Showing papers on "Iodide published in 2010"

An organic redox electrolyte to rival triiodide/iodide in dye-sensitized solar cells

Abstract: Dye-sensitized solar cells (DSCs) have achieved impressive conversion efficiencies for solar energy of over 11% with an electrolyte that contains triiodide/iodide as a redox couple. Although triiodide/iodide redox couples work efficiently in DSCs, they suffer from two major disadvantages: electrolytes that contain triiodide/iodide corrode electrical contacts made of silver (which reduces the options for the scale up of DSCs to module size) and triiodide partially absorbs visible light. Here, we present a new disulfide/thiolate redox couple that has negligible absorption in the visible spectral range, a very attractive feature for flexible DSCs that use transparent conductors as current collectors. Using this novel, iodide-free redox electrolyte in conjunction with a sensitized heterojunction, we achieved an unprecedented efficiency of 6.4% under standard illumination test conditions. This novel redox couple offers a viable pathway to develop efficient DSCs with attractive properties for scale up and practical applications.

Palladium-Catalyzed Aminosulfonylation of Aryl Halides

Abstract: The palladium-catalyzed three-component coupling of aryl iodides, sulfur dioxide, and hydrazines to deliver aryl N-aminosulfonamides is described. The colorless crystalline solid DABCO·(SO2)2 was used as a convenient source of sulfur dioxide. The reaction tolerates significant variation of both the aryl iodide and hydrazine coupling partners.

Modified Ta3N5 Powder as a Photocatalyst for O2 Evolution in a Two-Step Water Splitting System with an Iodate/Iodide Shuttle Redox Mediator under Visible Light

Abstract: Modification of tantalum nitride (Ta3N5), which has a band gap of 2.1 eV, with nanoparticulate iridium (Ir) and rutile titania (R-TiO2) achieved functionality as an O2 evolution photocatalyst in a two-step water-splitting system with an IO3−/I− shuttle redox mediator under visible light (λ > 420 nm) in combination with a Pt/ZrO2/TaON H2 evolution photocatalyst. The loaded Ir nanoparticles acted as active sites to reduce IO3− to I−, while the R-TiO2 modifier suppressed the adsorption of I− on Ta3N5, allowing Ta3N5 to evolve O2 in the two-step water-splitting system.

