Reaction Of Iodine Research Articles

Gallium Triiodide Catalyzed Organic Reaction: A Convenient Synthesis of α‐Amino Phosphonates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Kinetics of thyroglobulin iodination and thyroid hormone synthesis catalyzed by peroxidases: the role of H2O2.

1 When thyroglobulin iodination by thyroid peroxidase or lactoperoxidase is studied with optimal concentrations of H2O2-generating system, thyroid hormone synthesis (coupling reaction) begins after a constant lag period which is independent of the concentration of iodide, thyroglobulin or enzyme. Increasing the concentration of the H2O2-generating system inhibited the iodination reaction whereas the length of the lag period was decreased. When thyroglobulin containing iodinated tyrosine residues but no hormone was incubated with increasing concentrations of iodide and limiting amounts of the H2O2-generating system the iodination reaction was stimulated and the coupling reaction was inhibited. 2 To analyze whether the iodination and coupling reactions require different enzyme-H2O2 species the iodination and coupling reactions and the absorbance at 430 nm (compound II) were measured simultaneously with lactoperoxidase. Under these conditions: (a) the coupling reaction occurred only in the presence of sufficient amounts of H2O2 whereas the level of iodination was the same; (b) an increase in absorbance at 430 nm was observed only when the iodination reaction leveled off, i.e. just before the beginning of the coupling reaction; (c) during the lag period, i.e. the iodination step, the only enzyme species seen in the Soret region was the native enzyme; and (d) adding iodinated thyroglobulin containing no hormone to preformed compound II or III resulted in a prompt coupling reaction. These data suggest that the iodination and coupling reactions are catalyzed by different enzyme-H2O2 species. 3 When thyroid peroxidase or lactoperoxidase were preincubated for varying periods of time in the presence of the H2O2-generating system their activity towards guaiacol decreased progressively: with thyroid peroxidase the Km for guaiacol was increased 10-fold after 5 min of preincubation and 40-fold with lactoperoxidase. The activity of the preincubated enzymes was restored by iodide. Preincubated lactoperoxidase had the Soret spectrum of compound III. Similarly, the rate of iodination of thyroglobulin was inhibited with the preincubated enzyme, but increasing the iodide concentration restored the iodinating activity. 4 The proposal is made that different enzyme-H2O2 species are the active agents in the catalysis of the iodination and coupling reaction respectively.

A Comparison of Microwave-Accelerated and Conventionally Heated Iodination Reactions of Some Arenes and Heteroarenes, Using ortho-Periodic Acid as the Oxidant†

A fast and simple method for the oxidative iodination of some activated arenes and heteroarenes, either under microwave irradiation or by conventional heating, is reported, using diiodine and ortho-periodic acid as the oxidant. The reactions were carried out in hot 95% ethanol under a reflux condenser. For the microwave assisted reactions, the reaction times were always notably shortened, but the yields were nearly the same as those afforded by the conventional method.

Theoretical study of the iodination of methoxybenzene by iodine monochloride

The pathway of the iodination of methoxybenzene by electrophilic iodine monochloride (ICl) was studied by using density functional theory (DFT) calculations at the B3LYP/6–311G* and MP2/6–311G*//B3LYP/6–311G* levels. The iodination occurs in the position para to the methoxy group, and proceeds in two steps. Initially, a π-complex forms between ICl and aromatic ring of methoxybenzene. With a barrier of 60.81 kcal mol−1 (1 kcal = 4.184 kJ), the π-complex can be activated to an intermediate σ-complex with energy 42.02 kcal mol−1 higher than that of the π-complex. The σ-complex then transforms easily (barrier 3.56 kcal mol−1) into the final products, 1-iodo-4-methoxybenzene and HCl. The total iodination is slightly exothermic. Accompanying to the ICl bond breaking and CI bond formation, a hydrogen atom migrates first to iodine and then to chlorine. According to NBO charge, Wiberg bond index and molecular orbital analysis, both charge separation and charge transfer occur during the iodination. Solvent effects were examined with the IEFPCM method and the B3LYP/6–311G* level. The results imply that polar solvents should play a key role in lowering the energy barrier, and favor the ion-pair route of the iodination reaction. Copyright © 2005 John Wiley & Sons, Ltd.

