Sulfur Oxoanions Research Articles

Monovalent sulfur oxoanions enable millimeter-long single-crystalline h-WO3 nanowire synthesis.

Here, we discuss a misunderstanding regarding chemical capping, which has intrinsically hindered the extension of the length of hexagonal (h)-WO3 nanowires in previous studies. Although divalent sulfate ions (SO42-) have been strongly believed to be efficient capping ions for directing anisotropic h-WO3 nanowire growth, we have found that the presence of SO42- is highly detrimental to the anisotropic crystal growth of the h-WO3 nanowires, and a monovalent sulfur oxoanion (HSO4-) rather than SO42- only substantially promotes the anisotropic h-WO3 nanowire growth. Ab initio electronic structure simulations revealed that the monovalent sulfur oxoanions were preferentially able to cap the sidewall plane (100) of the h-WO3 nanowires due to the lower hydration energy when compared with SO42-. Based on this capping strategy, using the monovalent sulfur oxoanion (CH3SO3-), which cannot generate divalent sulfur oxoanions, we have successfully fabricated ultra-long h-WO3 nanowires up to the millimeter range (1.2 mm) for a wider range of precursor concentrations. We have demonstrated the feasibility of these millimeter-long h-WO3 nanowires for the electrical sensing of molecules (lung cancer biomarker: nonanal) on flexible substrates, which can be operated at room temperature with mechanical flexibility with bending cycles up to 104 times due to the enhanced textile effect.

Dissociation, absorption and ionization of some important sulfur oxoanions (S2On2−n = 2, 3, 4, 6, 7 and 8)

In this work, a systematic theoretical study was performed on the dissociation, absorption and ionization of several important sulfur oxoanions (S2On2− (n=2, 3, 4, 6, 7 and 8)). ΔEelec (thermal corrected energy), ΔH° and ΔG° of the dissociation reactions of the oxoanions to their radical monoanions were calculated using combined computational levels of theories such as Gaussian-3 (G3) and a new version of complete basis set method (CBS-4M) in different environments including gas phase, microhydrated in gas phase and different solvents. Calculations showed S2O72− is the most stable anion against the dissociation to its radical monoanions (SO4−+SO3−). It was also found that S2O42− has more tendency to dissociate to its radical anions (SO2−+SO2−) compared to the other anions. The absorption spectra of the anions were also calculated using the time-dependent density functional theory (TD-DFT) employing M062X functional. The effect of microhydration and electrostatic field of solvent on the different aspects (intensity, energy shift and assignment) of the absorption spectra of these anions were also discussed. It was observed that both hydrogen bonding and electrostatic effect of water increases the intensity of the absorption spectrum compared to the gas phase. Effect of microhydration in shifting the spectra to the shorter wavelength is considerably higher than the effect of electrostatic field of water. Finally, several gas phase ionization energies of the anions were calculated using the symmetry-adapted cluster–configuration interaction methodology (SAC–CI) and found that the first electron detachment energies of S2O22−, S2O32− and S2O42− are negative. Natural bonding orbital (NBO) calculations were also performed to assign the electron detachment bands of the anions.

Chain of water hexamers and tetramers hosted in a redox product of a Co(III) metal complex: Syntheses, characterization and single crystal X-ray structure determination of Co(II/III) complexes with sulfur oxo-anions

In the present study, four new Co(II/III) metal complexes, [Co(phen)3]S4O6·2H2O (1), [Co(phen)3]S4O6·7H2O (2), [Co(phen)3]2(S4O6)3·6.5H2O (3) and [Co(phen)3]S2O3·9H2O (4), have been synthesized and characterized by elemental analysis, TGA and various spectroscopic techniques. In the case of 1 and 2, an unexpected redox reaction took place and the complexes formed are different in terms of their water of crystallization. The structures of 1–3 have been determined by single crystal X-ray crystallography. Complex salts 1–3 crystallize in the orthorhombic (Pbca), triclinic (P1¯) and monoclinic (P21/c) crystal systems, respectively. Their X-ray crystal structure determination revealed the presence of non-covalent cation-to-anion (C–H⋯Oanion hydrogen bonds), anion-to-cation (anion⋯π interactions) and cation-to-cation (C–H⋯π and π⋯π stacking interactions) interactions. Interestingly, a detailed packing analysis has shown the presence of rare chains of cyclic water hexamers (chair form) and tetramers, stabilized by O–H⋯O and C–H⋯O hydrogen bond interactions in the supramolecular complex [Co(phen)3]S4O6·7H2O (2).

