Presence Of Iodide Research Articles

An Imidazolium‐Based Fluorescent Cyclophane for the Selective Recognition of Iodide

For your I's only: A new imidazolium-based fluorescent cyclophane 1 was designed and synthesized that was quenched selectively in the presence of iodide but not other anions, as assessed by fluorimetry. In addition, fluorescence titration experiments, 1H NMR spectroscopic data, and theoretical calculations provide evidence that 1 encapsulates two iodides inside its cavity.

Oligo(poly)thiophene Sensitization of CdSe Nanocrystal and TiO2 Polycrystalline Electrodes: A Photoelectrochemical Investigation

Oligo(poly)thiophenes were investigated by photoelectrochemical methods as monolayer sensitizers of CdSe nanocrystal (CdSe-NCs) and TiO2 polycrystalline films on ITO electrodes. 7.5 nm diameter CdSe-NCs layers and polycrystalline (anatase, ca. 40 nm crystallite size) TiO2 films were functionalized with an α,ω-dicarboxylic sexithiophene and with two polythiophenes, bearing differently spaced side carboxylic terminals, including regioregular poly(thiophene-3-propionic acid). The modified electrodes were investigated in a three-electrode photoelectrochemical cell in the presence of iodide as sacrificial generator of intense and steady oxidative photocurrents. The oligo(poly)thiophenes act in general as moderate hypersensitizers (roughly twice more efficient than calculated). Poly(thiophene-3-propionic acid) monolayers, formed on CdSe-NC structures from ethanol, generate a strong hypersensitization, i.e., a response 5 times higher than expected. From optical and photoluminescence analysis such a result is att...

Nickel-iron dithiolates related to the deactivated [NiFe]-hydrogenases.

Described herein are preparations of synthetic models for the deactivated Ni(II)Fe(II) states of the [NiFe]-hydrogenases. Iodination of the S = ½ species [(dppe)Ni(pdt)Fe(CO)(3)](+) afforded the diamagnetic iodo complex [(dppe)Ni(pdt)IFe(CO)(3)](+). Crystallographic analysis of this species confirmed the presence of square-pyramidal Ni linked to an octahedral Fe centre. The NiFe separation of 3.018 Å indicated the absence of metal-metal bonding. This complex could be reduced to give (dppe)Ni(pdt)Fe(CO)(3) and, in the presence of iodide, decarbonylated to afford (dppe)Ni(pdt)FeI(2). Derivatives of the type [(diphosphine)Ni(dithiolate)XFe(CO)(2)L](+) (X = Cl, Br, I) were prepared by halogenation of mixed-valence precursors [(diphosphine)Ni(dithiolate)Fe(CO)(2)L](+) (diphosphine = dppe, dcpe; L = tertiary phosphine or CO). The Fe(CO)(2)(PR(3))-containing derivatives are more robust than the related tricarbonyl derivatives. Exploiting this greater stability, we characterised examples of chloride and bromide derivatives. Related fluorides could be prepared by F(-) abstraction from BF(4)(-). Spectroscopic evidence is presented for the hydroperoxide [(dppe)Ni(pdt)(OOH)Fe(CO)(2)L](+), which represents a model for the Ni-SU state.

Calf thymus DNA-stabilized polythiophene fluorescence probe for label-free detection of spermine

It is a challenge to detect molecules lacking a chromophore, such as polyamines, by optical methods since they are insensitive to light. In order to detect the optical signals, it is compulsory to derive these molecules with optical labels, which, however, is complicated, time-consuming and may be expensive. In this work, a highly specific strategy for spermine detection is developed on the basis of the iodide-induced conformational change of polythiophene. By using the triplex complex of negatively charged double-stranded calf thymus DNA (ctDNA)-stabilized cationic polythiophene as a fluorescent probe, the highly specific detection of spermine could be realized since polythiophene, which will be released from the triplex complex owing to the condensation and aggregation of ctDNA with spermine, undergoes a conformational change from the random-coiled non-planar state to the highly conjugated planar form in the presence of iodide, resulting in a yellow-to-red color conversion and fluorescence quenching. The quenched fluorescence was found to be proportional to the spermine concentrations in the range of 1.2-50 μM with the limit of detection (LOD) being 0.5 μM (3σ/k).

