Showing papers on "Iodide published in 2002"

Substituted polypyridine complexes of cobalt(II/III) as efficient electron-transfer mediators in dye-sensitized solar cells.

Abstract: A number of cobalt complexes of substituted polypyridine ligands were synthesized and investigated as possible alternatives to the volatile and corrosive iodide/triiodide redox couple commonly used as an electron-transfer mediator in dye-sensitized solar cells (DSSCs). The extinction coefficients in the visible spectrum are on the order of 10(2) M(-1) cm(-1) for the majority of these complexes, diminishing competition with the light-harvesting dye. Cyclic voltammetric studies revealed a dramatic surface dependence of the heterogeneous electron-transfer rate, which is surprisingly different for gold, carbon, and platinum electrodes. DSSCs were assembled using a mediator that consisted of a mixture of Co(II) and Co(III) complexes in a 10:1 ratio. DSSCs containing these mediators were used to characterize incident photon-to-current conversion efficiency and photoelectrochemical responses. The best performing of these mediators were identified and subjected to further study. As suggested by electrochemical results, gold and carbon are superior cathode materials to platinum, and no evidence of corrosion on any cathode material was observed. Addition of lithium salts to the mediator solution resulted in a dramatic improvement in cell performance. The observed Li(+) effect is explained in terms of the recombination of injected electrons in the photoanode with the oxidized mediator. The best mediator, based on tris(4,4'-di-tert-butyl-2,2'-dipyridyl)cobalt(II/III) perchlorate, resulted in DSSCs exhibiting efficiencies within 80% of that of a comparable iodide/triiodide-mediated DSSC. Due to the commercial availability of the ligand and the simplicity with which the complex can be made, this new mediator represents a nonvolatile, noncorrosive, and practical alternative as an efficient electron-transfer mediator in DSSCs.

The Copper-Catalyzed N-Arylation of Indoles

Abstract: A general method for the N-arylation of indoles using catalysts derived from CuI and trans-1,2-cyclohexanediamine (1a), trans-N,N'-dimethyl-1,2-cyclohexanediamine (2a), or N,N'-dimethyl-ethylenediamine (3) is reported. N-Arylindoles can be produced in high yield from the coupling of an aryl iodide or aryl bromide with a variety of indoles.

Iodide Electron Transfer Kinetics in Dye-Sensitized Nanocrystalline TiO2 Films

Abstract: Electron transfer kinetics plays a key role in determining the energy conversion efficiency of dye-sensitized photoelectrochemical solar cells. Photoinduced charge separation in such cells results in oxidation of the sensitizer dye. The resulting dye cation may be rereduced by recombination with injected electrons or by electron transfer from iodide ions in the redox electrolyte, often referred to as the regeneration reaction. In this paper, we employ transient absorption spectroscopy to investigate the kinetic competition between these two pathways in Ru(dcbpy)2(NCS)2-sensitized nanocrystalline film TiO2 electrodes immersed in a propylene carbonate electrolyte. The experiments monitored both the dye cation decay kinetics and the yield of product species, assigned to I2- radicals generated by electron transfer from iodide ions to the dye cation. The kinetic competition between the recombination and the regeneration processes is found to be dependent upon both the iodide concentration and the electrical bi...

Nucleophilicity in ionic liquids. 2.(1) Cation effects on halide nucleophilicity in a series of bis(trifluoromethylsulfonyl)imide ionic liquids.

Abstract: In this work, the nucleophilicities of chloride, bromide, and iodide have been determined in the ionic liquids [bmim][N(Tf)2], [bm2im][N(Tf)2], and [bmpy][N(Tf)2] (where bmim = 1-butyl-3-methylimidazolium, bm2im = 1-butyl-2,3-dimethylimidazolium, bmpy = 1-butyl-1-methylpyrrolidinium, and N(Tf)2 = bis(trifluoromethylsulfonyl)imide). It was found that in the [bmim]+ ionic liquid, chloride was the least nucleophilic halide, but that changing the cation of the ionic liquid affected the relative nucleophilicities of the halides. The activation parameters ΔH⧧, ΔS⧧, and ΔG⧧ have been estimated for the reaction of chloride in each ionic liquid, and compared to a similar reaction in dichloromethane, where these parameters were found for reaction by both the free ion and the ion pair.

Removal and sequestration of iodide using silver-impregnated activated carbon.

