Sulfite Anion Research Articles

Reduction of l-methionine selenoxide to seleno- l-methionine by endogenous thiols, ascorbic acid, or methimazole

Seleno- l-methionine (SeMet) can be oxidized to l-methionine selenoxide (MetSeO) by flavin-containing monooxygenase 3 (FMO3) and rat liver microsomes in the presence of NADPH. MetSeO can be reduced by GSH to yield SeMet and GSSG. In the present study, the potential reduction of MetSeO to SeMet by other cellular components and antioxidants was investigated. Besides GSH, other thiols ( l-cysteine, or N-acetyl- l-cysteine) and antioxidants (ascorbic acid and methimazole) also reduced MetSeO to SeMet. This reduction is unique to MetSeO since methionine sulfoxide was not reduced to methionine under similar conditions. The MetSeO reduction by thiols was instaneous and much faster than the reduction by ascorbic acid or methimazole. However, only one molar equivalent of ascorbic acid or methimazole was needed to complete the reduction, as opposed to two molar equivalents of thiols. Whereas the disulfides produced by the reactions of MetSeO with thiols are chemically stable, methimazole disulfide readily decomposed at pH 7.4, 37 °C to yield methimazole, methimazole-sulfenic acid, methimazole sulfinic acid, methimazole S-sulfonate, 1-methylimidazole (MI) and sulfite anion. Collectively, the results demonstrate reduction of MetSeO to SeMet by multiple endogenous thiols, ascorbic acid, and methimazole. Thus, oxidation of SeMet to MetSeO may result in depletion of endogenous thiols and antioxidant molecules. Furthermore, the novel reduction of MetSeO by methimazole provides clear evidence that methimazole should not be used as an alternative FMO substrate when studying FMO-mediated oxidation of SeMet.

New Organically Templated Ln(III)−Cu(I) Heteronuclear Sulfite Bromides

Two novel organically templated 3d−4f mixed metal sulfites, namely, [H2pip][Ln4Cu4(SO3)8Br2(H2O)6] (Ln = Eu, 1; Gd, 2; pip = piperazine) have been synthesized and structurally characterized. Compounds 1 and 2 are isostructural and feature a 2D inorganic anion layer of [Ln4Cu4(SO3)8Br2(H2O)6]2−. Among two unique lanthanide(III) ions in the asymmetric unit, one is eight coordinated by seven oxygen atoms from six sulfite groups (five of them in unidentate fashion and one in bidentate chelating fashion) and an aqua ligand; the other one is eight-coordinated by six oxygen atoms from five sulfite groups (four of them in unidentate fashion and one in bidentate chelating fashion) and two aqua ligands. Cu(1) is four coordinated by two S and one O from three SO32− anions, as well as a Br anion, and Cu(2) is three coordinated by one S and one O atom from two SO32− anions, as well as a Br anion. The Ln(III) ions and Cu(I) ions are interconnected by sulfite anions and Br anions to form a layered structure. The piperazine molecules are located at the interlayer spaces. Magnetic properties for both compounds were also studied.

Cadmium sulfite hexahydrate revisited

The present structural revision of the title compound, tetra­cadmium tetra­sulfite hexa­hydrate, [Cd4(SO3)4(H2O)5]·H2O, is a low-temperature upgrade (T = 100 K and R = 0.017) of the original room-temperature structure reported by Kiers & Vos [Cryst. Struct. Commun. (1978). 7, 399–403; T = 293 K and R = 0.080). The compound is a three-dimensional polymer with four independent cadmium centres, four sulfite anions and six water mol­ecules, five of them coordinated to two cadmium centres and the remaining one an unbound solvent mol­ecule which completes the asymmetric unit. There are two types of cadmium environment: CdO8 (through four chelating sulfite ligands) and CdO6 (by way of six monocoordinated ligands). The former groups form planar arrays [parallel to (001) and separated by half a unit cell translation along c], made up of chains running along [110] and [10], respectively. These chains are, in turn, inter­connected both in an intra­planar as well as in an inter­planar fashion by the latter CdO6 polyhedra into a tight three-dimensional framework. There is, in addition, an extensive network of hydrogen bonds, in which all 12 water H atoms act as donors and eight O atoms from all four sulfite groups and two water mol­ecules act as acceptors.

