Oxidation State Compounds Research Articles

Electrochemical studies of gold ore processing wastewater containing cyanide, copper, and sulfur compounds

The electrochemistry of real gold ore processing wastewater solutions from copper sulfide containing gold ore has been investigated. Analysis shows that the wastewater contains a range of sulfur compounds in various oxidation states from sulfide to sulfate. The electrochemical characteristics of the gold ore processing wastewater were evaluated using rotating disk, cyclic voltammetric, polarization and preparative electrolysis studies. The solutions show clear differences versus synthetic alkaline copper cyanide solutions. The copper cyanide/copper oxide catalysis normally seen in synthetic alkaline copper cyanide solutions is strongly inhibited. Two components of the wastewater solution identified as inhibiting the copper cyanide/copper oxide catalysis are copper sulfide complexes and thiocyanate. The inhibition of the copper cyanide/copper oxide catalysis appears to have an initiation time possibly related to the accumulation of copper-sulfur compounds at the electrode surface. The passivated surface is still able to oxidize cyanide, though at a maximum rate that corresponds to the limiting current for free cyanide assuming 1 electron per cyanide. The lack of the copper oxide coating that typically forms during oxidation of synthetic alkaline copper cyanide solutions, plus possibly the presence of various sulfur compounds, results in corrosion at higher anodic potentials when stainless steel is used as an electrode. However, stainless steel can be successfully used as an electrode material to treat the solutions if the potential is carefully controlled.

Thin Films of Molecular Materials Grown on Silicon Substrates by Chemical Vapor Deposition and Electrodeposition

Chemical vapor deposition (CVD) and electrodeposition (ED) were applied to grow thin films of molecule-based magnets and conductors. Chemical vapor deposited films are illustrated by the M(TCNE)x (M=V, Cr, Nb, Mo) magnet series. V(TCNE)x and Cr(TCNE)x are room-temperature magnets. XANES/EXAFS studies on the air-stable Cr(TCNE)x have been performed to determine the chemical environment of the chromium within the polymeric network. Electrodeposition on a silicon working electrode was applied to process thin films of numerous molecule-based conductors, namely, non-integral oxidation state compounds, charge transfer complexes, and singlecomponent molecular conductors. Among the series of conductive thin films, TTF[Ni(dmit)2]2 and Ni(tmdt)2 exhibit a metal-like behavior.

Determination of tin equilibrium isotope fractionation factors from synchrotron radiation experiments

A method of determination of the reduced isotopic partition function ratio (β-factor) from the partial density of state (PDOS) obtained by inelastic nuclear resonant X-ray scattering (INRXS) in synchrotron radiation experiments has been established. The method has been demonstrated by the example of tin isotopes. The tin β-factors for CaSnO 3, SnO 2, SnO have been computed from the INRXS-derived PDOSs. ln ⁡ β Sn 122 / 116 = ( 0.390 ± 0.0076 ) x − ( 0.00160 ± 0.0000242 ) x 2 + ( 1.099 ± 0.0573 ) ⋅ 10 − 5 x 3 ) for SnO ln ⁡ β Sn 122 / 116 = ( 0.771 ± 0.0150 ) x − ( 0.00392 ± 0.000061 ) x 2 + ( 3.548 ± 0.287 ) ⋅ 10 − 5 x 3 for SnO 2 ln ⁡ β Sn 122 / 116 = ( 0.776 ± 0.0157 ) x − ( 0.00334 ± 0.000064 ) x 2 + ( 2.561 ± 0.157 ) ⋅ 10 − 5 x 3 for CaSnO 3 Equilibrium 122/116Sn isotope fractionation between di- and tetravalent tin compounds is about 0.4‰ at 1000 K and about 4.1‰ at room temperature and can be measured by modern multicollector inductively-coupled plasma mass-spectrometers. Tin β-factors reveal dependence on oxidation state previously detected for iron isotopes. A comparison of the tin β-factors for SnO 2 obtained on the basis of the INRXS-derived PDOS with those obtained by the Mössbauer spectroscopy method shows that both methods give similar results, but application of synchrotron radiation provides more accurate and reliable data. Equilibrium stable isotope fractionation of transition metals between different oxidation state compounds is not negligible even for elements as heavy as tin.