Room Temperature C ? H Activation and Cross‐Coupling of Aryl Ureas in Water

Abstract: Palladium-catalyzed cross-coupling reactions of aryl halides with aromatic C–H bonds have emerged as a powerful method for the preparation of biaryls.[1,2] Despite substantially increased attention to the field, typical reaction conditions still require high temperatures (> 120°C) for insertion into aromatic C–H bonds, which can be viewed as a major drawback to this chemistry. Such forcing conditions often appear to be critical to overcoming the low reactivity of aryl C–H bonds. A much milder C–H activation reaction at ambient temperatures would, in particular, likely be more dependent on activation by the catalyst.[3] Although there are many ortho-directing groups for C–H activation reactions,[1] the amide residue in anilides is especially attractive as a coupling partner for the synthesis of valuable aniline derivatives. In 1984, Tremont and co-workers used acetanilides for C–H alkylation with alkyl iodides, albeit promoted by stoichiometric Pd(OAc)2.[4] Both the Daugulis[5] and Sanford[6] groups have demonstrated Pd-catalyzed ortho-arylations of anilides with aryl iodides or iodonium salts at temperatures above 100°C. Moreover, ortho-directed C–H activation can suffer from double arylations with respect to the directing group.[1,5] C–H arylations of reactive indoles have been reported at room temperature,[7] but to the best of our knowledge C–H arylation of anilide derivatives with aryl halides at ambient temperatures have not yet been achieved.[1,8] Herein, we describe the first room temperature mono-C–H activation of urea derivatives and their cross-couplings with aryl iodides in water (Scheme 1). This methodology provides a convenient route to various aniline derivatives by means of C–H activation under mild conditions. Scheme 1 C–H activation at room temperature in water. Optimization studies employed the combination of anilides (1a–f) and 4-iodoanisole (2a, 2 equiv) in the presence of Pd(OAc)2 (10 mol%), AgOAc (2 equiv) and aqueous HBF4 (5 equiv) in 2 wt% surfactant/water solutions at room temperature (Table 1). The effectiveness of various directing groups was initially examined, and among a number of different anilide derivatives 1a–f explored, only the aromatic urea 1f smoothly underwent C–H arylation at room temperature (Table 1, runs 1–6). Recently, Lloyd-Jones and Booker-Milburn have also found aryl ureas to be more active coupling partners for C–H functionalizations than other anilides.[9] Acetanilide 1a reacted with 2a only upon heating to 50°C. Pivaloylanilide 1c has been reported as an effective directing group at 130°C,[1,2,5] but gave a low yield under these room temperature conditions (run 3). Generally, acetic acid or trifluoroacetic acid (TFA) is required to carry out C–H activation;[1,2] in this case, HBF4 was found to be critical for generation of biaryl 3 in good yield (run 6). Table 1 Optimization of C–H arylations at room temperature.[a] Although use of the surfactant PTS[10] gave good yields, comparable results were realized with several commercially available amphiphiles. Best yields were obtained using 2 wt% Brij35 in water (Table 1, runs 7–13). Reduced amounts of HBF4, silver salt, or palladium catalyst led to lower yields. A plausible rationale for these results involves generation of a highly active cationic palladium species (Scheme 2).[7c,11] Scheme 2 Generation of a cationic palladium(II) species. As illustrated by several representative examples in Table 2, the scope of this transformation is broad, applying to aryl urea derivatives and aryl iodides bearing a variety of functional groups with yields in the 70–97% range, all done in water at room temperature. Under these mild conditions, only mono-arylated products of net substitution were typically obtained. Table 2 Products from reactions of aryl ureas with aryl iodides.[a] Especially noteworthy are aniline derivatives lacking ortho- or meta-substitution, which have previously been shown to be prone to double arylation. Under these conditions, couplings are selective for singly arylated products (3f, 3r, 3s, 3v). Only reactions of the aryl urea bearing a 4-sec-butyl group with phenyliodide and 4-tolyl iodide produced small amounts (10–15% yields) of doubly arylated products. Reduced aryl iodide loading or reaction time, however, suppressed double arylation to less than 3% (3t, 3u). While current reaction conditions were effective for a variety of substrates, products resulting from sterically hindered aryl iodides having ortho-substituents, such as 2-anisyl iodide and 2-tolyl iodide, were not formed (3b, 3n). The reactivity of N-methyl substituted ureas (e.g., 3x) appears to be much lower than that of their non-N-methyl-substituted analogues, possibly due to palladium coordination in the initial C–H activation step. Electron-deficient ureas (e.g., 3q) were also inert, suggesting that electrophilic attack of cationic palladium may be critical for activating aromatic C–H bonds. The reactivity of aryl iodides possessing electron-rich groups is also much higher than that of more electron-withdrawing aryl iodides (3a vs. 3e). Further advantage can also be taken of the reaction conditions associated with these cross-couplings to allow for tandem processes. Thus, in the presence of silver nitrate, arylation afforded a product of type 3 exclusively, following standard treatment with hydrogen carbonate (Scheme 3). Without exposure to this aqueous workup, nitrated biaryl 4 was isolated. Since use of silver acetate gave only arylated product 3a regardless of quenching conditions, the potential for carrying out secondary electrophilic aromatic substitution could readily be demonstrated. Simple introduction of bromine prior to workup afforded the C-arylated, regiospecifically brominated adduct 5 in good overall isolated yield (70%). The identities of products 3a and 4 were confirmed by X-ray analyses (see Supporting Information). Scheme 3 Tandem C–H arylation–electrophilic trapping. While the exact reaction mechanism is currently unclear, one possibility involves a cationic PdII complex-catalyzed electrophilic C–H activation step.[7,11] Nevertheless, the reaction of 1f and 2a (see Table 2) in the presence of [Pd(MeCN)4](BF4)2, a commercially available cationic palladium(II) complex, did not result in the formation of product (Scheme 4, top). It was found, however, that adding 40 mol% MeCN under the standard, optimized, and otherwise successful conditions (cf. Table 2, product 3a; 76% yield), only traces of product formation was observed (Scheme 4, bottom). This suggests that the low reactivity of the pre-formed cationic palladium complex may actually be due to suppression of the reaction by MeCN coordination to the Lewis acidic PdII. Scheme 4 Effect of cationic palladium species. With the goal of generating a highly active cationic PdII complex without the aid of strong acid, and in the absence of coordinating ligands, the combination of Pd(OAc)2 and AgBF4 was examined (Scheme 5). As expected, these conditions led to C–H activation. Unlike the reaction with AgOAc, the reaction with AgBF4 produced the corresponding C–H arylated product 3a without assistance of external acid at room temperature. This result, under such mild conditions, is indicative of the potential for highly active cationic palladium species to serve as especially effective catalysts for C–H arylation reactions. The silver salt may not only weaken the C–I bond and/or function as halogen scavenger, but may also play an important role in the generation of cationic palladium(II) species. Scheme 5 C–H activation without acids at room temperature in water. In summary, the first room temperature C–H arylation of anilides with aryl iodides to give biaryl derivatives in good yields is described. These are accomplished using aryl urea derivatives, and are all done in water in the absence of phosphine ligands. Further studies of metal-catalyzed C–H activation reactions at room temperature, including both Heck couplings and mechanistic studies, are currently under investigation.

