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Selenium Atoms (selenium + atom)
Selected AbstractsInhibition of recombinant human maltase glucoamylase by salacinol and derivativesFEBS JOURNAL, Issue 12 2006Elena J. Rossi Inhibitors targeting pancreatic ,-amylase and intestinal ,-glucosidases delay glucose production following digestion and are currently used in the treatment of Type II diabetes. Maltase-glucoamylase (MGA), a family 31 glycoside hydrolase, is an ,-glucosidase anchored in the membrane of small intestinal epithelial cells responsible for the final step of mammalian starch digestion leading to the release of glucose. This paper reports the production and purification of active human recombinant MGA amino terminal catalytic domain (MGAnt) from two different eukaryotic cell culture systems. MGAnt overexpressed in Drosophila cells was of quality and quantity suitable for kinetic and inhibition studies as well as future structural studies. Inhibition of MGAnt was tested with a group of prospective ,-glucosidase inhibitors modeled after salacinol, a naturally occurring ,-glucosidase inhibitor, and acarbose, a currently prescribed antidiabetic agent. Four synthetic inhibitors that bind and inhibit MGAnt activity better than acarbose, and at comparable levels to salacinol, were found. The inhibitors are derivatives of salacinol that contain either a selenium atom in place of sulfur in the five-membered ring, or a longer polyhydroxylated, sulfated chain than salacinol. Six-membered ring derivatives of salacinol and compounds modeled after miglitol were much less effective as MGAnt inhibitors. These results provide information on the inhibitory profile of MGAnt that will guide the development of new compounds having antidiabetic activity. [source] A generalized exo -anomeric effect.ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2000Substituent, solvent effects on the conformational equilibria of 2-(arylseleno)cyclohexanones The effects of substitution and solvent on the conformational equilibria of 2-[(4-R-substituted-phenyl)seleno]cyclohexanones are described. The conformational equilibria were determined by comparison of the linewidths of the H-2 resonances in the 1H NMR spectra of the conformationally averaged systems with those of the anancomeric (highly biased) 4-isopropyl-2-substituted cyclohexanones. The substituent (R = NMe2, OMe, Me, H, F, Cl, CF3, NO2) and solvent ((CD3)2CO, CD3CN, CD2Cl2, CDCl3) effects are discussed in terms of electrostatic effects and the possible stabilizing orbital interactions. The values of Keq (axial-equatorial) increase as the substituent becomes more electron withdrawing, in agreement with the dominance of nSe , ,*C=O or ,C-Se , ,*C=O orbital interactions in the axial conformers. The increase in the proportion of the equatorial isomers in more polar solvents for a given substituent suggests a damping of the dipolar interactions in the equatorial isomers. However, the proportion of the equatorial isomers in a given solvent increases as the substituent becomes more electron withdrawing, indicating that electrostatic interactions do not dominate in controlling the conformational equilibria. Analysis of the equilibrium data by means of a dual substituent parameter approach indicates the best correlation with ,I and ,+R substituent constants in CD2Cl2 and with ,I and ,°R substituent constants in CD3CN, with similar sensitivities to the resonance and polar effects. The correlations are interpreted in terms of accommodation of effective positive charge on the selenium atom in the axial isomers in CD2Cl2, and a lesser sensitivity to the buildup of positive charge in the more polar solvent CD3CN. Comparison of the IR ,CO -stretching frequencies for the axial and equatorial ArSe-substituted anancomeric systems (R = NO2, NMe2) indicates a higher stretching frequency for the NO2 -substituted isomers. In the case of the NMe2 -substituted compounds, ,CO appears at a higher frequency in the equatorial isomer, whereas in the case of the NO2 -substituted compounds, ,CO is less sensitive to the axial or equatorial orientation of the substituent. The results are consistent with the operation of nse , ,*c=0 or ,C-Se , ,*C=O orbital interactions in the axial isomers. The JC2-H2 values in the axially-substituted anancomeric isomers are of greater magnitude than those in the equatorially-substituted isomers, which is also consistent with the operation of the orbital interactions described above. There is, however, no marked substituent effect on the JC2,H2 values within the series of axial or equatorial isomers. We argue that this does not support the dominance of ,C-Se , ,*C=O orbital interactions. Examination of crystal structures reported in the literature for related compounds indicates a