Showing papers on "Iodide published in 1998"

Reaction of myeloperoxidase compound I with chloride, bromide, iodide, and thiocyanate.

Abstract: Myeloperoxidase plays a fundamental role in oxidant production by neutrophils. The enzyme uses hydrogen peroxide to oxidize chloride (Cl-), bromide (Br-), iodide (I-), and the pseudohalide thiocyanate (SCN-) to their respective hypohalous acids. This study for the first time presents transient kinetic measurements of the oxidation of these halides and thiocyanate by the myeloperoxidase intermediate compound I, using the sequential mixing stopped-flow technique. At pH 7 and 15 degrees C, the two-electron reduction of compound I to the native enzyme by Cl- has a second-order rate constant of (2.5 +/- 0.3) x 10(4) M(-1) s(-1), whereas reduction of compound I by SCN- has a second-order rate constant of (9.6 +/- 0.5) x 10(6) M(-1) s(-1). Iodide [(7.2 +/- 0.7) x 10(6) M(-1) s(-1)] is shown to be a better electron donor for compound I than Br- [(1.1 +/- 0.1) x 10(6) M(-1) s(-1)]. The pH dependence studies suggest that compound I reduction by (pseudo-)halides is controlled by a residue with a pKa of about 4.6. The protonation of this group is necessary for optimum (pseudo-)halide anion oxidation. These transient kinetic results are underlined by steady-state spectral and kinetic investigations. SCN- is shown to be most effective in shifting the system myeloperoxidase/hydrogen peroxide from the peroxidatic cycle to the halogenation cycle, whereas iodide is shown to be more effective than bromide which in turn is much more effective than chloride. Decreasing pH increases the rate of this transition. Our results show that thiocyanate is an important substrate of myeloperoxidase in most environments and that hypothiocyanate is likely to contribute to leukocyte antimicrobial activity.

Hydrogen-Bond Distances to Halide Ions in Organic and Organometallic Crystal Structures: Up-to-date Database Study

Abstract: Geometrical data on hydrogen bonds to halide ions are compiled from the currently available crystal structures. Hydrogen bonds from 25 donor types to fluoride, chloride, bromide and iodide ions are considered. Compared with earlier compilations, the increased data volume allows a finer subdivision of O—H and N—H donors, and the donors C—H, S—H and P—H can be included. For a given donor type, the hydrogen-bond distance typically increases by over 0.5 A from fluoride to chloride, 0.15 A from chloride to bromide and 0.25 A from bromide to iodide acceptors. The strongest of the C—H donors considered, chloroform, forms hydrogen bonds with chloride ions with an average H⋯Cl separation of only 2.39 A and an average C⋯Cl separation of 3.42 A. The lengthening of the N—H covalent bond in hydrogen bonds to chloride ions is quantified from neutron diffraction data.

Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodide

Abstract: Sporophytes of Laminaria digitata (L.) Lamour. were assayed for their content of accumulated iodine, which ranged from 0.4% of dry weight in adult plants up to 4.7% for young plantlets. Sporophyte tissue from Laminaria saccharina (L.) Lamour. and L. digitata took up iodide according to Michaelis-Menten kinetics. Hydrogen peroxide and various substances known to interfere with oxidative metabolism were shown to either inhibit or enhance the uptake of iodide, confirming that apoplastic oxidations play a key role in iodide uptake in Laminaria. Consistently, iodide uptake was triggered in L. saccharina protoplasts by incubation in the presence of hydrogen peroxide. Similarly, the uptake of iodide was enhanced in L. digitata gametophytes by addition of haloperoxidase, suggesting that this enzyme catalyses the oxidation of iodide by hydrogen peroxide and plays a key role in iodine uptake. Oxidative stress resulted in a marked efflux of the intracellular iodine. In both influx and efflux experiments, a marked proportion (10–30%) of the tracer was not accounted for, indicating volatilisation of iodine. The mechanism and possible functions of the accumulation of iodine by kelps are discussed.