Iodine to calcium ratios in marine carbonate as a paleo-redox proxy during oceanic anoxic events

Abstract: Periods of globally distributed extreme oxygen depletion, so-called oceanic anoxic events (OAEs), have been recognized in the Mesozoic geological record and appear to be characteristic of episodes of extreme warmth. Here we explore the application of iodine/calcium ratios (I/Ca) in marine carbonate as a new geochemical proxy to constrain seawater redox change, and provide additional insights into the response of ocean chemistry to ancient climatic warming. Iodine has long been known as a redox-sensitive and biophilic element, mainly present as iodate and iodide in seawater, iodate converting to iodide under anoxic conditions. Laboratory experiments growing calcite crystals from solutions spiked with iodate show that this is the ionic species incorporated into the carbonate structure, likely substituting for the CO 3 2− ion. A fall in the I/Ca ratio measured in carbonates formed in shallow water by marine calcifiers during the early Toarcian and Cenomanian-Turonian OAEs is interpreted both as a response to a decrease in the iodate/iodide ratio in ocean waters and the drawdown of the global iodine inventory under conditions of accelerated organic-matter burial. The results suggest that I/Ca ratios in carbonates may be used to monitor seawater oxidation levels throughout Earth history.

Iodide Chemistry in Dye-Sensitized Solar Cells: Making and Breaking I−I Bonds for Solar Energy Conversion

Abstract: The photo-oxidation of iodide (I−) results in the formation of I−I bonds relevant to solar energy conversion. The making (and breaking) of I−I bonds is specifically important to the operation of high-efficiency dye-sensitized solar cells. In this Perspective, the redox chemistry of iodide in aqueous solution is briefly reviewed, followed by recent photoinduced studies in nonaqueous solution. Analogous to thermal electron-transfer studies, two mechanisms have been identified for photodriven I−I bond formation in solution. With regard to breaking I−I bonds, the photodriven cleavage of I−I bonds has been quantified by the reduction of diiodide (I2•−) and triiodide (I3−). Studies at the solution-semiconductor interface present in dye-sensitized solar cells have also revealed that I−I bonds are formed, and I2•− is a product of iodide oxidation. Rapid disproportionation of I2•− to yield I3− and I− products that are not easily reduced by electrons injected into TiO2 is proposed to be key to the success of the I−...