Aqueous Chemistry of the VanadiumIII (VIII) and the VIII−Dipicolinate Systems and a Comparison of the Effect of Three Oxidation States of Vanadium Compounds on Diabetic Hyperglycemia in Rats

The aqueous vanadium(III) (V(III)) speciation chemistry of two dipicolinate-type complexes and the insulin-enhancing effects of V-dipicolinate (V-dipic) complexes in three different oxidation states (V(III), V(IV), and V(V)) have been studied in a chronic animal model system. The characterization of the V(III) species was carried out at low ionic strength to reflect physiological conditions and required an evaluation of the hydrolysis of V(III) at 0.20 M KCl. The aqueous V(III)-dipic and V(III)-dipic-OH systems were characterized, and complexes were observed from pH 2 to 7 at 0.2 M KCl. The V(III)-dipic system forms stable 1:2 complexes, whereas the V(III)-dipic-OH system forms stable 1:1 complexes. A comparison of these complexes with the V-pic system demonstrates that a second ligand has lower affinity for the V(III), presumably reflecting bidentate coordination of the second dipic(2)(-) to the V(III). The thermodynamic stability of the [V(III)(dipic)(2)](-) complex was compared to the stability of the corresponding V(IV) and V(V) complexes, and surprisingly, the V(III) complexes were found to be more stable than anticipated. Oral administration of three V-dipicolinate compounds in different oxidation states {H[V(III)(dipic)(2)H(2)O].3H(2)O, [V(IV)Odipic(H(2)O)(2)].2H(2)O, and NH(4)[V(V)O(2)dipic]} and the positive control, VOSO(4), significantly lowered diabetic hyperglycemia in rats with streptozotocin-induced diabetes. The diabetic animals treated with the V(III)- or V(IV)-dipic complexes had blood glucose levels that were statistically different from those of the diabetic group. The animals treated with the V(V)-dipic complex had the lowest blood glucose levels of the treated diabetic animals, which were statistically different from those of the diabetic group at all time points. Among the diabetic animals, complexation to dipic increased the serum levels of V after the administration of the V(V) and V(IV) complexes but not after the administration of the V(III) complex when data are normalized to the ingested dose of V. Because V compounds differing only in oxidation state have different biological properties, it is implied that redox processes must be important factors for the biological action of V compounds. We observe that the V(V)-dipic complex is the most effective insulin-enhancing agent, in contrast to previous studies in which the V(IV)-maltol complex is the most effective. We conclude that the effectiveness of complexed V is both ligand and oxidation state dependent.

Oxorhenium Complexes as Aldehyde‐Olefination Catalysts

Several oxorhenium compounds in the formal oxidation states V and VII are examined as catalysts for the aldehyde-olefination starting from diazo compounds, phosphines, and aldehydes. Of these, [ReMeO2(eta2-alkyne)] complexes provide the simplest catalysts to study, although [ReOCl3(PPh3)2] still remains the most efficient rhenium catalyst for aldehyde-olefination described to date. Prior to the reaction with the Re catalysts the phosphine and the diazo compound react to form a phosphazine. No catalytic reaction occurs in cases where no phosphazine formation is observed. The first step of the catalytic cycle involves the formation of a carbene intermediate by the reaction of phosphazine and catalyst under extrusion of phosphine oxide and dinitrogen. In a second step the carbene reacts with aldehyde under olefin formation and catalyst regeneration. Excess of alkyne as well as the presence of ketones slows down the catalytic reaction. The olefination of 4-nitrobenzaldehyde with diazomalonate is possible with these Re catalysts. In contrast, this reaction does not take place either in the classical Wittig fashion from Ph3P=C(CO2Et)2 and aldehyde or by use of all other catalysts for aldehyde olefination reactions reported to date. Catalytic ylide formation from diazo compounds seems therefore not to be the only pathway through which catalytic aldehyde-olefination reactions can proceed.