Synthesis, Structure, and Physical Properties of a New Anions-Controlled Cd(II)-Guanazole (3,5-Diamino-1,2,4-triazole) Hybrid Family

Nine members of a new anions-controlled Cd(II)-guanazole (3,5-diamino-1,2,4-triazole=Hdatrz) hybrid family, that is, [Cd3(datrz)6(H2O)2] (1), [Cd3(datrz)4F2] (2), [Cd5(datrz)4Cl4(OH)2] (3), [Cd5(datrz)4Br4(OH)2] (4), [Cd3(datrz)2(SO3)2].(H2O) (5), [Cd3(datrz)2(O2CMe)4] (6), [Cd(datrz)(O2CEt)] (7), [Cd(Hdatrz)(O2CtBu)2] (8), and [Cd(Hdatrz)2(H2Edta)] (9) have been synthesized by exploiting hydrothermal reactions of guanazole with suitable cadmium salts under appropriate reaction conditions. With effective control of inorganic or organic anions, the coordination diversity of the guanazole ligand in 1-9 manifests an unprecedented enrichment with five bridging modes varying from bidentate to quadridentate, two of which are first reported. Compound 1 is the first reported three-dimensional chiral complex constructed from the guanazole ligand which adopts a novel N1, N2, amino N-bridging mode. Halogen anions F-, Cl-, and Br- controlled compounds 2-4 are all three-dimensional, with their guanazole ligands possessing another novel quadridentate bridging mode. Sulfite anions controlled compound 5 displays a three-dimensional network with peculiar cage-like hexnuclear cadmium clusters. As for organic anions, low dimensional structures have been found for alkylcarboxylate anions MeCO2-, EtCO2-, and tBuCO2- controlled compounds 6, 7, and 8 (two-dimensional) and for H2Edta2- controlled compound 9 (zero-dimensional), and their guanazole ligands manifest low coordination numbers as well. These hybrid materials also present interesting structure-induced physical properties. The chiral compound 1 exhibits the second-order nonlinear optical properties at room temperature. Compounds 2-9 except 6 all exhibit photoluminescence of blue fluorescent emissions in the solid state at ambient temperature, which may be assigned to the intraligand pi-pi* transitions. Some structure related red or blue emission shifts have been investigated. Thermal studies show that most compounds of this study possess a high thermal stability.

Reversible electron-transfer reactions within a nanoscale metal oxide cage mediated by metallic substrates

Transition metal oxides exhibit a rich collection of electronic properties and have many practical applications in areas such as catalysis and ultra-high-density magnetic data storage. Therefore the development of switchable molecular transition metal oxides has potential for the engineering of single-molecule devices and nanoscale electronics. At present, the electronic properties of transition metal oxides can only be tailored through the irreversible introduction of dopant ions, modifying the electronic structure by either injecting electrons or core holes. Here we show that a molybdenum(VI) oxide 'polyoxometalate' molecular nanocluster containing two embedded redox agents is activated by a metallic surface and can reversibly interconvert between two electronic states. Upon thermal activation two electrons are ejected from the active sulphite anions and delocalized over the metal oxide cluster cage, switching it from a fully oxidized state to a two-electron reduced state along with the concomitant formation of an S-S bonding interaction between the two sulphur centres inside the cluster shell.

New Organically Templated Copper(I) Sulfites: the Role of Sulfite Anion as Both Soft and Hard Ligand

Two new organically templated layered copper(I) sulfites, namely, {H2pip}{Cu3(CN)3(SO3)} (1) and {H2pip}{NaCu2(SO3)2Br(H2O)}.2H2O (2) (pip = piperazine), have been synthesized by hydrothermal reactions of copper(I) cyanide or copper(I) bromide with NaHSO3 and piperazine. Both compounds exhibit a layered structure. The 2D layer of {Cu3(CN)3(SO3)}2- in 1 is composed of 1D chains of copper(I) cyanide interconnected by sulfite anions via both Cu-S and Cu-O bonds, whereas the 2D layer of {NaCu2(SO3)2Br}2- in 2 is formed by 1D chains of copper(I) bromide and 1D sodium(I) aqua chains that are interconnected by sulfite anions via Na-O, Cu-S, and Cu-O bonds. Chemical bonding in 1 and 2 has been also investigated by theoretical calculations based on DFT methods.

Amine-Controlled Assembly of Metal−Sulfite Architecture from 1D Chains to 3D Framework