Kinetic Study of the Electrochemical Oxidation of Methylene Blue with Pt Electrode

Kinetic study of the indirect oxidation of methylene blue on Pt electrode in presence of several strong electrolytes is undertaken. Different operating conditions that affected the treatment process were studied in order to find the best conditions. The order with respect to methylene blue is zero order in presence of chloride, but it is second order in presence of bromide. The oxidation rate was affected by current density, halide concentration (KCl, KBr), nature of supporting electrolyte and initial pH. However, the initial dye concentration and temperature did not show a significant effect. The oxidation of methylene blue in presence of iodide, fluoride and sulfate is absent, but it is important in presence of chloride and bromide. The product of the indirect oxidation is the chloronated (bromonated) methylene violet bernthsen.

An alternative way to use the triplet energy of fluorescent dyes in organic light-emitting devices via an external iodide

An unusual heavy atom effect has been identified in an organic light emitting device (OLED) containing polyvinylcarbazole (PVK) as the host, the red fluorescent dye 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)-vinyl]-pyran-4-ylidene}-malononitrile (DCM2) as the emitter, and non-emitting 1,8-diiodooctane (RI) as a heavy atom source instead of a rare metal. The intensity of electroluminescence (EL) of DCM2 changes with the concentration of RI, with a maximum EL intensity obtained for DCM2 at a concentration of 0.25% of RI. Photoluminescence (PL) spectra of PVK–DCM2 films show increased singlet emission from DCM2 in the presence of iodide at 12 K. The enhanced fluorescence induced by iodide is caused by energy transfer from both the singlet and triplet states of PVK to the singlet states of DCM2. These results suggest an alternative way to use the triplet energy of fluorescent materials with external heavy atoms rather than conventional phosphorescent dyes containing rare heavy metal atoms.

Pyridine Carboxylate Complexes of Mo(II) as Active Catalysts in Homogeneous and Heterogeneous Olefin Epoxidation

[MoBr2(CO)3(L)2] complexes were synthesized with L = nicH (pyridine-3-carboxylate), picH (pyridine-2- carboxylate) and pydcH2 (pyridine – 2,6 – dicarboxylic acid). New lamellar materials intercalated with molybdenum(II) complexes were prepared by first calcinating the starting lamellar material at 823 K for four hours, to eliminate all the carbonate ions; the layered structure was reconstructed after treatment with a basic solution of either nicH, picH, or pydcH2 in a dmf solution of NaOH at 343 K. Impregnation with a solution of the organometallic precursor [MoX2(CO)3(NCCH3)2] (X= Br, X= I) led to substitution of the nitriles by two L ligands. All the Mo(II) complexes were characterized by FTIR, elemental analysis, and 1H and 13C solution NMR, and the materials by powder X-ray diffraction, FTIR and 13C CP MAS-DD solid state NMR. Both the complexes, their iodide analogues, these new materials (3.80 wt% and 1.25 wt% Mo for pic or pydc) and their iodide analogues (4.54 wt% and 6.33 wt% Mo for pic or pydc) catalyze the epoxidation of ciclooctene and styrene and the chiral olefins R(+)- and S(-)-limonene at 328 K. Higher activity is associated with presence of iodide and nicH. Keywords: Molybdenum, layered materials, epoxidation, heptacoordination, catalysis, hydrotalcite, Clays, NCCH3, Organometallic Fragments, Epoxidation of Olefins

Selective cloud point extraction for the determination of cadmium in food samples by flame atomic absorption spectrometry