Preparation and Characterization of GCE Coatings Combining DDDMAB and PDADMAC with FAD and HCM for Electrocatalytic Detection of Oxygen and Sulfur Oxoanions

AbstractElectrochemically active hybrid coatings based on cationic films, didodecyldimethylammonium bromide (DDDMAB), and poly(diallyldimethylammonium chloride) (PDADMAC) are prepared on glassy carbon electrode surface by cycling the film‐covered electrode repetitively in a pH 7 solution containing flavin adenine dinucleotide (FAD), and anionic hexacyanometalate (HCM) complexes, Fe(CN)63− and Ru(CN)64−. Cyclic voltammetric features of hybrid coatings resemble that of electron transfer process of surface‐confined redox species. Electrochemical quartz crystal microbalance (EQCM) was used to monitor the deposition of FAD on DDDMAB film. Cyclic voltammetric peak potentials of modified electrode were found to be shifted to more negative region with increasing pH of contacting solution with a slope value of 63.3mV per pH unit. The electrocatalytic behavior of FAD‐modified DDDMAB‐coated GCE and hybrid film electrodes was tested towards reduction of oxygen, S2O82−, SO52− and oxidation of SO32−. The application of FAD‐modified DDDMAB‐coated GCE for S2O82− estimation was demonstrated in amperometric mode. The sensitivity and detection limit (S/N=3) were 267.6 μA mM−1 and 2×10−6 M, respectively.

Synthesis, structure and electrochemical properties of the cationic complex tris-(imidazolidine-1,10-phenanthroline)iron(II)

The complex [Fe II(Imz-phen) 3](PF 6) 2, (Imz-phen = imidazolidine-[4,5-f]-1,10-phenanthroline) has been prepared and characterized using X-ray diffraction, UV–vis and IR spectroscopy, elemental analysis, fast atomic bombardment (FAB) mass spectrometry, and cyclic voltammetry. Its crystal lattice includes acetonitrile (π–π bound to phenanthroline), methanol, and water molecules. Scanning continuously between 1000 mV and 1650 mV in CH 3CN, a modified electrode that includes the iron (II) complex is obtained; after the 25th continuous cycle a stable film is formed that is electrocatalytically active in the reduction of sulfur oxoanions. When the electrocatalytic properties are evaluated in ethanol/water solution, the current achieved from the electroreduction of these sulfur species is linearly dependent on the respective concentrations, suggesting potential application in sulfite determination.

Electrochemical Polymerization of 3,4‐Ethylenedioxythiophene from Aqueous Solution Containing Hydroxypropyl‐β‐cyclodextrin and the Electrocatalytic Behavior of Modified Electrode Towards Oxidation of Sulfur Oxoanions and Nitrite

AbstractPoly(3,4‐ethylenedioxythiophene) (PEDOT) film was prepared on glassy carbon electrode from 0.1 M LiClO4 aqueous solution containing 3,4‐ethylenedioxythiophene (EDOT) monomer and hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD), by multiple scan cyclic voltammetry. The effect of oxidation potentials on electropolymerization of EDOT was examined by chronoamperometry and cyclic voltammetric techniques. The results of potentiostatic experiments show that optimum potential range to obtain compact stable film was 0.9 to 1.05 V (vs. Ag/AgCl). At higher positive potential, i.e. above 1.05 V, polymer growth was hindered by passivation effect. The PEDOT film exhibited a strong absorption at 550 nm in the UV‐vis region and also a multicolor electrochromism in different buffer solutions (sky blue‐purple red). Cyclic voltammetric features of PEDOT‐coated electrode in pure supporting electrolyte suggested that charge transfer of the film resembles that of surface‐confined redox species. Finally, the electrocatalytic behavior of PEDOT‐modified electrode was tested towards oxidation of sulfur oxoanions and nitrite using cyclic voltammetry.