Uptake of inorganic and organic derivatives of arsenic associated with induced cytotoxic and genotoxic effects in Chinese hamster ovary (CHO) cells

Humans are exposed to arsenic and their organic derivatives, which are widely distributed in the environment, via food, water, and to a lesser extent, via air. Following uptake, inorganic arsenic undergoes biotransformation to mono- and dimethylated metabolites. Recent findings suggest that the methylation reactions represent a toxification rather than a detoxification pathway. In the present study, the genotoxic effects and the cellular uptake of inorganic arsenic [arsenate, As i(V); arsenite, As i(III)] and the methylated arsenic species monomethylarsonic acid [[MMA(V)], monomethylarsonous acid [MMA(III)], dimethylarsinic acid [DMA(V)], dimethylarsinous acid [DMA(III)], trimethylarsenic oxide [TMAO(V)] were investigated in Chinese hamster ovary (CHO-9) cells. The chemicals were applied at different concentrations (0.1 μM to 10 mM) for 30 min and 1 h, respectively. Cytotoxic effects were investigated by the trypan blue extrusion test and genotoxic effects by the assessment of micronucleus (MN) induction, chromosome aberrations (CA), and sister chromatid exchanges (SCE). Intracellular arsenic concentrations were determined by ICP-MS techniques. Our results show that MMA(III) and DMA(III) induce cytotoxic and genotoxic effects to a greater extent than MMA(V) or DMA(V). Viability was significantly decreased after incubation (1 h) of the cells with ≥ 1 μM As i(III), ≥ 1 μM As i(V), ≥ 500 μM MMA(III), ≥ 100 μM MMA(V), and 500 μM DMA(V) and ≥ 0.1 μM DMA(III). TMAO(V) was not cytotoxic at concentrations up to 10 mM. A significant increase of the number of MN, CA and SCE was found for DMA(III) and MMA(III). As i(III + V) induced CA and SCE but no MN. TMAO(V), MMA(V) and DMA(V) were not genotoxic in the concentration range tested (up to 5 mM). The nuclear division index (NDI) was not affected by any of the tested arsenic compounds after a recovery period of 14 to 35 h. When the uptake of the chemicals was measured by ICP-MS analysis, it was found that only 0.03% MMA(V) and DMA(V), and 2% MMA(III), As i(III) and (V) were taken up by the cells. In comparison, 10% of the DMA(III) dose was taken up. The total intracellular concentration of all arsenic compounds increased with increasing arsenic concentrations in the culture medium. Taken together, these data demonstrate that arsenic compounds in the trivalent oxidation state exhibit the strongest genotoxic effects. Trivalent organoarsenic compounds are more membrane permeable than the pentavalent species. The potency of the DNA damage decreases in the order DMA(III) > MMA(III) > As i(III and V) > MMA(V) > DMA(V) > TMAO(V). We postulate that the induction of genotoxic effects caused by the methylated arsenic species is primarily dependent upon their ability to penetrate cell membranes.

2-(Anilinomethyl)imidazolines as alpha1 adrenergic receptor agonists: the discovery of alpha1a subtype selective 2'-alkylsulfonyl-substituted analogues.

A series of 2'-alkylthio-2-(anilinomethyl)imidazolines were prepared to examine the effect of the alkyl group size, sulfur oxidation state, and phenyl ring substitution on ligand binding and agonism of alpha-adrenergic receptor subtypes alpha1a, alpha1b, alpha1d, alpha2a, and alpha2c. Binding at all receptor subtypes decreased for compounds in the sulfone oxidation state as compared to their sulfide analogues. While sulfides were generally potent, nonselective agonists, sulfones exhibited alpha1a subtype selectivity in a cell-based functional assay. Sulfone (32) was 250-7000-fold selective for alpha1a vs all other subtypes.

Mn K-edge XANES and Kbeta XES studies of two Mn-oxo binuclear complexes: investigation of three different oxidation states relevant to the oxygen-evolving complex of photosystem II.