Characterization of the Alzheimer's Disease-associated CLAC Protein and Identification of an Amyloid β-Peptide-binding Site

Amyloid beta-peptide (Abeta) deposition into amyloid plaques is one of the invariant neuropathological features of Alzheimer's disease. Other proteins co-deposit with Abeta in plaques, and one recently identified amyloid-associated protein is the collagen-like Alzheimer amyloid plaque component CLAC. It is not known how CLAC deposition affects Abeta plaque genesis and the progress of the disease. Here, we studied the in vitro properties of CLAC purified from a mammalian expression system. CLAC displays features characteristic of a collagen protein, e.g. it forms a partly protease-resistant triple-helical structure, exhibits an intermediate affinity for heparin, and is glycosylated. Purified CLAC was also used to investigate the interaction between CLAC and Abeta. Using a solid-phase binding assay, we show that CLAC bound with a similar affinity to aggregates formed by Abeta-(1-40) and Abeta-(1-42) and that the interaction was impaired by increasing salt concentrations. An 8-residue-long sequence located in non-collagenous domain 2 of CLAC was found to be crucial for the interaction with Abeta. These findings may be useful for future therapeutic interventions aimed at finding compounds that modulate the binding of CLAC to Abeta deposits.

Trans Dialkoxylation of Cyclic Alkenes: A Prévost-Type Reaction

Reaction of anhydrous silver perchlorate, sym-collidine, and iodine (2:1:1 molar ratio) with cyclic alkenes and an excess of an alcohol in CH2Cl2 affords trans-1,2-dialkoxycycloalkanes in high yields and purity. The reaction occurs via initial formation of the trans-iodoethers, which undergo Ag-assisted iodide abstraction to give the trans-diethers.

Aerobic Oxidation of Alkenes to Esters of Vicinal Diols with asyn-Configuration Catalyzed by I2and the H5PV2Mo10O40Polyoxometalate

A new method for the synthesis of vicinal diols from ­alkenes has been developed. Reaction of molecular iodine in the presence of a polyoxometalate as oxidation catalyst under aerobic conditions in acetic acid solvent leads to the oxidative iodoacetoxyl­ation of an alkene, i.e. formation of a 1,2-iodoacetate. Further in situ substitution of the iodide by water yields the 1,2-diol monoacetate with a predominantly (ca. 4.5:1) cis-configuration. Further esterification under the reaction’s acidic conditions leads also to the cis-diacetate. The method may be valuable for the synthesis of cis-vicinal diols without use of toxic osmium catalysts.

Spectroelectrochemical Measurements of Iodine with an ITO Electrode Slab Optical Waveguide

An ITO electrode slab optical waveguide spectroelectrochemical measurement system was built for simultaneous Visible attenuated total reflection (ATR) and electrochemical measurements and was applied to study the spectroelectrochemical behavior of iodine at the ITO electrode. The cyclic voltamogram and the potential-absorbance curve at 430 nm for the redox reaction of iodine were observed and the formation of iodine was confirmed by the Visible ATR spectra of iodine (λmax = 430 nm) which showed blue-shift compared with those of gasous iodine as well as iodine in non-polar solvents (λmax = 500 ∼ 600 nm). Moreover, the linear responses of the peak current and the maximum absorbance for the oxidation reaction of iodide were obtained to the concentration of iodide in aqueous samples.

Gallium Triiodide Catalyzed Organic Reaction: A Convenient Synthesis of α‐Amino Phosphonates

In dichloromethane, the three‐component coupling reaction of carbonyl compounds, amines, and diethyl phosphite was catalyzed effectively by gallium triiodide that was generated in situ by the reaction of gallium metal and iodine to give the corresponding α‐amino phosphonates in good to excellent yields. The method was appropriate for both primary and secondary amines.

O‐Phenylenediamine as a New Catalyst in the Highly Regioselective Conversion of Epoxides to Halohydrins with Elemental Halogens.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Gal3 catalyzed tetrahydropyranylation of alcohols and phenols

AbstractIn dichloromethane, the nucleophilic addition of alcohols or phenols to 3,4‐dihydro‐2H‐pyran (DHP) was catalyzed effectively by gallium triiodide which was generated in situ by the reaction of gallium metal and iodine to give the corresponding tetrahydropyranyl acetals in good to excellent yields.

