SYNTHESIS AND STRUCTURE CHARACTERIZATION OF SELENIUM METABOLITES

The difficulty in determining trace-level organoseleno metabolites and the lack of commercially available standards have been major barriers to a molecular-level understanding of Se biogeochemistry, ecotoxicolo gy and nutrition, particularly in aquatic ecosystems, To overcome the problem, three important precursors of volatile alkyl selenides were s ynthesized, including dimethylselenonium propionate (DMSeP), which has only been postulated to exist in nature. A combination of 2-D multinu clear NMR, electrospray MS and GC-MS methods was employed to identify DMSeP, methylselenomethionine and methylselenocysteine in synthetic pr eparations without extensive clean-up. An alkaline hydroelimination te st coupled with GC-MS analysis for the release pattern of dimethyl sel enide (DiMSe) and dimethyl diselenide (DMDSe) was developed for a diag nostic determination of the three products. The DMSe release pattern o f DMSeP confirmed the presence of a DMSeP-like compound in the biomass of 100 mg l(-1) Se-treated Chlorella investigated previously. Silylat ion-GC-MS was tested for the determination of selenomethionine, seleno cysteine and methylselenocysteine in a standard mixture with a detecti on limit of better than 1 pmol per 0.5 mu l injection volume for selen omethionine. This method was applied to the analysis of the acid diges t of the proteinaceous fraction of the Chlorella culture. Selenomethio nine was found to contain > 70% of the protein-bound Se, although this constituted only a minor fraction of the total Se in the Chlorella bi omass, These findings revealed the metabolic relationship between Se v olatilization and selenomethionine incorporation into proteins. This k nowledge is critical to advancement in Se biogeochemistry, ecotoxicolo gy and the development of in situ bioremediation schemes.