Effect Of Different Oxidation States Research Articles

Sulfur-bridged chromophores for photofunctional materials: using sulfur oxidation state to tune electronic and structural properties.

The use of a heteroatom, such as sulfur, as a linker or bridge, in π-conjugated materials has advantages over purely carbon-based ones due to the accessibility of higher oxidation states as a result of hypervalence. Materials containing a sulfide bridge (S) can be systemically oxidized into sulfoxides (SO) and sulfones (SO2), each of which can then influence how a material interacts with light, playing a large role in dictating the photophysical and sometimes photochemical properties. In this perspective, we summarize the progress that our group and others have made, showing how oxidation of a sulfur bridge in symmetric bichromophoric dimers and in diimine ligands can influence the excited state behavior in organic π-conjugated materials and metal complexes.

Role of different oxidation states of Crn+-TiO2 nanocomposites for the degradation of drugs under solar irradiation

The present work focuses on the effect of different oxidation states of impregnated Crn + ionic species over TiO2 surface. The resulting Crn + -TiO2 nanocomposites have been revealed to have improved optical response, charge carrier relaxation dynamics, adsorption and photocatalytic behaviour which is correlated to variable oxidation states of these composite materials. The optical absorption spectra (400–500 nm and 583–800 nm) covered the entire visible region after Crn + incorporation to have maximum photoresponse. These bands have been assigned to the 4A2g → 4T1g and 4A2g → 4T2g transitions, respectively. A remarkable quenching of photoluminescence peaks and further successive enhanced carrier relaxations from 3.62 ns (bare TiO2) to 3.73 and 4.09 ns for Cr3+ and Cr6+ loaded TiO2 catalysts were observed. The XPS analysis confirmed the presence of Cr3+ and Cr6+ oxidation states while a reduction in particle sizes with increased oxidation state (Cr3+; 16.9 nm and Cr6+; 8.6 nm) was witnessed by HRTEM images. The electrokinetic parameters such as surface charge demand, zeta and streaming potentials were also found to vary as a function of the oxidation state of the nanocatalysts. These Crn + -TiO2 catalysts were then analyzed for the photooxidation of aspirin and paracetamol drugs with some interesting behaviour. For aspirin, Cr6+-TiO2 with rate constant, k = 18.815 × 10−3 min−1 while in case of paracetamol, Cr3+-TiO2 catalyst with k = 8.052 × 10−1 h−1 showed maximum activity under solar irradiation. The observed photoactivity has been correlated to the different chemical nature of substrate molecules, catalyst oxidation state effects and catalyst-substrate associations.

A Series of Tetrathiafulvalene Bismuth Chlorides: Effects of Oxidation States of Cations on Structures and Electric Properties.

Most large organic cations in the low-dimensional hybrid halide perovskites deteriorate the photoelectric conversion efficiency of the cells. Integrating electronically active organic components into hybrid metal halides is an effective method to improve their photoelectric properties. In this work, a series of compounds obtained by hybridizing redox-active tetrakis(methylthio)tetrathiafulvalene (TMT-TTF) with bismuth chloride, formulated as [TMT-TTF]4[Bi6Cl22] (1 and 1'), [TMT-TTF]3[Bi4Cl16] (2), [TMT-TTF]2[Bi3Cl13] (3), [TMT-TTF]2[Bi2Cl10] (4), and {[TMT-TTF][Bi2Cl8]}n (5), were crystallographically characterized. These hybrids exhibit changeable oxidation states of the TTF moiety. The radical cation TTF•+ exists in 1 and 1', while a mixed-valence TTF•+/TTF2+ appears in 2 that has never been documented in any compounds and the dication TTF2+ exists in 3-5 that has never been introduced into hybrid organic-inorganic materials. The different charged states of the TTF cations lead to various degrees of connectivity of metal chloride anions, which exert a significant effect on the cation-anion arrangement and result in different supramolecular interactions between TMT-TTF and between cations and anions. The changeable oxidation states of the TTF moiety and varying degrees of metal chloride connectivity provide a good comparison among these hybridized bismuth chlorides. The order of conductivity is 2 > 1 > 1' > 3 ≈ 4 ≫ 5, which results from the synergistic effect of different oxidation states, the packing of TMT-TTF cations, and back charge transfer from the Bi-Cl anion to the TMT-TTF cation. Notably, the electrical conductivity and carrier mobility can be modulated with the fact that compound 2 has the highest performances in the dark, while in light, these properties of 1 and 1' are in turn higher than that of 2. The order of the photocurrent densities is in accordance with the increase of carrier mobility under irradiation of light. This work is the first systematic study of hybrid metal halides with various oxidation states of TTFs and presents a clear structure-property relationship and offers a fresh view on the design of new perovskite materials at the molecular level.