Whereas open-framework materials have been made in a variety of chemical compositions, few are known in which 3-connected SO3(2)- anions serve as basic building units. Here, we report four new metal-sulfite polymeric structures, (ZnSO3)Py (1, py = pyridine), (ZnSO3)2(2,2'-bipy)H2O (2, 2,2'-bipy = 2,2'-bipyridine), (ZnSO3)2(TMDPy) (3, TMDPy = 4,4'-trimethylenedipyridine), and (MnSO3)2en (4, en = ethylenediamine) that have been synthesized hydrothermally and structurally characterized. In these compounds, low-dimensional 1D and 2D inorganic subunits are assembled into higher 2D or 3D covalent frameworks by organic ligands. In addition to the structure-directing effect of organic ligands, the flexible coordination chemistry of Zn2+ and SO3(2)- also contributes to the observed structural diversity. In compounds 1-3, Zn2+ sites alternate with trigonal pyramidal SO3(2)- anions to form three types of [ZnSO3]n chains, whereas in compound 4, a 2D-corrugated [MnSO3]n layer is present. Compound 1 features a rail-like chain with pendant pyridine rings. The pi-pi interaction between 2,2'-bipy ligands is found between adjacent chains in compound 2, resulting in 2D sheets that are further stacked through interlayer hydrogen bonds. Compound 3 exhibits a very interesting inorganic [(ZnSO3)2]n chain constructed from two chairlike subunits, and such chains are bridged by TMDPy ligands into a 2D sheet. In compound 4, side-by-side helical chains permeate through 2D-corrugated [MnSO3]n layers, which are pillared by neutral ethylenediamine molecules into a 3D framework that can be topologically represented as a (3,6)-connected net. The results presented here illustrate the rich structural chemistry of metal-sulfites and the potential of sulfite anions as a unique structural building block for the construction of novel open-framework materials, in particular, those containing polymeric inorganic subunits that may have interesting physical properties such as low-dimensional magnetism or electronic properties.

Polyoxomolybdenum(V/VI)−Sulfite Compounds: Synthesis, Structural, and Physical Studies

Reaction of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) in the mixed-solvent system H(2)O/CH(3)CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH(4))(4)[Mo(4)(VI)SO(16)] x H(2)O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH(4))(4)[Mo(5)(VI)S(2)O(21)] x 3H(2)O (2). Compound {(H(2)bipy)(2)[Mo(5)(VI)S(2)O(21)] x H(2)O}(x) (3) was obtained from the reaction of aqueous acidic solution of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) (pH = 2.5) and 4,4'-bipyridine (4,4'-bipy). The mixed metal/sulfite species (NH(4))(7)[Co(III)(Mo(2)(V)O(4))(NH(3))(SO(3))(6)] x 4H(2)O (4) was synthesized by reacting Na(2)Mo(VI)O(4) x 2H(2)O with CoCl(2) x 6H(2)O and (NH(4))(2)SO(3) with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing Mo(VI)O(6) octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo(4) ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo(5)(VI)S(2)O(21)](4-), and these coordinatively saturated clusters are joined by diprotonated 4,4'-H(2)bipy(2+) through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [Co(III)Mo(2)(V)SO(3)(2-)] cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d(6) octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported.

Riboflavin-sensitized photochemical radical ion chain reaction of sulfo-group substitution for halogen in halogenated hydroxynaphthalenes

It was shown that riboflavin (RF) is a sensitizer for the radical ion chain reaction of sulfo group substitution for halogen in halogenated hydroxynaphthalenes. The initaition mechanism involves the electron transfer reaction between the sulfite ion and excited riboflavin. The quantum yields of RF radical anions from the singlet and the triplet states upon excitation in an aqueous sodium sulfite solution are 0.01 and 0.15, respectively, as determined by means of flash photolysis. The principal decay reaction for RF radical anions is their recombination with sulfite radical anions in the bulk of solution at a rate constant of (3.8 ± 0.5) × 109 dm3 mol−1 s−1. The quantum yields of the riboflavin-sensitized substitution reaction increases in the presence of electron scavengers (chloranil, dinitrobenzene) and inorganic salts in the system.

Metal−Organic Frameworks from Zinc Sulfite Clusters, Chains, and Sheets: 4-Connected, (3,4)-Connected 3-D Frameworks and 2-D Arrays of Catenane-Like Interlocking Rings

Even though open-framework solids have been made in a variety of compositions such as silicates, phosphates, germanates, borates, and phosphites, few are known that are based on trigonal-pyramidal sulfite anions. We report here the first synthetic and structural studies of metal-organic framework materials in the zinc sulfite composition. It is demonstrated here that Zn2+ and SO32- can form various neutral inorganic subunits that can be 0-D clusters, 1-D chains, or 2-D sheets. These inorganic subunits of different dimensionality can subsequently be connected into extended frameworks of higher dimensionality through bifunctional ligands. In (ZnSO3)2en, infinite corrugated ZnSO3 layers are pillared by ethylenediamine (en) molecules into a 3-D network that can be classified as a (3,4)-connected net based on tetrahedral Zn nodes and trigonal-pyramidal S nodes. In (ZnSO3)pip, infinite ZnSO3 chains are cross-linked with piperazine molecules into a 3-D framework that can be classified as 4-connected net based on tetrahedral Zn nodes only. In (ZnSO3)2(TMDPy)2, (ZnSO3)2 dimers are doubly bridged by trimethylenedipyridine molecules into an infinite chain with a string of circles. Each circle along the chain is interlocked with another circle from a chain in the perpendicular direction, creating a 2-D pattern with an infinite-square array of catenane-like units.