Total Synthesis of (+)-Discodermolide

Abstract: The total synthesis of (+)-discodermolide is described. The approach involves assemblage of three key stereotriad subunits through addition of nonracemic allenyltin, -indium, and -zinc reagents to (S)-3-silyloxy-2-methylpropanal derivatives, followed by reduction of the resulting anti,syn- or syn,syn-homopropargylic alcohol adducts to the (E)-homoallylic alcohols and subsequent Sharpless epoxidation. Addition of methyl cuprate reagents or Red-Al to the resultant epoxy alcohols yielded the key precursors, alkyne 4, aldehyde 9, and alcohol 24. Addition of alkyne 4 (as the lithio species 10) to aldehyde 9 afforded the propargylic alcohol 11 as the major stereoisomer. Lindlar hydrogenation and installation of appropriate protecting groups led to aldehyde 17. This was converted to the (Z)-vinylic iodide 18 upon treatment with α-iodoethylidene triphenylphosphorane. Suzuki coupling of this vinylic iodide with a boranate derived from iodide 25 led to the coupled product 27 with the complete carbon backbone of (+)...

Mechanism and Kinetics of Iodide-Mediated Polymerization of Styrene

Abstract: The kinetics of the bulk polymerization of styrene in the presence of a model -polystyryl iodide (Mn 2000, and Mw/Mn 1.26) as mediator and benzoyl peroxide as initiator was studied. The rate of polymerization, Rp, was found to be independent of the iodide concentration, showing that the stationary concentration of polymer radicals, [P*], is determined by the balance of initiation and termination rates, as in the conventional (iodide-free) system. The pseudo-first-order activation rate constant kact of the model iodide was determined as a function of BPO concentration and temperature (5080 C) by both the GPC curve-resolution and polydispersity-analysis methods. The results showed that kact is directly proportional to [P*], which means that degenerative transfer (active species-exchanging transfer) is the only important mechanism of activation in this system. The activation energy for the transfer rate constant kex was found to be 27.8 kJ mol-1, somewhat smaller than the known activation energy for the styr...

Femtosecond Real-Time Probing of Reactions. 23. Studies of Temporal, Velocity, Angular, and State Dynamics from Transition States to Final Products by Femtosecond-Resolved Mass Spectrometry

Abstract: In this contribution, we give a full account of the approach of femtosecond, time-resolved mass spectrometry in molecular beams for the studies of the elementary steps of complex reactions and the application to different systems. The level of complexity varies from diatomics to polyatomics, from direct-mode to complex-mode, from one-center, to two-center, to four-center, and from uni- to bimolecular reactions. The systems studied are iodine, cyanogen iodide, methyl iodide, iodobenzene, 1,2-diiodotetrafluoroethane, mercury iodide, benzene· iodine complexes, and methyl iodide dimers. By resolving the femtosecond dynamics and simultaneously observing the evolution of velocity, angular, and state distribution(s) of the reaction, we are able to study multiple reaction paths, the nature of transition-state geometry and dynamics, coherent wave-packet motion, evolution of energy disposal, and the nonconcerted motion in multicenter reactions. These phenomena and concepts are elucidated in dissociation, elimination, and charge-transfer reactions and in the inelastic and reactive pathways of bimolecular reactions. Theoretical phenomenology, using frontier orbitals and molecular dynamics, are invoked to provide a relationship between the observed dynamics and molecular structures.

Role of Iodide in Photoelectrochemical Solar Cells. Electron Transfer between Iodide Ions and Ruthenium Polypyridyl Complex Anchored on Nanocrystalline SiO2 and SnO2 Films

Abstract: Nanostructured thin films of SiO2 and SnO2 cast on an optically transparent electrode were modified with ruthenium(II) polypyridyl complex, Ru(bpy)2(bpy-COOH)2+, Ru(II). Kinetic and mechanistic details of interaction between iodide ions and excited Ru(II), as well as regeneration of the sensitizer by iodide ions, were elucidated using emission spectroscopy and laser flash photolysis. The reaction between excited Ru(II) and I- in SiO2 films which occurred with a rate constant of 1.0 × 108 M-1 s-1 produced low yields of electron-transfer products. In the case of SnO2 films modified with Ru(II), the charge injection was the dominant process with the production of oxidized sensitizer, Ru(III). The reaction between Ru(III) and I- controls the regeneration of sensitizer in a photochemical solar cells. The oxidation of I- by Ru(III) in SnO2 films as confirmed from the production of I2•- occurred with a rate constant of 1.2 × 1010 M-1 s-1.