A new cloud point extraction (CPE) procedure for preconcentration of cadmium prior to the determination by flame atomic absorption spectrometry (FAAS) was developed. The method is based on the fact that cadmium could form hydrophobic ion-associated complex in the presence of iodide and methyl green (MG), and the hydrophobic ion-associated complex could be extracted into surfactant-rich phase. The main factors affecting CPE procedure, such as pH, concentration of KI, MG and surfactant, equilibrium temperature and incubation time, sample volume were investigated. Potential interference from co-existing ions was largely eliminated as most of co-existing ions can not form extractable ion-associated complex with iodide and MG. Under the optimum conditions, the limit of detection (3σ) and limit of quantity (10σ) were 0.90ngmL−1 and 3.0ngmL−1 for cadmium, respectively, and relative standard deviation was 4.2% (c=50ngmL−1, n=7). The proposed method was successfully applied to determination of cadmium in the certified reference rice sample (GBW08510) and food samples with satisfactory results.

Sequestration of Hg2+ by Some Biologically Important Thiols

A potentiometric and 1H NMR investigation on the interactions between Hg2+ and some biologically important sulfhydryl ligands, such as cysteine (H2CYS), penicillamine (H2PSH), and glutathione (H3GSH), is reported. Equilibria were studied at T = 298.15 K, in the ionic strength range (0.1 to 1) mol·kg–1, using as ionic medium NaCl in the presence of iodide (NaI) as a competitive ligand. Results show the formation of HgL2–z, HgLH3–z, HgLH24–z, HgL22–2z, HgL2H3–2z, and HgL2H24–2z species (Lz– = CYS2–, PSH2–, or GSH3–) together with HgL2H3– for GSH3– only. Formation constant values are very high with, as an example, log β = 34.54, 34.24, and 32.05 for Hg(CYS)0, Hg(PSH)0, and Hg(GSH)− species, respectively (at I = 0.25 mol·kg–1, T = 298.15 K). 1H NMR measurements at I = 0.25 mol·kg–1 (NaCl) fully confirm the potentiometric findings. The speciation diagrams show that most of the metal fraction is present as complex species in a wide pH range, and the hydrolysis of the cation is completely suppressed. The sequest...

Pendrin mediates uptake of perchlorate in a mammalian in vitro system

Perchlorate is a known endocrine disruptor present in groundwater, vegetables and dairy food products in many regions of the United States. It interferes with the uptake of iodide into the thyrocyte by the sodium–iodide symporter at the basolateral surface, thus potentially disrupting the synthesis of thyroid hormone. Because transport of iodide from the thyroid follicular cells to the follicular lumen is mediated by the protein pendrin at the apical surface, we hypothesized that perchlorate may also interact with this protein. Therefore, HeLa cells were transfected with the human SLC26A4 gene, which encodes pendrin, to generate an in vitro mammalian system expressing the recombinant pendrin protein (HeLa-PDS). The HeLa-PDS cells, along with untransfected cells, were then cultured in presence of iodide and/or perchlorate. Intracellular levels of these two chemicals were measured by ion chromatography tandem mass spectrometry. Results from this study show that iodide and perchlorate uptake increases significantly in HeLa-PDS cells as compared to untransfected cells. Thus, recombinant HeLa cells expressing pendrin protein accumulate iodide and perchlorate intracellularly, indicating that pendrin is involved in the uptake of perchlorate. Additional results from this study suggest that iodide and perchlorate competitively inhibit each other for uptake by pendrin. The ability of perchlorate to compete with iodide for uptake by both basal and apical transporters may increase the potential of perturbation of thyroid homeostasis and therefore the estimated risk posed to susceptible human populations.

Observable Temperature-Dependent Compaction−Decompaction of Cationic Polythiophene in the Presence of Iodide

Investigation on compaction and decompaction of polymers is very important since it is a fundamental problem in polymer physics. With the aids of atomic force microscope (AFM) and dynamic light scattering (DLS) measurements in this contribution, the temperature-dependent compaction/decompaction transition process of water-soluble cationic polythiophene (PT) was investigated in the presence of KI. The above process is characterized by the red-to-yellow color change and fluorescence recovery and is reversible during the heating-cooling cycles in the range from 25 to 55 °C, indicating that the compaction and decompaction of polymer can be employed as a temperature indicator.