Two structurally homologous Mn compounds in different oxidation states were studied to investigate the relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edge structure (XANES) and Mn Kbeta X-ray emission spectroscopy (Kbeta XES). The two manganese compounds are the di-mu-oxo compound [L'2Mn(III)O2Mn(IV)L'2](ClO4)3, where L' is 1,10-phenanthroline (Cooper, S. R.; Calvin, M. J. Am. Chem. Soc. 1977, 99, 6623-6630) and the linear mono-mu-oxo compound [LMn(III)OMn(III)L](ClO4)2, where L- is the monoanionic N,N-bis(2-pyridylmethyl)-N'-salicylidene-1,2-diaminoethane ligand (Horner, O.; Anxolabéhère-Mallart, E.; Charlot, M. F.; Tchertanov, L.; Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd, J.-J. Inorg. Chem. 1999, 38, 1222-1232). Preparative bulk electrolysis in acetonitrile was used to obtain higher oxidation states of the compounds: the Mn(IV)Mn(IV) species for the di-mu-oxo compound and the Mn(III)Mn(IV) and Mn(IV)Mn(IV) species for the mono-mu-oxo compound. IR, UV/vis, EPR, and EXAFS spectra were used to determine the purity and integrity of the various sample solutions. The Mn K-edge XANES spectra shift to higher energy upon oxidation when the ligand environment remains similar. However, shifts in energy are also observed when only the ligand environment is altered. This is achieved by comparing the di-mu-oxo and linear mono-mu-oxo Mn-Mn moieties in equivalent oxidation states, which represent major structural changes. The magnitude of an energy shift due to major changes in ligand environment can be as large as that of an oxidation-state change. Therefore, care must be exercised when correlating the Mn K-edge energies to manganese oxidation states without taking into account the nature of the ligand environment and the overall structure of the compound. In contrast to Mn K-edge XANES, Kbeta XES spectra show less dependence on ligand environment. The Kbeta1,3 peak energies are comparable for the di-mu-oxo and mono-mu-oxo compounds in equivalent oxidation states. The energy shifts observed due to oxidation are also similar for the two different compounds. The study of the different behavior of the XANES pre-edge and main-edge features in conjunction with Kbeta XES provides significant information about the oxidation state and character of the ligand environment of manganese atoms.

A theoretical study of plutonium diketone complexes for solvent extraction

We present a relativistic density functional study on some plutonium compounds with thenoyltrifluoroacetone and similar ligands which can be used in the extraction of plutonium. The method of effective core potentials is used on plutonium. The binding energies of the complexes of plutonium in the formal oxidation states II, IV and VI have been determined and the geometries of some of the complexes have been fully optimized. The stability of the compounds in the different oxidation states and the effect of varying the side groups in the ligands are discussed. Comparisons with analogous uranium compounds are presented.

Carbonaceous aerosols and their potential role in atmospheric chemistry

This paper considers the nature of carbonaceous surfaces, the means by which they are activated, the nature of some functional groups that they support, and some reaction mechanisms that may be involved. Because of the strong affinity of carbonaceous surfaces for organic species and because of the ease with which compounds in a high oxidation state can oxidize the carbonaceous surface, it is highly likely that carbonaceous aerosols are interacting chemically with a range of organic species in ways that have, as yet, not been fully characterized but may significantly affect the oxidizing capacity of our atmosphere. If HONO is formed on the surface of carbonaceous aerosols then this could be a significant source of HOx as HONO is readily photolyzed to give OH, and it could explain the large values of HONO often observed in the troposphere. In general, the reduction of NOy on carbonaceous aerosols is an important consideration, and it is addressed here.

Analysis of Total Non-Volatile Non-Sulfide Reduced Sulfur in Potable and Untreated Surface and Groundwaters

An analytical method was developed to measure the total concentration of non-volatile non-sulfide reduced sulfur in treated and untreated surface and groundwater. The method was based on the alkaline reduction by Raney nickel (prepared in situ from Raney alloy) of organic and inorganic sulfur compounds (in oxidation states below +6) to sulfide. Sulfide was swept out of the reflux apparatus under nitrogen into a trap of zinc acetate and determined colorimetrically as ethylene blue. The recoveries obtained from solutions of elemental sulfur, sulfide, sulfite, thiosulfate, tetrathionate, cysteine, cystine, methionine, glutathione, allylthiourea, sulfanilamide and thiocyanate ranged from 84–102% with typical recoveries of approximately 90%. Sulfate was not detectable by the procedure. Chlorine present in potable water samples interfered in the procedure and was removed with sodium borohydride. The relative standard deviation of the method varied from 0.25 to 5.6% and averaged 3%. The detection limit based on a 500 mL sample was 3 mg m−3.