Di-μ2-sulfito-κ8O,O′:O′,O′′-bis[(2,4,6-tri-2-pyridyl-1,3,5-triazine-κ3N2,N1,N6)cadmium(II)] octahydrate

The title compound, [Cd2(SO3)2(C18H12N6)2].8H2O, is a dimer built up around a symmetry center, where the sulfite anion displays a so far unreported coordination mode in metal-organic complexes; the anion binds as a mu2-sulfite-kappa4O,O':O',O'' ligand to two symmetry-related seven-coordinate Cd(II) cations, binding through its three O atoms by way of two chelate bites with an O atom in common, which acts as a bridge. The cation coordination is completed by a 2,4,6-tri-2-pyridyl-1,3,5-triazine ligand acting in its usual tridentate mode.

Investigation on Capacitance Mechanisms of Fe3O4 Electrochemical Capacitors

The capacitance mechanisms of magnetite electrochemical capacitor in , , and KOH aqueous solutions have been investigated by electrochemical quartz-crystal microbalance analysis, along with cyclic voltammetry and X-ray photoelectron spectroscopy. The oxide thin-film electrode was prepared by an electroplating method, and exhibits a capacitance of , 25, and in , , and , respectively. Strong specific adsorption of the anion species was evidenced in all solutions. Experimental results indicate that, in , the capacitive current of magnetite electrode originates from the combination of electric double-layer capacitance (EDLC) and the pseudocapacitance that involves successive reduction of the specifically adsorbed sulfite anions, from through, e.g., , and vice versa. In , the current is due entirely to EDLC. Furthermore, due to the specific adsorption behavior, magnetite exhibits high EDLC, , in both and solutions. The lowest capacitance of magnetite was observed in KOH, which is attributed to the formation of an insulating layer on the magnetite surface.

Combination of Sulfite Anion and Phase Transfer Catalysts for Green Cyclotrimerization of Aryl Isocyanates.

Abstract The catalytic cyclotrimerization of aryl and alkyl isocyanates by the novel combination catalysts of sulfite ion and Phase Transfer Catalysts (PTCs), as selective anionic catalysts, has been investigated. The use of phase transfer catalyst features the catalytic potency of sulfite anion and promotes the reaction in green conditions. Diverse aryl derivatives have been involved in the reaction condition giving corresponding isocyanurates in good to excellent yields. †Previous Name: Shadpour E. Mallakpour

Cover Picture: Confined Electron‐Transfer Reactions within a Molecular Metal Oxide “Trojan Horse” (Angew. Chem. Int. Ed. 22/2005)

Upon thermal stimulation the two templating sulfite anions embedded in the “Trojan Horse” polyoxometalate cluster shown in the cover picture release electron “soldiers” to the cluster's surface, turning the cluster from colorless to blue (background). The formation of the mixed‐valence cluster shell is commensurate with the oxidation of the sulfite to sulfate anions. More details about this coupled structural and electronic rearrangement are given in the Communication by L. Cronin et al. on page 3415 ff.

Confined Electron‐Transfer Reactions within a Molecular Metal Oxide “Trojan Horse”

Cores and effect: Heating the cluster [W18O56(SO3)2(H2O)2]8− causes an electron transfer from the core sulfite anions to the cluster shell resulting in a color change from colorless to dark blue (see backgrounds). The electron transfer is coupled with a structural reorganization of the cluster shell and oxidation of the sulfite to sulfate anions (see scheme).

Optimal Conditions for Masking of Sulfite Anions with Formaldehyde in Iodometric Titration of Photographic Fixing Solutions

The iodometric titration of photographic fixing solutions can be simplified by masking sulfite anions with 3% aqueous formaldehyde in a weakly acidic medium, instead of their standard masking with concentrated aqueous formaldehyde in weakly alkaline solutions.

