Home About us Contact
|
Home About us Contact | ||
|
|
||
Halide Ions (halide + ion)
Selected AbstractsChemInform Abstract: Role of Halide Ions in Divalent Palladium-Mediated Reactions: Competition Between ,-Heteroatom Elimination and ,-Hydride Elimination of a Carbon,Palladium Bond.CHEMINFORM, Issue 50 2001Zhaoguo Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Voltammetric Determination of Mercury(II) at Poly(3-hexylthiophene) Film Electrode.ELECTROANALYSIS, Issue 24 2007Effect of Halide Ions Abstract The well-known method for the determination of mercury(II), which is based on the anodic stripping voltammetry of mercury(II), has been adapted for applications at the thin film poly(3-hexylthiophene) polymer electrode. Halide ions have been found to increase the sensitivity of the mercury response and shift it more positive potentials. This behavior is explained by formation of mercuric halide which can be easily deposited and stripped from the polymer electrode surface. The procedure was optimized for mercury determination. For 120,s accumulation time, detection limit of 5,ng mL,1 mercury(II) has been observed. The relative standard deviation is 1.3% at 40,ng mL,1 mercury(II). The performance of the polymer film studied in this work was evaluated in the presence of surfactants and some potential interfering metal ions such as cadmium, lead, copper and nickel. [source] Pyridine-facilitated phenylselenoetherification of some tertiary alkenolsHETEROATOM CHEMISTRY, Issue 6 2001Biljana M. Mojsilovic An improved procedure for intramolecular cyclization of tertiary alkenols using benzeneselenyl halides has been developed. We found that cyclization can be facilitated by pyridine. Thus, in the presence of an equimolar amount of pyridine, a chemospecific reaction could be observed that resulted in formation of corresponding cyclic ethers, and quantitative yields were achieved instantaneously under extremely mild experimental conditions. The effect of the halide ion of the selenylating reagent is not significant, both halides generally giving equal results © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:475,479, 2001 [source] Dipole induced photodetachment dynamics of halide anionsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2008Chandan Kumar MondalArticle first published online: 1 MAY 200 Abstract In this article the dynamics of photodetachment from closed shell anion in the presence of two color (bichromatic) laser field have been explored in the context of polar environmental situation. The electronic states of halide ions are modeled by a one dimensional Hamiltonian with a potential V(x) = ,V0e. The two parameters V0 and , are fixed by requiring V(x) to reproduce the experimentally observed ground state ionization energy of the halide ion concerned. The potential so generated are shown to support only one bound state. The time-dependent Fourier grid Hamiltonian method is used to follow the detachment dynamics with fairly high intensities of light. The environmental effects on the dynamics are sought to be modeled by two ways i) allowing the well depth (V0) to fluctuate randomly V0(t) = V0[1+,VR(t)]; R(t) randomly fluctuates between +1 and ,1 with time, when ,V (strength of fluctuation) is fixed and ii) in the presence of perturbation produced by a neighboring solvent dipole, which changes the effective potential. The detachment rate constant is studied as a function of important system parameters of the used light field. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Functionally relevant motions of haloalkane dehalogenases occur in the specificity-modulating cap domainsPROTEIN SCIENCE, Issue 5 2002Michal Otyepka Abstract One-nanosecond molecular dynamics trajectories of three haloalkane dehalogenases (DhlA, LinB, and DhaA) are compared. The main domain was rigid in all three dehalogenases, whereas the substrate specificity-modulating cap domains showed considerably higher mobility. The functionally relevant motions were spread over the entire cap domain in DhlA, whereas they were more localized in LinB and DhaA. The highest amplitude of essential motions of DhlA was noted in the ,4,-helix-loop-,4-helix region, formerly proposed to participate in the large conformation change needed for product release. The highest amplitude of essential motions of LinB and DhaA was observed in the random coil before helix 4, linking two domains of these proteins. This flexibility is the consequence of the modular composition of haloalkane dehalogenases. Two members of the catalytic triad, that is, the nucleophile and the base, showed a very high level of rigidity in all three dehalogenases. This rigidity is essential for their function. One of the halide-stabilizing residues, important for the catalysis, shows significantly higher flexibility in DhlA compared with LinB and DhaA. Enhanced flexibility may be required for destabilization of the electrostatic interactions during the release of the halide ion from the deeply buried active site of DhlA. The exchange of water molecules between the enzyme active site and bulk solvent was very different among the three dehalogenases. The differences could be related to the flexibility of the cap domains and to the number of entrance tunnels. [source] Photoluminescence of Uranium(VI): Quenching Mechanism and Role of Uranium(V)CHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2010Satoru Tsushima Dr. Abstract The photoluminescence of uranium(VI) is observed typically in the wavelength range 400,650,nm with the lifetime of several hundreds ,s and is known to be quenched