Showing papers on "Iodide published in 2009"

Iodine/Iodide-Free Dye-Sensitized Solar Cells

Abstract: Dye-sensitized solar cells (DSSCs) are built from nanocrystalline anatase TiO2 with a 101 crystal face (nc-TiO2) onto which a dye is absorbed, ruthenium complex sensitizers, fluid I−/I3− redox couples with electrolytes, and a Pt-coated counter electrode. DSSCs have now reached efficiencies as high as 11%, and G24 Innovation (Cardiff, U.K.) is currently manufacturing them for commercial use. These devices offer several distinct advantages. On the basis of the electron lifetime and diffusion coefficient in the nc-TiO2 layer, DSSCs maintain a diffusion length on the order of several micrometers when the dyed-nc-TiO2 porous layer is covered by redox electrolytes of lithium and/or imidazolium iodide and their polyiodide salts. The fluid iodide/iodine (I−/I3−) redox electrolytes can infiltrate deep inside the intertwined nc-TiO2 layers, promoting the mobility of the nc-TiO2 layers and serving as a hole-transport material of DSSCs. As a result, these materials eventually give a respectable photovoltaic performan...

Zn-mediated, Pd-catalyzed cross-couplings in water at room temperature without prior formation of organozinc reagents.

Abstract: Mix in water, stir. That is all that is required in this new approach to sp(3)-sp(2) cross-couplings between an alkyl iodide and an aryl bromide, both potentially bearing functionality. They react under catalysis by Pd(0) in the presence of zinc powder, aided by a nonionic amphiphile, to give the alkylated aromatic. No organic solvents and no heating; just add water.

Iodide in CTAB prevents gold nanorod formation.

Abstract: The gold nanocrystal seed-mediated approach using cetyltrimethylammonium bromide (CTAB) as a stabilizing surfactant is commonly used to make large quantities of monodisperse gold nanorods. This method, however, has been at times difficult to reproduce in different laboratories. We recently showed [Smith, D. K.; Korgel, B. A. Langmuir 2008, 24, 644-649] that a very low concentration impurity in CTAB obtained from some suppliers prevents nanorod growth but were not able to identify the impurity. Here, we report that the impurity is iodide. Inductively coupled plasma mass spectroscopy (ICP-MS) revealed that iodide concentrations vary in CTAB from different suppliers, from less than 2.75 ppm up to 840 ppm. When CTAB with iodide concentrations greater than 50 ppm is used, nanorods do not form and the product consists entirely of spherical nanocrystals. Iodide slows the reduction of Au(III) to Au0. Iodide adsorption on Au {111} surfaces inhibits nanorod growth.

One- versus two-electron oxidation with peroxomonosulfate ion: reactions with iron(II), vanadium(IV), halide ions, and photoreaction with cerium(III).

Abstract: The kinetics of the redox reactions of the peroxomonosulfate ion (HSO(5)(-)) with iron(II), vanadium(IV), cerium(III), chloride, bromide, and iodide ions were studied. Cerium(III) is only oxidized upon illumination by UV light and cerium(IV) is produced in a photoreaction with a quantum yield of 0.33 +/- 0.03. Iron(II) and vanadium(IV) are most probably oxidized through one-electron transfer producing sulfate ion radicals as intermediates. The halide ions are oxidized in a formally two-electron process, which most likely includes oxygen-atom transfer. Comparison with literature data suggests that the activation entropies might be used as indicators distinguishing between heterolytic and homolytic cleavage of the peroxo bond in the redox reactions of HSO(5)(-).

Photoinduced oxidation of sea salt halides by aromatic ketones: a source of halogenated radicals

Abstract: The interactions between triplet state benzophenone and halide anion species (Cl , Br and I have been studied by laser flash photolysis (at 355 nm) in aqueous solutions at room temperature. The decay of the triplet state of benzophenone was followed at 525 nm. Triplet lifetime measurements gave rate constants, k q (M −1 s ), close to diffusion controlled limit for iodide (~8×10 9 M −1 s ), somewhat less for bromide (~3×10 8 M −1 s ) and much lower for chloride ( 6 M −1 s ). The halide (X − ) quenches the triplet state; the resulting product has a transient absorption at 355 nm and a lifetime much longer than that of the benzophenone triplet state, is formed. This transient absorption feature matches those of the corresponding radical anion (X 2 ). We therefore suggest that such reactive quenching is a photosensitized source of halogen in the atmosphere or the driving force for the chemical oxidation of the oceanic surface micro layer.

