Complexation of tellurium(II) with thioglycolic acid and reactivity patterns of the system

Mechanism of selenium-glutathione peroxidase and its inhibition by mercaptocarboxylic acids and other mercaptans.

Abstract: In a systematic search for effectors of glutathione peroxidase, a number of mercaptocarboxylic acids and tertiary mercaptans were found to be strong and specific inhibitors of the enzyme glutathione peroxidase Assessment of various models was made by linear and nonlinear least squares fitting techniques The results support the formation of reversible enzyme-inhibitor complexes The active site selenium is trapped by the rapid binding of the inhibitor in competition with GSH Data are consistent with the formation of thioselenenate adducts of the active site The kinetic model which best describes the observed inhibition by the very strong inhibitor mercaptosuccinate implies that a selenenic acid with a kinetically significant lifetime is not formed when hydroperoxide is reduced A noncovalent binding site for GSH or the presence of a cysteine residue at the active site of the enzyme provides a mechanistic rationale for the observed kinetics Three of the most potent inhibitors found in this study, mercaptosuccinate, penicillamine, and alpha-mercaptopropionylglycine, are currently used as slow-acting drugs in the treatment of rheumatoid arthritis Overall, the evidence suggests that glutathione peroxidase may be involved in the etiology of this disease

Synthesis, spectral, thermal and biological studies on N(-)(2,4-dinitro-phenyl)-2-mercaptoacetohydrazide and its metal complexes.

Abstract: Complexes of VO2+, Cr3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Hg2+ ions with N−(2,4-dinitrophenyl)-2-mercaptoacetohydrazide (H2L) have been prepared and characterized on the basis of elemental analysis, molar conductance, thermal (TGA, DTGA), spectral (IR, NMR, UV–Visible, MS) and magnetic measurements. The IR spectra show that H2L behaves in a mononegative and/or binegative bidentate manner. The sulfate bridged the two complex molecules in [Cu(HL)(H2O)2(½SO4)]⋅3H2O. The acetate functions as a monodentate in [Ni(HL)(OAc)(H2O)3] and [Cr(HL)(OAc)2(H2O)(EtOH)]. Different stereochemistries are proposed: octahedral for Cr(III), Ni(II), Hg(II) and [Cu(HL)(H2O)2(SO4)0.5]⋅3H2O, square-based pyramid for [VO(HL)2]⋅EtOH, square-planar for [Co(L)(EtOH)(H2O)]⋅H2O, [Cu(L)(H2O)2] and tetrahedral for [Zn(L)(EtOH)(H2O)], [Cd(L)(EtOH)(H2O)] and [Cu2(HL)(H2O)6]Cl3⋅H2O according to the data of electronic spectra and magnetic measurements. The TGA data support the formula and indicate the outer and inner solvents as well as the final residue. The thermodynamic parameters are calculated using the Coats–Redfern and Horowitz–Metzger methods. H2L and [Zn(L)(EtOH)(H2O)] showed the highest cytotoxic activity while H2L has a higher antioxidant activity than ascorbic acid. The ionization constant of the ligand and the stability constant of the Cu(II) H2L in absence and presence of hexamine buffer were calculated.

Synthesis, properties, and molecular structure of bis(thiobenzoato-S)tellurium(II), C14H10O2S2Te(II)

Abstract: The synthesis, properties, and structural characterization of the title compound, C14H10O2S2Te, are reported. The crystals are monoclinic, space groupC2/c (No. 15) witha=24.369(6),b=4.333(2),c=14.569(3) A, andβ=109.56(2)°,V=1449.57 A3,M=402, andD x =1.843 g cm−3 forZ=4. The structure was solved by the heavy-atom method and refined by full-matrix least squares toR=0.029 andR w =0.027 for 772 diffractometer data. Crystal structure analysis and IR spectroscopic study indicate that the tellurium is covalently bonded to sulfur. There are weak secondary interactions between tellurium and oxygen which complete an S2O2 coordination around tellurium.

