Showing papers on "Iodide published in 2011"

Quantifying Regeneration in Dye-Sensitized Solar Cells

Abstract: We propose and apply a new experimental pro-tocol for determining the kinetics of the oxidation of iodide (aka dye regeneration) in dye sensitized solar cells (DSSCs) using measurements on full cells under operating conditions. Transient absorption (TA) decays of the oxidized dye after a laser pulse are correlated with the short circuit current (Jsc) and electron concentration in the TiO2, measured during the TA experiment. Results for a series of cells with N719 [(Bu4N)2][Ru(dcbpyH)2(NCS)2] (dcbpy = 4,4′-dicarboxy-2,2′-bipyridyl), a standard electrolyte, and varying iodide concentration allow us to fit for the fundamental regeneration rate constant (krg = 7.8 × 105 M−1 s−1) and to determine that the order in iodide, in these cells, is near 1 (0.98 ± 0.16) and clearly not 2. The rate and order allow us to rank various reaction mechanisms and to discuss possible rate-limiting steps that could be catalyzed to improve regeneration. The method can also give estimates of the fundamental rate constant for elect...

Electrochemical Carbon Nanotube Filter for Adsorption, Desorption, and Oxidation of Aqueous Dyes and Anions

Abstract: An electrochemically active multiwalled carbon nanotube (MWNT) filter is observed to be effective toward the adsorptive removal and electrochemical oxidation of the aqueous dyes, methylene blue and methyl orange, and the oxidation of the aqueous anions, chloride and iodide. In the absence of electrochemistry, the MWNT filter completely removed all dye from the influent solution until a near monolayer of dye molecules adsorbed to the MWNT filter surface. Electrochemical filtration at 2 V resulted in >98% oxidation of the influent dye during a single pass through the 41 μm thin porous MWNT network with a ≤1.2 s residence time. The electrochemical MWNT filter was also able to oxidize aqueous chloride and iodide with minimal overpotential. However, the oxidation of these anions was limited by the number of electrochemically active MWNT surface sites. These results show the potential of an electrochemical MWNT filter for the adsorptive removal and oxidative degradation of aqueous contaminants.

Topochemical synthesis of Co-Fe layered double hydroxides at varied Fe/Co ratios: unique intercalation of triiodide and its profound effect.

Abstract: Co-Fe layered double hydroxides at different Fe/Co ratios were synthesized from brucite-like Co(2+)(1-x)Fe(2+)(x)(OH)(2) (0 ≤ x ≤ 1/3) via oxidative intercalation reaction using an excess amount of iodine as the oxidizing agent. A new redoxable species: triiodide (I(3)(-)), promoted the formation of single-phase Co-Fe LDHs. The results point to a general principle that LDHs with a characteristic ratio of total trivalent and divalent cations (M(3+)/M(2+)) at 1/2 may be the most stable in the oxidative intercalation procedure. At low Fe content, e.g., starting from Co(2+)(1-x)Fe(2+)(x)(OH)(2) (x < 1/3), partial oxidation of Co(2+) to Co(3+) takes place to reach the M(3+)/M(2+) threshold of 1/2 in as-transformed Co(2+)(2/3)-(Co(3+)(1/3-x)-Fe(3+)(x)) LDHs. Also discovered was the cointercalation of triiodide and iodide into the interlayer gallery of as-transformed LDH phase, which profoundly impacted the relative intensity ratio of basal Bragg peaks as a consequence of the significant X-ray scattering power of triiodide. In combination with XRD simulation, the LDH structure model was constructed by considering both the host layer composition/charge and the arrangement of interlayer triiodide/iodide. The work provides a clear understanding of the thermodynamic and kinetic factors associated with the oxidative intercalation reaction and is helpful in elucidating the formation of LDH structure in general.

Copper-catalyzed cross-coupling reaction of organoboron compounds with primary alkyl halides and pseudohalides.

Abstract: With the crucial use of LiOtBu as the base, the copper-catalyzed cross-coupling of non-activated aryl electrophiles with organoboron compounds tolerates iodide, bromide, tosylate, mesylate, and even chloride as the leaving group.

Copper-catalyzed arylation of 1H-perfluoroalkanes.

Abstract: A general method has been developed for arylation of readily available 1H-perfluoroalkanes. The method employs aryl iodide and 1H-perfluoroalkane reagents, DMPU solvent, TMP2Zn base, and a copper chloride/phenanthroline catalyst. Preliminary mechanistic studies are reported.

