Showing papers on "Iodide published in 2004"

Vibrational Spectroscopy of Aqueous Sodium Halide Solutions and Air-Liquid Interfaces: Observation of Increased Interfacial Depth

Abstract: Air−aqueous sodium halide solution interfaces are examined using vibrational sum frequency generation spectroscopy. Raman and ATR-FTIR (attenuated total reflection Fourier transform infrared) spectroscopies are also used to compare the effects of halide anions on the water structure of the bulk solution to that of the interface. The interfacial water structures for the sodium fluoride and chloride aqueous solutions are found to be similar to the air−water interface, whereas sodium bromide and iodide aqueous solutions cause significant distortion of the hydrogen-bonding network. Analysis of the spectra indicates higher concentrations of bromide and iodide anions in the interfacial region with an increase in interfacial depth.

Relative potencies and additivity of perchlorate, thiocyanate, nitrate, and iodide on the inhibition of radioactive iodide uptake by the human sodium iodide symporter.

Abstract: The presence of perchlorate (ClO(4) (-)) in some U.S. drinking water supplies has raised concern about potential adverse thyroidal health effects, because ClO(4) (-) is known to competitively inhibit iodide uptake at the sodium iodide symporter (NIS). Humans are nutritionally and environmentally exposed to other competitive inhibitors of iodide uptake, including thiocyanate (SCN(-)) and nitrate (NO(3) (-)). The joint inhibiting effects of these three anions was studied by exposing Chinese hamster ovary cells stably expressing human NIS to varying concentrations of each anion separately, and in combination, and conducting measurements of (125)I(-) uptake. The entire data set was fit to a single Hill equation using maximum likelihood. The relative potency of ClO(4) (-) to inhibit (125)I(-) uptake at the NIS was found to be 15, 30 and 240 times that of SCN(-), I(-), and NO(3) (-) respectively on a molar concentration basis, with no evidence of synergism. These results are consistent with a common mode of action by these anions of simple competitive interaction, in which a concentration of any one of ClO(4) (-) SCN(-), and NO(3) (-), occurring either individually or as part of a mixture of the three anions, is indistinguishable from a concentration or dilution of either one of the remaining two ions in inhibiting iodine uptake at the NIS.

High performance dye-sensitized solar cells using ionic liquids as their electrolytes

Abstract: Room temperature ionic liquids have been used as electrolytes to investigate the performance and the characteristics in dye-sensitized solar cells (DSSCs). The ionic liquids used are 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (EMImTFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4), 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6), 1-ethyl-3-methylimidazolium dicyanamide (EMImDCA), and 1-butylpyridinium bis(trifluoromethane sulfonyl)imide (BPTFSI), in which 1-ethyl-3-methylimidazolium iodide (EMImI) and I2 are dissolved as a redox couple. The structure and the property greatly influence the DSSC performances. Especially, the photocurrents are affected by the ionic conductivity (viscosity) and charge transport by the exchange reaction between the iodide/tri-iodide redox couple. EMImDCA is specific in terms of enhancement of the open-circuit voltages. The photo-energy conversion efficiency of DSSCs with EMImDCA under 100 mW cm−2 can be optimized up to 5.5%, when [I−] + [I3−] = 2 M and [I−]:[I2]=10:1 with the addition of 4-t-butylpyridine and LiI.

A highly efficient, preorganized macrobicyclic receptor for halides based on CH... and NH...anion interactions.

Abstract: The preorganized, macrobicyclic azaphane (1) exhibits remarkable strong, selective fluoride binding comparable to the most effective bis(tren) cryptands despite binding anions via only three NH groups coupled with three CH hydrogen bond donors. The lower intrinsic affinity of CH donors is compensated by the high degree of preorganization exhibited by azacyclophane 1. Compound 1 is prepared via a tripod−tripod cyclization reaction between 1,3,5-tris-bromomethyl-benzene and an aliphatic tripodal hexatosylated polyamine, followed by the reduction of the resulting bicyclic tosylamine. The crystal structures of the bicyclic tosylamine 2 and four macrobicyclic polyammonium halide salts of 1 are reported. X-ray studies revealed the formation of inclusive 1:1 complexes of 1 with fluoride, chloride, bromide, and iodide. Potentiometric titrations showed very high binding constants for fluoride and chloride with a F-/Cl- selectivity of more than five logarithmic units. The final geometry of the anion cryptates is la...

