Role Of Iodide Research Articles

The Role of Iodide in the Formation of Gold Nanotriangles

The Role of Iodide in the Formation of Gold Nanotriangles

Iodide promotes bisphenol A (BPA) halogenation during chlorination: Evidence from 30 X-BPAs (X = Cl, Br, and I)

As a well known endocrine-disrupting and model chemical, bisphenol A (BPA) may pose a serious threat to human health, since it and its disinfection by-products (DBPs) have been detected in drinking water, urine, human colostrum, adipose tissue, and placenta samples. Although chlorinated BPAs (Cl-BPAs) and iodinated BPAs (I-BPAs) have been well studied, brominated BPAs (Br-BPAs), and mixed halogenated DBPs like bromo-iodo-BPAs (Br-I-BPAs), and bromo-chloro-iodo-BPAs (Cl-Br-I-BPAs) are less well understood. Notably, the role of iodide (I-) during chlorination is not well understood, since the studies of the I-DBPs mainly focus on their genotoxicity and cytotoxicity. To understand the formation mechanisms of halogenated bisphenol A (HBPs) during chlorination with bromide (Br-) and/or I-, and the role of I- during chlorination, three set of reactions were performed in the laboratory (“BPA + chlorine + Br-”, “BPA + chlorine + I-” and “BPA + chlorine + Br- +I-” assigned as group A, B and C respectively). Thirty HBPs were identified and 18 of them were never reported before. I- increases the transformation rate of BPA into HBPs as I-BPAs act as intermediate HBPs during chlorination that easily react with HClO/ClO- and HBrO/BrO- to form Cl-BPAs and Br-BPAs. HIO/IO- showed higher reactivity towards BPA and HBPs than that of HBrO/BrO- and HClO/ClO-. The recycling of I- was observed in the reactions of “BPA + chlorine + I-” and “BPA + chlorine + Br- +I-”, which may explain why I- can induce BPA to transform into HBPs and suggests that I- may act as a catalyst during the BPA chlorination reactions. The reaction pathways are proposed which present the reactions of BPA and HBPs with HClO/ClO-, HBrO/BrO-, and HIO/IO-, as well as the recycling of I-. This study describes the potential DBP formation and transformation mechanisms of BPA and its 16 alternatives, as well as the role of I- on the transformation of phenol compounds during chlorination.

The role of iodide in the formation of lithium hydroxide in lithium–oxygen batteries

Iodide ions promote deprotonation of water; in consequence LiOH/LiOH·H2O is formed as a final discharge product.

Iodide-Mediated Control of Rhodium Epitaxial Growth on Well-Defined Noble Metal Nanocrystals: Synthesis, Characterization, and Structure-Dependent Catalytic Properties

Metal nanocrystals (NCs) comprising rhodium are heterogeneous catalysts for CO oxidation, NO reduction, hydrogenations, electro-oxidations, and hydroformylation reactions. It has been demonstrated that control of structure at the nanoscale can enhance the performance of a heterogeneous metal catalyst, such as Rh, but molecular-level control of NCs comprising this metal is less studied compared to gold, silver, platinum, and palladium. We report an iodide-mediated epitaxial overgrowth of Rh by using the surfaces of well-defined foreign metal crystals as substrates to direct the Rh surface structures. The epigrowth can be accomplished on different sizes, morphologies, and identities of metal substrates. The surface structures of the resulting bimetallic NCs were studied using electron microscopy, and their distinct catalytic behaviors were examined in CO stripping and the electro-oxidation of formic acid. Iodide was found to play a crucial role in the overgrowth mechanism. With the addition of iodide, the Rh epigrowth can even be achieved on gold substrates despite the rather large lattice mismatch of ~7%. Hollow Rh nanostructures have also been generated by selective etching of the core substrates. The new role of iodide in the overgrowth and the high level of control for Rh could hold the key to future nanoscale control of this important metal's architecture for use in heterogeneous catalysis.

