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A new approach was used to determine the reaction products of methylcobalamin and ionic mercury: purge-and-trap gas chromatography in line with Fourier transform infrared spectroscopy (PT GCIFTIR). This technique simultaneously and specifically determines the spectrum of dimethylmercury (DMeHg) and methylmercury produced by the reaction. No interference from other known organic mercury species could be detected. The method is different from others because it does not require solvent extraction of the organomercurials from aqueous solution, but relies on immediate volatilization from the reaction vessel by addition of 100 pl of 10 m~ NaBH,,. The sample was purged with nitrogen for 10 min. The volatile species of mercury were trapped in a column at -120 "C, injected into the gas chromatograph and detected by FTIR. The efficiency of DMeHg and MeHg formation depended on different parameters: pH, temperature, reaction time, and the methylcobalamin/ionic mercury ratio. The initial reaction product was MeHg which was further transformed to DMeHg. The first methylation rate was two times faster than the second. MeHg formed first, reaching a maximum at higher temperatures (28 "C and 37 "C) and later decreasing as DMeHg formed. At lower temperatures (2OOC) the rate of MeHg formation was slower, being similar to the formation rate of DMeHg. Different species of inorganic mercury such as

Klebsiella oxytoca BAS-10 is a Gram-negative micro-organism capable of growing on high concentrations of heavy metals. This bacterium produces large amounts of an iron-binding exopolysaccharide that, in the presence of metallic cations, precipitates as a dense gel. The primary and secondary structure of the repeating unit of such polysaccharide has been characterised by chemical and spectroscopic methods, resulting in the following heptasaccharide: 2)-α-Rha-(13)-β-Gal-(12)-α-Rha-(14)-β-GlcA-[β-GlcA-(14)]-(13)-α-Rha-(13)-α-Rha-(1. The absolute configurations for the Rha units are L, while those for the GlcA and Gal residues are D. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)