K and L III-edge XAS studies of Ni-, Cu- and Pd-fluorides in high oxidation states

The M-F chemical bonds in various fluorides have been studied on the basis of structural features and K- and L III-edges investigations. The observation of the main peak on K-edge spectra led to specify the transition metal environment; a shoulder was observed on Ni 2+ and Cu 2+ fluorides showing that the interactions with cations belonging to further coordination shells must be taken into account, whereas no shoulder on Ni 3+, Ni IV and Cu 3+ compounds was observed, characterizing thus isolated regular octahedra. The K-edge features changed gradually as a result of the strengthening of the M-F chemical bond. The L III-edge study gave evidence for the presence of (CiF 6) 3− isolated entities where CuF bond had a rather covalent character. Some Pd compounds in high oxidation state have been investigated.

ChemInform Abstract: New Chemistry of Vanadium(II)

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Electrosynthesis of coordination compounds by the dissolution of metal anodes using ligand precursors

Electrosynthesis of complex compounds by the dissolution of metal anodes is an established method for the preparation of a wide variety of compounds in different oxidation states in a single step. The electrolyte is an aqueous, nonaqueous or mixed solvent containing the ligand. During electrolysis the anode goes into solution and forms a complex with the ligand. The latter may also be generated in the electrolytic phase by a chemical reaction or by the cathodic reduction of the ligand precursor. A variety of thiolato, xanthato, dithiocarbamato, amine and Schiff base complexes have been synthesized using appropriate ligand precursors. Compounds obtained by anodic dissolution are in normal or lower oxidation states of the metals. The method has been utilized to synthesize some compounds of In(I), Ga(II), Th(II), Mo(II), Cr(II), Ti(III) etc. in a single step. Attempts have been made to synthesize higher valent compounds by the anodic oxidation of the initial product by a second stage electrolysis using a platinum anode.

Molecular Compounds Exhibiting Coupled Conducting and Magnetic Properties and Based on (cation)n[M(dmit)]2 and (BETS)2(anion) Salts

Abstract A systematic study has been carried out on a range of metal complexes of the type (cation)n[M(dmit)2] (cation = NHyR4-y; y = 1 or 2; n = x, 1, 2; R = ethyl, propyl or butyl, or cation = organic radical cations containing one or two TTF moieties; M = Ni or Pd and dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato). The synthesis of these complexes, the crystal structure of (NHBu3)2[Ni(dmit)2] and neutral [Ni(dmit)2], their solution redox behaviour and the solid state conductivities of the non-integer oxidation state compounds obtained by electrocrystallization techniques are presented. Synthesis, structure and properties of new compounds of the family of (BETS)2(anion) compounds with (CuxCly)n- and [(FeCl4)1−x(GaCl4)x]− anions are described.

Metal Complexes of Dithiolate Ligands: 5,6-Dihydro-1,4-dithiin-2,3-dithiolato (dddt(2-)), 5,7-Dihydro-1,4,6-trithiin-2,3-dithiolato (dtdt(2-)), and 2-Thioxo-1,3-dithiole-4,5-dithiolato (dmit(2-)). Synthesis, Electrochemical Studies, Crystal and Electronic Structures, and Conducting Properties.