Enhanced vaporization of volatile halide of antimony(iii) for sample introduction in atomic spectroscopy: kinetic mechanism

The volatilization of Sb(III) with bromide could be stimulated by the presence of iodide. The mixture of halides showed a significant effect that enhanced this chemical vaporization. The kinetic mechanism was characterized and adjusted to a first order kinetic under the experimental conditions. It could be demonstrated that the vaporization took place in two different periods. The procedure was proposed to be an alternative for sample introduction and determination of antimony by inductively coupled plasma-optical emission spectrometry. Variables influencing the analytical procedure, such as concentration of sulfuric acid, bromide and iodide potassium and flow of carrier gas, were studied and optimized by experimental design. Under optimal conditions, the LD was 12 ng mL−1, with 2 ng absolute LD, after injection of 130 μL of antimony solutions. The linear response range was maintained between 0.05–50.0 μg mL−1. The precision of the method (RSD), for a sample injection of 1.0 μg mL−1, was in the order of 4.0%. The method was relatively free of interferences with the exception of oxidant anions.

Formation of methyl iodide on a natural manganese oxide

This paper demonstrates that manganese oxides can initiate the formation of methyl iodide, a volatile compound that participates to the input of iodine into the atmosphere. The formation of methyl iodide was investigated using a natural manganese oxide in batch experiments for different conditions and concentrations of iodide, natural organic matter (NOM) and manganese oxide. Methyl iodide was formed at concentrations ≤1 μg L −1 for initial iodide concentrations ranging from 0.8 to 38.0 mg L −1. The production of methyl iodide increased with increasing initial concentrations of iodide ion and Mn sand and when pH decreased from 7 to 5. The hydrophilic NOM isolate exhibited the lowest yield of methyl iodide whereas hydrophobic NOM isolates such as Suwannee River HPOA fraction produced the highest concentration of methyl iodide. The formation of methyl iodide could take place through the oxidation of NOM on manganese dioxide in the presence of iodide. However, the implication of elemental iodine cannot be excluded at acidic pH. Manganese oxides can then participate with ferric oxides to the formation of methyl iodide in soils and sediments. The formation of methyl iodide is unlikely in technical systems such as drinking water treatment i.e. for ppt levels of iodide and low contact times with manganese oxides.

Selective spectrophotometric determination of periodate based on its reaction with methylene green and its application to indirect determination of ethylene glycol and glycerol

A rapid, simple, accurate, and highly selective spectrophotometric method is proposed for the determination of periodate in water samples. This method is based on the reaction of methylene green with periodate in the presence of iodide. The decrease in the absorbance of methylene green is used to monitor the reaction spectrophotometrically at 613 nm. Under the optimum conditions, periodate could be determined in the concentration range 0.18-6.0 microg mL(-1). The detection limit for the method is 0.010 microg mL(-1). The influence of various foreign species was studied, and it was found that iodate did not interfere with the determination even in the presence of 200-fold of periodate. The relative standard deviations for six replicate determinations of 0.30, 0.50, 1.0, 1.5, 4.0, and 5.5 microg mL(-1) of periodate were 3.33, 2.0, 1.6, 1.33, 0.50, and 0.55%, respectively. The proposed method was applied to the determination of periodate in water samples and indirect determination of ethylene glycol in antifreeze and glycerol in vegetable oil via malaprade reaction, and satisfactory results were obtained.

