Showing papers on "Iodide published in 1997"

Potassium Iodide as a Chemical Actinometer for 254 nm Radiation: Use of Iodate as an Electron Scavenger

Abstract: — A solution of 0.6 M iodide and 0.1 M iodate in 0.01 M borate buffer (pH 9.25) can be used as a chemical actinometer to measure the incident fluence from a low-pressure mercury lamp that puts out more than 85% of its energy at 254 nm. The actinometric solution is optically opaque to light below 290 nm and is optically transparent to wavelengths greater than 330 nm. Hence, the solution absorbs all of the germicidal wavelengths but little if any of the ambient light normally present in the laboratory. Iodate acts as an electron scavenger and prevents the back reaction of the free electron with the iodine atom following UV excitation of KI. Irradiation results in the linear formation of triiodide, which is quantitated by measuring its absorbance at 352 nm. The quantum yield for this system is approximately 0.75 0.03 at 20.7AoC or approximately three times greater than that obtained previously using nitrous oxide as an electron scavenger. A model is proposed to account for this difference. A precise expression to account for the concentration and temperature dependence of the quantum yield is given by pH = 0.75(1 + 0.23[C - 0.577])(1 + 0.02[T - 20.7]) where C is the concentration of iodide and T is the temperature. The concentration of iodide can be obtained from the absorbance at 300 nm prior to irradiation using 1.061 MJ cm−1 as the molar extinction coefficient. This actinometric system meets the quality criteria established by the International Union of Pure and Applied Chemistry with the caveat that it is designed to measure only germicidal radiation (i.e. wavelengths less than 290 nm).

Removal of permanganate reducing compounds and alkyl iodides from a carbonylation process stream

Abstract: Disclosed is a method to manufacture high purity acetic acid. Although described in relation to that produced by a low water carbonylation process the present invention is applicable to other mechanisms for production of acetic acid which results in formation of permanganate reducing compounds such as acetaldehyde, propionic acid, and alkyl iodide impurities in intermediate process streams. It has been found that permanganate reducing compounds and alkyl iodides may be conveniently removed from a light phase of an intermediate stream in the reaction process by employing a multiple distillation process coupled with an optional extraction of acetaldehyde. The distillation process involves first distilling a light phase to concentrate the permanganate reducing compounds, and in particular the acetaldehyde, and then separating the permanganate reducing compounds and alkyl iodides in a second distillation tower. The second distillation serves to remove the permanganate reducing compounds and alkyl iodides from methyl iodide, methyl acetate, and methanol mixture. As an optional third step, the twice distilled stream may be directed to an extractor to remove any remaining quantities of methyl iodide from the aqueous acetaldehyde stream to obtain acetic acid as a final product in greater than 99 % purity.

Visible Light Photolysis of Hydrogen Iodide Using Sensitized Layered Metal Oxide Semiconductors: The Role of Surface Chemical Modification in Controlling Back Electron Transfer Reactions

Abstract: The internally platinized wide bandgap semiconductor K4Nb6O17 can be sensitized by [(bpy)2Ru(4-(2,2‘-bipyrid-4-yl)-phenylphosphonic acid](PF6)2 (1). In aqueous iodide solutions at pH 2, the visible...

A Homozygous Missense Mutation of the Sodium/Iodide Symporter Gene Causing Iodide Transport Defect

Abstract: Iodide transport defect is a disorder characterized by an inability of the thyroid to maintain an iodide concentration difference between the plasma and the thyroid. The recent cloning of the sodium/iodide symporter (NIS) gene enabled us to characterize the NIS gene in this disorder. We identified a homozygous missense mutation of A-->C at nucleotide +1060 in NIS complementary DNA in a male patient who was born from consanguineous marriage, had a huge goiter, and lacked the ability to accumulate iodide but was essentially euthyroid. The mutation results in an amino acid replacement of Thr354-->Pro in the middle of the ninth transmembrane domain. COS-7 cells transfected with the mutant NIS complementary DNA showed markedly decreased iodide uptake, confirming that this mutation was the direct cause of the disorder in the patient. Northern analysis of thyroid ribonucleic acid revealed that NIS messenger ribonucleic acid level was markedly increased (> 100-fold) compared with that in the normal thyroid, suggesting possible compensation by overexpression.