Palladium complexes of abnormal N-heterocyclic carbenes as precatalysts for the much preferred Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium

Abstract: A series of new PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed precatalysts of abnormal N-heterocyclic carbenes for the highly desirable Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium is reported. Specifically, the PEPPSI themed (NHC)PdI2(pyridine) type precatalysts, 1b–4b, efficiently carried out the highly convenient Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes in air in a mixed aqueous medium. Complexes, 1b–4b, were synthesized by the direct reaction of the corresponding imidazo[1,2-a]pyridinium iodide salts, 1a–4a, with PdCl2 in pyridine in the presence of K2CO3 as a base while the imidazo[1,2-a]pyridinium iodide salts, 1a–4a, were in turn synthesized by the alkylation reactions of the respective imidazo[1,2-a]pyridine derivatives with alkyl iodides. The density functional theory (DFT) studies revealed that these imidazol-3-ylidene[1,2-a]pyridine derived abnormal carbenes are strongly σ-donating and consequently significantly weaken the catalytically important labile trans pyridine ligand in 1b–4b.

A new source of volatile organoiodine compounds in surface seawater

Abstract: [1] Volatile organoiodine compounds (VOIs) are the main carrier of iodine from the oceans to the atmosphere. We have identified a novel, sea-surface source of the short-lived VOIs CH2I2, CHClI2 and CHI3 in a series of laboratory experiments. These compounds were formed when seawater, collected during winter in the North Sea, was exposed to ambient levels of ozone. The VOIs are produced from the reaction of marine dissolved organic matter with hypoiodous acid/molecular iodine, which are formed at the sea surface when ozone reacts with dissolved iodide. The same three VOIs were formed when we incubated seawater of different productivity levels with molecular iodine during a cruise in the tropical Atlantic Ocean. We suggest that the presence of dissolved iodide, dissolved organic matter and ozone can lead to the sea-surface production of CH2I2, CHClI2 and CHI3. As such, this process could provide a ubiquitous source of iodine to the marine atmosphere.

Palladium-catalyzed decarboxylative cross-coupling reaction of cinnamic acid with aryl iodide

Abstract: A highly effective decarboxylative cross-coupling reaction of cinnamic acid with aryl iodide catalyzed by the combination of palladium chloride and CyJohnPhos in the presence of Ag2CO3 as an additive is described. The desired carbon-carbon bond formation proceeds efficiently with good functional-group tolerance.

Copper(I)-catalyzed aryl bromides to form intermolecular and intramolecular carbon-oxygen bonds.

Abstract: A highly efficient Cu-catalyzed C−O bond-forming reaction of alcohol and aryl bromides has been developed. This transformation was realized through the use of copper(I) iodide as a catalyst, 8-hydroxyquinoline as a ligand, and K3PO4 as a base. A variety of functionalized substrates were found to react under these reaction conditions to provide products in good to excellent yields.

Inorganic–organic hybrid materials incorporating primary cyclic ammonium cations: The lead bromide and chloride series

Abstract: Twelve inorganic–organic hybrids have been synthesized and characterised by single-crystal X-ray diffraction experiments. The inorganic component is based on lead(II) bromide and lead(II) chloride units and the organic component on various cyclic hydrocarbons, each with only a primary ammonium group as a ring substituent. When the organic component is cyclopropylammonium, cyclobutylammonium, cyclopentylammonium and cyclohexylammonium, the inorganic motif observed is based on the cubic perovskite structure type and consists of 2-D layers of corner-sharing octahedra, in the ratio of 1 : 2 inorganic–organic. Lead(II) bromide and cycloheptylammonium combined to give 1-D chains of corner-sharing PbBr6 octahedra and similarly, lead(II) bromide and cyclooctylammonium gave 1-D ribbons of corner-sharing PbBr6 octahedra. Lead(II) chloride and cycloheptylammonium have a ribbon motif, and lead(II) chloride and cyclooctylammonium have 2-D layers of corner-, edge- and face-sharing octahedra. These results are compared with a similar study involving lead(II) iodide units and the same set of six cations. General trends and conclusions are discussed.

Effect of cation size on solid polymer electrolyte based dye-sensitized solar cells.

