endoperoxide; as final product, the episulfide (R*,R*,R*)-3Bb is produced diastereoselectively by immediate [4 + 2] cycloaddition of the thiirene with the heterodiene 4B.     

A planar chiral six-membered cyclic (amino)(ferrocenyl)carbene and its sulfur adduct

A planar chiral ferrocene-fused cyclic aldimine was synthesized and a series of iminium salts were divergently prepared from it. The new carbene was generated from a salt by simple deprotonation with a strong base and identified by a carbene trapping experiment with sulfur. The sulfur adduct was fully characterized and its crystal structure implied that the new carbene would create an excellent chiral environment when used as a catalyst or a ligand in catalytic asymmetric synthesis.     

The effect of the sixth sulfur ligand in the catalytic mechanism of periplasmic nitrate reductase

The catalytic mechanism of nitrate reduction by periplasmic nitrate reductases has been investigated using theoretical and computational means. We have found that the nitrate molecule binds to the active site with the Mo ion in the +6 oxidation state. Electron transfer to the active site occurs only in the proton‐electron transfer stage, where the Mo^V species plays an important role in catalysis. The presence of the sulfur atom in the molybdenum coordination sphere creates a pseudo‐dithiolene ligand that protects it from any direct attack from the solvent. Upon the nitrate binding there is a conformational rearrangement of this ring that allows the direct contact of the nitrate with Mo^VI ion. This rearrangement is stabilized by the conserved methionines Met141 and Met308. The reduction of nitrate into nitrite occurs in the second step of the mechanism where the two dimethyl‐dithiolene ligands have a key role in spreading the excess of negative charge near the Mo atom to make it available for the chemical reaction. The reaction involves the oxidation of the sulfur atoms and not of the molybdenum as previously suggested. The mechanism involves a molybdenum and sulfur‐based redox chemistry instead of the currently accepted redox chemistry based only on the Mo ion. The second part of the mechanism involves two protonation steps that are promoted by the presence of Mo^V species. Mo^VI intermediates might also be present in this stage depending on the availability of protons and electrons. Once the water molecule is generated only the Mo^VI species allow water molecule dissociation, and, the concomitant enzymatic turnover. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

渣油超临界萃取馏分中硫化物的分离富集研究

采用选择性氧化与色谱结合的方法分离渣油中的硫醚硫化物和噻吩硫化物,该法是基于不同类型硫的选择性氧化、氧化组分与未氧化组分间极性的差异实现的。首先用高碘酸四丁铵在不氧化噻吩硫的情况下将硫醚硫选择性氧化为高极性的亚砜,经色谱柱分离富集后,利用红外色谱和硫元素分析仪,研究了馏分中硫化物的类型分布。结果表明,在俄罗斯渣油中噻吩硫和硫醚硫的质量分数随组分变重均呈增长趋势,噻吩硫相对质量分数(指硫醚硫+噻吩硫)随馏分变重呈下降趋势,相对质量分数在70%以上,噻吩硫是俄罗斯渣油中硫的主要存在形态。     

Promotion of cobalt catalyst for Fischer–Tropsch synthesis by molybdenum as protection against sulfur poisoning

Molybdenum promotion was used to increase the resistance of a cobalt catalyst for the Fischer–Tropsch synthesis to sulfur poisoning. A series of experiments on adding 1,3,5-trithiane to synthesis gas (sulfur content of 1 ppm) showed that the Co–Mo /Al₂O₃ catalyst regained its initial activity after 8 h of operation. In comparison, catalysts not containing molybdenum experienced a significant irreversible loss of activity that was not recovered after stopping the addition of 1,3,5-trithiane to the feed.     