Cis-bis(isothiocyanato)-bis(2,2′-bipyridyl-4,4′dicarboxylato)-Ru(II) (N719) dark-reactivity when bound to fluorine-doped tin oxide (FTO) or titanium dioxide (TiO 2) surfaces

The solar cell sensitizer cis-bis(isothiocyanato)-bis(2,2′-bipyridyl-4,4′dicarboxylato)-ruthenium(II) (N719) is adsorbed and investigated at two electrode surfaces: (i) at a bare fluorine-doped tin oxide (FTO) and (ii) at a nano-particulate anatase (TiO 2) film in contact with FTO. N719 is adsorbed from acetonitrile onto FTO surfaces giving poor quality partial or multi-layer coverage commencing at 10 −7 M concentration. In contrast, from 50% acetonitrile 50% t BuOH solution of N719 Langmuirian adsorption occurs with well-defined mono-layer coverage and a binding constant ca. 2 × 10 5 mol −1 dm 3. The adsorbed N719 exhibits voltammetric oxidation/back-reduction responses with E mid ≈ 0.56 (weaker) and 0.68 (dominant) V vs. Ag/AgCl (3 M KCl) and with chemically reversible characteristics at sufficiently high scan rates (ca. 16 V s −1). A chemical reaction step involving oxidised N719 at the electrode surface leads to the loss of electrochemical activity at slower scan rates with a first order chemical rate constant of ca. 2.4 s −1. The electro-catalytic oxidation of iodide is demonstrated for both the intact metal complex N719 and the reaction product formed after oxidation. When adsorbed onto TiO 2 (porous films made from approximately 9 nm diameter TiO 2 particles, Langmuirian binding constant ca. 10 5 mol −1 dm 3), immersed in acetonitrile (0.1 M NBu 4PF 6), and at sufficiently fast scan rates (ca. 16 V s −1), the N719 metal complex exhibits reversible voltammetric responses (with E mid ≈ 0.68 V vs. Ag/AgCl (3 M KCl)). At slower scan rates, the voltammetric response again appears irreversible, however, this time without significant degradation of the N719 metal complex at the TiO 2 surface. It is shown that the conduction mechanism via electron hopping becomes ineffective due to degradation of FTO-adsorbed N719. In the presence of iodide, the electro-catalytic iodide oxidation process (dark electro-catalysis) is shown to occur predominantly at the N719-modified FTO electrode surface. Implications of this dark-reactivity for the solar cell performance are discussed.

Activation of lactoperoxidase by heme‐linked protonation and heme‐independent iodide binding

Lactoperoxidase (LPO), a mammalian secretory heme peroxidase, catalyzes the oxidation of thiocyanate by hydrogen peroxide to produce hypothiocyanate, an antibacterial agent. Although LPO is known to be activated at acidic pH and in the presence of iodide, the structural basis of the activation is not well understood. We have examined the effects of pH and iodide concentration on the catalytic activity and the structure of LPO. Electrochemical and colorimetric assays have shown that the catalytic activity is maximized at pH 4.5. The heme Soret absorption band exhibits a small red-shift at pH 5.0 upon acidification, which is ascribable to a structural transition from a neutral to an acidic form. Resonance Raman spectra suggest that the heme porphyrin core is slightly contracted and the Fe-His bond is strengthened in the acidic form compared to the neutral form. The structural change of LPO upon activation at acidic pH is similar to that observed for myeloperoxidase, another mammalian heme peroxidase, upon activation at neutral pH. Binding of iodide enhances the catalytic activity of LPO without affecting either the optimum pH of activity or the heme structure, implying that the iodide binding occurs at a protein site away from the heme-linked protonation site.

Formation of Iodinated Organic Compounds by Oxidation of Iodide-Containing Waters with Manganese Dioxide

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.

Indirect determination of iodide by tungsten coil atomic emission spectrometry

The spectroscopic determination of iodide is a difficult challenge, especially in small sample volumes. The strongest transition lines for this element lie in the vacuum ultraviolet region of the spectrum, so most conventional instruments produce very weak signals. This work describes a tungsten coil atomic emission procedure for the indirect determination of iodide. A 25 μl aliquot of a solution containing a known amount of indium is deposited on the tungsten coil and dried with a simple heating program. Once the coil is dry, 25 μl of an iodide solution is added to the coil. The solution is dried and vaporized at high current. The atomic emission signal for In at 451.1 nm is monitored. In the presence of iodide, InI is formed and the In emission signal is attenuated. This attenuation is proportional to iodide concentration with a method detection limit of 0.6 mg l − 1 iodide using an In concentration of 10 mg l − 1 , and 3 mg l − 1 iodide using an In concentration of 50 mg l − 1 . Linear calibration curves span a range of two orders of magnitude. Analysis of a deionized water sample spiked with 50 mg l − 1 iodide gives a recovery of 100% and a precision of 5.5% relative standard deviation. Analysis of a tap water sample spiked with 50 mg l − 1 iodide gives a recovery of 140% and a precision of 7.1% relative standard deviation. The poor accuracy for the tap water analysis may arise from the reaction of In with other halides in the sample. This is the first report of determination of a halogen using the tungsten coil atomizer.