Synergistic Influence of Poly(4-Vinylpyridine) and Potassium Iodide on Inhibition of Corrosion of Mild Steel in 1M HCl

Abstract: The corrosion and inhibition behavior of mild steel in 1 M HCl in the presence of poly(4-vinylpyridine)(P4VP) and potassium iodide (KI) was investigated using weight loss measurements, potentiodynamic polarization studies and impedance measurements. The inhibition efficiency increased with increasing P4VP concentration. The inhibiting action of P4VP is considerably enhanced by the addition of potassium iodide. The adsorption of this compound either alone or in combination with iodide ions on the metal surface is found to obey Lamgmir's adsorption isotherm. The experimental results suggest that the presence of iodide ions in the solution increases the surface coverage Θ and, therefore, indicate the joint adsorption of P4VP and iodide ions. On the other hand, it was found that the inhibiting effect of P4VP and (P4VP + KI) increased with increasing temperature of the corrosion medium. The presence of these species in the solution decreases the double layer capacitance and increases the charge transfer resistance, both derived from Nyquist plots obtained from a.c. impedance studies. The variation of charge transfer resistance with time suggests that the inhibitive action of (P4VP + KI) depends mainly on the protective inhibitor film formed on the steel surface.

Magnesium-induced copper-catalyzed synthesis of unsymmetrical diaryl chalcogenide compounds from aryl iodide via cleavage of the Se-Se or S-S bond.

Abstract: The methodology for a copper-catalyzed preparation of diaryl chalcogenide compounds from aryl iodides and diphenyl dichalcogenide molecules is reported. Unsymmetrical diaryl sulfide or diaryl selenide can be synthesized from aryl iodide and PhYYPh (Y = S, Se) with a copper catalyst (CuI or Cu2O) and magnesium metal in one pot. This reaction can be carried out under neutral conditions according to an addition of magnesium metal as the reductive reagent. Furthermore, it is efficiently available for two monophenylchalcogenide groups generated from diphenyl dichalcogenide.

Ambient temperature plastic crystal electrolyte for efficient, all-solid-state dye-sensitized solar cell.

Abstract: Doping the molecular plastic crystal of succinonitrile with solid N-methyl-N-butylpyrrolidinium iodide salt and iodine has produced a highly conductive solid iodide/triiodide conductor. Furthermore, it was employed for a highly efficient, all-solid-state dye-sensitized solar cell.

Alkyl- or Arylthiolation of Aryl Iodide via Cleavage of the S−S Bond of Disulfide Compound by Nickel Catalyst and Zinc

Abstract: Various aryl sulfides can be synthesized by nickel-catalyzed alkyl- or arylthiolation of aryl iodide with a disulfide compound. This reaction produces Ni(0) from NiBr2−bpy by the reduction with zinc, and this generated complex works as an activating species to convert ArI into ArSR under neutral conditions. Furthermore, this system enables the use of two RS groups in (RS)2.

Perturbation of Fluorescence by Nonspecific Interactions between Anionic Poly(phenylenevinylene)s and Proteins: Implications for Biosensors

Abstract: The use of anionic water-soluble conjugated polymers (CPs) for sensing the presence of avidin by use of a biotin-modified fluorescence quencher was studied. The molecules involved in the study included poly[2-methoxy-5-(3‘-propyloxysulfonate)-1,4-phenylenevinylene] with either lithium (Li+-MPS-PPV) or sodium (Na+-MPS-PPV) countercations, the well-defined oligomer pentasodium 1,4-bis(4‘(2‘ ‘,4‘ ‘-bis(butoxysulfonate)-styryl)-styryl)2-butoxysulfonate-5-methoxybenzene (5R5-), the quenchers N-methyl-4,4‘-pyridylpyridinium iodide (mMV+) and [N-(biotinoyl)-N‘-(acetyl 4,4‘-pyridylpyridinium iodide)] ethylenediamine (BPP+), which contains a molecular recognition fragment (biotin) attached to a unit that accepts an electron from a CP excited state, and the proteins avidin, tau, BSA, and pepsin A. Fluorescence quenching experiments were examined in a variety of conditions. Experiments carried out in water and in ammonium carbonate buffer (which ensures avidin/biotin complexation) reveal that nonspecific interaction...