Flow injection gas chromatography with sulfur chemiluminescence detection for the analysis of total sulfur in complex hydrocarbon matrixes

A fast and reliable analytical technique for the determination of total sulfur levels in complex hydrocarbon matrices is introduced. The method employed flow injection technique using a gas chromatograph as a sample introduction device and a gas phase dual‐plasma sulfur chemiluminescence detector for sulfur quantification. Using the technique described, total sulfur measurement in challenging hydrocarbon matrices can be achieved in less than 10 s with sample‐to‐sample time <2 min. The high degree of selectivity and sensitivity toward sulfur compounds of the detector offers the ability to measure low sulfur levels with a detection limit in the range of 20 ppb w/w S. The equimolar response characteristic of the detector allows the quantitation of unknown sulfur compounds and simplifies the calibration process. Response is linear over a concentration range of five orders of magnitude, with a high degree of repeatability. The detector's lack of response to hydrocarbons enables direct analysis without the need for time‐consuming sample preparation and chromatographic separation processes. This flow injection‐based sulfur chemiluminescence detection technique is ideal for fast analysis or trace sulfur analysis.     

Sensing of sulfur dioxide by base metal thiolates: structures and properties of molecular NiN2S2/SO2 adducts

The cis-dithiolate N2S2Ni complex bismercaptoethanediazacycloheptanenickel(II), (bme-dach)Ni or Ni-1', takes up two equivalents of sulfur dioxide in which thiolate-sulfur to SO2-sulfur interactions are well-defined by X-ray crystallography. Ni-1' x 2SO2, C9H18N2NiO4S4, yields monoclinic crystals belonging to the P2(1)/c space group: a = 10.308(4) angstroms, b = 13.334(5) angstroms, c = 10.842(4) angstroms, alpha = 90 degrees, beta = 91.963(6) degrees, gamma = 90 degrees, and Z = 4. Further characterization by nu(SO) IR spectroscopy, thermal gravimetric analysis, electronic spectroscopy, and visual color changes upon reversible SO2 adduct formation establish Ni-1' and the analogous bismercaptoethanediazacyclooctane derivative, (bme-daco)Ni, Ni-1, to be viable candidates for technical development as chemical sensors of this noxious gas. Visual SO2 detection limits of Ni-1 and Ni-1' are established at 25 and 100 ppm, respectively. Both the Ni-1' x 2SO2 adduct and the Ni-1' reactant are air stable. In addition, the stability of Ni-1' x SO2 to vacuum and removal of SO2 by heating make Ni-1' a possible storage/controlled release complex for SO2 gas.     

Models for the Active Center of Pterin-Containing Molybdenum Enzymes: Crystal structure of a molybdenum complex with sulfur and pterin ligands

The first crystal structure of a molybdenum complex 9 with a hydrogenated pterin and a sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex 9 was synthesized through a redox reaction of [Mo^VIO₂ (LN-S₂)] ( 8 ; LN-S₂ = pyridine-2, 6-bis(methanethiolato)) with 5, 6, 7, 8-tetrahydropterin ( 7 ). 2 HCl (H₄Ptr.2 HCl). The complex crystallizes, with a non-coordinating Cl-atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensions a = 22.900(5), b = 10.716(2), c = 17.551(4) Å, β = 120.36(3)°, and Z = 8. We interpret 9 as [Mo^IVO(LN-S₂)(H⁺-q-H₂Ptr)]Cl (q = quinonoid; H₂Ptr = dihydropterin), i.e., a Mo^IV monooxo center coordinated by a pyridine-2, 6-bis(methanethiolato) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S-coordination. The slightly H₂O-soluble complex 9 reacts with the natural enzyme substrate DMSO very slowly, possibly due to the lack of easily dissociable ligands at the metal center.     