Synthesis of derivatives of 7,8-dihydrothiazolo[2,3-i]purine by halocyclization of 6-allylthiopurine

7-Halomethyl-7,8-dihydrothiazolo[2,3-i]purines were synthesized by the reaction of bromine and iodine with 6-allylthiopurine.

Synthesis of 4‐Methylene‐2‐cyclohexenones and Their Aromatization Reaction Toward para‐Methoxylmethyl Anisole Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Microwave-Accelerated or Conventionally Heated Iodination Reactions of Some Aromatic Amines, Using ortho-Periodic Acid as the Oxidant †

A fast and simple method for the oxidative iodination of some aromatic amines, either under microwave irradiation or conventional heating, is reported, using diiodine and ortho-periodic acid as the oxidant. The reactions were carried out in boiling CH2Cl2 solutions under a reflux condenser. For the microwave assisted reactions, the reaction times were always notably shortened, but the yields were usually less influenced as compared with the conventional method.

O-Phenylenediamine as a New Catalyst in the Highly Regioselective Conversion of Epoxides to Halohydrins with Elemental Halogens

The regioselective ring opening of epoxides using elemental iodine and bromine in the presence of o-phenylenediamine as a new catalyst affords vicinal iodo alcohols and bromo alcohols in high yields. The major advantages of this method are versatility, high regioselectivity, a cheap and commercially available catalyst, mild and neutral reaction conditions, and short reaction times. Fourier transform Raman spectroscopy was used to study the reaction of iodine with o-phenylenediamine. The results indicate that the complex [(Diamine)I]+·I5− is formed, and we suggest that the major nucleophile is the pentaiodide ion. This bulky nucleophile has a fundamental role in the high regioselectivity observed attacking the less sterically hindered epoxide carbon.

Inorganic reactions of iodine(+1) in acidic solutions

AbstractWe present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H2OI+ ⇌ HOI + H+ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO3. Our new value, K(H2OI+ ⇌ HOI + H+) ∼ 2 M at 25°C, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI → IO3− + 2I− + 3H+ in perchloric acid solutions from 5 × 10−2 M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M−1 s−1 at 25°C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI ⇌ I2O·H2O in the mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:480–493, 2004

Selective Preparation of 1,3‐Butadienyl Phosphines, 1‐Iodo‐ and 1,4‐Diiodo‐butadienyl Phosphine Oxides via Zirconocene‐Mediated Cross‐Coupling of Alkynylphosphines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electrochemical Detection of As(III) via Iodine Electrogenerated at Platinum, Gold, Diamond or Carbon‐Based Electrodes

AbstractThe reaction of iodine, electrogenerated from iodide, is used for the detection of As(III) via electrocatalytic reaction in the diffusion layer of a boron‐doped diamond electrode. The merits of this electrode material for this purpose (over platinum, gold or glassy carbon) are demonstrated and the kinetics of the reaction between I2 and As(III) in acid reported.

Taxonomic status of section Neuropogon in the genus Usnea elucidated by morphological comparisons and ITS rDNA sequences

The taxonomic position of the Neuropogon group, as inferred from the morphology of representative species of the group and ITS sequences from Usnea antarctica and U. sphacelata, is discussed. Morphological observations revealed that the Neuropogon group does not have annular-pseudocyphellae, which are characteristic of the subgenus Dolichousnea, or a fistulose axis, which is characteristic of the subgenus Eumitria. In addition, the hypothecium of Neuropogon is thin, and the iodine reaction in the axis is negative. These features are consistent with those of the subgenus Usnea. Within the subgenus Usnea, Neuropogon is morphologically distinct from sections Usnea and Ceratinae (i.e. having a sphacelata-type cortex, black pigmentation of the upper thallus and a dark brown apothecial disc). The molecular data suggest that U. antarctica and U. sphacelata are members of the subgenus Usnea and are less closely related to subgenera Dolichousnea and Eumitria. The morphological and molecular phylogenetic analysis suggest that the Neuropogon group is a member of the subgenus Usnea at the level of a section, and the appropriate name for this group is subgenus Usnea section Neuropogon (Nees & Flot.) Mont.

Aspects of Stereoselectivity in Electrophilic Addition Reactions of Iodine with 5‐Allenyl‐2,3,5‐trichloro‐4,4‐dimethoxycyclopent‐2‐en‐1‐one and Its Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.