Selective photometric determination of peroxycarboxylic acids in the presence of hydrogen peroxide

Abstract: A method for the determination of peroxyacetic acid (PAA) and related peroxycarboxylic acids is presented. 2,2′-Azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), one of the most popular substrates for the enzyme peroxidase, is oxidized selectively by PAA to an intensely green radical cation (ABTS ·+ ) in the presence of hydrogen peroxide. Photometric detection of the product can be performed in four characteristic regions of the visible and near infrared spectrum in the range 405–815 nm. The reaction is accelerated considerably by the addition of iodide without any loss of selectivity. A quantitative reaction, a limit of detection of 1 × 10 - 6 mol l - 1 (76 µg l - 1 ) for PAA and linear calibration graphs over three orders of magnitude are obtained under these conditions. No interferences by several ions at their typical concentrations in tap water could be observed under pH control. Comparative HPLC measurements were used to demonstrate the reliability of the proposed method. The recovery and standard deviation for PAA in real samples (n = 53) using the proposed method was 98 ± 4% of the respective HPLC measurements. Microplates were used as an alternative to cuvettes to analyse a large number of samples per timescale. The method may become a valuable tool for the determination of PAA in disinfection solutions, because reliable analysis results are obtained using standard laboratory equipment. Direct calibration for rapid on-site analysis is performed by using the molar absorptivity of the reaction product.

Determination of Iodide in Seawater by Ion Chromatography

Abstract: A simple and highly sensitive ion chromatographic method with UV detection was developed for iodide (I-) in seawater. A high-capacity anion-exchange resin with polystyrene−divinylbenzene matrix was used for both preconcentration and separation of iodide. Iodide in artificial seawater (salinity, 35‰) was trapped quantitatively (98.8 ± 0.6%) without peak broadening on a preconcentrator column and was separated with 0.35 M NaClO4 + 0.01 M phosphate buffer (pH 6.1). On the other hand, the major anions in seawater, chloride and sulfate ions, were partially trapped (5−20%) and did not interfere in the determination of I-. The detection limit for I- was 0.2 μg/L for 6 mL of artificial seawater. The present method was applied to determination of I- (ND − 18.3 μg/L) and total inorganic iodine (I- + IO3- − I, 50.0−52.7 μg/L) in seawater samples taken near Japan.

Solvent, Temperature, and Excitonic Effects in the Optical Spectra of Pseudoisocyanine Monomer and J-Aggregates

Abstract: The absorption and fluorescence spectra of 1,1‘-diethyl-2,2‘-cyanine (pseudoisocyanine, PIC) aggregates have been studied between 8 and 293 K in water/glycerol glass containing 2−4 M of alkali halogenides In this system the J-aggregates have a single sharp band and there is practically no contamination with the monomeric dye, dimers, or H-aggregates This allowed us to better resolve the high-energy portion of the spectrum and to assign the middle 535 nm band to the upper exciton transition The excitonic splitting at 8 K is the same for both the blue and the red forms of aggregates (1270 ± 10 cm-1) The average energy of exciton components (18195 ± 15 cm-1 for the blue form) was found to be very close to the 0−0 energy of the first strong site of PIC monomer (18223 cm-1) embedded in a 9-aza-PIC iodide matrix, which is transparent above 500 nm [Marchetti, A P; Scozzafava, M Chem Phys Lett 1976, 41, 87] The 0−0 frequency of the nonsolvated PIC monomer cation (ν00 = 19716 ± 40 cm-1 or 5072 ± 1 nm)

Quantum yields of singlet oxygen of metal complexes of meso-tetrakis(sulphonatophenyl) porphine