Electrochemical Preparation of VPtCl6 Film and Its Electrocatalytic Properties with NAD + and Sulfur Oxoanions

A modified electrode with vanadium hexachloroplatinate film has been fabricated directly from the mixing of and ions, and its electrochemical behavior was investigated. The deposition of a film occurred when was electrochemically reduced to and to . The electrochemical quartz crystal microbalance (EQCM), ultraviolet-visible absorption spectroscopy, stopped-flow, chronoamperometry, and cyclic voltammetry techniques were used to study the deposition and growth mechanism of the above film. In the EQCM studies, the reversibility of the vanadium (II/III) hexachloroplatinate film during cycling and the corresponding frequency change was found to be good, and the ion exchange obviously occurred in the redox couple. For the surface morphological analysis, the film was further electrochemically deposited on a transparent semiconductor indium tin oxide (ITO) electrode for scanning electron microscopy and atomic force microscopy studies. It was found that the deposited film formed as a film with platinum and vanadium particles on ITO. To validate the electroanalytical properties, a -modified glassy carbon electrode was applied for the electrocatalytic reduction of the (β-Nicotinamide adenine dinucleotide) and sulfur oxoanions, and the results showed a quite effective electrocatalytic reduction for the corresponding substances.

Preparation, characterization, and electrocatalytic properties of hybrid coatings of hexacyanometalate-doped-cationic films

Electrochemically active hybrid coatings based on cationic films, didodecyldimethylammonium bromide (DDAB), and poly(diallyldimethylammonium chloride) (PDDAC) are prepared on electrode surface by cycling the film-covered electrode repetitively in a pH 6.5 solution containing Fe(CN)63− and Ru(CN)64− anions. Modified electrodes exhibited stable and reversible voltammetric responses corresponding to characteristics of Fe(CN)63−/4− and Ru(CN)64−/3− redox couples. The cyclic voltammetric features of hybrid coatings resemble that of electron transfer process of surface-confined redox couple. Electrochemical quartz crystal microbalance results show that more amounts of electroactive anionic complexes partitioned into DDAB coating than those doped into PDDAC coating from the same doping solution. Peak potentials of hybrid film-bound redox couples showed a negative shift compared to those at bare electrode and this shift was more pronounced in the case of DDAB. Finally, the advantages of hybrid coatings in electrocatalysis are demonstrated with sulfur oxoanions.

Electrocatalytic Properties of Electrodes which are Functionalized with Composite Films of f-MWCNTs Incorporated with Poly(neutral red)

A conductive composite film which is composed of functionalized multiwalled carbon nanotubes with poly(neutral red) (PNR) has been synthesized using the potentiostatic method. It is produced on glassy carbon, gold and transparent semiconductor tin oxide electrodes for electrocatalysis, electrochemical quartz crystal microbalance (EQCM), and scanning electron microscopy (SEM) studies. The incorporation of PNR on the is revealed by the EQCM technique and their morphology has been studied using the SEM method. The composite film exhibits a promising electrocatalytic activity toward biochemical compounds (in pH 6.0), halogen oxyanions (pH 1.0), and sulfur oxoanions (pH 6.0). Among these, the biochemical compounds which have been studied are (−)-epigallocatechin gallate, nicotinamide adenine dinucleotide, epinephrine, and serotonin. The sulfur oxoanions are , , , and . The presence of amplifies the electrocatalytic peak current and the film background current. The results confirm also that the enhance electrocatalytic oxidation and PNR enhances reduction. Further, the halogen oxyanions electrocatalytic reduction potential for , and no peak for clearly reveal that the activity is dependent on its electronegativity, which is one of the basic science properties.

Electrochemical Preparation of Poly(acriflavine) Film‐Modified Electrode and Its Electrolcatalytic Properties Towards NADH, Nitrite and Sulfur Oxoanions