The Limiting Role of Iodide Oxidation in cis-Os(dcb)2(CN)2/TiO2 Photoelectrochemical Cells

Abstract: Porous nanostructured photoanodes prepared from colloidal solutions of DeGussa or sol−gel processed TiO2 material have been derivatized with cis-M(dcb)2(CN)2, where M = Ru(II) or Os(II) and dcb is 4,4‘-(COOH)2-2,2‘-bipyridine. When employed in a regenerative solar cell with iodide donors, cis-Ru(dcb)2(CN)2/TiO2 converts absorbed photons to electrons nearly quantitatively while cis-Os(dcb)2(CN)2/TiO2 does not. In-situ time-resolved diffuse reflectance measurements reveal a sluggish iodide oxidation rate is responsible for the low photocurrent efficiency of cis-Os(dcb)2(CN)2/TiO2. Transient absorption measurements support this conclusion and allow full wavelength characterization of the charge-transfer processes.

Novel, Missense, and Loss-of-Function Mutations in the Sodium/Iodide Symporter Gene Causing Iodide Transport Defect in Three Japanese Patients

Abstract: Iodide transport defect is a disorder affecting the active transport of iodide, an essential step in the synthesis of thyroid hormones. We have identified novel germ-line mutations in the Na+/I− symporter (NIS) gene from these Japanese patients with iodide transport defect. One patient had a compound heterozygous mutation of T354P/G93R (Gly93 → ARg [GGC → CGC]), and two sibling patients had a homozygous mutation of G543E (Gly543 → Glu [CGA → GAA]). G93R and G543E, two novel mutations, are located in the 3rd and 12th transmembrane domains of NIS which are encoded by exons 1 and 13, respectively. The NIS mutants carring these mutations had minimal iodide uptake activity when expressed in COS-7 cells, confirming that the identified mutations are the direct cause of the iodide transport defect in these patients. Genotyping of unaffected family members and functional assays of co-transfected COS-7 cells indicate that expression of one normal NIS allele in the heterozygote (T354P, G93R, or G543E) is sufficient ...

Enhanced Acceptor Character in Fullerene Derivatives. Synthesis and Electrochemical Properties of Fulleropyrrolidinium Salts

Abstract: A family of N-methylpyrrolidinium fullerene iodide salts, possessing one (or two) solubilizing chain(s), has been synthesized. As evidenced by CV and steady-state voltammetry experiments, carried out in tetrahydrofuran (THF) solutions, these species show enhanced electron-accepting properties with respect to both the parent fulleropyrrolidines and C60. CV measurements performed at −60 °C and scan rates of 50 V/s, made possible by the use of ultramicroelectrodes, have allowed the observation, for the first time in fullerene derivatives, of six fullerene-centered reductions. Bulk electrolysis of these novel compounds, performed at the stage of the first reduction potential, generates a stable zwitterion, with both anion and cation located on the fullerene derivative.

Electrosorption Valency and Partial Charge Transfer in Halide and Sulfide Adsorption on Ag(111)

Abstract: The electrosorption valency lB of an adsorbed species is usually obtained from the slope of plots of the charge density on the metal against the surface concentration of the given species, at constant applied potential. Herein, two alternative procedures for the estimate of lB are proposed and applied to the formation of ordered overlayers of chloride, bromide, iodide, and sulfide on Ag(111). One of these procedures applies to strongly adsorbing anions, whose incipient adsorption turns out to be diffusion controlled under limiting conditions when stepping from a potential negative enough to exclude their specific adsorption. This procedure allows lB to be estimated as a function of the applied potential. Partial charge-transfer coefficients λ estimated from lB values on the basis of some modelistic assumptions decrease in the order sulfide ≈ iodide > bromide > chloride, namely in the order of increasing Pauling's electronegativity. Some direct procedures for the estimate of λ, which avoid the intermediate...