Abstract: Two silver-impregnated activated carbons (SIACs) (0.05 and 1.05 wt % silver) and their virgin (i.e., unimpregnated) granular activated carbon (GAC) precursors were investigated for their ability to remove and sequester iodide from aqueous solutions in a series of batch sorption and leaching experiments. Silver content, total iodide concentration, and pH were the factors controlling the removal mechanisms of iodide. Iodide uptake increased with decreasing pH for both SIACs and their virgin GACs. The 0.05% SIAC behaved similarly to its virgin GAC in all experimental conditions because of its low silver content. At pH values of 7 and 8 there was a marked increased in iodide removal for the 1.05% SIAC over that of its virgin GAC, while their performances were similar at a pH of 5. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analyses prior to reaction with iodide showed the presence of metallic silver agglomerates on the 1.05% SIAC surface. After the reaction, elemental mapping with EDX showed the formation of silver iodide agglomerates. Oxidation of metallic silver was observed in the presence of oxygen, and the carbon surface appears to catalyze this reaction. When the molar ratio of silver to iodide was greater than 1 (i.e., M(Ag,SIAC) > M(I,TOTAL)), precipitation of silver iodide was the dominant removal mechanism. However, unreacted silver leached into solution with decreasing pH while iodide leaching did not occur. When M(Ag,SIAC) < M(I,TOTAL), silver iodide precipitation occurred until all available silver had reacted, and additional iodide was removed from solution by pH-dependent adsorption to the GAC. Under this condition, silver leaching did not occur while iodide leaching increased with increasing pH.

Syntheses of 1-Alkyl-1,2,4-triazoles and the Formation of Quaternary 1-Alkyl-4-polyfluoroalkyl-1,2,4-triazolium Salts Leading to Ionic Liquids

Abstract: 1,2,4-Triazole was alkylated (alkyl = methyl, butyl, heptyl, decyl) at N-1 in >90% isolated yields. The resulting 1-alkyl triazoles were quaternized at N-4 in >98% isolated yields using fluorinated alkyl halides with >98% isolated yields, under neat reaction conditions at 100−120 °C to form N1-CH3-N4-(CH2)2CmF2m + 1-triazolium (Taz) iodide (m = 1, 6), N1-C4H9-N4-(CH2)2CmF2m + 1-Taz iodide (m = 1, 4, 6), N1-C7H15-N4-(CH2)2CmF2m + 1-Taz iodide (m = 1, 4, 6), N1-C10H21-N4-(CH2)2CmF2m + 1-Taz iodide (m = 1, 4), and N1-CnH2n + 1-N4-(CH2)2F-Taz bromide (n = 4, 7, 10). Single-crystal X-ray analyses confirmed the structure of [1-CH3-4-CH2CH2CF3-Taz]+I-. It crystallized in the orthorhombic space group Pccn, and the unit cell dimensions were a = 13.8289(9) A, b = 17.3603(11) A, c = 9.0587(6) A (α = β = γ = 90°). Metathesis of these polyfluoroalkyl-substituted triazolium halides with other salts led to the formation of quaternary compounds, some of which comprise ionic liquids, namely, [R(Rf)-Taz]+Y- (Y = NTf2, BF4,...

Reaction of lactoperoxidase compound I with halides and thiocyanate.

Abstract: Lactoperoxidase (LPO) is found in mucosal surfaces and exocrine secretions, including milk, tears, and saliva, and has physiological significance in antimicrobial defense which involves (pseudo-) halide oxidation. This study for the first time presents transient kinetic measurements of the reactivity of its competent redox intermediate compound I with halides and thiocyanate, using the sequential stopped-flow technique. Compound I was produced with either H2O2 [(1.1 ± 0.1) × 107 M-1 s-1] or hypochlorous acid [(3.2 ± 0.1) × 107 M-1 s-1]. At pH 7 and 15 °C, the two-electron reduction of compound I to native LPO by bromide and iodide has a second-order rate constant of (4.1 ± 0.1) × 104 M-1 s-1 and (1.2 ± 0.04) × 108 M-1 s-1, respectively. With thiocyanate the reaction is extremely fast (2.0 × 108 M-1 s-1), whereas chloride cannot function as electron donor. The results are discussed with respect to known kinetic data of homologous mammalian peroxidases and to the physiological role of LPO in antimicrobial d...

Leisingera methylohalidivorans gen. nov., sp. nov., a marine methylotroph that grows on methyl bromide.