AbstractElectrochemical polymerization of acriflavine (AF) was carried out onto glassy carbon electrodes (GCE) from the aqueous buffer solution containing 1.5×10−3 M AF monomer (pH 3.5) which produced a thin electrochemically active film. This is noted as poly(AF) film modified electrodes (PAF/GCE). This modified electrode was shown a stable reversible redox couple centered at +0.22 V in pH 3.5 buffer solutions. PAF/GCE was found to be more stable in acidic solutions and its formal potential was found to be pH dependent with a slope close to −60 mV/pH. The electrochemical deposition kinetics of poly(AF) onto gold coated quartz crystal was studied by using electrochemical quartz crystal microbalance (EQCM) combined with cyclic voltammetry (CV). PAF/GCE was found be good mediator for electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) in pH 5 buffer solutions. The electrocatalytic oxidation of SO$\rm{ _3^{2 - } }$ and electrocatalytic reduction of NO$\rm{ _2^ - }$, SO$\rm{ _5^{2 - } }$ and S2O$\rm{ _8^{2 - } }$ were carried out at PAF/GCE electrode in acidic aqueous solutions. The electrocatalytic oxidation of NADH was also investigated by using amperometric method.

Preparation and electrocatalytic properties of osmium oxide/hexacyanoruthenate films modified electrodes for catecholamines and sulfur oxoanions

Abstract Osmium oxide/hexacyanoruthenate films have been prepared using repeated cyclic voltammetry, and their electrocatalytic properties have been investigated. The osmium oxide/hexacyanoruthenate films were deposited directly from mixed Os3+ and Ru ( CN ) 6 4 - ions in a pH 2 solution. Electrochemical quartz crystal microbalance (EQCM), cyclic voltammetry, and UV–visible spectroscopy were used to study the growth mechanism of the osmium oxide/hexacyanoruthenate films. The EQCM data indicated that the redox process was confined to the immobilized osmium oxide/hexacyanoruthenate film, which showed a single redox couple with a formal proton-dependent potential at 0.35 V. The electrocatalytic oxidation of dopamine, epinephrine, and norepinephrine and S 2 O 3 2 - and SO 5 2 - by the osmium oxide/hexacyanoruthenate films was studied. The electrocatalytic reactions of the osmium oxide/hexacyanoruthenate films were also investigated by the rotating ring-disk electrode method.

Preparation and characterization of CePtCl6 films and their electrocatalytic properties with NAD+, l-cystine and sulfur oxoanions

Cerium hexachloroplatinate (CePtCl6) films have been prepared by mixing Ce3+ and PtCl62- ions in an aqueous KCl pH 3.0 solutions. The deposition of a cerium hexachloroplatinate film occurred when PtIVCl62- was electrochemically reduced to PtIICl64- and Ce4+ to Ce3+. The electrochemical quartz crystal microbalance (EQCM), UV–visible absorption spectroscopy, stopped-flow kinetic method, amperometry and cyclic voltammetry techniques were used to study the deposition and growth mechanism of the cerium hexachloroplatinate films. The electrochemical properties of this film indicated a single redox process which was corresponding to reduction of PtIVCl62- to PtIICl64- immobilized cerium hexachloroplatinate films. In the aqueous KCl pH 3.0 solution, PtIVCl62- was electrochemically reduced to PtIICl64- and the Ce3+ reacted with the film to maintain the electrochemical neutrality. The reversibility of the cerium (III) hexachloroplatinate film during cycling and with changing frequency has been found good, and the Ce3+ ion exchange obviously occurred in the redox couples. The electrocatalytic reduction properties of (β-nicotinamide adenine dinucleotide) NAD+, l-cystine, SO52- and S4O62- were determined using the cerium hexachloroplatinate films. The electrocatalysis and electrochemical reactions of NAD+ with cerium hexachloroplatinate film were measured by amperometry using the rotating disk electrodes.

Micromolar determination of sulfur oxoanions and sulfide at a renewable sol–gel carbon ceramic electrode modified with nickel powder

The sol–gel technique was used to fabricate nickel powder carbon composite electrode (CCE). The nickel powder successfully used to deposit NiO x thin film on conductive carbon ceramic electrode for large surface area catalytic application. Repetitive cycling in potential range −0.2 to 1.0 V was used to form of a thin nickel oxide film on the surface carbon composite electrode. The thin film exhibits an excellent electro-catalytic activity for oxidation of SO 3 2−, S 2O 4 2−, S 2O 3 2−, S 4O 6 2− and S 2− in alkaline pH range 10–14. Optimum pH values for detection of all sulfur derivatives is 13 and catalytic rate constants are in range 2.4 × 10 3–8.9 × 10 3 M −1 s −1. The hydrodynamic amperometry at rotating modified CCE at constant potential versus reference electrode was used for detection of sulfur derivatives. Under optimized conditions the calibration plots are linear in the concentration range 10 μM–15 mM and detection limit 1.2–34 μM and 0.53–7.58 nA/μM (sensitivity) for electrode surface area 0.0314 cm 2. The nickel powder doped modified carbon ceramic electrode shows good reproducibility, a short response time (2.0 s), remarkable long term stability, less expense, simplicity of preparation, good chemical and mechanical stability, and especially good surface renewability by simple mechanical polishing and repetitive potential cycling. This sensor can be used into the design of a simple and cheap chromatographic amperometry detector for analysis of sulfur derivatives.