Palladium-Catalyzed Carbohalogenation: Bromide to Iodide Exchange and Domino Processes

Abstract: Aryl bromides have been used to prepare a variety of nitrogen- and oxygen-containing heterocycles featuring new carbon–carbon and carbon–iodine bonds. This palladium-catalyzed carbohalogenation requires potassium iodide for the reaction to proceed in high yields. Additionally, the first examples of domino carbohalogenation reactions have been demonstrated using both aryl iodide and aryl bromide starting materials. Complex products with multiple rings and stereogenic centers are generated in excellent yields with moderate to excellent diastereoselectivities.

Colorimetric iodide recognition and sensing by citrate-stabilized core/shell Cu@Au nanoparticles.

Abstract: In the light of the significance and urgency for the recognition and sensing of anions specifically, especially those of biological relevance, herein, we wish to demonstrate a novel colorimetric avenue for highly selective iodide recognition and sensing using simple citrate-stabilized core/shell Cu@Au nanoparticles. No other ions than iodide can induce an appreciable color change of the Cu@Au nanoparticles solution from purple to red by transforming the interconnected, irregularly shaped nanoparticles to the single, separated, and nearly spherical ones, as confirmed by the transmission electron microscopy (TEM). On the basis of the optical spectra and TEM studies, a mechanism of iodide-induced aggregating/fusion, fragmentation, and reorganization of atoms is proposed. With this strategy, 6 μM (0.76 ppm) of iodide can be recognized within 20 min by naked-eye observation. This sensitive and selective colorimetric assay opens up a fresh insight of facile, rapid, and reliable detection of iodide and may find its future application in the analysis of the total iodine in edible salt as well as the clinical diagnosis of urinary iodide.

Palladium-Catalyzed Cycloisomerizations of (Z)-1-Iodo-1,6-dienes: Iodine Atom Transfer and Mechanistic Insight to Alkyl Iodide Reductive Elimination

Abstract: A palladium-catalyzed iodine atom transfer cycloisomerization of (Z)-1-iodo-1,6-diene has been developed, which provides a facile method to construct six-memebered heterocycles bearing an alkyl iodide group. The ligand screening shows that both the type and the quantity of ligand impose significant influences on this transformation, and the combination of 30 mol % 1,1'-bis(diphenylphosphino)ferrocene (DPPF) and 10 mol % Pd(OAc)(2) is the optimal choice. The catalytic cycle, consisting of oxidative addition of Pd(0) to vinyl iodide, intramolecular alkene insertion, and alkyl iodide reductive elimination, has been proposed and eventually supported by convincing evidence from a series of control experiments. More importantly, these control experiments disclose some features of the event of alkyl iodide reductive elimination: (1) this reductive elimination is proved to be a stereospecific process; and (2) both alkyl iodide oxidative addition and reductive elimination are not effected by a TEMPO additive. Besides its ability to undergo oxidative addition, the catalyst (palladium + DPPF) could also promote a radical transfer process. The findings described in this paper will be helpful for further development of the metal-catalyzed formation of a carbon-halide bond.

Iodine and Iodine Compounds

Abstract: Iodine is used in a wide variety of fields, among which are included industrial, pharmaceutical, nutritional, agricultural, electrical, and metallurgical. Iodine is produced as a nitrate ore by-product or from brines or seaweed. As found in nature it has only one stable isotope. Several radioactive isotopes have been prepared and have found use as radiopharmaceuticals or radioactive tracers for medical imaging. Iodine is the only halogen that is solid at ambient temperatures and pressures. Having the highest atomic weight of the common halogens, iodine begins to exhibit metallic properties. Besides exhibiting properties of luster and opacity, it is classed as a semiconductor of electricity. It is an essential human nutrient. Commercially available inorganic and organic compounds are described. Keywords: Occurrence; Properties; Manufacture; Economics; Analytical methods; Health and safety; Uses; Environmental concerns; Iodine; Solubility; Brines; catalysts; Stabilizers; Phtography; Animal feeds; Dyes; Inks; Colorants; Sanitary uses; Radioactive iodine; Pharmaceuticals; Water purification; Potassium iodide; Sodium iodide; Hydrogen iodide; Iodates; Methyl iodide; Methyline iodide; Thymol iodide; Ethyl iodide