Abstract: A marine methylotroph, designated strain MB2T, was isolated for its ability to grow on methyl bromide as a sole carbon and energy source. Methyl chloride and methyl iodide also supported growth, as did methionine and glycine betaine. A limited amount of growth was observed with dimethyl sulfide. Growth was also noted with unidentified components of the complex media marine broth 2216, yeast extract and Casamino acids. No growth was observed on methylated amines, methanol, formate, acetate, glucose or a variety of other substrates. Growth on methyl bromide and methyl iodide resulted in their oxidation to CO2 with stoichiometric release of bromide and iodide, respectively. Strain MB2T exhibited growth optima at NaCl and Mg2+ concentrations similar to that of seawater. Phylogenetic analysis of the 16S rDNA sequence placed this strain in the alpha-Proteobacteria in proximity to the genera Ruegeria and Roseobacter. It is proposed that strain MB2T (= ATCC BAA-92T = DSM 14336T) be designated Leisingera methylohalidivorans gen. nov., sp. nov..

Rapid, Specific Determination of Iodine and Iodide by Combined Solid-Phase Extraction/Diffuse Reflectance Spectroscopy

Abstract: A new, rapid methodology for trace analysis using solid-phase extraction is described The two-step methodology is based on the concentration of an analyte onto a membrane disk and on the determination by diffuse reflectance spectroscopy of the amount of analyte extracted on the disk surface This method, which is adaptable to a wide range of analytes, has been used for monitoring ppm levels of iodine and iodide in spacecraft water Iodine is used as a biocide in spacecraft water For these determinations, a water sample is passed through a membrane disk by means of a 10-mL syringe that is attached to a disk holder assembly The disk, which is a polystyrene-divinylbenzene composite, is impregnated with poly(vinylpyrrolidone) (PVP), which exhaustively concentrates iodine as a yellow iodine-PVP complex The amount of concentrated iodine is then determined in only 2 s by using a hand-held diffuse reflectance spectrometer by comparing the result with a calibration curve based on the Kubelka-Munk function The same general procedure can be used to determine iodide levels after its facile and exhaustive oxidation to iodine by peroxymonosulfate (ie, Oxone reagent) For samples containing both analytes, a two-step procedure can be used in which the iodide concentration is calculated from the difference in iodine levels before and after treatment of the sample with peroxymonosulfate With this methodology, iodine and iodide levels in the 01-50 ppm range can be determined with a total workup time of approximately 60 s with a RSD of approximately 6%

The transformation of iodate to iodide in marine phytoplankton cultures

Abstract: Six species of phytoplankton, representing 6 major phylogenetic groups (2 oceanic species: a cyanobacteria, Synechococcus sp., and a coccolithophorid, Emiliania huxleyi; and 4 coastal species: a prasinophyte, Tetraselmis sp., the green algae Dunaliella tertiolecta, the diatom Skele- tonema costatum and a dinoflagellate Amphidinium carterae) were tested for their ability to reduce iodate to iodide in batch cultures. They all did so to varying degrees. Thus, the reduction of iodate to iodide by phytoplankton may be a general phenomenon in the marine environment. At ambient con- centrations of iodate, the rates of depletion of iodate and appearance of iodide varied between 0.8 and 0.02, and between 0.3 and 0.02 nmol µg chlorophyll a -1 d -1 , respectively. E. huxleyi was the least efficient while A. carterae was the most efficient in the depletion of iodate. However, in the formation of iodide, while E. huxleyi was also the least efficient, Synechococcus sp. were the most efficient. The rates of appearance of iodide were noticeably slower than the corresponding rates of depletion of iodate, suggesting that part of the iodate might have been converted to forms of iodine other than iodide in these cases. The slight mismatch in the rank order of the rates of depletion of iodate and appearance of iodide between the phytoplankton species was traced to this variable and incomplete conversion of iodate to iodide. These rates were increased by up to over an order of magnitude upon enriching the culture medium with 5 and 10 µM of iodate. The depletion of iodate and appearance of iodide occurred in all growth phases. However, the rates might vary with growth phase and the patterns of these variations might be species-specific. Phytoplankton growth was not impeded even under unnaturally high concentrations of iodate implying that there is little interaction between iodine processing and the metabolic activity of cell growth.

Effect of iodide ions on corrosion inhibition of mild steel by 3,5-bis(4-methylthiophenyl)-4H-1,2,4-triazole in sulfuric acid solution

Abstract: The synergistic effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M sulfuric acid (H2SO4) in the presence of 3,5-bis(4-methylthiophenyl)-4H-1,2,4-triazole (4-MTHT) was investigated using weight loss measurements and different electrochemical techniques such as potentiostatic polarization curves and electrochemical impedance spectroscopy (EIS). The inhibition efficiency (E, %) increased with 4-MTHT concentration, but the desorption potential (Ed) remained unchanged with increasing 4-MTHT concentration. The addition of potassium iodide (KI) enhanced E considerably and increased the value of Ed. A synergistic effect was observed between KI and 4-MTHT with an optimum mass ratio of [4-MTHT]/[KI] = 4 × 10−2. The synergism parameters (SΘ) calculated from surface coverage were found to be more than unity. This result clearly showed the synergistic influence of iodide ions on the corrosion inhibition of mild steel in 0.5 M H2SO4 by 4-MTHT. The adsorption of this inhibitor alone and in combination with iodide ions followed Langmuir's adsorption isotherm.