The modulation of the human sodium iodide symporter activity by Graves' disease sera

Abstract: The transport of iodide into the thyroid, catalyzed by the Na+/I− symporter (NIS), is the initial and rate-limiting step in the formation of thyroid hormones. To study the basic characteristics of the human (h) NIS, we have established a Chinese hamster ovary cell line stably expressing the hNIS (CHO-NIS9). In agreement with previous work on the rat NIS, iodide uptake in these cells was initiated within 2 min of the addition of 131I, reaching a plateau after 30 min. Both perchlorate and thiocyanate inhibited iodide uptake in a dose-dependent manner, with inhibition evident at concentrations of 0.01 and 0.1 μmol/L, respectively, and reaching complete inhibition at 20 μmol/L and 500 μmol/L, respectively. Ouabain, which blocks the activity of the Na+/K+ adenosine triphosphatase, also inhibited iodide uptake in a dose-dependent manner, starting at concentrations of 100 μmol/L and reaching maximum inhibition at 1600 μmol/L, indicating that iodide uptake in these cells is sodium dependent. CHO-NIS9 cells were f...

Synthesis and Characterization of [NH2C(I)NH2]2ASnI5 with A = Iodoformamidinium or Formamidinium: The Chemistry of Cyanamide and Tin(II) Iodide in Concentrated Aqueous Hydriodic Acid Solutions

Abstract: Crystals of the organic−inorganic compounds [NH2C(I)NH2]2ASnI5 (A = NH2C(I)NH2+ and NH2CHNH2+) have been grown in an inert atmosphere from slowly cooled aqueous hydriodic acid solutions, each with the same starting concentration of dissolved cyanamide and tin(II) iodide. Each compound can be achieved in high purity and yield simply by varying the thermal history of the solution during cooling. If one starts from lower temperatures, cyanamide rapidly undergoes an addition reaction to generate the iodoformamidinium cation, yielding crystals of [NH2C(I)NH2]3SnI5. At higher temperatures, iodoformamidinium is reduced to formamidinium and is ultimately hydrolyzed if heated further or left for long periods of time. When the solution is subjected to an intermediate thermal treatment of 24 h at 80 °C before slow cooling, both cations can be stabilized in the solid-state compound [NH2C(I)NH2]2(NH2CHNH2)SnI5. The [NH2C(I)NH2]3SnI5 structure has recently been reported in the monoclinic space group P21/c and consists ...

Synthesis of perfluoroalkyl-substituted aryl bromides and their purification over fluorous reverse phase silica

Abstract: (1H,1H,2H,2H-Perfluoroooctyl)-substituted aryl bro- mides 3a,b were synthesized via copper catalyzed cross-coupling of the iodide 1 with the corresponding arylmagnesium bromides 2a,b. A new, efficient method for the purification of highly fluorinated compounds by column chromatography on fluorous reverse phase silica is also described.

Intramolecular Ketone−Nitrile Reductive Coupling Reactions Promoted by Samarium(II) Iodide

Abstract: Samarium(II) iodide (SmI2) has been successfully utilized as a reducing agent for the intramolecular coupling of ketones with nitriles. The use of visible light to promote the reductive coupling represents an improvement over previously reported protocols. The procedure also avoids overreduction of the resulting α-hydroxy ketones. Monocyclic, fused bicyclic, and bridged bicyclic α-hydroxy ketones composed of a number of substitution patterns have been synthesized in moderate to excellent yield via this method. A sequential reaction consisting of a nucleophilic acyl substitution followed by a ketyl−nitrile coupling has also been accomplished.

Chlorination and formation of organoiodinated compounds : The important role of ammonia

Abstract: This study has been undertaken to determine the conditions of formation of organoiodinated compounds responsible for medicinal tastes and odors frequently observed after chlorination of waters containing iodides. It has been shown that iodoform was formed in the presence of chloramines, in a region where the formation of the most classical chlorinated and brominated THMs is usually unfavored. Reactions would take place between monochloramine, organic matter, and iodides to yield iodoform. These interactions are favored when iodide ions are replaced by iodine. Oxidation by iodine alone in the presence of ammonia and without monochloramine does not explain the yield of the iodinated THMs observed. However, nitrogenated molecules such as amines and amino acids would take part during chlorination in the production of organoiodinated compounds to a small extent.