Abstract: The iodide method and the method of bleaching of p -nitroso- N , N ′-dimethylaniline (RNO) were used to measure the quantum yields of singlet oxygen from the tetrasodium salt of meso-tetrakis(4-sulphonatophenyl) porphine (H2TPPS4) and its water-soluble metal complexes with divalent metals, Ag(II)TPPS4, Cd(II)TPPS4, Co(II)TPPS4, Cu(II)TPPS4, Mg(II)TPPS4, Ni(II)TPPS4, Pd(II)TPPS4, Pt(II)TPPS4 and Zn(II)TPPS4. Complexes of metals that have completely full or completely empty d-orbitals (Cd(II), Mg(II) and Zn(II)) are characterized by high quantum yields of singlet oxygen and are more efficient photosensitizers than the ligand alone. Comparison of the quantum yields of 1 O 2 obtained by the two methods confirmed the assumption that the iodide method yields identical values to the standard method of bleaching of RNO. However, the sensitivity of the iodide method is ten times higher.

Thermal (Iodide) and Photoinduced Electron-Transfer Catalysis in Biaryl Synthesis via Aromatic Arylations with Diazonium Salts

Abstract: The dediazoniative arylation of various aromatic hydrocarbons (Ar‘H) with diazonium salts (ArN2+) in acetonitrile can be readily effected to biaryls (Ar-Ar‘) in high yields, simply by the addition of small (catalytic) amounts of sodium iodide. [In the absence of Ar‘H, the competitive iodination to ArI is nearly quantitative.] Iodide catalysis of biaryl formation is efficiently mediated by aryl radicals (Ar•) that participate in an efficient homolytic chain process in which ArN2+ acts as a 1-electron oxidant. The complex kinetics of such an electron-transfer chain or ETC process (Scheme 1) is quantitatively verified by computer simulation of the Ar‘H-dependent (a) competition between arylation vs iodination and (b) catalytic efficiency of iodide, using the GEAR algorithms. ETC catalysis also pertains to the alternative photochemical procedure for arylation (in the absence of iodide), in which the deliberate irradiation of the charge-transfer band of the precursor complex [ArN2+, Ar‘H] initiates the same ho...

Microbial Reduction of Iodate

Abstract: The different oxidation species of iodine have markedly different sorption properties. Hence, changes in iodine redox states can greatly affect the mobility of iodine in the environment. Although a major microbial role has been suggested in the past to account for these redox changes, little has been done to elucidate the responsible microorganisms or the mechanisms involved. In the work presented here, direct microbial reduction of iodate was demonstrated with anaerobic cell suspensions of the sulfate reducing bacterium Desulfovibrio desulfuricans which reduced 96% of an initial 100 µM iodate to iodide at pH 7 in 30 mM NaHCO3 buffer, whereas anaerobic cell suspensions of the dissimilatory Fe(III)-reducing bacterium Shewanella putrefaciens were unable to reduce iodate in 30 mM NaHCO3 buffer (pH 7). Both D. desulfuricans and S. putrefaciens were able to reduce iodate at pH 7 in 10 mM HEPES buffer. Both soluble ferrous iron and sulfide, as well as iron monosulfide (FeS) were shown to abiologically reduce iodate to iodide. These results indicate that ferric iron and/or sulfate reducing bacteria are capable of mediating both direct, enzymatic, as well as abiotic reduction of iodate in natural anaerobic environments. These microbially mediated reactions may be important factors in the fate and transport of129 I in natural systems.

Gaseous protein cations are amphoteric

Abstract: Singly- and multiply-protonated ubiquitin molecules are found to react with iodide anions, and certain other anions, by attachment of the anion, in competition with proton transfer to the anion. The resulting adduct ions are relatively weakly bound and dissociate upon collisional activation by loss of the neutral acid derived from the anion. Adduct ions that behave similarly can also be formed via ion/molecule reactions involving the neutral acid. The ion/molecule reaction phenomenology, however, stands in contrast with that expected based on the reaction site(s) being charged. Reaction rates increase inversely with charge state and the total number of neutral molecules that add to the protein cations increases inversely with cation charge. These observations are inconsistent with the formation of proton-bound clusters but are fully consistent with the formation of ion pairs or dipole/dipole bonding involving the neutral acid and neutral basic sites in the protein. The ion/ion reactions can be interpreted...