Iodine chemistry reflects productivity and denitrification in the Arabian Sea: evidence for flux of dissolved species from sediments of western India into the OMZ

Abstract: Dissolved iodine species and total iodine concentrations were measured in the Arabian Sea during the Spring Intermonsoon of 1995. Two separate regimes of iodine chemistry are highlighted in this study: (1) the well-oxygenated surface layer (WOSL) where iodide concentrations were in the range of 158–558 nM, and (2) the oxygen minimum zone (OMZ) where total iodine concentrations [primarily as iodide and in excess to the oceanic iodine/salinity ratio of ∼13] varied from ∼200 to 950 nM. Iodine data in the WOSL of the Arabian Sea are contrasted with data from the Bermuda Atlantic Time-series Station (BATS), the Hawaii Ocean Time-series Station ALOHA (HOT), VERTEX in the Pacific and the Black Sea. Total iodine concentrations in excess of 400 nM were observed in eastern portions of the OMZ. The eastern portion of the basin has a permanent denitrification zone as well as high concentrations of dissolved Mn2+ (d-Mn2+) and iodide. While there is precedent for high values of iodide and total iodine in several other isolated basins, this is the first report of such values in open-ocean waters. Potential sources of excess total iodine to the OMZ include advection along isopycnals, from hydrothermal vents or margin sediments; atmospheric deposition; and remineralization of sinking particulate organic iodine (POI) associated with elevated productivity in surface waters. We estimate that only 3.6% of the excess total iodine can result from remineralization of sinking POI from the WOSL to the OMZ. Advection from margin sediments off of India is the most plausible source of iodine to the OMZ and contributes ∼96% of the total excess iodine to the OMZ. I− is maintained as the dominant form of iodine via in situ reduction of iodate by bacteria.

Rectification and Nonlinear Optical Properties of a Langmuir−Blodgett Monolayer of a Pyridinium Dye

Abstract: Rectification was observed across a monolayer of 2,6-di[dibutylamino-phenylvinyl]-1-butylpyridinium iodide, (Bu2NφV)2BuPy+I-, 1 sandwiched between gold electrodes. The current is enhanced at a forward bias above 0.5 to 1.0 V, as electrons flow preferentially from the iodide ions to the pyridinium ring, and is as high as 100 000 electrons molecule-1 s-1, with a rectification ratio of up to 90.

Stunning of Iodide Transport by 131I Irradiation in Cultured Thyroid Epithelial Cells

Abstract: The existence of thyroid stunning (i.e., inhibited thyroidal iodide uptake after administration of diagnostic amounts of 131I) is controversial and is currently a subject of debate. To our knowledge, the stunning phenomenon has not been investigated previously in vitro. Methods: Growth-arrested porcine thyroid cells that formed a tight and polarized monolayer in a bicameral chamber were irradiated with 3–80 Gy 131I present in the surrounding culture medium for 48 h. The iodide transport capacity after irradiation was evaluated 3 d later by measuring the transepithelial (basal to apical) flux of trace amounts of 125I. Results: The basal-to-apical 125I transport decreased with increasing absorbed dose acquired from 131I; a nearly 50% reduction was observed already at 3 Gy. Stable iodide at the same molarity as 131I (10−8 mol/L) had no effect on the 125I transport. Cell number and epithelial integrity were not affected by irradiation. Conclusion: Stunning of iodide transport is detected after 131I irradiation of cultured thyroid cells. The degree of inhibition of transport is dependent on the absorbed dose.

Capillary electrophoretic determination of thiosulfate, sulfide and sulfite using in-capillary derivatization with iodine.

Abstract: A new capillary electrophoresis (CE) method was developed for the rapid, simple and selective determination of thiosulfate, sulfide and sulfite species. The proposed method is based on the in-capillary derivatization of separated sulfur anions by mixing their zones with the iodine zone during the electrophoretic migration and direct UV detection of iodide formed. The optimal conditions for the separation and derivatization reaction were established by varying electrolyte pH, electrolyte counter-ion, concentration of iodine, and applied voltage. The optimized separations were carried out in 20 mmol/L Tris-chloride electrolyte (pH 8.5) using direct UV detection at 214 nm. All three sulfur species were well resolved in less than 4 min. The method gives repeatability comparable or even better than this obtained for sulfur anions using standard CE technique. The proposed CE system was applied to the monitoring of sulfur anions in spent fixing solutions during the electrolytic oxidation.