Abstract: We report the preparation of a series of solid polymer electrolytes with different cations but with the same anion. We have chosen a PEO:PEG blend (at 40:60 by w/w) and complexed it with LiI, NaI, KI, NH4I, 1-ethyl-3-methylimidazolium iodide (EMII), and 1-hexyl-3-methylimidazolium iodide (HMII) with the same ion to monomer ratio. The role of different cations in terms of their size has been investigated on the conductivity of the polymer electrolyte films. The electrolyte properties have been explained in terms of the changes in the number of free charge carriers and the variation in crystallinity of the matrix. The cell performance of the dye-sensitized solar cells (DSSC) fabricated with these systems also showed strong dependence on the cation radii. The concept of ion intercalation and surface adsorption used for the liquid electrolyte systems has been extended to the polymer electrolytes and discussed in this paper.

Formation of iodinated organic compounds by oxidation of iodide-containing waters with Manganese Dioxide

Abstract: This study shows that iodinated organic compounds can be produced when iodide-containing waters are in contact with manganese oxide birnessite (delta-MnO2) in the pH range of 5-7. In the absence of natural organic matter (NOM), iodide is oxidized to iodate that is also adsorbed onto delta-MnO2. In the presence of iodide and NOM, adsordable organic iodine compounds (AOI) are formed at pH < 7 because of the oxidation of iodide to iodine by delta-MnO2 and the reactions of iodine with NOM. In addition, iodoacetic acid and iodoform have been identified as specific iodinated byproducts. Formation of iodoform is not observed for high NOM/delta-MnO2 ratios due to inhibition of the catalytic effect of delta-MnO2 by NOM poisoning. Experiments with model compounds such as resorcinol and 3,5-heptanedione confirmed that the delta-MnO2/l(-) system is very effective for the formation of iodinated organic compounds. These results suggest that birnessite acts as a catalyst through the oxidation of iodide to iodine and the polarization of the iodine molecule, which then reacts with NOM moieties. Furthermore, our results indicate that during water treatment in the presence of manganese oxide, iodinated organic compounds may be formed, which may lead to taste and odor or toxicological problems.

Computational investigation of the first solvation shell structure of interfacial and bulk aqueous chloride and iodide ions.

Abstract: Molecular dynamics simulations with polarizable interaction potentials were carried out to understand the solvation structure of chloride and iodide anions in bulk and interfacial water, showing qualitative similarities between the first solvation shell structures at the interface and bulk. For the more polarizable iodide, its solvation structure was found to be more anisotropic than chloride, and this trend persisted at both the interface and in the bulk. The anisotropy of the solvation structure correlated with polarizability, but it was also found to inversely correlate with anion size. When polarizability was reduced to near zero, a very small anisotropy in the water solvation structure around the ion still persisted. Polarizable anions were found to have on average an induced dipole in the bulk that was significantly larger than zero. This induced dipole resulted in the water hydrogen atoms having stronger interactions with the anions on one side of them, in which the dipole was pointing. In contrast, the other side of the anions, in which the induced dipole was pointing away from, had fewer water molecules present and, for the case of iodide, was rather devoid of water molecules all together at both the interface and in the bulk. This region formed a small cavity in the bulk, whereas at the air-water interface it was simply part of the air interface. In the bulk, this small cavity may be viewed as somewhat hydrophobic, and the need for the extinction of this cavity may be one of the major driving forces for the more polarizable anions to reside at the air-water interface.

Release of reactive bromine and iodine from diatoms and its possible role in halogen transfer in polar and tropical oceans

Abstract: An in situ incubation assay measuring the bromination and iodination of phenol red was developed to detect the release of reactive bromine and iodine (primarily hypobromous acid [HOBr] and hypoiodous acid [HOI], respectively) from a putative extracellular bromoperoxidase of marine diatoms. Six of 11 species showed significant release compared to controls. Polar species were particularly active, releasing 0.6–180 fmol HOBr cell21 h21 (0.04–1.8 mmol HOBr [mg total chlorophyll]21 h21; at the seawater bromide concentration, 840 mmol L21) and 1.9–271 fmol HOI cell21 h21 (0.02–2.7 mmol HOI [mg total chlorophyll]21 h21, at 100 mmol L21 iodide). Porosira glacialis consistently showed the highest rates of release. Several temperate diatoms, including Achnanthes cf longipes, known to have a bromide-sensitive peroxidase involved in stalk formation, and warmwater species also showed the ability to release reactive bromine and iodine. This release was influenced by light, temperature, bromide (and iodide) concentration, H2O2 concentration, and pH. The rate of HOBr release by polar diatoms was much greater than bromoform emissions measured by others from laboratory cultures and seaice algae in the field. This indicates that most of the HOBr released may react with dissolved organic matter (DOM) to form nonvolatile bromine organics. Some fraction of diatom-produced HOBr and HOI may also form volatile Br2 and I2, which could transfer to the polar troposphere. The reaction of diatom-released reactive bromine and iodine with seawater DOM may represent the major mechanism in the formation of oceanic polybromo- and polyiodo-methanes.