溶剂热一步法制备二硫化钼/亚氧化钛电解水析氢催化剂

通过水热法一步合成了系列二硫化钼/亚氧化钛（MoS₂/Ti_xO_y）复合催化剂,研究了溶剂、硫源和钼源等合成条件对所合成的催化剂电催化析氢活性的影响以及亚氧化钛的作用。结果表明,溶剂、硫源、钼源、亚氧化钛等因素都对催化剂的结构和电解水析氢性能有重要影响。溶剂水、水解可产生铵根离子的硫源和钼源以及亚氧化钛的加入有利于获得具有高析氢活性的催化剂。其中,以水为溶剂、硫代乙酰胺为硫源、钼酸铵为钼源得到的催化剂析氢活性最高,电解水析氢测试中达到10 mA/cm²电流密度时需要的过电势仅为280 mV。     

Role of SH groups and chemisorbed hydrogen in the formation of sulfur vacancies on an edge of a molybdenum disulfide crystallite

Kinetics and Catalysis - The formation of sulfur vacancies on an edge of a molybdenum disulfide crystallite with the participation of SH groups has been considered using density functional theory...     

X-ray crystal structure of arsenite-inhibited xanthine oxidase: μ-sulfido,μ-oxo double bridge between molybdenum and arsenic in the active site

Xanthine oxidoreductase is a molybdenum-containing enzyme that catalyzes the hydroxylation reaction of sp(2)-hybridized carbon centers of a variety of substrates, including purines, aldehydes, and other heterocyclic compounds. The complex of arsenite-inhibited xanthine oxidase has been characterized previously by UV-vis, electron paramagnetic resonance, and X-ray absorption spectroscopy (XAS), and the catalytically essential sulfido ligand of the square-pyrimidal molybdenum center has been suggested to be involved in arsenite binding through either a μ-sulfido,μ-oxo double bridge or a single μ-sulfido bridge. However, this is contrary to the crystallographically observed single μ-oxo bridge between molybdenum and arsenic in the desulfo form of aldehyde oxidoreductase from Desulfovibrio gigas (an enzyme closely related to xanthine oxidase), whose molybdenum center has an oxo ligand replacing the catalytically essential sulfur, as seen in the functional form of xanthine oxidase. Here we use X-ray crystallography to characterize the molybdenum center of arsenite-inhibited xanthine oxidase and solve the structures of the oxidized and reduced inhibition complexes at 1.82 and 2.11 ? resolution, respectively. We observe μ-sulfido,μ-oxo double bridges between molybdenum and arsenic in the active sites of both complexes. Arsenic is four-coordinate with a distorted trigonal-pyramidal geometry in the oxidized complex and three-coordinate with a distorted trigonal-planar geometry in the reduced complex. The doubly bridged binding mode is in agreement with previous XAS data indicating that the catalytically essential sulfur is also essential for the high affinity of reduced xanthine oxidoreductase for arsenite.     

Reaction of 3-aminopropanol with sulfur and red phosphorus

Conclusions The reaction of 3-aminopropanol with sulfur and red phosphorus gave the 11 adduct of 3-aminopropyl mercaptan with 3-iminopropyl mercaptan, and its mass spectrum was discussed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1608–1610, July, 1979.     

Photochemical reaction of magnesium tetraphenyl porphyrin with sulfur dioxide

<正>The photochemical reaction of magnesium tetraphenyl porphyrin(MgTPP) with sulfur dioxide(SO_2) was investigated in dichloromethane(CH_2Cl_2) by steady-state fluorescence,UV-vis absorption,MS,and XRD spectroscopic techniques.These spectra showed that under irradiation MgTPP reacted with SO_2 to form 1:1 molecular adduct at first step.During the process of keeping irradiation and maintaining the flow of SO_2,SO_2 was reduced into S~(2-) by MgTPP and the results were detected using MS and XRD techniques.Understanding the photochemical reaction of MgTPP with SO_2 is of key interest in elucidating fundamental photochemical reaction mechanisms associated with this class of chlorophyll in the presence of SO_2.     