SiO2-Supported CeCl3·7H2O−NaI Lewis Acid Promoter: Investigation into the Garcia Gonzalez Reaction in Solvent-Free Conditions⊥

The Knoevenagel condensation of aldose sugars with beta-dicarbonyl compounds produces furan derivatives having polyhydroxyalkylated alkyl side chains; this reaction is known as the Garcia Gonzalez reaction. Despite the fact that these polyhydroxyalkyl furans are interesting scaffolds for synthetic chemists to utilize in the synthesis of a variety of biologically interesting molecules, the reported approach suffers from harsh conditions. The development of a general and more efficient protocol is of considerable importance, and in this manuscript, we wish to explore the role of the NaI in enhancing the activity of CeCl3.7H2O as a useful water-tolerant Lewis acid promoter for the Garcia Gonzalez reaction. The procedure proceeds with good yields at 50 degrees C using our system supported on SiO2 in solvent-free conditions and represents a simple and convenient methodology for the preparation of densely functionalized molecules. Furthermore, the first qualitative results obtained on mechanistic investigation on the role of iodide on this our heterogeneous reaction may be of value for optimization of existing organic transformations and for the development of new ones.

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

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 role of iodide in the strain-ageing of silver iodobromide

Experimental results are presented for the growth of the hardness that is attributed to the presence of iodide, produced during the strain-ageing of silver iodobromide (0.35 mol% AgI) at room temperature. It is proposed that the atmospheres around the slip dislocations are formed by the Cottrell-Bilby interaction rather than the Snoek effect. Les reesultats experimentaux sont presentes pour la croissance du durcissement, qu'on attribue a la presence de l'iodide, pendant le veillisement par les efforts meeaniques du AgBr: I (0,35 mol% AgI) a la temperature ambiante. On propose que les atmospheres autour de les dislocations de glissement se developpent par l'interaction Cottrell-Bilby plutǒt que l'effet Snoek.

Thiourea and Cyanamide as Inhibitors of Thyroid Peroxidase: The Role of Iodide*

Thiourea, methylmercaptoimidazole, propylthiouracil, and thiouracil are all potent inhibitors of thyroid peroxidase (TPO)-catalyzed iodination. Unlike the cyclic thioureylenes, thiourea at 5 mM has no effect on guaiacol oxidation. If iodide is added to guaiacol assays containing thiourea, enzyme activity is lost. The latter observation may be explained as follows. In the presence of iodide, the iodinating species [TPO.Ioxid], oxidizes thiourea to formamidine disulfide. This product decomposes to cyanamide at neutral pH. We have shown cyanamide to be an inhibitor of the peroxidative and iodinating functions of TPO. Studies in rats demonstrate that doses of thiourea which completely inhibit in vivo protein-bound iodine formation have no irreversible effect on TPO, as measured by guaiacol peroxidation after removal of the thyroids. The major in vivo action of cyanamide is similar to that of thiourea. The data suggest that the primary in vivo and in vitro mode of action of thiourea is the reversible Ioxid-trapping mechanism. The anomalous inhibition of guaiacol peroxidation seen in the presence of thiourea plus iodide derives from the formation of formamide disulfide, followed by its nonenzymic decomposition to cyanamide.

Kinetics of thyroglobulin iodination and of hormone synthesis catalysed by thyroid peroxidase. Role of iodide in the coupling reaction.

The kinetics of tyrosine iodination and of thyroxine synthesis in thyroglobulin, different reactions catalyzed by the same enzyme (thyroid peroxidase), have been compared. Thyroxine synthesis always began after a lag period of 3-5 min. This lag was constant whatever the rate of iodination; this rate of iodination was increased either by increasing the concentration of iodide or enzyme or by decreasing the concentration of thyroglobulin. Increasing the rate of iodination resulted in increasing the number of iodine atoms incorporated during the lag period. Thus the lag observed for thyroxine synthesis was constant and did not depend on the fact that free iodide or non-iodinated tyrosine residues of thyroglobulin were exhausted before thyroxine synthesis occurred. Finally, it appeared that, whatever the explanation of the lag, the enzyme catlyzes thyroid hormone synthesis at a slower rate than iodination. The existence of a lag also allowed us to prepare thyroglobulin samples with different iodine contents but without thyroid hormones. Thus iodination and thyroxine synthesis could be studied independently and the following results were obtained. 1. Iodotyrosine residues which can couple to form thytoxine are made considerably before coupling occurs. 2. H2O2 is required for coupling of these hormonogenic residues; thus the coupling reaction requires enzymic oxidation of the iodotyrosine residues. 3. In addition a strict requirement for iodide was needed for coupling; the requirement was dependent on the concentration of iodide. Thus iodide, a substrate of the iodination reaction, may also have other effects on the activity of thyroid peroxidase.