Showing papers on "Iodide published in 1980"

Spectrophotometric determination of hydrogen peroxide using potassium titanium(IV) oxalate

Abstract: A simple and rapid method for the spectrophotometric determination of hydrogen peroxide using potassium titanium(IV) oxalate is described. The method can be used to measure peroxide concentrations down to about 10 µM(0.3 mg kg–1) under the most favourable conditions. A variety of complexing and reducing agents, and catalysts of peroxide decomposition, known to interfere with the alternative iodide method for peroxide determination, had no effect. Fluoride was found to interfere.

A resonance Raman/iodine Moessbauer investigation of the starch-iodine structure. Aqueous solution and iodine vapor preparations

Abstract: : The structure of the blue-black iodine complex of amylose (the linear, helical component of starch) prepared either from iodine and iodide in aqueous solution or from crystalline amylose and iodine vapor, has been studied by resonance Raman and iodine -129 Mossbauer spectroscopy. In both cases it is concluded that the identity of the major chromophore is essentially the same: the pentaiodide (I(5-1)) anion. For the material prepared from iodine vapor, the iodide required for (I(5-1)) formation is produced by hydrolysis or alcoholysis of iodine. The other product of this reaction, a hypoiodite, has been assigned in the iodine Mossbauer spectrum. (Author)

Bactericidal activity of eosinophil peroxidase.

Abstract: A partially purified preparation of guinea pig eosinophil peroxidase was found to be bactericidal when combined with H2O2 and either iodide, bromide, chloride, or thiocyanate ions. The EPO-H2O2-halide bactericidal system had an acid pH optimum and was inhibited by the proteins albumin and gelatin and by the hemeprotein inhibitors azide, cyanide, and aminotriazole. When the EPO concentration of the reaction mixture was lowered, the bactericidal effect at pH 7.0 was lost first with chloride, then with bromide, and finally with iodide as the halide. Activity with physiologic concentrations of chloride was favored by a relatively high EPO level, a decrease in pH below neutrality and an absence of extraneous protein. These findings are discussed in relation to the potential role of the peroxidase system in the intracellular and extracellular toxic reactions of eosinophils.

Semi-automatic method for the determination of total iodine in food

Abstract: A simple method for the determination of total iodine in food, based on the catalytic destruction of thiocyanate by nitrite in the presence of iodide, has been evaluated and the colorimetric finish technique automated. Optimum conditions for the destruction of organic matter and the liberation of iodine have been investigated and a set of conditions applicable to the automated finish technique developed. The method, when applied to 160 foods, had a precision of about 10%, a detection limit for iodine of 1 µg per 100 g of food, a mean recovery of added iodide of 90% and an output of about 70 samples per week. The effect of storage conditions on the iodine content of fish and eggs has also been examined, and the effect of some possible interfering substances, such as chloride, bromide and mercury, investigated.

Semiconductor Electrodes XXIX . High Efficiency Photoelectrochemical Solar Cells with Electrodes in an Aqueous Iodide Medium

Abstract: which maximizes the output voltage, and cond i t ions which minimize recombination processes in the semiconductor and so lu t ion and at the in ter face. The solut ion redox couple and solvent are selected to s tab i l i ze the semiconductor from photoinduced corrosion processes (8,9) . The highest published power e f f i c iency for such ce l l s is the 12% reported for a s ingle crysta l n-GaAs electrode in a selenide medium ( I0 ) . We describe here a PEC cel l based on s ingle crysta l nWSe 2 which shows comparable e f f i c i enc ies .

Mechanistic studies of the homogeneous catalysis of the water gas shift reaction by rhodium carbonyl iodide

Abstract: The water gas shift reaction, H/sub 2/O + CO = H/sub 2/ + CO/sub 2/, is effectively catalyzed at low temperatures and pressures by a catalyst system based on rhodium carbonyl iodide. The results of semiquantitative kinetic studies and of quenching experiments are reported. In the temperature range 80 to 100/sup 0/C the catalytic reaction shows first-order dependence on the partial pressure of CO and inverse dependence on acid and iodide concentrations. The major species in solution are rhodium (III) carbonyls. However, below 65/sup 0/C the reaction is independent of CO pressure, and exhibits second-order dependence on iodide concentration and positive dependence on acid concentration. Rhodium (I) species now become predominant in solution. The temperature dependence of the rate shows corresponding behavior. Above 80/sup 0/C the Arrhenius plot is linear with a slope which yields an apparent activation energy of 9.3 kcal mol/sup -1/. However, below 70/sup 0/C it is concave downwards with a slope at 55/sup 0/C corresponding to 25.8 kcal mol/sup -1/. Limiting behavior is not reached on the low-temperature side. These results are explained in terms of a change in the rate-limiting step of the catalysis. At high temperature CO/sub 2/ production from reduction of Rh(III) speciesmore » by CO is viewed as rate determining, while at lower temperature hydrogen production from oxidation of Rh(I) species by protons is thought to be limiting.Possible intermediates are discussed and a mechanistic scheme is proposed. A steady-state kinetic analysis and assumptions about rate-determining steps show the mechanism to be consistent with the observed behavior of the system. 46 references, 3 figures, 3 tables.« less