Radical terpolymerization of sulfur dioxide,styrene, and methyl methacrylate

The radical terpolymerization of sulfur dioxide, styrene, and methyl methacrylate in o-dichlorobenzene with 2,2′-azobisisobutyronitrile was carried out in order to clarify the propagation mechanism of the radical copolymerization of sulfur dioxide and styrene, especially as a function of total concentration of sulfur dioxide and styrene. From the analysis of the trigonal composition diagrams it has been definitely shown that the radical copolymerization of sulfur dioxide and styrene proceeds by the propagation of two monomers, but the usual type of copolymerization mechanism, explicable in terms of the Lewis-Mayo equation, is not applicable to this copolymerization. The participation in the propagation of a monomer charge-transfer complex consisting of sulfur dioxide and styrene was also ruled out.     

Modified cyclodextrins solubilize elemental sulfur in water and enable biological sulfane sulfur delivery

An important form of biological sulfur is sulfane sulfur, or S⁰, which is found in polysulfide and persulfide compounds as well as in elemental sulfur. Sulfane sulfur, often in the form of S₈, functions as a key energy source in the metabolic processes of thermophilic Archaean organisms found in sulfur-rich environments and can be metabolized both aerobically and anaerobically by different archaeons. Despite this importance, S₈ has a low solubility in water (∼19 nM), raising questions of how it can be made chemically accessible in complex environments. Motivated by prior crystallographic data showing S₈ binding to hydrophobic motifs in filamentous glycoproteins from the sulfur reducing Staphylothermus marinus anaerobe, we demonstrate that simple macrocyclic hydrophobic motifs, such as 2-hydroxypropyl β-cyclodextrin (2HPβ), are sufficient to solubilize S₈ at concentrations up to 2.0 ± 0.2 mM in aqueous solution. We demonstrate that the solubilized S₈ can be reduced with the common reductant tris(2-carboxyethyl)phosphine (TCEP) and reacts with thiols to generate H₂S. The thiol-mediated conversion of 2HPβ/S₈ to H₂S ranges from 80% to quantitative efficiency for Cys and glutathione (GSH). Moreover, we demonstrate that 2HPβ can catalyze the Cys-mediated reduction of S₈ to H₂S in water. Adding to the biological relevance of the developed systems, we demonstrate that treatment of Raw 264.7 macrophage cells with the 2HPβ/S₈ complex prior to LPS stimulation decreases NO₂⁻ levels, which is consistent with known activities of bioavailable H₂S and sulfane sulfur. Taken together, these investigations provide a new strategy for delivering H₂S and sulfane sulfur in complex systems and more importantly provide new insights into the chemical accessibility and storage of S⁰ and S₈ in biological environments.

Sulfane sulfur, or S⁰, is found in polysulfide and persulfide compounds in biology. We demonstrate that modified cyclodextrins can solubilize S₈ in water, increase its reactivity with biological nucleophiles, and enable delivery to live cells.     

Direct synthesis of mesostructured lamellar molybdenum disulfides using a molten neutral n-alkylamine as the solvent and template

A series of novel mesostructured lamellar molybdenum disulfides with the d spacings from 17 to 30 A can be prepared by the reaction of Mo(CO)6 with elemental sulfur using a molten n-alkylamine as the solvent as well as the template at 140 degrees C. Such intercalated phases can be transformed into mesoporous molybdenum disulfides by slow thermal treatments at 200 degrees C.     

Polarographic and liquid chromatographic methods for the determination of sulfur residues on grapes and wheat

Sampled d.c. and differential pulse polarography are used, in batch mode, to determine sulfur in methanol/0.1 M ammonium acetate (pH 5.0). A two-electron reaction (reduction of sulfur to sulfide) is shown to be involved. Differential pulse polarography is sensitive for the determination of sulfur in relatively clean solutions; the detection limit is 7.2 μg l^?1. The interference of heavy metals (Pb and Cd) is avoided by addition of EDTA. For complex matrices, such as extracts of wheat and grapes, matrix effects are serious. For such samples, reversed-phase liquid chromatography with amperometric detection (dropping mercury electrode) gives excellent results. A relatively simple procedure is described for the determination of sulfur residues in wheat and grapes at levels ? 0.5 mg kg ^?1; linear response is obtained up to ca. 7 mg kg^?1.