Combination of Sulfite Anion and Phase Transfer Catalysts for Green Cyclotrimerization of Aryl Isocyanates

The catalytic cyclotrimerization of aryl and alkyl isocyanates by the novel combination catalysts of sulfite ion and Phase Transfer Catalysts (PTCs), as selective anionic catalysts, has been investigated. The use of phase transfer catalyst features the catalytic potency of sulfite anion and promotes the reaction in green conditions. Diverse aryl derivatives have been involved in the reaction condition giving corresponding isocyanurates in good to excellent yields. †Previous Name: Shadpour E. Mallakpour

Interaction of oxyanions with thioredoxin-activated chloroplast coupling factor 1

Interaction between F 1-ATPase activity stimulating oxyanions and noncatalytic sites of coupling factor CF 1 was studied. Carbonate, borate and sulfite anions were shown to inhibit tight binding of [ 14C]ATP and [ 14C]ADP to CF 1 noncatalytic sites. The demonstrated change of their inhibitory efficiency in carbonate–borate–sulfite order coincides with the previously found change in efficiency of these anions as stimulators of CF 1-ATPase activity [Biochemistry (Mosc.) 43 (1978) 1206–1211]. Inhibition of tight nucleotide binding to noncatalytic sites was accompanied by stimulation of nucleotide binding to catalytic sites. This suggests that stimulation of CF 1-ATPase activity is caused by interaction between oxyanions and noncatalytic sites. A most efficient stimulator of CF 1-ATPase activity, sulfite oxyanion, appeared to be a competitive inhibitor with respect to ATP and a partial noncompetitive inhibitor with respect to ADP. The inhibition weakened with increasing time of CF 1 incubation with sulfite and nucleotides. Sulfite is believed to inhibit fast reversible interaction between nucleotides and noncatalytic sites and to produce no effect on subsequent tight binding of nucleotides. A possible mechanism of the oxyanion-stimulating effect is discussed.

NMR and EPR studies of the reaction of nucleophilic addition of (bi)sulfite to the nitrone spin trap DMPO

AbstractThe reaction of the nitrone spin trap 5,5‐dimethylpyrroline‐N‐oxide (DMPO) with sodium (bi)sulfite in aqueous solutions was investigated using NMR and EPR techniques. Reversible nucleophilic addition of (bi)sulfite anions to the double bond of DMPO was observed, resulting in the formation of the hydroxylamine derivative 1‐hydroxy‐5,5‐dimethylpyrrolidine‐2‐sulfonic acid, with characteristic 1H and 13C NMR spectra. The reaction mechanism was suggested and corresponding equilibrium constants determined. The mild oxidation of the hydroxylamine results in the formation of an EPR‐detected spectrum identical with that for the DMPO adduct with sulfur trioxide anion radical. The latter demonstrates that a non‐radical addition reaction of (bi)sulfite with DMPO may contribute to the EPR detection of SO3−• radical. This possibility must be taken into account in spin trapping analysis of sulfite radical. Copyright © 2003 John Wiley & Sons, Ltd.

Free radical and drug oxidation products in an intensive care unit sedative: Propofol with sulfite*

Some propofol emulsion formulations contain EDTA or sodium metabisulfite to inhibit microbe growth on extrinsic contamination. EDTA is not known to react with propofol formulation components; however, sulfite has been shown to support some oxidation processes and may react with propofol. This study compared the oxidation of propofol and the formation of free radicals by electron paramagnetic resonance analysis in EDTA and sulfite propofol emulsions during a simulated intensive care unit 12-hr intravenous infusion. Controlled laboratory study. University laboratory. Propofol emulsions (3.5 mL) were dripped from spiked 50-mL vials at each hour for 12 hrs. Two propofol oxidation products, identified as propofol dimer and propofol dimer quinone, were detected in sulfite and EDTA propofol emulsions; however, sulfite propofol emulsion contained higher quantities of both compounds. After initiation of the simulated infusion, the quantities of propofol dimer and propofol dimer quinone increased in the sulfite propofol emulsion, but the lower levels in the EDTA propofol emulsion remained constant. Sulfite propofol emulsion began to visibly yellow at about 6-7 hrs. The EDTA propofol emulsion remained white at all times. The absorbance spectra of the propofol dimer and propofol dimer quinone extracted from sulfite propofol emulsion showed that propofol dimer did not absorb in the visible spectrum, but the propofol dimer quinone had an absorbance peak at 421 nm, causing it to appear yellow. Electron paramagnetic resonance analysis of the propofol emulsion containing metabisulfite revealed that the sulfite propofol emulsion yielded a strong free radical signal consistent with the formation of the sulfite anion radical (SO3*-). The EDTA propofol emulsion yielded no free radical signal above background. Sulfite from the metabisulfite additive in propofol emulsion creates an oxidative environment when these emulsions are exposed to air during a simulated intravenous infusion. This oxidation results in propofol dimerization and emulsion yellowing, the latter of which is caused by the formation of propofol dimer quinone. These processes can be attributed to the rapid formation of the reactive sulfite free radical.