New precursors to potentially conductive noninteger oxidation state (NIOS) compounds based on metal complexes [ML(2)](n)()(-) [M = Ni, Pd, Pt; L = 5,6-dihydro-1,4-dithiin-2,3-dithiolato (dddt(2)(-)), 5,7-dihydro-1,4,6-trithiin-2,3-dithiolato (dtdt(2)(-)), and 2-thioxo-1,3-dithiole-4,5-dithiolato (dmit(2)(-)); n = 2, 1, 0] have been investigated. Complexes of the series (NR(4))[ML(2)] (R = Me, Et, Bu; L = dddt(2)(-), dtdt(2)(-)) have been isolated and characterized, and the crystal structure of (NBu(4))[Pt(dtdt)(2)] (1) has been determined {1 = C(24)H(44)NPtS(10), a = 12.064(2) Å, b = 17.201(3) Å, c = 16.878(2) Å, beta = 102.22(2) degrees, V = 3423(1) Å(3), monoclinic, P2(1)/n, Z = 4}. Oxidation of these complexes affords the corresponding neutral species [ML(2)](0). Another series of general formula (cation)(n)()[M(dmit)(2)] [cation = PPN(+), BTP(+), and (SMe(y)()Et(3)(-)(y)())(+) with y = 0, 1, 2, and 3, n = 2, 1, M = Ni, Pd] has also been studied. All of these (cation)(n)()[M(dmit)(2)] complexes have been isolated and characterized [with the exception of (cation)[Pd(dmit)(2)] for cation = (SMe(y)()Et(3)(-)(y)())(+)]. The crystal structures of (PPN)[Ni(dmit)(2)].(CH(3))(2)CO (2) and (SMeEt(2))[Ni(dmit)(2)] (3) have been determined {2 = C(45)H(36)NNiS(10)P(2)O, a = 12.310(2) Å, b = 13.328(3) Å, c = 15.850(3) Å, alpha = 108.19(3) degrees, beta = 96.64(2) degrees, gamma = 99.67(2) degrees, V = 2373(1) Å(3), triclinic, P&onemacr;, Z = 2; 3 = C(11)H(13)NiS(11), a = 7.171(9) Å, b = 17.802(3) Å, c = 16.251(3) Å, beta = 94.39(4) degrees, V = 2068(2) Å(3), monoclinic, P2(1)/n, Z = 4} NIOS salts derived from the preceding precursors were obtained by electrochemical oxidation. Electrochemical studies of the [M(dddt)(2)] complexes show that they may be used for the preparation of NIOS radical cation salts and [M(dddt)(2)][M'(dmit)(2)](x)() compounds, but not for the preparation of (cation)[M(dddt)(2)](z)() NIOS radical anion salts. The electrochemical oxidation of the [M(dtdt)(2)](-) complexes always yields the neutral [M(dtdt)(2)](0) species. The crystal structure of [Pt(dddt)(2)][Ni(dmit)(2)](2) (4) has been determined and is consistent with the low compaction powder conductivity (5 x 10(-)(5) S cm(-)(1) at room temperature) {4 = C(20)H(8)Ni(2)PtS(28), a = 20.336(4) Å, b = 7.189(2) Å, c = 14.181(2) Å, beta = 97.16(2) degrees, V = 2057(1) Å(3), monoclinic, C2/m, Z = 2}. The crystal structures of the semiconducting NIOS compounds (BTP)[Ni(dmit)(2)](3) (5) and (SMe(3))[Ni(dmit)(2)](2) (6) have been determined {5 = C(43)H(22)PNi(3)S(30), a = 11.927(2) Å, b = 24.919(2) Å, c = 11.829(3) Å, alpha = 93.11(1) degrees, beta = 110.22(1) degrees, gamma = 83.94(1) degrees, V = 3284(1) Å(3), triclinic, P&onemacr;, Z = 2; 6 = C(15)H(9)Ni(2)S(21), a = 7.882(1) Å, b = 11.603(2) Å, c = 17.731(2) Å, alpha = 77.44(1) degrees, beta = 94.39(1) degrees, gamma = 81.27(1) degrees, V = 1563(1) Å(3), triclinic, P&onemacr;, Z = 2}. The parent compound (SEt(3))[Ni(dmit)(2)](z) (unknown stoichiometry) is also a semiconductor with a single-crystal conductivity at room temperature of 10 S cm(-)(1). By contrast, the single-crystal conductivity at room temperature of (SMeEt(2))[Pd(dmit)(2)](2) (7) is rather high (100 S cm(-)(1)). 7 behaves as a pseudometal down to 150 K and undergoes an irreversible metal-insulator transition below this temperature. The crystal structure of 7 has been determined {7 = C(17)H(13)NPd(2)S(21), a = 7.804(4) Å, b = 36.171(18) Å, c = 6.284(2) Å, alpha = 91.68(4) degrees, beta = 112.08(4) degrees, gamma = 88.79(5) degrees, V = 1643(1) Å(3), triclinic, P&onemacr;, Z = 2}. The electronic structure of (SMeEt(2))[Pd(dmit)(2)](2) (7) and the possible origin of the metal-insulator transition at 150 K are discussed on the basis of tight-binding band structure calculations.