The electrochemical properties of NADH and NAD + and their electrocatalytic reactions with tin hexachloroplatinate films

Tin hexachloroplatinate (SnPtCl 6) films have been prepared by mixing Sn 2+ and PtCl 6 2− ions in an aqueous KCl solution. An electrochemical quartz crystal microbalance (EQCM), a rotating ring-disk electrode, UV–Vis absorption spectroscopy, and cyclic voltammetry were used to study the deposition and growth mechanism of the tin hexachloroplatinate films. The electrochemical properties of the films indicate that the redox processes were confined to the immobilized tin hexachloroplatinate films. Deposition of a tin hexachloroplatinate film occurs when Pt IVCl 6 2− is electrochemically reduced to Pt IICl 6 4−, or when Sn 2+ reacts with Pt IVCl 6 2− and Pt IICl 6 4− ions in an aqueous KCl solution. The electrocatalytic reduction of NAD + and of sulfur oxoanions (S 4O 6 2−, S 2O 8 2−, and SO 5 2−) was studied using tin hexachloroplatinate films. The electrochemical reactions of NAD + and NADH were investigated using cyclic voltammetry and the rotating ring-disk electrode method.

Initial oxidation of fractured surfaces of FeS2(1 0 0) by molecular oxygen, water vapor, and air

Synchrotron-based Fe 2p, S 2p, and O 1s photoemission spectroscopy was used to study the initial stages of oxidation of UHV-fractured (1 0 0) surfaces of pyrite by molecular oxygen, water vapor, and ambient air. Molecular oxygen alone reacts measurably with pyrite surface to yield new oxidized species only for high doses of ∼10 7 L, while reaction with water vapor does not take place even at doses as high as 10 10 L. In both cases, however, monosulfide defects on fractured pyrite surfaces are eradicated by the dosing with O 2 and H 2 O. For high O 2 partial pressures, the extent of reaction with oxygen is comparable to that produced by equivalent air exposures, indicating that the presence of water is not strictly necessary for initial oxidation of pyrite(1 0 0) to occur in our experiments. The formation of several intermediate oxidation products, including sulfur oxoanions and zero-valent sulfur, are quantified by spectral decomposition as a function of dose, and the mode of their formation is discussed.

Initial oxidation of fractured surfaces of FeS 2( [formula omitted]) by molecular oxygen, water vapor, and air

Synchrotron-based Fe 2p, S 2p, and O 1s photoemission spectroscopy was used to study the initial stages of oxidation of UHV-fractured (1 0 0) surfaces of pyrite by molecular oxygen, water vapor, and ambient air. Molecular oxygen alone reacts measurably with pyrite surface to yield new oxidized species only for high doses of ∼10 7 L, while reaction with water vapor does not take place even at doses as high as 10 10 L. In both cases, however, monosulfide defects on fractured pyrite surfaces are eradicated by the dosing with O 2 and H 2O. For high O 2 partial pressures, the extent of reaction with oxygen is comparable to that produced by equivalent air exposures, indicating that the presence of water is not strictly necessary for initial oxidation of pyrite(1 0 0) to occur in our experiments. The formation of several intermediate oxidation products, including sulfur oxoanions and zero-valent sulfur, are quantified by spectral decomposition as a function of dose, and the mode of their formation is discussed.