Samarium(II) Iodide Mediated Reductions − Influence of Various Additives

Abstract: Samarium(II) iodide is a one-electron transfer reagent that has become highly appreciated as a mild and selective reducing agent in recent years. It has been found experimentally that various additives and co-solvents largely control the reactivity of SmI2. This microreview provides an overview of the current knowledge of the reagent SmI2 as a reducing agent, in particular with additives that increase its reactivity. The use of various proton sources is covered, as well as the effect of co-solvents. Furthermore, the very powerful reagent mixture SmI2/H2O/amine is also described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Cuprophilic interactions in luminescent copper(I) clusters with bridging bis(dicyclohexylphosphino)methane and iodide ligands: spectroscopic and structural investigations.

Abstract: Polynuclear copper(I) complexes with bridging bis(dicyclohexylphosphino)methane (dcpm) and iodide ligands, [Cu(2)(dcpm)(2)(CH(3)CN)(2)](BF(4))(2) (1), [Cu(2)(dcpm)(2)](BF(4))(2) (2), [(CuI)(3)(dcpm)(2)] (3), [(CuI)(4)(dcpm)(2)] (4), and [(CuI)(2)(dcpm)(2)] (5) were prepared and their structures determined by X-ray crystal analysis. The shortest Cu--Cu distance found in these complexes is 2.475(1) A for 3. Powdered samples of 1, 3, 4, and 5 display intense and long-lived phosphorescence with lambda(max) at 460, 626, 590, and 456 nm and emission quantum yields of 0.26, 0.11, 0.12, and 0.56 at room temperature, respectively. In the solid state, 2 displays both a weak emission at 377 and an intense one at 474 nm with an overall emission yield 0.42. The difference in emission properties among complexes 1-5 suggests that both Cu--Cu interaction and coordination around the copper(I) center affect the excited state properties. A degassed solution of 2 in acetone gives a bright red emission with lambda(max) at 625 nm at room temperature. The difference absorption spectra of the triplet excited states of 1-5 in acetonitrile show broad absorption peaks at 340-410 and 850-870 nm.

Transport properties in a family of dialkylimidazolium ionic liquids

Abstract: The transport properties of 1,3-methylalkylimidazolium based ionic liquids are sensitive to their chemical structure. In this work, two key features of the chemical structure were investigated: the role of the anion and the length of the alkyl chain. Four different anions were examined for the 1,3-methylethylimidazolium salt (MeEtImX): bromide (Br−), iodide (I−), trifluoromethanesulfonate (Tf−) and bis(trifluoromethanesulfonyl)amide (NTf2−) anions. Increasing the size of the anion resulted in a decrease of the melting point and a slight increase in the cation diffusion coefficient. The differences in cation diffusion behaviour reflect the differences in viscosity, with much higher viscosities expected for the halide salts. In contrast to this diffusion behaviour, the melt conductivities are all very similar. The inconsistency between the calculated conductivity (based on diffusion measurements) and the conductivity measured, however, is attributed to correlated ion motions and/or the diffusion of neutral species that do not contribute to the conductivity. The effect of the length of the alkyl substituent was also studied for 1,3-methylalkylimidazolium iodide (MeRImI). Increasing the length of the alkyl chain, from methyl to a linear heptyl chain, suppresses the melting point and decreases both the conductivity and cation diffusion coefficients. In this case, the viscosity, as well as the size of the cation, influence ion transport in these materials.

Indium(I) iodide-promoted cleavage of diaryl diselenides and disulfides and subsequent condensation with alkyl or acyl halides. One-pot efficient synthesis of diorganyl selenides, sulfides, selenoesters, and thioesters

Abstract: Diphenyl diselenides and disulfides undergo facile cleavages by indium(I) iodide and the corresponding generated selenate and thiolate anions condense in situ with alkyl or acyl halides present in the reaction mixture. Thus, a simple, efficient, and general procedure has been developed for the synthesis of unsymmetrical diorganyl selenides, sulfides (thioethers), selenoesters, and thioesters by this one-pot reaction at room temperature.

The first (ferrocenylmethyl)imidazolium and (ferrocenylmethyl)triazolium room temperature ionic liquids.