Vanadium distribution in rats and DNA cleavage by vanadyl complex: implication for vanadium toxicity and biological effects.

Vanadium ion is toxic to animals. However, vanadium is also an agent used for chemoprotection against cancers in animals. To understand both the toxic and beneficial effects we studied vanadium distribution in rats. Accumulation of vanadium in the liver nuclei of rats given low doses of compounds in the +4 or +5 oxidation state was greater than in the liver nuclei of rats given high doses of vanadium compounds or the vanadate (+5 oxidation state) compound. Vanadium was incorporated exclusively in the vanadyl (+4 oxidation state) form. We also investigated the reactions of vanadyl ion and found that incubation of DNA with vanadyl ion and hydrogen peroxide (H2O2) led to intense DNA cleavage. ESR spin trapping demonstrated that hydroxyl radicals are generated during the reactions of vanadyl ion and H2O2. Thus, we propose that the mechanism for vanadium-dependent toxicity and antineoplastic action is due to DNA cleavage by hydroxyl radicals generated in living systems.

Electronic absorption spectra of reduction products of pentavalent niobium and tantalum in different alkali chloride and oxychloride melts

We have studied the electronic absorption spectra of niobium chloride and oxychloride compounds in different oxidation states and of the reduction products of pentavalent niobium and tantalum in various alkali chloride melts at different temperatures up to 1000 K. Furthermore, we present spectra of the corresponding cluster compounds Na 4 Nb 6 Cl 18 and Na 4 Ta 6 Cl 18 dissolved in alkali chloride melts at elevated temperatures. It is found that these compounds decompose at these temperatures. In comparing the spectra corresponding to the different oxidation states of the niobium systems, it is concluded that reduction of NbCl 5 with excess metal yields Nb(II) or Nb(III), whereas in NbOCl 3 the oxidation state IV is stabilized

Electrochemical Studies of the Formation Mechanism of (cation) x [Ni(dmit)2 Conductive Compounds and of their Non-Integer Oxidation State

Abstract The mechanism of electrocrystallization of (cation) x [Ni(dmit)2 (cation = NHMe+ 3, NMe+ 4) conductive compounds is studied under non-stationary conditions by cyclic voltammetry using ultramicroelectrodes at high potential-scan rates. It is shown that the formation of non-integer oxidation state compounds proceeds through one-electron transfers combined with chemical reaction between [Ni(dmit)2 − and [Ni(dmit)2 0 electrogenerated species exhibiting integer charges. The non-integer oxidation state in (cation) x [Ni(dmit)2 compounds (cation = NBu+ 4, AsPh+ 4, NH2Me+ 2, NH3Me+), measured by the non-integer value of x, is determined under stationary conditions by use of the carbon paste electrode at very low potential-scan rates.

Semiempirical calculation technique for transition metal compounds in low oxidation states

The feasibility of employing the semiempirical MC SCF method to model chemical processes is analyzed with the aid of transition metal compounds in the lowest oxidation states. Using the nickel compounds Ni2, NiCO, Ni4, NiO, and Ni(CO)4 as examples, it is shown that with the multiconfiguration INDO method it is possible to give an accurate description of the molecular wave function form over a broad range of interatomic distances and to convey the relative order of the lowest molecular terms and the shape of potential curves. Parametrization of the transition metals M is proposed on the basis of spectroscopic data on the lowest term energies of the M0 atoms and the M+ ions.