Copper nano-catalyst: sustainable phenyl-selenylation of aryl iodides and vinyl bromides in water under ligand free conditions.

Abstract: A simple and efficient procedure for the synthesis of aryl- and vinyl-selenides has been developed by a copper nanoparticle catalysed reaction of aryl iodide/vinyl bromide with diphenyl diselenide in the presence of zinc in water. (E)-Vinyl bromides produce (E)-vinyl selenides stereoselectively, whereas (Z)-vinyl bromides provide mixtures of (E) and (Z) isomers. The catalyst was recycled.

PdCl2-promoted electrophilic annulation of 2-alkynylphenol derivatives with disulfides or diselenides in the presence of iodine.

Abstract: An efficient synthesis of 3-chalcogen-benzo[b]furans via palladium-promoted annulation reactions of 2-alkynylphenol derivatives with disulfides or diselenides and iodide has been developed. In the presence of I(2) and PdCl(2), both 3-sulfenylbenzofurans and 3-selenenylbenzofurans were selectively prepared from the cyclization of 2-alkynyanisoles with disulfides or diselenides in moderate to excellent yields.

Fluorescence turn-on detection of iodide, iodate and total iodine using fluorescein-5-isothiocyanate-modified gold nanoparticles.

Abstract: Selective turn-on fluorescence detection of I(-) was accomplished using fluorescein isothiocyanate-decorated gold nanoparticles (FITC-AuNPs). FITC molecules, which fluoresce strongly in an alkaline solution, were severely quenched when they were attached to the surface of AuNPs through their isothiocyanate group. Upon the addition of I(-), FITC molecules were detached because of I(-) adsorption on the surface of AuNPs. As a result, released FITC molecules were restored to their original fluorescence intensity. Because I(-) has a higher binding affinity to the surface of Au than do Br(-), Cl(-), or F(-), the FITC-AuNPs obviously have a higher selectivity toward I(-) than toward these other anions. Meanwhile, after IO(3)(-) was reduced to I(-) with ascorbic acid, the detection of IO(3)(-) was successfully achieved using the FITC-AuNPs. Under an optimum pH and AuNP concentration, the lowest detectable concentrations of I(-) and IO(3)(-) using this probe were 10.0 and 50.0 nM, respectively. The FITC-AuNPs provide a number of advantages, including easy preparation, selectivity, sensitivity, and low cost. This unique probe was applied to an analysis of the total iodine in edible salt and seawater.

(Salen)Co(II)/n-Bu4NX Catalysts for the Coupling of CO2 and Oxetane: Selectivity for Cyclic Carbonate Formation in the Production of Poly-(trimethylene carbonate)

Abstract: The (salen)Co(II) complex ((1R,2R)-(−)-1,2-cyclohexanediamino-N,N′-bis(3,5-di-tert-butylsalicylidene)cobalt(II)) in the presence of an anion initiator, e.g. bromide, has been shown to be a very effective catalytic system for the coupling of oxetane and carbon dioxide, to provide the corresponding polycarbonate with minimal amount of ether linkages. The mechanism of the coupling of oxetane and carbon dioxide has been studied by in situ infrared spectroscopy, where the first formed product is trimethylene carbonate (TMC). TMC is formed by a backbiting mechanism following ring-opening of oxetane by the anion initiator, subsequent to CO2 insertion into the cobalt−oxygen bond. The formation of the copolymer is shown to proceed mostly by way of the anionic ring-opening polymerization of preformed trimethylene carbonate in the presence of an anion in solution. Anions that are good leaving groups, i.e., bromide and iodide, are most effective at affording copolymer via this route. In the presence of greater than 2...