Abstract: N-(Ferrocenylmethyl)imidazole (3a), 1-(ferrocenylmethyl)-1,2,4-triazole (3b), 1,1'-bis[(1H-imidazol-1-yl)methyl]ferrocene (8a), 1,1'-bis([1H-(2-methyl)imidazol-1-yl]methyl]ferrocene (8b), and 1,1'-bis[(1H-1,2,4-triazol-1-yl)methyl]ferrocene (8c) were synthesized in moderate yields. These compounds were quaternized with methyl iodide to form 1-(ferrocenylmethyl)-3-methylimidazolium iodide (4a), 1-(ferrocenylmethyl)-4-methyl-1,2,4-triazolium iodide (4b), 1,1'-bis([1-(2,3-dimethyl)imidazolium]methyl)ferrocene diiodide (9b), and 1,1'-bis([1-(4-methyl)-1,2,4-triazolium]methyl)ferrocene diiodide (9c), respectively, in excellent yields. Compounds 4a, 4b, 9b, and 9c were metathesized with bis(trifluoromethanesulfonyl)amide to give high yields of 5a, 5b, 10b, and 10c. With potassium hexafluorophosphate, 9b forms 10d. Salts 5a, 5b, and 10c are the first room-temperature ionic liquids with cations containing an organometallic moiety that exhibit T(g) values well below room temperature, i.e., -32, -16, and -11 degrees C. The compounds were characterized by (1)H, (19)F, and (13)C NMR, MS, and elemental analyses. T(g) values and melting points were determined by DSC. T(d) values (5% weight loss temperature) were recorded by TGA. X-ray single-crystal structures show that 9c and 10d crystallize in the triclinic space group P.

Effect of ions on the vibrational relaxation of liquid water.

Abstract: We study the relaxation of the O-H stretch vibration of water in aqueous salt solutions using femtosecond two-color pump-probe spectroscopy. The vibrational lifetimes are measured for a series of salts consisting of the anions Cl(-), Br(-), and I(-) and the cations Li(+), Na(+), and Mg(2+), for a range of concentrations from 0.5 M up to 6 M (chloride salts), 9 M (bromide salts), and 10 M (iodide salts). In addition to the previously found dependence of the vibrational lifetime on the nature of the anion, the lifetime is found to depend on concentration and is observed to show a small but significant dependence on the nature of the cation. We present a model in which all the effects of ions on the vibrational relaxaton of liquid water are accounted for.

Dye-sensitized photocatalysts for efficient hydrogen production from aqueous I− solution under visible light irradiation

Abstract: H2 production from a water–acetonitrile (AN) mixed solution containing iodide electron donor was investigated over dye-sensitized Pt/TiO2 photocatalysts under visible light irradiation. It was found that H2 production with good quantum efficiency (∼2.5%) took place using merocyanine and coumarin dye-sensitized Pt/TiO2 photocatalysts, respectively, and an I− electron donor in a water–acetonitrile mixture (water, 5% by volume). The rates of H2 evolution were decreased with the increase of the water amount in the mixed solution because of the decrease in energy gap between the redox potential of I3−/I− and the HOMO level of the dye. H2 evolution was also decreased with the accumulation of produced I3− from I−. However, we have also found that it is possible to prevent the backward reaction, reduction of I3− to I− on Pt metal by using the internally platinized semiconductor K4Nb6O17 instead of Pt/TiO2 in water–AN mixed solution.

Iodide effects in transition metal catalyzed reactions.

Abstract: The unique properties of I− allow it to be involved in several different ways in reactions catalyzed by the late transition metals: in the oxidative addition, the migration, and the coupling/reductive elimination steps, as well as in substrate activation. Most steps are accelerated by I− (for example through an increased nucleophilicity of the metal center), but some are retarded, because a coordination site is blocked. The “soft” iodide ligand binds more strongly to soft metals (low oxidation state, electron rich, and polarizable) such as the later and heavier transition metals, than do the other halides, or N- and O-centered ligands. Hence in a catalytic cycle that includes the metal in a formally low oxidation state there will be less tendency for the metal to precipitate (and be removed from the cycle) in the presence of I− than most other ligands. Iodide is a good nucleophile and is also easily and reversibly oxidized to I2. In addition, I− can play key roles in purely organic reactions that occur as part of a catalytic cycle. Thus to understand the function of iodide requires careful analysis, since two or sometimes more effects occur in different steps of one single cycle. Each of these topics is illustrated with examples of the influence of iodide from homogeneous catalytic reactions in the literature: methanol carbonylation to acetic acid and related reactions; CO hydrogenation; imine hydrogenation; and C–C and C–N coupling reactions. General features are summarised in the Conclusions.