in the presence of various halide ions (case,A) or alcohols (case,B). Here, we show by density functional theory (DFT) calculations that the quenching involves an intermediate triplet excited state that exhibits uranium(V) character. The DFT results are consistent with previous experimental findings suggesting the presence of photoexcited uranium(V) radical pair during the quenching process. In the ground state of uranyl(VI) halides, the ligand contributions to the highest occupied molecular orbitals increase with the atomic number (Z) of halide ion allowing larger ligand-to-metal charge transfer (LMCT) between uranium and the halide ion. Consequently, a larger quenching effect is expected as Z increases. The quenching mechanism is essentially the same in cases,A and B, and is driven by an electron transfer from the quencher to the UO22+ entity. The relative energetic stabilities of the triplet excited state define the "fate" of uranium, so that in case,A uranium(V) is oxidized back to uranium(VI), while in case,B uranium remains as pentavalent. [source] Dipole induced photodetachment dynamics of halide anionsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2008Chandan Kumar MondalArticle first published online: 1 MAY 200 Abstract In this article the dynamics of photodetachment from closed shell anion in the presence of two color (bichromatic) laser field have been explored in the context of polar environmental situation. The electronic states of halide ions are modeled by a one dimensional Hamiltonian with a potential V(x) = ,V0e. The two parameters V0 and , are fixed by requiring V(x) to reproduce the experimentally observed ground state ionization energy of the halide ion concerned. The potential so generated are shown to support only one bound state. The time-dependent Fourier grid Hamiltonian method is used to follow the detachment dynamics with fairly high intensities of light. The environmental effects on the dynamics are sought to be modeled by two ways i) allowing the well depth (V0) to fluctuate randomly V0(t) = V0[1+,VR(t)]; R(t) randomly fluctuates between +1 and ,1 with time, when ,V (strength of fluctuation) is fixed and ii) in the presence of perturbation produced by a neighboring solvent dipole, which changes the effective potential. The detachment rate constant is studied as a function of important system parameters of the used light field. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Synergistic effect of halide ions and polyethylene glycol on the corrosion inhibition of aluminium in alkaline mediumJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009S.A. Umoren Abstract The corrosion inhibition of aluminium in alkaline medium was studied at 30 and 40°C in the presence of polyethylene glycol (PEG) using gravimetric (weight loss) and thermometric techniques. The effect of halides (KCl, KBr, and KI) on the inhibitory action of PEG was also studied. It was found that PEG acted as inhibitor for aluminium corrosion in the alkaline medium. Inhibition efficiency increased with increasing inhibitor concentration. An increase in temperature led to increase in both the corrosion rate and inhibition efficiency in the absence and presence of inhibitor and halides. Phenomenon of chemical adsorption mechanism is proposed from the values of Ea, Qads, and ,G obtained. The adsorption of PEG on the surface of aluminium was found to obey Flory,Huggins and Temkin adsorption isotherms. The synergism parameter, S1 evaluated was found to be greater than unity indicating that the enhanced inhibition efficiency caused by the addition of halides is synergistic in nature. The inhibition efficiency, surface coverage and synergism parameter increased in the order; I,> Br,> Cl, showing that a joint adsorption of PEG and halide ions on aluminium plays a significant role in the adsorption process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Extraction and recovery of gold from KAu(CN)2 using cetyltrimethylammonium bromide microemulsionsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2001Tian-Xi Zhang Abstract Extraction and stripping of KAu(CN)2 from alkaline solution by a w/o microemulsion formed with cetyltrimethylammonium bromide (CTAB) using 198Au(I) tracer has been investigated. Various parameters, such as the Au(I) concentration in aqueous phase, concentrations of halide ions, NH4SCN and thiodiethylene glycol in stripping solution as well as the relationship between water and Au(I) concentration in the organic phase in the extraction and stripping of Au(I) were studied. The results show that almost all of the Au(I) in the aqueous phase was extracted into the organic phase. The water content decreased significantly with an increase in Au(I) concentration in the organic phase, contrary to the results of a system with tributyl phosphate (TBP) as cosolvent. Almost all of the extracted Au(I) (,98%) can be recovered with pure thiodiethylene glycol as the stripping agent, and ,93% of the Au(I) is stripped with high concentrations of NH4SCN(>3.0,mol,dm,3) or KI (>2.0,mol,dm,3). © 2001 Society of Chemical Industry [source] Pitting corrosion on 316L pipes in terephthalic acid (TA) dryerMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2009Y. Gong Abstract Grade 316L is a type of austenitic stainless steel with ultra-low carbon content and it exhibits superior corrosion resistance. However, pitting is always observed in 316L steel when it is exposed to media containing halide ions. In the present study, we found that in the presence of acetate acid (HAc) containing chloride or bromide ions, pitting