| 1. |
- Chen, Baowei, et al.
(författare)
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Methylation mechanism of tin(II) by methylcobalamin in aquatic systems
- 2007
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Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 68:3, s. 414-419
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Tidskriftsartikel (refereegranskat)abstract
- The methylation reaction of tin(II) with methylcobalamin (CH(3)B(12)) in aquatic systems was modeled in the laboratory. The products were detected by a sensitive gas chromatography-flame photometric detector (GC-FPD), and further identified by gas chromatography-mass spectrometry (GC-MS). Both monomethyltin (MMT) and dimethyltin (DMT) were found as methylation products. Three important effecting factors during the methylation reaction, salinity, pH and aerobic or anaerobic, were studied. The results showed that methyl group can be transferred from CH(3)B(12) to tin in aquatic solutions as a radical or carbonium, as well as a carbanion. Two explanations for the pH-dependency of the methylation reaction between tin(II) and CH(3)B(12) were proposed: pH-dependency of the equilibrium states of CH(3)B(12), and pH-dependency of inorganic tin(II) species whose reactivity vary with the redox potential in the solution. Salinity can influence the activity of the methyl donor, which cause changes in the methylation efficiency. Kinetic experiments showed that the methylation reaction was pseudo-first-order for CH(3)B(12).
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| 2. |
- Chen, Baowei, et al.
(författare)
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Methylation of inorganic mercury by methylcobalamin in aquatic systems
- 2007
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Ingår i: Applied organometallic chemistry. - : John Wiley & Sons. - 0268-2605 .- 1099-0739. ; 21:6, s. 462-467
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Tidskriftsartikel (refereegranskat)abstract
- The methylation of inorganic Hg(II) by methylcobalamin in aquatic systems was studied using high-performance liquid chromatography coupled with UV-digestion cold vapor atomic fluorescence spectrometry (HPLC-UV-CV AFS). Monomethylmercury (MMC) could be positively identified as the reaction product in the aqueous solution. The salinity and pH of the aquatic system have great effects on the formation of MMC, because they could change the species of the reactants in the solution. From an electrophile reaction point of view, salinity and pH alter the electron density of the methyl donor and the electrophilicity of metal ion in the reaction system. This methylation of inorganic Hg(II) is shown to be possible even in highly saline solutions, which indicates its importance in aquatic environments. Kinetic experiments showed that the methylation reaction was fast and first-order for Hg(II). The first-order reaction rate was determined to be 0.00612 and 0.000287 min-1 for pH 5.0 and 1.5, respectively. It is suggested that this methylation could occur in the absence of enzymes, in which Hg(II) acts as an electrophile to attack methylcobalamin with a subsequent transfer of carbanion methyl group to the higher oxidized state of Hg(II).
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| 3. |
- Chen, Baowei, et al.
(författare)
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Simulate methylation reaction of arsenic(III) with methyl iodide in an aquatic system
- 2006
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Ingår i: Applied organometallic chemistry. - : John Wiley & Sons. - 0268-2605 .- 1099-0739. ; 20:11, s. 747-753
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Tidskriftsartikel (refereegranskat)abstract
- The methylation reaction of inorganic arsenic occurring in aquatic systems was studied by HPLC-HGAFS as a method to separate and detect soluble methylarsenic species. Transformation from inorganic arsenic to methylarsenic was essential for major changes in toxicity to organisms. Monomethylarsenic [AsOCH(3)(OH)(2)] was the only product in the methylation reaction of inorganic arsenic(III) with methyl iodide (MeI). This process can be described as an oxidative carbonium-ion transfer, with MeI acting as a methyl donor. From a thermodynamic point of view, the activity of the carbonium ion and pH were the two major influencing factors. The pH dependence of redox potential of As(III) was the reason for the effect of pH on methylation of arsenic. The influences of salinity and concentration of the methyl donor may be explained by their effects on the activity of carbonium. Moreover, kinetics experiments demonstrated that the methylation reaction was first-order for both As(III) and methyl iodide. First-order reaction rates were also calculated at different pH, salinity and MeI, and were found to be in the range 0.0026-0.0123 h(-1). The methylation rate varied largely under different reaction conditions.
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