Conjugate Addition Reactions Mediated by Samarium(II) Iodide.

Abstract: Samarium(II) iodide in conjunction with a catalytic low-valent transition metal species has been employed to promote the conjugate addition reaction of primary and secondary alkyl halides onto α,β-unsaturated esters and amides. The method has been determined to be quite general and hence has been extended to the cyclization reactions of alkyl halides onto α,β-unsaturated lactones, lactams, and nitriles. The cyclization reactions described herein provide a very general approach to the synthesis of functionalized carbocycles from simple acyclic precursors with excellent diastereoselectivity and under very mild reaction conditions.

Catalytic Action of Azolium Salts. VIII. Oxidative Aroylation with Arenecarbaldehydes Catalyzed by 1, 3-Dimethylbenzimidazolium Iodide

Abstract: Refluxing of a mixture of benzaldehyde (1a), 1, 3-dimethylbenzimidazolium iodide (7), p-nitroaniline (9b) as an oxidizing agent, and 1, 8-diazabicyclo[5, 4, 0]-7-undecene (DBU) in MeOH afforded methyl benzoate (2a) in good yield. Other methyl arenecarboxylates 2 were similarly obtained from arenecarbaldehydes 1. We showed that this aroylation proceeds via the 2-aroyl-1, 3-dimethylbenzimidazolium salt (8). The 1, 2, 4-triazolium salt (18) and the naphtho[1, 2-d]imidazolium salt (19) were also effective catalysts for this oxidative aroylation. However, the aroylation did not proceed with the imidazolium salt (20). In the presence of flavins (25a-c), arenecarbaldehydes 1 reacted in MeOH under aerobic conditions catalyzed by the benzimidazolium salt 7 to give the corresponding methyl arenecarboxylates 2. 1-Methyl-3-[3-(10-phenylisoalloxazin-3-yl)propyl]benzimidazolium bromide (27) is an effective complex catalyst for this oxidative aroylation.

Iodide, caesium and strontium adsorption by organophilic vermiculite

Abstract: A B S T R A C T: Distribution coefficients and isotherms for the adsorption of radioiodide, caesium and strontium ions (125I-, 134Cs+ and 85Sr2+) were determined in untreated vermiculite and in vermiculite treated with the chloride salt of hexadecylpyridinium (HDPy+). Experimental data reveal that some of the alkylammonium ions were incorporated as HDPyCI ion pairs into the vermiculite. The fraction of ion pairs adsorbed is reflected by an increase in distribution coefficients with increasing saturation levels. Consequently, a considerable part of the iodide adsorption could be attributed to an anion exchange process. At smaller amounts of Cs § and Sr z+ adsorbed, distribution coefficients of the modified clay mineral are significantly reduced in comparison with the original material. These differences are less pronounced when greater amounts of cations are adsorbed. Generally, larger distribution coefficients were found for the Cs + compared with the Sr z§ ion in the untreated and modified samples. Soils represent an important filter and buffer system for many cations and anions. Generally, their sorption properties are determined by the contents and compositions of clay minerals and humic substances. A great part of the soil organic matter is associated with clay minerals forming organomineral complexes (Greenland, 1965) which are of pronounced importance with respect to element transport and/or retention and to aggregate stability. Clay minerals also interact with organic cations. The replacement of inorganic cations by alkylammonium ions causes considerable modification in the hydration and swelling properties of the clays. Research in this area has significantly increased the

Sub-surface iodide maxima: evidence for biologically catalyzed redox cycling in Arabian Sea OMZ during the SW intermonsoon