A Fluorescence Turn‐on Sensor for Iodide Based on a Thymine–HgII–Thymine Complex

Abstract: Iodide plays a vital role in many biological processes, including neurological activity and thyroid function. Due to its physiological relevance, a method for the rapid, sensitive, and selective detection of iodide in food, pharmaceutical products, and biological samples such as urine is of great importance. Herein, we demonstrate a novel and facile strategy for constructing a fluorescence turn-on sensor for iodide based on a T-Hg(II)-T complex (T=thymine). A fluorescent anthracene-thymine dyad (An-T) was synthesized, the binding of which to a mercury(II) ion lead to the formation of a An-T-Hg(II)-T-An complex, thereby quenching the fluorescent emission of this dyad. In this respect, the dyad An-T constituted a fluorescence turn-off sensor for mercury(II) ions in aqueous media. More importantly, it was found that upon addition of iodide, the mercury(II) ion was extracted from the complex due to the even stronger binding between mercury(II) ions and iodide, leading to the release of the free dyad and restoration of the fluorescence. By virtue of this fluorescence quenching and recovery process, the An-T-Hg(II)-T-An complex constitutes a fluorescence turn-on sensor for iodide with a detection limit of 126 nM. Moreover, this sensor is highly selective for iodide over other common anions, and can be used in the determination of iodide in drinking water and biological samples such as urine. This strategy may provide a new approach for sensing some other anions.

Formation of organic iodine supplied as iodide in a soil-water system in Chiba, Japan.

Abstract: Speciation of iodine in a soil−water system was investigated to understand the mechanism of iodine mobility in surface environments. Iodine speciation in soil and pore water was determined by K-edge XANES and HPLC−ICP-MS, respectively, for samples collected at a depth of 0−12 cm in the Yoro area, Chiba, Japan. Pore water collected at a 0−6 cm depth contained 50%−60% of organic iodine bound to dissolved organic matter, with the other portion being I−. At a 9−12 cm depth, 98% of iodine was in the form of dissolved I−. In contrast, XANES analysis revealed that iodine in soil exists as organic iodine at all depths. Iodine mapping of soil grains was obtained using micro-XRF analysis, which also indicated that iodine is bound to organic matter. The activity of laccase, which has the ability to oxidize I− to I2, was high at the surface of the soil−water layer, suggesting that iodide oxidizing enzymes can promote iodine organification. The distribution coefficient of organic iodine in the soil−water system was mo...

Synthesis of pyrazoles via CuI-mediated electrophilic cyclizations of α,β-alkynic hydrazones.

Abstract: Synthesis of pyrazoles via electrophilic cyclization of α,β-alkynic hydrazones by copper(I) iodide is described. When treated with copper(I) iodide in the presence of triethylamine in refluxing acetonitrile, α,β-alkynic hydrazones, prepared readily from hydrazines and propargyl aldehydes and ketones, undergo electrophilic cyclization to afford pyrazole derivatives in good to excellent yields. The reaction appears to be general for a variety of α,β-alkynic hydrazones and tolerates the presence of aliphatic, aromatic, and ferrocenyl moieties with electron-withdrawing and electron-donating substituents.

Photomodulated Voltammetry of Iodide/Triiodide Redox Electrolytes and Its Relevance to Dye-Sensitized Solar Cells

Abstract: Photomodulated voltammetry was used to determine the redox potentials of the diiodide radical (I2–•) in water, acetonitrile, and 3-methoxypropionitrile. Iodide/triiodide redox electrolytes were exposed to modulated blue light, resulting in I2–• generation. Using transparent fluorine-doped tinoxide (FTO) electrodes, two modulated photocurrent waves could be discerned in the voltammogram, from which the formal potentials for oxidation and reduction reactions of the diiodide radical were determined. E0′(I2–•/I–) was found to be +0.79 and +1.04 V versus NHE in acetonitrile and water, respectively. These values give guidelines for E0′(D+/D) required for efficient regeneration of dyes used in dye-sensitized solar cells .

Hofmeister ion interactions with model amide compounds.

Abstract: Dissolved electrolytes interact with peptides and proteins in aqueous solution. Herein, we study small amide compounds in aqueous electrolyte solutions and link their salting-in and salting-out propensities to molecular-level structural details obtained with molecular simulations. Aqueous solutions of NaF, NaCl, NaBr, NaI, NaNO(3), and NaClO(4) with N-isopropylacrylamide (NiPAM) and N-methylacetamide (NMA) have been investigated. Our results show that NiPAM is salted-in by NaI, mediated through iodide interactions with nonpolar groups, while being salted-out by the other salts. Hydrogen-bonding interactions of anions with the amide group of NiPAM could not be identified, while in the systems with NMA all Hofmeister anions formed stable hydrogen bonds with the amide group. These results indicate that the immediate chemical environment of the backbone amide groups should be considered in studies of protein destabilization by dissolved electrolytes. We furthermore report that all salts but NaI provoke a hydrophobic collapse transition of poly(N-isopropylacrylamide) in water at 300 K, in qualitative agreement with experimentally measured salt effects on the lower critical solution temperature of this system.