Radiation-Stimulated Oxidation Reactions of Oxo Anions in Aqueous Solutions

The common features of oxidation processes for inorganic oxo anions under the action of ionizing radiation are considered. The radiation-stimulated oxidation reactions of lower nitrogen, phosphorus, arsenic, and sulfur oxo anions occur via a chain mechanism. The kinetics of these processes can be explained in terms of the peroxide oxidation theory. A correlation between the kinetic and thermodynamic characteristics of the assumed rate-determining step is observed, thus proving the uniformity of oxidation mechanisms. Ways to use the processes of interest in practice are proposed.

Renewable-surface sol-gel derived carbon ceramic electrode fabricated by [Ru(bpy)(tpy)Cl]PF6 and its application as an amperometric sensor for sulfide and sulfur oxoanions.

A highly sensitive and fast responding sensor for the determination of thiosulfate, sulfite, sulfide and dithionite is described. It consists of a chemically modified carbon ceramic composite electrode (CCE) containing [Ru(bpy)(tpy)Cl]PF6 complex that was constructed by the sol-gel technique. A reversible redox couple of Ru(II)/Ru(III) was observed as a solute in acetonitrile solution and as a component of carbon based conducting composite electrode. Electrochemical behavior and stability of modified CCE were investigated by cyclic voltametry, the apparent electron transfer rate constant (kappa(S)) and transfer coefficient (a) were determined by cyclic voltametry which were about 28 s(-1) and 0.43 respectively. Electrocatalytic oxidation of S(2-), SO3(2-), S2O4(2-) and S2O3(2-) were effective at the modified electrode at significantly reduced overpotentials and in the pH range 1-11. Optimum pH values for amperometric detection of thiosulfate, dithionite, sulfide and sulfite are 7, 9, 2 and 2. Under the optimized conditions the calibration curves are linear in the concentration ranges 1-500, 3-80, 2-90 and 1-100 microM for S2O3(2-), SO3(2-), S2- and S2O4(2-) determination. The detection limit (signal to noise is 3) and sensitivity are 0.5 and 12, 2.8 and 6, 1.6 and 8, and 0.65 microM and 80 nA microM(-1) for thiosulfate, sulfite, sulfide and dithionite detection. The modified carbon ceramic electrode doped with Ru-complex shows good reproducibility, a short response time (t < 2 s), remarkable long term stability (> 6 month) and especially good surface renewability by simple mechanical polishing (RSD for eight successive polishing is 2%). The advantages of this sulfur compound amperometric detector based on ruthenium doped CCE are high sensitivity, inherent stability at a broader pH range, excellent catalytic activity, less expense and simplicity of preparation in comparison with recently published papers. This sensor can be used as a chromatographic detector for analysis of sulfur derivatives.

The photocatalytic autoxidation of sulfur oxoanions by water-soluble porphyrin complexes

The photocatalytic autoxidation of S 4O 6 2− and S 2O 3 2− by water-soluble porphyrin complexes Fe(2-TMPyP), Mn(4-TMPyP), and Co(2-TMPyP) were compared under illumination with a 419 nm visible light in oxygen-saturated aqueous solutions at room temperature. The process involves S 2O 3 2− as an intermediate product and SO 4 2− is the final oxidation product. The trend in photocatalytic activity of the porphyrin complexes for S 4O 6 2− oxidation is Co(2-TMPyP)>Mn(4-TMPyP)>Fe(2-TMPyP). For S 2O 3 2− oxidation, the trend is Co(2-TMPyP)>Fe(2-TMPyP)>Mn(4-TMPyP).

Use and Removal of Sulfite by Conversion to Sulfate in the Preservation of Salt-Free Cucumbers

Cucumbers (Cucumis sativus) were microbiologically stable in cover liquid containing 300 ppm of added sodium metabisulfite (calculated as SO2), 20mM calcium chloride, and HCl to give an equilibrated pH of 3.5. The sulfur(IV) oxoanions could be easily removed to nondetectable levels (<3 ppm) by addition of an equimolar amount of hydrogen peroxide, which rapidly converted S(IV) primarily to sulfate ions. When sulfur(IV) oxoanions were removed from stored fresh cucumbers, 85% of the added metabisulfite could be accounted for by formation of sulfate ions. If cucumbers were heated before addition and removal of sulfur(IV) oxoanions, 96% of that added was converted to sulfate by hydrogen peroxide. Preservation of cucumbers in this way does not require fermentation, so addition of salt is not needed to select for lactic acid bacteria.