particular gauche orientation about the C2,Se bond, which lends further support to the operation of an nSe , ,*C=O orbital interaction. We suggest that the latter interaction is a manifestation of a generalized exo -anomeric effect. [source] Effect of temperature and isomorphic atom substitution on optical absorption edge of TlInS2xSe2(1-x) mixed crystals (0.25 , x , 1)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2010N. M. Gasanly Abstract The optical properties of the TlInS2xSe2(1-x)mixed crystals (0.25 , x , 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400,1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS2xSe2(1-x)mixed crystals. The transmission measurements carried out in the temperature range of 10,300 K revealed that the rates of change of the indirect band gaps with temperature are , = ,9.2×10,4 eV/K, ,6.1×10,4 eV/K, ,4.7×10,4 eV/K and ,5.6×10,4 eV/K for TlInS2, TlInS1.5Se0.5, TlInSSe and TlInS0.5Se1.5 crystals, respectively. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hybrid Organic/Inorganic Supramolecular Conductors D2[Au(CN)4] [D = Diiodo(ethylenedichalcogeno)tetrachalcogenofulvalene], Including a New Ambient Pressure SuperconductorEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2007Tatsuro Imakubo Abstract Five diiodo(ethylenedichalcogeno)tetrachalcogenofulvalenes, DIEDSS {2-(5,6-dihydro[1,3]diselenolo[4,5- b][1,4]diselenin-2-ylidene)-4,5-diiodo-1,3-dithiole}, DIET-STF {2-(4,5-diiodo-1,3-diselenol-2-ylidene)-5,6-dihydro[1,3]dithiolo[4,5- b][1,4]dithiine}, DIEDS-STF {2-(4,5-diiodo-1,3-diselenol-2-ylidene)-5,6-dihydro[1,4]diselenino[2,3- d][1,3]dithiole}, DIETSe {2-(4,5-diiodo-1,3-diselenol-2-ylidene)-5,6-dihydro[1,3]diselenolo[4,5- b][1,4]dithiine}, and DIEDSSe {2-(4,5-diiodo-1,3-diselenol-2-ylidene)-5,6-dihydro[1,3]diselenolo[4,5- b][1,4]diselenine},have been synthesized without the use of the highly toxic reagent CSe2, and their Au(CN)4 salts have been prepared by electrochemical oxidation. Characteristic I···N iodine bonds are constructed in all crystals, and their packing motifs are classified into two groups by the difference in the space group symmetry. The salt of DIEDSS crystallizes in the monoclinic C2/c space group and a novel helical supramolecular architecture is constructed by the strong and directional I···N iodine bond. On the other hand, the rest of the four salts crystallize in the triclinic P space group and their donor packing motifs belong to the so-called ,-type. Conducting properties of the ,-type salts strongly depend on the number and positions of the selenium atoms on the donor molecule. The salts based on the diselenadithiafulvalene (DSDTF) derivatives, DIET-STF and DIEDS-STF, show metal,semiconductor transition and the salt of fully selenated ,-donor DIEDSSe shows stable metallic behavior down to 1.6 K. On the other hand, (DIETSe)2[Au(CN)4] is semimetallic down to low temperature and the superconducting transition occurs at around 2 K (onset).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Structural Studies of Lithium Telluro- and Seleno-Phosphorus CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2003Robert P. Davies Abstract Lithium tellurophosphinite [Ph2PTe][Li(TMEDA)1.33(THF)1.33] (4), ditellurophosphinate, [Ph2PTe2][Li(THF)3.5(TMEDA)0.25] (5), and selenotellurophosphinate [Ph2P(Se)Te][Li(THF)2(TMEDA)] (6) complexes have been prepared from the insertion/oxidation reactions of lithiated secondary phosphanes with elemental chalcogens and characterised by X-ray crystallography. Compounds 4,6 contain no tellurium,lithium bonding interactions in the solid state, instead existing as ion-separated species with THF/TMEDA-solvated lithium cations. Reaction of dilithiated primary phosphanes with more than three equivalents of elemental selenium gives [{(c -C6H11)P(Se)(SeLi)}2·2TMEDA] (7) via a phosphorus-phosphorus coupling reaction. Solid state characterisation of 7 reveals the organo groups in the tetradentate tetraselenohypodisphosphinate ligand to be in an anti conformation to one another and each lithium atom to be coordinated by two selenium atoms, one from each of the diselenophosphinate groups. Multinuclear NMR spectroscopic data are consistent with retention of the solid-state structures of 4,7 in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Crystallographic report: p -Bis(N -methylimidazolyl)xylylene tetra (selenocyanate)cadmium(II), [XylIm2][Cd(SeCN)4]APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2003Daojie Liu Abstract The title compound [XylIm2][Cd(SeCN)4] [XylIm2 = p -bis(N -methylimidazolyl)xylylene] comprises discrete p -bis(N -methylimidazolyl)xylylene cations and [Cd(SeCN)4]2, anions in which the cadmium atoms are tetrahedrally coordinated by four selenium atoms. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||