Effect of pH, Oxidation States of Arsenic and, Inorganic and Organic Fertilizers on Accumulation of Arsenic in Vegetables

Background/Objectives: The groundwater of 60 districts out of 64 in Bangladesh was contaminated with arsenic, whose irrigation usage is increasing over last two decades to raise food production. In this context, we studied the effects of pH and different oxidation states of arsenic (As3+ and As5+) in irrigation water and of both inorganic and organic fertilizers on arsenic-accumulation in vegetables. Method/Statistical Analysis: Five vegetable plants were grown with sandy clay loamy soil in pots under open field conditions and irrigated with model water of 10 mg As L-1. The pot experiments were well justified by field trails (n=80) that roughly showed 1:1 correlation. The samples were acid-digested and analyzed by GF-AAS for total concentration of arsenic. The regression equations of the fitted models were cross-checked by analyzing ANOVA, P value, r value and Durbin-Watson statistics. Findings: Prolonged use of irrigation water of pH range 5.00-11.00 for 90 days changed pH of surface soil of 0-3 cm depth from 6.22 to 8.93. The concentration of As in vegetables, [As]veg, although varied irregularly, was comparatively higher at both lower pH (5.00) and higher pH (10.00) of irrigation water corresponding to soil pH of 6.22 and 8.34 respectively. Arsenic in +3 oxidation state accumulated more in vegetables than that in +5 oxidation state. Comparison showed that urea and TSP increased arsenic content in vegetables by 72.37% and 18.83% respectively, whereas potash and cattle manure decreased that by 14.76% and 51.16% respectively. The reduction of [As]veg by the cattle manure is probably due to adsorption of As by cellulosic materials and microorganism induced methylation of As in soil, as we found 50.72% organic matter, 30.32% Organic C in cattle manure and about 106 Fecal Coliform bacteria per 100g of cattle manure amended soil. Novelty/Improvements: To our knowledge, this is the first paper that reports the effect of different oxidation states of arsenic (As3+ and As5+) of irrigation water towards arsenicaccumulation in vegetables. Our findings reveal that for As phytoremediation, soil pH should be around 6.80 and application of cattle manure should be highly encouraged, whereas uses of urea and TSP should be controlled. This study highlights the appropriate practices in cultivation process towards safety of human health. Keywords: Arsenic, Effect, Fertilizer, Oxidation State, Vegetables, pH

Theoretical Investigation of Water Oxidation on Fully Saturated Mn2O3 and Mn2O4 Complexes.

Understanding the factors that affect efficiency of manganese oxides as water oxidation catalysts is an essential step toward developing commercially viable electrocatalysts. It is important to understand the performance of the smallest versions of these catalysts, which will in return be advantageous with bottom up catalytic design. Density functional theory calculations have been employed to investigate water oxidation processes on Mn2(μ-OH)(μ-O)(H2O)3(OH)5 (Mn2O4·6H2O), Mn2(μ-OH)2(H2O)3(OH)4 (Mn2O3·6H2O), and Mn2(μ-OH)2(H2O)4(OH)4 (Mn2O3·7H2O) complexes. The effect of different oxidation states of manganese is considered in this study. Thermodynamically, the lowest energy pathway for the fully saturated Mn2O4·6H2O complex occurs through a nucleophilic attack of a solvent water molecule to a Mn(IV1/2)O oxo moiety. The lowest energy pathway on the Mn2O3·6H2O complex proceeds with an attack of Mn(VI)O group to the surface hydroxo group on the same manganese atom; this pathway is related to the third lowest energy pathway on the Mn2O4·6H2O complex. The water oxidation process on the fully saturated Mn2O3·7H2O complex also involves a nucleophilic attack from a solvent water molecule to a Mn(V)O moiety. The formation of these manganese oxo groups can be used as a descriptor for selecting a manganese-based water splitting catalyst due to the high electrochemical potentials required for the generation of these groups.