occurred on the surface of the rotary steam pipes with the matrix material of 316L steel in terephthalic acid (TA) dryer. In order to identify the causes of the failure, metallographic structures and chemical compositions of the matrix material were inspected by an optical microscope (OM) and a photoelectric direct reading spectrometer. Beside these, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) as well as ion chromatography (IC) were used to analyze the micromorphologies of the corrosion pits and the chemical compositions of the corrosion deposits within them. Analysis of the results revealed the sources of halide ions and the factors accelerating the corrosion rate. Beside these, detailed mechanisms of pitting were discussed and six out of all the seven theoretical morphologies of pitting features were obtained in practice. [source] Halogeno(triazolyl)zinc complexes as molecular building blocks for metal,organic frameworksACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009Jörg Lincke The isomorphous title complexes, dichlorido[4-(3,5-dimethyl-4H -1,2,4-triazol-4-yl)benzoic acid-,N1]zinc(II) dihydrate, [ZnCl2(C11H11N3O2)2]·2H2O, and dibromido[4-(3,5-dimethyl-4H -1,2,4-triazol-4-yl)benzoic acid-,N1]zinc(II) dihydrate, [ZnBr2(C11H11N3O2)2]·2H2O, were synthesized and crystallized by slow evaporation of the solvent from a solution of the ligand and either zinc chloride or zinc bromide, respectively, in water/ethanol. The ZnII ions occupy twofold axes in the noncentrosymmetric orthorhombic space group Fdd2. The metal ion is approximately tetrahedrally coordinated by two monodentate triazole groups of the ligands and additionally by two halide ions. The water molecules incorporate the complexes into a three-dimensional framework made up by hydrogen bonds. Furthermore, each complex possesses two hydrogen-bond-donor sites represented by the carboxy groups and two acceptor sites at the noncoordinating N atoms of the triazoles. [source] Photoluminescence of Uranium(VI): Quenching Mechanism and Role of Uranium(V)CHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2010Satoru Tsushima Dr. Abstract The photoluminescence of uranium(VI) is observed typically in the wavelength range 400,650,nm with the lifetime of several hundreds ,s and is known to be quenched in the presence of various halide ions (case,A) or alcohols (case,B). Here, we show by density functional theory (DFT) calculations that the quenching involves an intermediate triplet excited state that exhibits uranium(V) character. The DFT results are consistent with previous experimental findings suggesting the presence of photoexcited uranium(V) radical pair during the quenching process. In the ground state of uranyl(VI) halides, the ligand contributions to the highest occupied molecular orbitals increase with the atomic number (Z) of halide ion allowing larger ligand-to-metal charge transfer (LMCT) between uranium and the halide ion. Consequently, a larger quenching effect is expected as Z increases. The quenching mechanism is essentially the same in cases,A and B, and is driven by an electron transfer from the quencher to the UO22+ entity. The relative energetic stabilities of the triplet excited state define the "fate" of uranium, so that in case,A uranium(V) is oxidized back to uranium(VI), while in case,B uranium remains as pentavalent. [source] Selection of a Pentameric Host in the Host,Guest Complexes {[{[P(,-NtBu)]2(,-NH)}5],I},[Li(thf)4]+ and [{[P(,-NtBu)]2(,-NH)}5],HBr,THFCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2004Felipe García Abstract The structures of the host,guest complexes {[{[P(,-NtBu)]2(,-NH)}5]I},,[Li(thf)4]+ [2,I{Li(thf)4}] and [{[P(,-NtBu)]2(,-NH)}5],HBr,THF (2,HBr,THF) show that increased distortion of the framework of the pentameric macrocycle [{[P(,-NtBu)]2(,-NH)}5] (2) occurs with the larger halide ions. Theoretical studies show that the thermodynamic stabilities of the model host,guest anions [2,X], (X=Cl, Br, I) are in the order Cl,,Br,>I,, that is, the reverse of the templating trend observed experimentally. These studies support the view that the selection of the pentamer 2 over the tetramer [{[P(,-NtBu)]2(,-NH)}4] (1) is kinetically controlled, a conclusion which is also consistent with the previous observation that the frameworks of 1 and 2 are not in dynamic equilibrium with each other. [source] Study on the Anion Recognition Properties of Synthesized Receptors (III): Convenient Synthesis and Anion Recognition Property of Bisthiosemicarbazone DerivativeCHINESE JOURNAL OF CHEMISTRY, Issue 10 2006You-Ming Zhang Abstract A new series of bisthiosemicarbazone derivative receptors (1, 2 and 3) have been synthesized by simple steps in good yields. Their anion recognition properties were studied by UV-Vis and 1H NMR spectroscopy. The result showed that the receptors 1, 2 and 3 all had a better selectivity to F,, CH3COO, and H2PO4,, but no evident binding with Cl,, Br,, I,, NO3, and HSO4,. Upon addition of the three anions to the receptors in DMSO, the solution acquired a color change from colorless to dark yellow that can be observed by the naked-eyes, thus the receptors can act as fluoride ion sensors even in the presence of other halide ions. The data showed that it was regular that the three receptors had different binding ability with the three anions. For the same anion, the association constants followed the trend: receptor 1>3>2. The UV-Vis data indicates that a 1:1 stoichiometry complex is formed through hydrogen bonding interactions between compound 1, 2 or 3 and anions. [source] | |||||||||||||||||||||||||