Iodine-free high efficient quasi solid-state dye-sensitized solar cell containing ionic liquid and polyaniline-loaded carbon black

Abstract: An incombustible and non-volatile paste with carbon black (CB), a conducting polymer (CP), and an ionic liquid (1-buty-3-methylimidazolium iodide, BMII or 1-methyl-3-propyl imidazolium iodide, PMII) was placed between the dye-sensitized porous TiO2 and the Pt counter electrode to fabricate a quasi solid-state DSSC, without the addition of iodine. While the solar-to-electricity efficiencies (η) were measured to be 4.38% and 3.68% for the cells with PMII/CB and BMII/CB, respectively, the corresponding values without CB were 0.6% and 0.3%; indicating the remarkable role played by the carbon material in the electrolyte. When the CB was replaced with polyaniline-loaded carbon black (PACB), an efficiency of 5.81% was obtained, at 100 mW cm−2 AM1.5 illumination using PMII, the highest ever reported for a quasi solid-state DSSC made without iodine. High thermal stability up to 250 °C for each component in the composite electrolytes was confirmed by thermogravimetric analyses (TGA). At-rest durability of the DSSC with PACB was studied both at room temperature and at 70 °C and was found to be far superior to that of a cell with an organic solvent electrolyte. Electrochemical impedance spectroscopy (EIS) and dark current measurements were used to substantiate the results.

One-Pot Thioetherification of Aryl Halides Using Thiourea and Alkyl Bromides Catalyzed by Copper(I) Iodide Free from Foul-Smelling Thiols in Wet Polyethylene Glycol (PEG 200)

Abstract: In this article, we have developed a new protocol for the thioarylation of structurally diverse alkyl bromides such as benzyl, cinnamyl, n-octyl, cyclohexyl, cyclopentyl, and tert-butyl bromides with aryl iodides, bromides and an activated chloride using thiourea catalyzed by copper(I) iodide in wet polyethylene glycol (PEG 200) as an eco-friendly medium in the presence of potassium carbonate at 80 and 100 °C under an inert atmosphere. The process is free from foul-smelling thiols which makes this method more practical for the thioetherification of aryl halides. Another important feature of this method is the variety of alkyl bromides which are commercially available for the in situ generation of thiolate ions with respect to the existing protocols in which the less commercially available thiols are directly used for the preparation of arylthio ethers.

Ion specificity at the peptide bond: molecular dynamics simulations of N-methylacetamide in aqueous salt solutions.

Abstract: Affinities of alkali cations and halide anions for the peptide group were quantified using molecular dynamics simulations of aqueous solutions of N-methylacetamide using both nonpolarizable and polarizable force fields. Potassium and, more strongly, sodium exhibit an affinity for the carbonyl oxygen of the amide group, while none of the halide anions shows any appreciable attraction for the amide hydrogen. Heavier halides, however, interact with the hydrophobic methyl groups of N-methylacetamide. Using the present results for a model of the peptide bond we predict that the destabilizing effect of weakly hydrated Hofmeister ions, such as bromide or iodide, is not due to direct interactions with the backbone but rather due to attraction to hydrophobic regions of the protein.

Mechanism of interaction of monovalent ions with phosphatidylcholine lipid membranes.

Abstract: Interactions of different anions with phospholipid membranes in aqueous salt solutions were investigated by molecular dynamics simulations and fluorescence solvent relaxation measurements. Both approaches indicate that the anion−membrane interaction increases with the size and softness of the anion. Calculations show that iodide exhibits a genuine affinity for the membrane, which is due to its pairing with the choline group and its propensity for the nonpolar region of the acyl chains, the latter being enhanced in polarizable calculations showing that the iodide number density profile is expanded toward the glycerol level. Solvent relaxation measurements using Laurdan confirm the influence of large soft ions on the membrane organization at the glycerol level. In contrast, chloride exhibits a peak at the membrane surface only in the presence of a surface-attracted cation, such as sodium but not potassium, suggesting that this behavior is merely a counterion effect.

Synthesis, Characterization, DNA Binding Properties, Fluorescence Studies and Antioxidant Activity of Transition Metal Complexes with Hesperetin-2-hydroxy Benzoyl Hydrazone