Urea‐, Squaramide‐, and Sulfonamide‐Based Anion Receptors: A Thermodynamic Study

Abstract: In this work, we compare the anion-binding capabilities of receptors 1-5, characterized by similar structures, but possessing different hydrogen- bond-donor moieties (urea, squara- mide, and sulfonamide). The presence of chromophoric substituents on the re- ceptors skeleton allowed the determi- nation of association constants by per- forming UV/Vis titrations with the in- vestigated anions on solutions of the receptors in pure acetonitrile. Addi- tional quantitative studies of the anion- binding properties of receptors 1-5 were performed by isothermal titration calorimetry (ITC). The experimental results indicated that 1 and 2 formed 1:1 hydrogen-bonded complexes with most of the anions investigated. In the case of receptors 3-5, the formation of the 1:1 adduct was observed only with anions of low basicity (i.e., chloride, bromide, iodide, and hydrogen sulfate). With more basic anions (i.e., acetate and dihydrogen phosphate), both spec- trophotometric and ITC titrations ac- counted for the deprotonation of the sulfonamide group, involving the for- mation of the conjugated base of the receptor.

Iodine biofortification in tomato

Abstract: Iodine is an essential element in the human diet, and iodine deficiency is a significant health problem. No attempts to increase iodine content in plant-derived food (biofortification) have so far been particularly effective. We studied iodine uptake in tomato (Solanum lycopersicum L.) to evaluate whether it is possible to increase the iodine concentration in its fruits. Iodine translocation and storage inside tomato tissues were studied using radioactive iodine. Potassium iodide was also supplied at different concentrations to tomato plants to evaluate the resulting iodide concentration both in the vegetative tissues and the fruits. The results indicate that iodine was taken up better when supplied to the roots using hydroponically grown plants. However, a considerable amount of iodine was also stored after leaf treatment, suggesting that iodine transport through phloem also occurred. We found that tomato plants can tolerate high levels of iodine, stored both in the vegetative tissues and fruits at concentrations that are more than sufficient for the human diet. We conclude that tomato is an excellent crop for iodine-biofortification programs.

Highly sensitive and selective determination of iodide and thiocyanate concentrations using surface-enhanced Raman scattering of starch-reduced gold nanoparticles.

Abstract: In this report, we propose a novel technique for the determination of the concentrations of iodide and thiocyanate by surface-enhanced Raman scattering (SERS) of starch-reduced gold nanoparticles. Starch-reduced gold nanoparticles show an intrinsic Raman peak at 2125 cm–1 due to the −C≡C– stretching mode of a synthesized byproduct. Because of the high adsorptivity of iodide on a gold surface, the intensity of the SERS peak at 2125 cm–1 decreases with an increase in the iodide concentration. Thiocyanate also strongly adsorbs on a gold surface, and a new peak appears at around 2100 cm–1, attributed to the −C≡N stretching vibration in a SERS spectrum of starch-reduced gold nanoparticles. These two peaks were successfully used to determine the iodide and thiocyanate concentrations separately, even in their mixture system. The detection limit of this technique for iodide is 0.01 μM with a measurement range of 0.01–2.0 μM, while the detection limit of this technique for thiocyanate is 0.05 μM with a measurement...

A Cu@Au Nanoparticle-Based Colorimetric Competition Assay for the Detection of Sulfide Anion and Cysteine

Abstract: As an extension of our previous work, which described the unique ability of the core/shell Cu@Au nanoparticle (NP) to selectively recognize iodide,(1) herein, we wish to report the development of an alternatively sensitive and selective colorimetric detection for sulfide anion and cysteine based upon the Cu@Au NP by a competition avenue. In the absence of sulfide anion or cysteine, iodide can induce an appreciable color change of the Cu@Au NP solution from purple to red by transforming the clusters of NP to single, nearly spherical, and larger ones. However, the transformation is severely interfered by the presence of sulfide or cysteine because of a higher binding strength of the S–Au bond than the I–Au one. As a result, the clear purple-to-red color change induced by iodide is affected as a correlation with the concentration of sulfide or cysteine. By taking advantage of this fact, we can detect a concentration of 3 μM for sulfide and 0.4 μM for cysteine with the naked eye or 0.3 μM (10 ppb) for sulfide...