Theoretical studies on the reaction mechanism of PP1 and the effects of different oxidation states of the Mn–Mn center on the mechanism

Protein phosphatase 1 (PP1) is a dinuclear metalloenzyme that catalyzes the dephosphorylation of serine and threonine residues. In this work, the catalytic reaction mechanism of PP1 was theoretically investigated by hybrid density functional theory. Firstly, an initial model of the Mn(II)-Mn(II) active site of PP1 was constructed on the basis of the high-resolution crystal structure, and stationary points along the reaction pathway were optimized and analyzed. The calculations provide strong support for the mechanism of the dephosphorylation by PP1 and suggest that His125 plays the role of donating a proton to the leaving group. Furthermore, reaction models with the Mn-Mn centers at different oxidation states [Mn(III)-Mn(II) and Mn(III)-Mn(III) centers] were designed. Our calculations show that increasing the oxidation state of one or both Mn(II) can shorten the bond lengths between the metal ions and the ligands, and increase the energy barrier of the related reactions. We found it interesting that artificially adding a negatively charged hydroxy ligand into the Mn(III)-Mn(II) center can recover the shortened coordination bonds and lower the increased energy barrier. Our investigation suggests that the definite oxidation states of the metal centers should be significantly correlated to the negative charges of the ligands not only in phosphoprotein phosphatases, but also in purple acid phosphatases and Escherichia coli 5'-nucleotidase. This means that all the members of phosphoprotein phosphatases adopt homodivalent centers, and suggests the heterovalent active sites of purple acid phosphatases have evolved from homodivalent ones.

The Effects of Mn Substitution and Oxidation States of Mn in BiFeO3 Thin Films

Multiferroic Bi(Fe0.9Mn x 0.1)O3 (x = 2+, 3+, and 4+) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a pulsed laser deposition method. The effects of different oxidation states of Mn used as a starting material on crystal structure, leakage current, dielectric, and ferroelectric properties were investigated. No significant change in the crystal structure was observed while electrical properties were affected by the oxidation states of Mn. A frequency-dependent dielectric relaxation region was observed in the films with Mn3+ and Mn2+, indicating the presence of space charges such as oxygen vacancies.

Cobalt(II) and cobalt(III) complexes with 4′-(4-cyanophenyl)-2,2′:6′,2′′-terpyridine

4'-Cyanophenyl-2,2':6',2''-terpyridine (cptpy) was employed as an N,N',N''-tridentate ligand to synthesize the compounds bis[4'-(4-cyanophenyl)-2,2':6',2''-terpyridine]cobalt(II) bis(tetrafluoridoborate) nitromethane solvate, [Co(II)(C(22)H(14)N(4))(2)](BF(4))(2) x CH(3)NO(2), (I), and bis[4'-(4-cyanophenyl)-2,2':6',2''-terpyridine]cobalt(III) tris(tetrafluoridoborate) nitromethane sesquisolvate, [Co(III)(C(22)H(14)N(4))(2)](BF(4))(3) x 1.5 CH(3)NO(2), (II). In both complexes, the cobalt ions occupy a distorted octahedral geometry with two cptpy ligands in a meridional configuration. A greater distortion from octahedral geometry is observed in (I), which indicates a different steric consequence of the constrained ligand bite on the Co(II) and Co(III) ions. The crystal structure of (I) features an interlocked sheet motif, which differs from the one-dimensional chain packing style present in (II). The lower dimensionality in (II) can be explained by the disturbance caused by the larger number of anions and solvent molecules involved in the crystal structure of (II). All atoms in (I) are on general positions, and the F atoms of one BF(4)(-) anion are disordered. In (II), one B atom is on an inversion center, necessitating disorder of the four attached F atoms, another B atom is on a twofold axis with ordered F atoms, and the C and N atoms of one nitromethane solvent molecule are on a twofold axis, causing disorder of the methyl H atoms. This relatively uncommon study of analogous Co(II) and Co(III) complexes provides a better understanding of the effects of different oxidation states on coordination geometry and crystal packing.

Vanadium species and their effect on the catalytic behavior of an FCC catalyst

Samples of a commercial FCC catalyst impregnated with 3000 ppm vanadium and subjected to oxidative and reductive treatments, were characterized by electron spin resonance (ESR) and tested in a microactivity test (MAT) to study the effect of different oxidation states of vanadium on the catalytic behavior when processing an atmospheric residue from the North Sea. MAT testing at 524 °C shows that samples containing a substantial part of V 4+ combined with a strong part of V 3+ or lower oxidation states give a considerably less catalytic effect of vanadium than samples containing mainly V 5+. The test results indicate that V 4+ and V 5+ have quite similar dehydrogenation activities, while V 3+ or lower oxidation states have almost no dehydrogenation effect. It has been found that different oxidation states of vanadium (V 3+ or lower, V 4+ and V 5+) co-exist when treating the catalyst samples in 5% hydrogen in nitrogen at elevated temperatures up to 760 °C. The initial conversion to V 3+ or lower oxidation states occurs no later than after only one-third of the vanadium is converted from V 5+ to V 4+. A relatively higher concentration of V 4+ is allowed when treating the catalyst in 5% carbon monoxide in nitrogen.