Abstract: A novel Schiff-base ligand (H5L), hesperetin-2-hydroxy benzoyl hydrazone, and its copper (II), zinc (II) and nickel (II) complexes (M·H3L) [M(II) = Cu, Zn, Ni], have been synthesized and characterized The ligand and Zn (II) complex exhibit green and blue fluorescence under UV light and the fluorescent properties of the ligand and Zn (II) complex in solid state and different solutions were investigated In addition, DNA binding properties of the ligand and its metal complexes have been investigated by electronic absorption spectroscopy, fluorescence spectra, ethidium bromide displacement experiments, iodide quenching experiments, salt effect and viscosity measurements Results suggest that all the compounds bind to DNA via an intercalation binding mode Furthermore, the antioxidant activity of the ligand and its metal complexes was determined by superoxide and hydroxyl radical scavenging methods in vitro The metal complexes were found to possess potent antioxidant activity and be better than the free ligand alone and some standard antioxidants like vitamin C and mannitol

Biofortification of lettuce (Lactuca sativa L.) with iodine: the effect of iodine form and concentration in the nutrient solution on growth, development and iodine uptake of lettuce grown in water culture

Abstract: BACKGROUND: Iodine is an essential trace element for humans. Two billion individuals have insufficient iodine intake. Biofortification of vegetables with iodine offers an excellent opportunity to increase iodine intake by humans. The main aim was to study the effect of iodine form and concentration in the nutrient solution on growth, development and iodine uptake of lettuce, grown in water culture. RESULTS: In both a winter and summer trial, dose rates of 0, 13, 39, 65, and 90 or 129 µg iodine L-1, applied as iodate (IO3-) or iodide (I-), did not affect plant biomass, produce quality or water uptake. Increases in iodine concentration significantly enhanced iodine content in the plant. Iodine contents in plant tissue were up to five times higher with I- than with IO3-. Iodine was mainly distributed to the outer leaves. The highest iodide dose rates in both trials resulted in 653 and 764 µg iodine kg-1 total leaf fresh weight. CONCLUSION: Biofortification of lettuce with iodine is easily applicable in a hydroponic growing system, both with I- and IO3-. I- was more effective than IO3-. Fifty grams of iodine-biofortified lettuce would provide, respectively, 22% and 25% of the recommended daily allowance of iodine for adolescents and adults

Boryltrihydroborate: synthesis, structure, and reactivity as a reductant in ionic, organometallic, and radical reactions.

Abstract: Reaction of lithium 1,3-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaborol-2-ide with borane·THF provides the first boryl-substituted borohydride: lithium [1,3-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaborol-2-yl]trihydroborate. The compound is fully characterized by 11B, 1H, and 7Li NMR spectra and other means, and these data are compared to neutral and anionic benchmark compounds. The compound crystallizes as a dimer complexed to four THF molecules. The dimer lacks the bridging B−H bonds seen in neutral boranes and is instead held together by ionic Li---HB interactions. A preliminary scan of reactions with several iodides shows that the compound participates in an ionic reduction (with a primary-alkyl iodide), an organometallic reduction (Pd-catalyzed with an aryl iodide), and a radical reduction (AIBN-initiated with a sugar-derived iodide). Accordingly the new borylborohydride class may share properties of both traditional borohydrides and isoelectronic N-heterocyclic carbene boranes.

Facile Synthesis of Koser’s Reagent and Derivatives from Iodine or Aryl Iodides

Abstract: The first one-pot synthesis of neutral and electron-rich [hydroxy(tosyloxy)iodo]arenes (HTIBs) from iodine and arenes is presented, thereby avoiding the need for expensive iodine(III) precursors. A large set of HTIBs, including a polyfluorinated analogue, can be obtained from the corresponding aryl iodide under the same conditions. The reaction proceeds under mild conditions, without excess reagents, and is fast and high-yielding. Together, the two presented routes give access to a wide range of HTIBs, which are useful reagents in a variety of synthetic transformations.

Probing the hydration structure of polarizable halides: a multiedge XAFS and molecular dynamics study of the iodide anion.

Abstract: A comprehensive analysis of the H2O structure about aqueous iodide (I−) is reported from molecular dynamics (MD) simulation and X-ray absorption fine structure (XAFS) measurements. This study establishes the essential ingredients of an interaction potential that reproduces the experimentally determined first-solvation shell of aqueous iodide. XAFS spectra from the iodide K, L1, and L3 edges were corefined to establish the complete structure of the first hydration shell about aqueous iodide. Further, we have utilized molecular dynamics simulations employing both DFT (+dispersion) and empirical polarizable interaction potentials to generate an ensemble of structures that were directly compared to the XAFS data. Our results indicate that DFT-MD simulations provide a description of the molecular structure that is more consistent with the XAFS experimental data. The experimental data yield approximately 6.3 water molecules located at I−H and I−O distances of 2.65 and 3.50 A, respectively. The differences in th...