Well cement additives, compositions and methods

Abstract: Improved well cement additives, compositions and methods of using the compositions are provided. The well cement additives are basically comprised of a first monomer selected from the group of 2-acrylamido-2-methylpropane sulfonic acid, 2-allyloxy-2-hydroxy-1-propane sulfonic acid and vinylsulfonic acid, a second monomer selected from the group of N,N-dimethylacrylamide, acrylamide, N-vinylpyrrolidone, N-vinylacetamide and acrylonitrile and a third monomer selected from the group of C6 to C22 dimethylaminopropylmethacrylamide bromide, chloride and iodide and C6 to C22 dimethylaminoethylmethacrylate bromide, chloride and iodide.

Iodine stability in salt double-fortified with iron and iodine.

Abstract: Deficiencies in small quantities of micronutrients, especially iodine and iron, severely affect more than a third of the world's population, resulting in serious public health consequences, especially for women and young children. Salt is an ideal carrier of micronutrients. The double fortification of salt with both iodine and iron is an attractive approach to the reduction of both anemia and iodine-deficiency disorders. Because iodine is unstable under the storage conditions found during the manufacturing, distribution, and sale of salt in most developing countries, the effects of packaging materials and environmental conditions on the stability of salt double-fortified with iron and iodine were investigated. Salt was double-fortified with potassium iodide or potassium iodate and with ferrous sulfate or ferrous fumarate. The effects of stabilizers on the stability of iodine and iron were followed by storing the salt under three conditions that represent the extremes of normal distribution and sale for salt in developing countries: room temperature (25 degrees C) with 50%-70% relative humidity, 40 degrees C with 60% relative humidity, and 40 degrees C with 100% relative humidity. The effects of stabilizers, such as sodium hexametaphosphate (SHMP), calcium carbonate, calcium silicate, and dextrose were investigated. None of the combinations of iron and iodine compounds was stable at elevated temperatures. Essentially all of the iodine was lost over a period of six months. SHMP effectively slowed down the iodine loss, whereas magnesium chloride, a typical hygroscopic impurity, greatly accelerated this process. Calcium carbonate did not have a sparing effect on iodine, despite contrary indications in the literature. Ferrous sulfate-fortified salts generally turned yellow and developed an unpleasant rusty flavor. Salt fortified with ferrous fumarate and potassium, iodide was reasonably stable and maintained its organoleptic properties, making it more likely to be acceptable to consumers. We confirmed that application of the iodine compounds as solutions resulted in a more even distribution of the iodine throughout the sample. The effect of the packaging materials was overshadowed by the other variables. None of the packaging materials was clearly better than any other. This may have been due to the fact that the polymer bags were not heat sealed, and thus some moisture penetration was possible. The results indicate that with careful control of processing, packaging, and storage conditions, a double-fortified salt could be stabilized for the six-month period required for distribution and consumption. Unfortunately, the processing and storage required are difficult to attain under typical conditions in developing countries.

Unique Reactivity of a Tetradentate N2S2 Complex of Nickel: Intermediates in the Production of Sulfur Oxygenates

Abstract: Complex 1 [(N,N‘-dimethyl-N,N‘-bis(2-sulfanylethyl)ethylenediamine)nickel(II)], previously shown to react with H2O2 to produce the fully oxygenated disulfonate 5 [diaqua(N,N‘-dimethyl-N,N‘-bis(2-sulfonatoethyl)ethylenediamine)nickel(II)], has been explored in detail to explain the observed reactivity of this compound and to discern intermediates in the oxygenation reaction. Reaction of 1 with 1 equiv of methyl iodide results in the monomethylated square-planar nickel complex 2 {[(N,N‘-dimethyl-N-(2-sulfanylethyl)-N‘-(2-methylthioethyl)(ethylenediamine)nickel(II)] iodide}, while a slight excess of methyl iodide results in the dimethylated complex 3 [diiodo(N,N‘-dimethyl-N,N‘-bis(2-methylthioethyl)ethylenediamine)nickel(II)], an X-ray structure of which has shown that the nickel ion is in an octahedral N2S2I2 environment. Crystal data of 3: monoclinic, a = 8.865(3) A, b = 14.419(4) A, c = 14.389(6) A, β = 100.19(3)°, V = 1810.2(12) A3, space group P21/n, Z = 4. The equatorial positions are occupied by the ...