Synthesis and characterisation of manganese(II) compounds with tetradentate ligands based on the bispidine backbone

Abstract: Reaction of the tetradentate ligand dimethyl 3,7-dimethyl-9-oxo-2,4-bis(2-pyridyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate (L1) with manganese(II) chloride or iodide in methanol yielded [MnL1Cl2] and [MnL1I2], respectively. Reaction with silver(I) triflate Ag(O3SCF3) converted these compounds into [MnL1(O3SCF3)2]. Reduction of L1 with NaBH4 in MeOH and LiAlH4 in THF led to the triol 1,5-bis(hydroxymethylene)-3,7-dimethyl-2,4-bis(2-pyridyl)-3,7-diazabicyclo[3.3.1]nonan-9-ol (L2); the reduction is stereoselective and yields the syn isomer. Complexation of manganese(II) chloride and iodide with L2 produced [MnL2Cl2] and [MnL2I2] and these have a higher thermal stability than [MnL1X2]. The complexes [MnL1Cl2], [MnL1I2], [MnL1(O3SCF3)2], [MnL2Cl2] and [MnL2I2] are characterised spectroscopically, electrochemically and by their magnetic, conductometric, thermal and structural properties (X-ray analyses of [MnL1Cl2] and [MnL2Cl2]).

Sequenced Reactions with Samarium(II) Iodide. Sequential Intermolecular Carbonyl Addition/Intramolecular Nucleophilic Acyl Substitution for the Preparation of Seven-, Eight-, and Nine-Membered Carbocycles

Abstract: Samarium(II) iodide has been employed to promote a tandem intermolecular carbonyl addition/intramolecular nucleophilic acyl substitution sequence, generating seven- through nine-membered monocyclic, bicyclic, and tricyclic ring systems with good yields and high diastereoselectivities. This tandem reaction consists of an intermolecular reaction followed by an intramolecular ring expansion that results in a formal [m + n] cycloaddition, starting from extremely simple, readily available substrates. The regioselectivity and stereoselectivity of the process arise from a tuning of the reducing power of samarium(II) iodide with nickel(II) iodide in the first step and irradiation with visible light in the second. By using this method, a variety of structural motifs have been assembled rapidly in good yields.

Stripping Voltammetric Determination of Iodide with Synergistic Accumulation at a Carbon Paste Electrode

Abstract: Carbon paste electrodes (CPEs) of various compositions were studied to elucidate the stripping voltammetric behavior of iodide. At an accumulation potential of +0.7 V (vs. Ag/AgCl), the CPE containing tricresyl phosphate as a pasting liquid was able to preconcetrate iodide effectively via ion-pairing reaction followed by oxidation to iodine and its extraction onto pasting liquid. In a supporting electrolyte containing 0.5 M NaCl and 0.1 M HCl, the reduction signal was proportional to iodide concentration from 5 × 10−6 to 5 × 10−7 mol/L with a detection limit of approximately 2.5 × 10−7 mol/L (accumulation for 5 min). Other halides and pseudohalides did not interfere with the determination, except for a high concentration excess of thiocyanate and bromide (100:1). The method was tested on model solutions and was applied to determine total iodine in samples of table salts and mineral water. The results were compared to those obtained by reference methods.

Deprotonated 2,3:5,6-Dibenzo-7- aza bicyclo[2.2.1]hepta-2,5-diene as a Nitrido Nitrogen Source by Anthracene Elimination: Synthesis of an Iodide(nitride)chromium(VI) Complex.

Abstract: Instead of azides, which can be explosive and poorly soluble in nonpolar solvents, azabicycloheptadienes can be used to synthesize nitrides. The reaction of diiodide 1 with the lithium amide 3 provides the red nitride 2 in 60 % yield with loss of lithium iodide and anthracene. The remaining iodo ligand in 2 can undergo an exchange reaction with lithium amide 3, but no more anthracene is released.