Combinatorial doping of TiO2 with platinum (Pt), chromium (Cr), vanadium (V), and nickel (Ni) to achieve enhanced photocatalytic activity with visible light irradiation

Abstract: Titanium dioxide (TiO_2) was doped with the combination of several metal ions including platinum (Pt), chromium (Cr), vanadium (V), and nickel (Ni). The doped TiO_2 materials were synthesized by standard sol-gel methods with doping levels of 0.1 to 0.5 at.%. The resulting materials were characterized by x-ray diffraction (XRD), BET surface-area measurement, scanning electron microscopy (SEM), and UV-vis diffuse reflectance spectroscopy (DRS). The visible light photocatalytic activity of the codoped samples was quantified by measuring the rate of the oxidation of iodide, the rate of degradation of methylene blue (MB), and the rate of oxidation of phenol in aqueous solutions at λ > 400 nm. 0.3 at.% Pt-Cr-TiO_2 and 0.3 at.% Cr-V-TiO_2 showed the highest visible light photocatalytic activity with respect to MB degradation and iodide oxidation, respectively. However, none of the codoped TiO_2 samples were found to have enhanced photocatalytic activity for phenol degradation when compared to their single-doped TiO_2 counterparts.

A novel approach for the simultaneous determination of iodide, iodate and organo-iodide for 127I and 129I in environmental samples using gas chromatography-mass spectrometry.

Abstract: In aquatic environments, iodine mainly exists as iodide, iodate, and organic iodine. The high mobility of iodine in aquatic systems has led to 129I contamination problems at sites where nuclear fuel has been reprocessed, such as the F-area of Savannah River Site. In order to assess the distribution of 129I and stable 127I in environmental systems, a sensitive and rapid method was developed which enables determination of isotopic ratios of speciated iodine. Iodide concentrations were quantified using gas chromatography−mass spectrometry (GC−MS) after derivatization to 4-iodo-N,N-dimethylaniline. Iodate concentrations were quantified by measuring the difference of iodide concentrations in the solution before and after reduction by Na2S2O5. Total iodine, including inorganic and organic iodine, was determined after conversion to iodate by combustion at 900 °C. Organo-iodine was calculated as the difference between the total iodine and total inorganic iodine (iodide and iodate). The detection limits of iodide-...

Iodide impurities in hexadecyltrimethylammonium bromide (CTAB) products: lot-lot variations and influence on gold nanorod synthesis.

Abstract: Recent reports [Smith and Korgel Langmuir 2008, 24, 644−649 and Smith et al.Langmuir 2009, 25, 9518−9524] have implicated certain hexadecyltrimethylammonium bromide (CTAB) products with iodide impurities, in the failure of a seed-mediated, silver and surfactant-assisted growth protocol, to produce gold nanorods. We used two of the three “suspect” CTAB products and a “good” CTAB product in the protocol, varying silver nitrate solutions in the growth solutions. We obtained excellent gold nanorod samples as witnessed in signature longitudinal plasmon peaks in optical extinction spectra, which we substantiated using electron microscopy. Analysis of these samples using inductively coupled plasma mass spectroscopy (ICP−MS) failed to detect iodide. We subsequently learnt from discussions with Smith et al. that different lot numbers within the same product had been analyzed by our respective laboratories. We can conclude that iodide impurities can vary significantly from lot to lot within a product, to such an extent that there is no guarantee that gold nanorods can be synthesized with one or other CTAB product. Conversely, labeling a CTAB product, identified by a product number or supplier name, as one whose use precludes the formation of nanorods, is also hasty.

