Activation of hydrogen peroxide by ionic liquids: mechanistic studies and application in the epoxidation of olefins.

Imidazolium-based ionic liquids that contain perrhenate anions are very efficient reaction media for the epoxidation of olefins with H2O2 as an oxidant, thus affording cyclooctene in almost quantitative yields. The mechanism of this reaction does not follow the usual pathway through peroxo complexes, as is the case with long-known molecular transition-metal catalysts. By using in situ Raman, FTIR, and NMR spectroscopy and DFT calculations, we have shown that the formation of hydrogen bonds between the oxidant and perrhenate activates the oxidant, thereby leading to the transfer of an oxygen atom onto the olefin demonstrating the special features of an ionic liquid as a reaction environment. The influence of the imidazolium cation and the oxidant (aqueous H2O2, urea hydrogen peroxide, and tert-butyl hydrogen peroxide) on the efficiency of the epoxidation of cis-cyclooctene were examined. Other olefinic substrates were also used in this study and they exhibited good yields of the corresponding epoxides. This report shows the potential of using simple complexes or salts for the activation of hydrogen peroxide, owing to the interactions between the solvent medium and the active complex.

Physicochemical properties of air and water stable rhenium ionic liquids.

Air and water stable ionic liquids (ILs) based on catalytic functional metal rhenium, [C(n)mim][ReO(4)](n = 2,4,5,6)(1-alkyl-3-methylimidazolium perrhenate), are designed and synthesized. Their density and surface tension are measured in the temperature range of 293.15-343.15 ± 0.05 K. Some physical-chemical properties of the ILs have been calculated or estimated by the empirical methods. The ion parachor is put forward and calculated by two extrathermodynamic assumptions. According to the interstice model, the thermal expansion coefficient of ILs [C(n)mim][ReO(4)], α, are calculated and in comparison with experimental values, their magnitude order is in good agreement.

(N-salicylidene)aniline derived Schiff base complexes of methyltrioxorhenium(VII): ligand influence and catalytic performance.

Methyltrioxorhenium(VII) (MTO) readily forms 1:1 adducts with several N-(salicylidene)aniline derived Schiff bases. If the aromatic rings of the N-(salicylidene)aniline ligands display non-donating or electron withdrawing substituent groups, the resulting MTO adducts show good activities in olefin epoxidations. However, steric effects seem to play a major role, leading often to instable o- and m-Schiff base-MTO adducts, while p-substituted Schiff bases usually lead to more stable adducts. In catalysis, electron-withdrawing substituents on the aniline moiety lead to better catalysts than electron donating ones. The gap between good catalysts and instable or non-existing compounds, however, is small. The general tendency, however, that good donors on the Schiff base ligands lead to shorter Re-O(Schiff base) bridges and lower catalytic activity, while the opposite is true with acceptor ligands on the Schiff bases, seems to be quite clear.

[Determination of rhenium in raffinate and residue from synthesis of methyltrioxorhenium by ICP-AES].

Methyltrioxorhenium is a novel and efficient organometallic catalyst. It has exhibited amazingly high activities in a variety of organic reactions, and can form compounds with Lewis base. Thus, the improvement of its synthesis rate has become a pop topic all over the world. The content of rhenium in raffinate and residue from the synthesis of methyltrioxorhenium is an important standard for the evaluation of synthesis rate and a foundation for the optimization of synthesis condition. UV spectrophotometry is the standard technique for the determination of rhenium. However, this method presents several disadvantanges such as low sensitivity, high interferences, and hard handling. Inductive coupled plasma-atomic emission spectrometry has many advantages such as high precision, rapid analysis speed and good stability, and can determine multi-elements simultaneously. It is widely used in determination in every walk of life. An ICP-AES method for determination of the content of rhenium in raffinate and residue from the synthesis of methyltrioxorhenium was used. The working parameters were optimized. The detection limit was 0.01 mg x L(-1). RSD was in the range of 0.48%-1.12% and recoveries in the range from 97.2%-104% were obtained. The spectrum interference can be neglected. Compared with spectrophotometer, the proposed method was proved to be simple, rapid and accurate, and the result was satisfactory.

[Interaction of tributyltin (TBT) compound and bovine serum albumin (BSA)].

Tributyltin (TBT) compound is one of the main components of antifouling paint for boats and ships. The interaction of TBT compound and bovine serum albumin (BSA) was investigated by ultraviolet, fluorescence and circular dichroism (CD) spectra. The influences of concentration, acidity and organic solvent were also studied. The results showed that the interaction of TBT and BSA was dual, showing not only the hydrophobic actions of butyl groups but also the coordination action of tin cation with BSA molecule, which resulted in the exposures of aromatic amino acids residues of tryptophane and tyrosine in BSA molecule, the destruction of BSA secondary structure, the decrease in alpha-helix content, and the transformation of the conformation.

MTO Schiff-base complexes: synthesis, structures and catalytic applications in olefin epoxidation.