Bactericidal Action of 4,4'-(α, ω-Polymethylenedithio)bis-(1-alkylpyridinium iodide)s

Abstract: Bactericidal action of novel bis-quaternary ammonium compounds (bis-QACs), 4,4'-(alpha,omega-polymethylenedithio)bis(1-alkylpyridinium iodide)s (4DTBP-m,n) was studied. The bactericidal activity of 4DTBP-m,n in water was not affected by the molecular hydrophobicity unlike general mono-QAC, N-dodecylpyridinium iodide (P-12), while the bacteriostatic activity in the medium was reduced with their hydrophobicity. This result suggested that the hydrophobic materials in the medium interact with 4DTBP-m,n and cover their active moiety. Since the bactericidal activity using the measurement system supplemented with peptone was influenced by the molecular hydrophobicity, this speculation was supported. The plots of the bacteriostatic activities of 4DTBP-m,n against the surface hydrophobicities of various bacteria accord to the straight line as in the case of P-12. The slope of the line of 4DTBP-6,12 was comparatively smaller than that of 4DTBP-6,8, indicating that the compounds having longer alkyl group tend to reduce their activities against the bacteria with hydrophobic cell surface because of their interaction with the hydrophobic materials. The novel bis-QACs have an ability to liberate rapidly and abundantly the turbid materials from cells, that is, a bacterioclastic activity. The bacterioclastic activity of P-n was influenced by the length of alkyl group, while 4DTBP-6,n had almost the same activity regardless of its length. Observation by scanning electron microscope (SEM) revealed that 4DTBP-6,8 fatally damaged Escherichia coli cells, and that the morphological alteration of the cells caused by the bis-QAC was greatly different from that of the usual QAC. Therefore, the effective bacterioclastic action, and excellent bactericidal action is due to the unique dimeric structure of 4DTBP-m,n.

New route to 2-cyanobenzothiazoles via N -arylimino-1,2,3-dithiazoles†

Abstract: N-Arylimino-1,2,3-dithiazole derivatives 2 of 2-bromoanilines are converted in high yield into 2-cyanobenzothiazoles 3 by heating or, more rapidly, by focused microwave irradiation at atmospheric pressure, in pyridine containing cuprous iodide.

Macrocyclic compounds as corrosion inhibitors

Abstract: The influence of three macrocyclic compounds on corrosion of mild steel (MS) in hydrochloric acid (HCl) was investigated using weight loss, potentiodynamic polarization, alternating current (AC) impedance, and hydrogen permeation techniques. All the investigated compounds showed significant efficiencies and reduced permeation of hydrogen through MS in HCl. Inhibition efficiency (IE) varied with the nature and concentrations of the inhibitors, temperature, and concentrations of the acid solutions. The addition of iodide ions (I−) increased IE of all the tested compounds as a result of the synergistic effect. Potentiodynamic polarization results revealed that macrocyclic compounds acted as mixed inhibitors in 1 M HCl to 5 M HCl. Adsorption on the metal surface obeyed Temkin's adsorption isotherm. Auger electron spectroscopy (AES) of the polished MS surface, exposed with tetraphenyldithia-octaazacyclotetradeca-hexaene (PTAT) proved adsorption of this compound on the surface through nitrogen and sulf...

Rapid urinary iodide test.

Abstract: Assessment of iodine deficiency and monitoring of iodine supplementation programs demand rapid, simple, and cost-effective methods for the determination of urinary iodide concentrations. We propose a semiquantitative rapid test, based on the iodide-catalyzed oxidation of 3,3′,5,5′-tetramethylbenzidine by peracetic acid/H2O2, to yield colored products. The color of the chemical reaction is compared with color categories of a pictogram corresponding to three ranges: 300μ g/L ( 2.36 μmol/L) of iodide concentrations. The test is very easy to perform and does not require any instrumentation or apparatus. Sample preparation is simple and consists of the removal of interfering substances by disposable columns, 65 × 10.5 mm, packed with purified activated charcoal. For comparison with a reference method for measuring urinary iodide, by high-performance liquid chromatography, we determined the iodide concentrations of 370 random (untimed) urine samples from consecutive pat...