THE VALENCE AND SPECIATION OF SULFUR IN GLASSES BY X-RAY ABSORPTION SPECTROSCOPY

The geochemical behavior of sulfur in magmas depends strongly on the oxidation state of sulfur, but this is not easily determined by standard analytical methods. We have measured XANES absorption spectra at the sulfur K-edge and have found that such measurements are useful to characterize the oxidation state and speciation of sulfur in silicate glasses of geological rel evance. Measured spectra of a set of reference minerals show the effects of different oxidation states and coordination numbers of sulfur; there is a large shift in energy (~10‐12 eV) of the sulfur K-edge between S 2‐ and S 6+ . This large and easily detectable difference makes possible the measurement of the valence of sulfur in unknown samples by measuring the shift in energy of the absorption edge. This approach is applicable to both crystalline and glassy materials, and useful results have been obtained on samples with as little as 450 ppm S. We have used XANES measurements to characterize oxidation state and speciation of sulfur in a set of natural and synthetic sulfur-bearing glasses. The samples cover a range of composition from basaltic to almost rhyo litic, and some were synthesized over a range of pressure, temperature and oxygen fugacity; glass S content varies between 450 and 3000 ppm. XANES analyses, carried out in fluorescence mode at LURE, allowed determination of the sulfur oxidation state in all of the samples and clearly show that some samples contain a mixture of S 2‐ and S 6+ ; no other sulfur species were observed. Quantitative determination of the abundance of sulfide and sulfate shows good agreement with independent measurements based on electron-microprobe determination of the wavelength shift of sulfur K X-rays.

An X-ray Spectroscopic Investigation of Bis(dithiolene)molybdenum(IV,V,VI) and -tungsten(IV,V,VI) Complexes: Symmetrized Structural Representations of the Active Sites of Molybdoenzymes in the DMSO Reductase Family and of Tungstoenzymes in the AOR and F(M)DH Families

Molybdenum and tungsten oxotransferase and hydroxylase enzymes catalyze the generalized reaction X + H2O ↔ XO + 2H+ + 2e- involving substrate and product X/XO. All such enzymes contain one or two pterin dithiolene ligands bound to a molybdenum or tungsten atom in the enzyme cofactor. Recent investigations in these laboratories together with earlier work by others have afforded a set of 10 complexes, all structurally characterized by X-ray diffraction, that are relevant to the active sites of several families of enzymes containing two pterin dithiolenes: [MIVO(bdt)2]2- (1, 6), [MV(bdt)2]1- (2, 7), [MIV(OSiButPh2)(bdt)2]1- (3, 8), [MVIO2(bdt)2]2- (4, 9), and [MVIO(OSiButPh2)(bdt)2]1- (5, 10) [M = Mo (1−5), W (6−10); bdt = benzene-1,2-dithiolate(2−)]. In particular, complexes 3 and 5 simulate the reduced and oxidized sites, respectively, of one DMSO reductase. This set of complexes of accurately known structure provides a heretofore unavailable opportunity to examine by X-ray absorption spectroscopy (XAS) the effects of different oxidation states, ligand types, and coordination geometries on absorption edge and EXAFS features. Molybdenum K-edge or tungsten L2,3-edge spectra and EXAFS analysis (using the GNXAS protocol) are reported for 1−10. Systematic shifts of edge energies over the M(IV,V,VI) oxidation states are observed, and features in the second derivative edge spectra are correlated with the number (0−2) of oxo ligands. While the field of molybdenum and tungsten enzymes has been substantially advanced by protein crystallography, there exist variances in metal−dithiolene interactions for a given enzyme and structural differences among closely related enzymes. Further, protein crystallographic results are not always consistent with conclusions from XAS and other spectroscopic studies. These molecules serve as benchmarks or calibrants with respect to the corresponding structural properties of enzyme sites containing two pterin dithiolene cofactor ligands and one or two oxygen-based ligands such as members of the DMSO family of molybdoenzymes and the AOR and F(M)DH families of tungstoenzymes. Because of the internal consistency of EXAFS and X-ray crystallography results, these complexes will prove useful for future comparisons with enzymes of both known and unknown structure and may help to clarify discrepancies seen in protein crystallography.