Interaction of heterocyclic thioamides with tellurium(II) and tellurium(IV). Syntheses and crystal structures of bis[2-(2-thioxo-1,3-thiazolidin-3-yl)-4,5-dihydro-1,3-thiazolium]hexabromotellurate-(IV) and tris(1-methylimidazole-2-(3H)-thione)tellurium(II) bromide

Abstract: Reaction of 1,3-thiazolidine-2-thione with tellurium(IV) in hydrobromic acid medium gave the hexabromotellurate, [C6H9N2S3]22+[TeIVBr6]2− (3). Reaction of 1-methylimidazoline-2-(3H)-thione (L″) with tellurium(IV), in hydrobromic acid medium, gave the mixed-ligand tellurium(II) complex [TeIIL″3Br]+Br− (4). The structures of [C6H9N2S3]22+[TeIVBr6]2− (3) and [TeIIL″3Br]+Br− were determined by single crystal X-ray diffraction methods. In 3 the unit cell contains [TeBr6]2− anions and two [C6H9N2S3]+ cations. There is no direct bonding between the metal atom and the cations. In the anion only slight angular deviations from the perfect octahedral geometry are observed. The lone pair of electrons on tellurium(IV) is found to be stereochemically inert. In the cation the two five-membered heterocyclic rings adopt different conformations. In complex 4, in the solid state, the planar [TeIIL″3Br]+ cation and Br− anion are held together by ionic interactions. In the cation, L″ is bonded to the central tellurium atom through the sulphur atom.

Synthesis, properties and crystal structure of bis(thiobenzoato-s) selenium(II)

Abstract: The synthesis, properties and crystal structure of bis(thiobenzoato)selenium(II) are described. The complex is formed on interaction of selenium(IV) in acid medium with thiobenzoic acid. It is highly stable towards most metal ions. Crystal structure analysis and ir spectroscopic study indicate that the selenium is covalently bonded to sulphur with weak secondary interactions between selenium and oxygen which complete an S2O2 coordination around selenium. There are no intermolecular interactions in the crystal structure.

Stereochemistry of tellurium(II) complexes and related compounds

Abstract: Linear three-centre systems of sixth-group atoms occur in the triselenocyanate ion and in a series of tellurium(ii) complexes. In the triselenocyanate ion, the Se—Se bonds are about 032 A longer than covalent single bonds. In centrosymmetric square-planar tellurium(n) complexes, the tellurium—ligand bonds are about 027 A longer than covalent single bonds. In tellurium(ii) complexes where the linear three-centre systems are not symmetrical, pronounced relative trans bond-lengthening effects of ligands are observed. The phenyl group has a particularly large trans bond-lengthening effect. The transition state in nucleophilic substitutions at divalent sulphur, selenium and tellurium is discussed. CHEMICAL bonds longer and weaker than covalent single bonds are known in various classes of compounds. Such bonds occur, for example, in the trihalide ions of the seventh Main Group of the Periodic Table. This article is concerned with similar aspects in the sixth Main Group; specifically, with linear three-atom systems centred on divalent selenium and tellurium, and also on divalent sulphur. Halogens add a halide ion to give linear trihalide ions. In the iodine molecule, in the gas phase, the iodine—iodine bond length1 is 267 A. In the triiodide ion, in the symmetrical case, the iodine—iodine bonds are 29O—293 A24, that is, &23—036 A longer than in molecular iodine. In the bromine molecule, the bromine—bromine bond length1 is 228 A; in the tribromide ion, in the symmetrical case, the bromine—bromine bonds are 254—255 A5 6, or 026—O27 A longer than in molecular bromine. Halogens and interhalogens also form linear adducts with electroneutral n donors like amines, suiphides and selenides7 In two iodine adducts where nitrogen is donor atom'° 12, the iodine—iodine bond is 2'83 A; in two adducts where sulphur is donor atom13 15 the iodine—iodine bond is 282 and 279 A; and in three adducts where selenium is donor atom 1618 the iodine—iodine bond is 287, 291 and 296 A. Thus, not only in the triiodide ion, the adduct of the halogen with its anion, but also in adducts with electroneutral n donors, the iodine—iodine bond is lengthened relative to molecular iodine.