Experimental and Theoretical Investigation of the Self-Reaction of Phenyl Radicals

Abstract: A combination of experiment and theory is applied to the self-reaction kinetics of phenyl radicals. The dissociation of phenyl iodide is observed with both time-of-flight mass spectrometry, TOF-MS, and laser schlieren, LS, diagnostics coupled to a diaphragmless shock tube for temperatures ranging from 1276 to 1853 K. The LS experiments were performed at pressures of 22 +/- 2, 54 +/- 7, and 122 +/- 6 Torr, and the TOF-MS experiments were performed at pressures in the range 500-700 Torr. These observations are sensitive to both the dissociation of phenyl iodide and to the subsequent self-reaction of the phenyl radicals. The experimental observations indicate that both these reactions are more complicated than previously assumed. The phenyl iodide dissociation yields approximately 6% C(6)H(4) + HI in addition to the major and commonly assumed C(6)H(5) + I channel. The self-reaction of phenyl radicals does not proceed solely by recombination, but also through disproportionation to benzene + o-/m-/p-benzynes, with comparable rate coefficients for both. The various channels in the self-reaction of phenyl radicals are studied with ab initio transition state theory based master equation calculations. These calculations elucidate the complex nature of the C(6)H(5) self-reaction and are consistent with the experimental observations. The theoretical predictions are used as a guide in the development of a model for the phenyl iodide pyrolysis that accurately reproduces the observed laser schlieren profiles over the full range of the observations.

A Physiological Systems Model for Iodine for Use in Radiation Protection

Abstract: This paper summarizes the biokinetic database for iodine in the human body and proposes a biokinetic model for systemic iodine for use in dose assessments for internally deposited radioiodine. The model consolidates and extends existing physiological systems models describing three subsystems of the iodine cycle in the body: circulating inorganic iodide, thyroidal iodine (trapping and organic binding of iodide and synthesis, storage and secretion of thyroid hormones), and extrathyroidal organic iodine. Thyroidal uptake of inorganic iodide is described as a function of stable iodine intake (Y, µg day−1) and thyroidal secretion of hormonal iodine (S, µg day−1). Baseline parameter values are developed for reference adults with typical iodine intake. Compared with the current systemic biokinetic model of the International Commission on Radiological Protection (ICRP) for occupational intake of radioiodine, the proposed model predicts higher absorbed doses to the thyroid per unit uptake to blood for ve...

Perchlorate and Iodide in Whole Blood Samples from Infants, Children, and Adults in Nanchang, China

Abstract: Perchlorate, ClO(4)(-), interferes with iodide (I(-)) uptake by the sodium-iodide symporter (NIS) and thereby affects thyroid hormone production in the body. Studies have reported human exposures to perchlorate based on measurements in urine, but little is known about the levels in blood. In this study, we determined concentrations of perchlorate, iodide, and other anions (e.g., chlorate [ClO(3)(-)], bromate [BrO(3)(-)], bromide [Br(-)]) in 131 whole blood samples collected from Chinese donors aged 0.4 to 90 yr, in Nanchang, China. Perchlorate, iodide, and bromide were detected in all of the samples analyzed, whereas chlorate was found in only 27% of the samples and bromate was found in only 2%. The mean (range) concentrations of perchlorate, iodide, and bromide were 2.68 (0.51-10.5), 42.6 (1.58-812), and 2120 (1050-4850) ng/mL, respectively. Perchlorate levels in blood from Nanchang adults were 10-fold greater than levels that have been previously reported for U.S. adults. The iodide/perchlorate molar ratio ranged from 3.05 to 15.3 for all age groups, and the ratio increased with age (r = 0.732, p < 0.01). Perchlorate and bromide concentrations decreased significantly with age, whereas iodide concentrations increased with age. No significant gender-related differences in blood perchlorate, iodide, or bromide levels were found. A significant negative correlation was found between the concentrations of perchlorate and iodide in blood. Exposure doses of perchlorate were estimated for infants, toddlers, children, adolescents, and adults based on the measured concentrations in blood, using a simple pharmacokinetic model. The mean exposure doses of perchlorate for our age groups ranged from 1.12 (adults) to 2.22 μg/kg bw/day (infants), values higher than the United States Environmental Protection Agency's (USEPA) reference dose (RfD: 0.7 μg/kg bw/day). This is the first study on perchlorate and iodide levels in whole blood from infants, toddlers, children, adolescents, and adults from a city in China with known high perchlorate levels.