Several Schiff-base ligands readily form complexes with methyltrioxorhenium(VII) (MTO) by undergoing a hydrogen transfer from a ligand-bound OH group to a ligand N atom. The resulting complexes are stable at room temperature and can be handled and stored in air without problems. Due to the steric demands of the ligands they display distorted trigonal-bipyramidal structures in the solid state, as shown by X-ray crystallography, with the O(-) moiety binding to the Lewis acidic Re atom and the Re-bound methyl group being located either in cis or trans position to the Schiff base. In solution, however, the steric differences seem not to be maintained, as can be deduced from (17)O NMR spectroscopy. Furthermore, the Schiff-base ligands exchange with donor ligands. Nevertheless, the catalytic behaviour is influenced significantly by the Schiff bases coordinated to the MTO moiety, which lead either to high selectivities and good activities or to catalyst decomposition. A large excess of ligand, in contrast to the observations with aromatic N-donor ligands, is detrimental to the catalytic performance as it leads to catalyst decomposition.

G-rich, a Drosophila selenoprotein, is a Golgi-resident type III membrane protein.

G-rich is a Drosophila melanogaster selenoprotein, which is a homologue of human and mouse SelK. Subcellular localization analysis using GFP-tagged G-rich showed that G-rich was localized in the Golgi apparatus. The fusion protein was co-localized with the Golgi marker proteins but not with an endoplasmic reticulum (ER) marker protein in Drosophila SL2 cells. Bioinformatic analysis of G-rich suggests that this protein is either type II or type III transmembrane protein. To determine the type of transmembrane protein experimentally, GFP-G-rich in which GFP was tagged at the N-terminus of G-rich, or G-rich-GFP in which GFP was tagged at the C-terminus of G-rich, were expressed in SL2 cells. The tagged proteins were then digested with trypsin, and analyzed by Western blot analysis. The results showed that the C-terminus of the G-rich protein was exposed to the cytoplasm indicating it is a type III microsomal membrane protein. G-rich is the first selenoprotein identified in the Golgi apparatus.

[Determination of trace selenium in edible fungi with graphite furnace atomic absorption spectroscopy].

In the present article, samples were digested by a quartz high-pressure digestion pot, reducing the loss of selenium in digestion. The content of selenium in edible fungi was determined by using graphite furnace atomic absorption spectroscopy, and the results showed that when the content of selenium in edible fungi was determined by using 1% Ni(NO3)2 as a matrix modifier, ashing temperature of 500 degreed C, and atomization temperature of 2 500 degrees C, and rectifying background by deuterium light, the recovery was in the range of 92.1%-115.5%, the relative standard deviation of the method was 1.28%, and the limit of detection was 15.8 microg x L(-1). The method was suitable for the determination of trace selenium in edible fungi with the advantages of being simple, rapid, sensitive, stable and accurate etc., and the results were satisfactory.

[Separation and determination of selenium polysaccharide in enriched-Se cordyceps militaris].

In the present paper, the water soluble selenium polysaccharide was extracted, and isolated and purified preliminarily. The traditional method was used to extract selenium polysaccharide, which was extracted by water and sank by ethanol. The work also focused on the determination of the experiment conditions, optimizing the experiment conditions such as proportion of extract solution, extract temperature, extract times, proportion of ethanol, and standing time. The recovery of selenium polysaccharide under these conditions is 5.76%. Polysaccharide content in the powder is 46.6%, and selenium content is 92.3 mg x kg(-1).

[Study on the method of using ICP-MS to determine Se in the edible fungi].

The sample was digested by the quartzose digestion pot at high-pressure under relatively low temperature, reducing the loss of Se during the digestion process. Study on the method of using ICP-MS to determine Se in the edible fungi shows that it exhibits positive correlation between the concentration of sample and integration time, and the response value. When the concentration of Se in the sample is higher than 50 microg x L(-1), the integration time can be 0.1 s; or it can be 2.0 s when the concentration of Se is lower than 5 microg L(-1). The standard curve was accomplished for 1.0-500 microg x L(-1) when determining the content of Se in the edible fungi. The recoveries are in the range of 99.96%-102.7%. This method has advantages of simplicity, speediness, delicacy, high stability, high accuracy, etc. It is suitable for the determination of trace Se in the edible fungi.

[Determination of active species of heavy metals in sewage sludge by ICP-MS].

Sewage sludge samples for the research from the sewage disposal plants of the north, Mantang River and Xiannu River in Shenyang were extracted and separated by H2O, HAc and organic solvents of different polarities. The active species of Cd, Pb, Cu, Zn and Cr existing in the sewage sludge were determined by ICP-MS, and the regularity and influential factors were studied under the alternation of environmental conditions. The results showed that the content of acid-soluble heavy metals was more than that of water-soluble ones, and both had coincident regularity under the alternation of time and temperature; the content of the organic solvents was positively correlated to the solvent polarity. The acid-soluble heavy metals were more active during the course of transforming, and the activity sequence of heavy metals in the same species was: water-soluble Zn>Cu>Cd> Pb>Cr, acid-soluble Cd>Cr>Cu>Zn>Pb, and organic-soluble Pb>Cd>Cr>Cu>Zn.