Abstract: Sub-surface I− maxima (200–600 nM) were found in five of the six profiles from the Somali and Arabian basins of the Northwest Indian Ocean. In addition to these maxima, dissolved I− exhibited normally high (100 nM or greater) values in the surface and values ranging from 3 to 40 nM at depth, which are higher than other open oceanic systems. Sulfide was generally found to be less than 2 nM in the water column, indicating that the chemical reduction of iodate by sulfide is not important in regulating iodine speciation in the Northwest Indian Ocean. These novel high iodide values below the euphotic zone do not appear to be related to other bulk chemical or hydrographic features (σθ) but may be the result of two distinct biologically mediated remineralization processes: (1) the direct reduction of I03− to I− as seen in the sub-surface maxima, and (2) release of I− from CI bonds during the decomposition of organic matter. Iodine normalized to salinity, specific iodine, is not found to be conservative in this system. Overall, our specific iodine data support the incorporation of iodine into organic material in the surface. Iodide, when present below the euphotic zone, is a product of the decomposition of that exported organic material. These data and processes are consistent with those found previously in the Black Sea and the Chesapeake Bay. However, in the Northwest Arabian Sea, iodide and oxygen are measurable throughout the water column, indicating that the system is not at equilibrium with the prevailing redox condition and that traditional thermodynamic considerations of pE do not appear to be applicable. Porewater iodide in the top 150 cm increased with depth to approximately 19 μM as a result of the release of I− during decomposition of organic matter.

Highly Selective Iodide Poly(vinyl chloride) Membrane Electrode Based on a Nickel(II) Tetraazaannulene Macrocyclic Complex

Abstract: A PVC membrane electrode based on a nickel(II) tetraazaannulene macrocyclic complex as the carrier is described. The electrode exhibits an anti-Hofmeister selectivity sequence with a preference for iodide at pH 3.0–4.0. It has a linear response to iodide from 8.0 × 10–6 to 1 × 10–1 mol dm–3 with a slope of –54.7 ± 0.2 mV per decade (20 °C), a satisfactory reproducibility and a rapid response time. The pH dependence of the potential response is discussed. The response mechanism of the electrode was investigated by ac impedance, quartz crystal microbalance and spectroscopic techniques. The electrode can be used for the determination of iodide in drug preparations.

Generation and Cyclization of Acyl Radicals from Thiol Esters Under Nonreducing, Tin-Free Conditions

Abstract: The preparation of 2-(2-((tert-butyloxycarbonyl)amino)phenyl)ethyl mercaptan from 2-(2-aminophenyl)ethanol is described. This thiol is condensed with a series of suitably unsaturated carboxylic acids to give a series of thiol esters. The Boc group is removed and the amine reacted with isoamyl nitrite to give a series of diazonium salts. Exposure to iodide in acetone solution then generates the aryl radical, which undergoes intramolecular homolytic substitution at sulfur with liberation of the acyl radical. Following acyl radical cyclization, quenching by iodine and then elimination of HI leads to the isolation of α-methylene cycloalkanones in good yield.

Electrochemistry in Near-Critical and Supercritical Fluids. 9. Improved Apparatus for Water Systems (23-385 °C). The Oxidation of Hydroquinone and Iodide

Abstract: The apparatus for electrochemical measurements in high-temperature water has been improved by replacing the alumina tube reactor with an oxidized titanium tube, producing a more rugged reactor. All metal fittings were replaced by titanium ones, decreasing corrosion problems. The working electrodes are Pt disks (radius, 14 μm) fabricated by sealing Pt−Ir wires in a high PbO-containing glass. This glass has the advantage over borosilicate glass in showing lower conductivity at temperatures above 230 °C, better corrosion resistance, and a coefficient of thermal expansion well-matched to Pt. Well-defined steady-state cyclic voltammograms for the oxidation of iodide ion and hydroquinone were obtained in (initially 23 °C) 0.2 M NaHSO4 solutions over a temperature range 23−385 °C. Diffusion coefficients (D) were determined from the limiting currents. The experimental D values were in excellent agreement with those calculated from the Stokes−Einstein equation and viscosity values for water at the relevant tempera...