Opposite effects of thiocyanate on tyrosine iodination and thyroid hormone synthesis.

Abstract: The effect of a pseudohalide, SCN−, an anion with the same molecular size as iodide, was studied on two reactions: thyroglobulin iodination and thyroid hormone synthesis (coupling reaction) catalyzed by peroxidases. The coupling reaction was studied separately from the iodination reaction by using labelled thyroglobulin samples previously iodinated but containing little or no hormones. 1 SCN− inhibits iodide oxidation (I− I2) whatever the enzyme, thyroid, lactoperoxidase or horseradish peroxidase. The amount of SCN− required to completely inhibit this reaction varies depending on the enzyme. Similarly tyrosine iodination is inhibited by SCN− with large variations, depending on the peroxidase, in the concentration of this anion required for inhibition. 2 In contrast SCN− stimulates the coupling reaction: (a) this effect is seen with the thyroid and lactoperoxidases but not with horseradish peroxidase; (b) the concentration of SCN− required for half-maximal stimulation of the coupling reaction is much lower (0.5–1 μM) than that required for the inhibition of iodide oxidation (60–80 μM); (c) CIO−4, an anion with the same molecular size as SCN− and I−, has no effect on the coupling reaction; (d) this stimulatory effect of SCN− does not depend on a modification of the thyroglobulin molecule since it is not seen with horseradish peroxidase or in purely chemical coupling conditions. 3 The stimulatory effect of SCN− is therefore seen as resulting from the binding of this anion to a limited number of high-affinity sites present at the surface of both thyroid and lactoperoxidases. The inhibitory effect depends, in contrast, on the binding of SCN− to the substrate site with lower affinities. Since iodide also behaves both as a substrate for the iodination reaction and as a stimulatory ligand for the coupling reaction, these data provide further support in favour of the existence of an enzyme-iodide (or SCN−) complex with catalytic properties different from those of the native peroxidase.

Process of preparing homogeneous resin-polyiodide disinfectants

Abstract: Demand-type disinfectants are prepared from strong base anion exchange resin beads and elemental iodine. The resin is in the iodide form, and the iodine is applied with a water carrier which is recycled in contact with the resin and the stoichiometric amount of iodine to form the desired polyiodide (viz. I 3 - , I 5 - , or mixtures thereof). A homogeneous product of pre-determined polyiodide content is obtained.

Recovery of gold and/or palladium from an iodide-iodine etching solution

Abstract: A method of recovering gold and palladium from a spent aqueous potassium iodide-iodine etching solution, and regenerating the etching solution for reuse, involves adjusting the spent solution to a strongly basic pH (e.g., 12.5) by the addition of an alkaline compound (e.g., potassium hydroxide) to precipitate metallic gold from the solution. Metallic palladium is precipitated from the resulting alkaline solution by the addition of a borohydride, (e.g., potassium borohydride). Following removal of the precipitated gold and palladium, the spent alkaline solution is made acidic-to-neutral in pH to change potassium hypoiodite and some potassium iodide in the solution to iodine. The solution then is adjusted back upward to a slightly alkaline pH value (e.g., 9.0), and precipitate is removed at room temperature. Potassium iodide and iodine crystals then are added to the solution, as necessary, to regenerate the solution to substantially its original composition and strength for reuse.

Alkynyl- and dialkynyl-quinoxalines. Synthesis of condensed quinoxalines

Abstract: Condensation of 2-chloro- and 2,3-dichloro-quinoxalines with alk-1-ynes in the presence of bis(triphenylphosphine)palladium(II) dichloride and copper(I) iodide gives mono- and di-alkynylquinoxalines. Addition of amines to these products gives stable enamines; hydration gives 2′-oxoalkyl compounds which exist predominantly in the intramolecularly hydrogen-bonded enol form. Condensation of the alkynylquinoxalines with diethyl sodiomalonate, and related compounds, yields pyrido[1,2-a]quinoxalin-4-one derivatives. 2-Alkynyl-3-chloro quinoxalines are intermediates for convenient syntheses of pyrrolo[2,3-b]quinoxalines.