Urine Test Strips as a Source of Iodine Contamination

In the course of conducting an analysis in a subset of the controlled antenatal thyroid screening study (1) samples, we recently noted that some urine samples from pregnant women in Wales, a region known to be iodine deficient, had urinary iodine concentrations in excess of 500mg=L. We suspected contamination from urine test strips. We obtained Combur Test D urine test strips (Roche Diagnostics, Mannheim, Germany), as were used in the Welsh study. We also obtained Multistix 10 SG urine test strips (Bayer Health Care, Elkhart, IN), used in our clinic, for comparison. Iodine was not mentioned in the package insets for either test strip. Two urine samples were obtained from healthy volunteers. Total urinary iodine concentrations were measured both spectrophotometrically by a modification of the method of Benotti et al. (2) and by mass spectroscopy. Measurements were obtained at baseline, after placing each test strip in the urine for 1 second, and again after placing each test strip in the urine for 30 seconds (Table 1). To determine which individual tests contained iodine, the test strips were cut into separate pieces for each test, and urine iodine concentrations were remeasured after placing individual pieces in a separate urine sample for 30 seconds. Iodine was present in the tests for glucose and blood in the Combur Test D and only in the Multistix test for glucose. The test strips for glucose rely on sequential reactions. First, glucose oxidase catalyzes the aerobic oxidation of glucose to gluconic acid and hydrogen peroxide. Second, in the presence of iodide, hydrogen peroxide oxidizes the iodide to free iodine, producing a color change in the indicator. The color change produced indicates the amount of hydrogen peroxide present, and therefore the glucose content of the urine. Although previously reported by Chanoine et al. (3) over 20 years ago, the contamination of urine with iodine by test strips is not well known. Since Combur and Multistix test strips still contain iodine as a reagent for blood and glucose testing, urine iodine concentrations should be assessed before test strip measurements. This is important in evaluating populations for iodine sufficiency. References

Flow injection analysis with on-line nylon powder extraction for room-temperature phosphorescence determination of thiabendazole

A fast and very selective flow-through phosphorescence optosensor was designed and characterized for the determination of the fungicide thiabendazole in water samples. For the first time, thiabendazole was determined using a flow-through optosensor based on the phosphorescence signals obtained when it is retained in a solid support. While thiabendazole does not phosphoresce in packing materials commonly used to fill the flow-cell, significant emission signals are observed when it is retained on nylon powder in the presence of iodide and sulfite. The experimental set-up was based on a flow-injection manifold coupled to an on-line phosphorescence detector containing nylon powder packed in a conventional flow-cell. Potassium iodide and sodium sulfite were added to sample aliquots to improve the thiabendazole phosphorescence and injected in the flow manifold using water as carrier. After the phosphorescence emission was registered, the analyte was eluted from the packed nylon with a 65% (v/v) methanol–water mixture. Optimal instrumentation, experimental and flow conditions were evaluated. Using a sample volume of 2000 μL, the analytical signal showed a very good linearity in the range 12.9–110 ng mL −1, with a detection limit of 4.5 ng mL −1, and a sample throughput of about 14 samples per hour. The effects of the presence of concomitant species in the thiabendazole phosphorescence signal were studied, and a comparison with the fluorescence nylon-powder optosensor was carried out and discussed. Finally, the applicability of the proposed optosensor was tested in water samples, and satisfactory recoveries ranging between 97% and 105% were obtained.