Studies on organic fluorine compounds. Part 27. Abnormal reactions in the trifluoromethylation of aromatic compounds with trifluoromethyl iodide and copper powder

Abstract: Reaction of 3-bromobenzofuran with trifluoromethyl iodide and copper powder in pyridine gave 2-(trifluoromethyl)-, 2- and 3-(pentafluoroethyl)-, and 2,3-bis(trifluoromethyl)-benzofuran, as well as the expected product, 3-(trifluoromethyl)benzofuran. Bromoanisole also gave (trifluoromethyl)anisole and (pentafluoroethyl)anisole, but introduction of the perfluoroalkyl group occurred at the position originally occupied by the bromine. Formation of pentafluoroethyl compounds is explained by decomposition of trifluoromethylcopper to cuprous fluoride and difluorocarbene, which can then react with a further molecule of trifluoromethylcopper to form pentafluoroethylcopper. This then reacts with aryl halide to give pentafluoroethyl compounds. Perfluoroalkylcopper is thermally cleaved to perfluoroalkyl radical, which then reacts with pyridine to give perfluoroalkylpyridines. This mechanism must be involved in the formation of 2,3-bis(trifluoromethyl)benzofuran. Introduction of a perfluoroalkyl group to the position originally unoccupied with halogen might be due to the rather localized double bond in benzofuran.

Electrically conductive fiber and method for producing the same

Abstract: An electrically conductive fiber having an electric resistivity of 1x10 12 ohm/cm or less under a D.C. voltage of 1 K.V., containing copper (I) iodide and a method for producing this fiber by depositing copper (I) iodide in the inside of at ieastthe peripheral surface layer of an electrically non-conductivefiber matrix by contacting iodine with copper (I) ions therein.

Anion selectivity of the chloride-transport process in dog tracheal epithelium

Abstract: We have measured the fluxes of 82Br or 131I across short-circuited dog tracheal epithelium following complete replacement of chloride in the bathing medium by either bromide or iodide. In addition, we have partly replaced the bathing chloride with bromide, iodide, or thiocyanate and studied the effects of these anions on 36Cl fluxes. Our results show that the affinity sequence for the chloride transport process is I > Br congruent to Cl, that Br is transported, but that I is not. Thiocyanate is a potent inhibitor of chloride transport, and its effects are greater than those predicted by a simple competitive interaction with chloride for transport sites.

Heterogeneous electron transfer at designed semiconductor/liquid interfaces. Rate of reduction of surface-confined ferricenium centers by solution reagents

Abstract: Reduction of surface-confined ferricenium by solution reductants iodide, diindenyliron, (eta/sup 5/-C/sub 5/H/sub 5/)/sub 4/Fe/sub 4/(CO)/sub 4/, 1,1'-dimethylferrocene, ferrocene, and phenylferrocene has been studied in EtOH-0.1 M (n-Bu/sub 4/N)ClO/sub 4/ and also in H/sub 2/O-NaClO/sub 4/ for iodide. The surface-confined ferricenium can be generated on n-type Si by illumination of the electrode at some potential more positive than approx. -0.2 V vs. SCE. Linear sweep voltammetry was used to directly measure the time dependence of the surface ferricenium concentration in the dark and in the presence of the various reducing agents. The rate constant for the reaction with iodide was measured in both solvents, and the value in EtOH is somewhat lower than would be estimated from homogeneous solution reaction of ferricenium with iodide under the same conditions. Values of reaction rate constants for reaction with all other reductants indicate that the reduction rate is mass transport, not charge transfer, limited under the conditions employed. The relative ordering of the fast reductants has been determined to be diindenyliron > (eta/sup 5/-C/sub 5/H/sub 5/)/sub 4/Fe/sub 4/(CO)/sub 4/ approx. 1,1'-dimethylferrocene > ferrocene approx. phenylferrocene. Most of the derivatized surfaces have been prepared from (1,1'-ferrocenediyl)dichlorosilane, but preliminary results with polyvinylferrocene modified and (1,1'-ferrocenediyl)dimethylsilane derivatizedmore » surfaces are similar. Very high coverage surfaces from (1,1'-ferrocenediyl)dichlorosilane show some evidence for selective reduction of the more accessible ferricenium centers when a fast reductant is used. Steady-state photoanodic current at a given concentration of reductant generally accords well with the measured k/sub et/ values, and for the iodide experiments the steady-state photocurrent is directly proportional to surface coverage of electroactive ferrocene.« less