Zhang, Limin, Synthesis of dimethyl selenone and studies on the biomethylation intermediates of selenium reduction and methylation. Master of Science (Chemistry), December, 1993, Sam Houston State University, Huntsville, Texas. 50 pp. (pdf version of this thesis)

This investigation was undertaken for the purpose of determining whether or not dimethyl selenone could be an intermediate of biomethylation and transformation of inorganic selenium in bacterial cultures. The possible pathways for the synthesis of dimethyl selenone were also investigated.
The reactions of the synthesis of dimethyl selenone were carried out in a methylene chloride solution of 3-chloroperoxybenzoic acid and dimethyl selenide. Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, elemental analysis and melting point analysis were used to characterize the dimethyl selenone formed. Pseudomonas fluorescens K27 was grown in tryptic soy broth containing 0.1% potassium nitrate, TSN medium. All test tubes and filters were autoclaved before using. Both medium and aqueous solutions of selenium containing salts were sterilized by using sterilized filters. A Hewlett Packard 5890 Series II gas chromatograph coupled with a Sievers Research Model 300 Sulfur Chemiluminescence Detector was used as the principal tool for this research.
3-Chloroperoxybenzoic acid (m-CPBA) (65%) was found to readily oxidize dimethyl selenide (DMSe) at 20 degrees C in 2 hours. The optimum ratio of m-CPBA to DMSe was 3:1 mole equivalents. Pseudomonas fluorescens K27 grew well in sterilized TSN medium. Dimethyl selenone was tentatively identified as one of the intermediates of biomethylation of inorganic selenium because very large amount of volatile selenium compounds such as dimethyl selenide, dimethyl diselenide (DMDSe) and probably dimethyl selenenyl sulfide (DMSeS) were observed after the K27 cultures were dosed with dimethyl selenone. Gas phase concentrations of volatile DMSe and DMDSe formed above selenone dosed cultures were about 4000 times and 1000 times more (respectively) than those observed above sodium selenate dosed cultures poisoned with the same concentration. If dimethyl selenone is a biological intermediate of the reduction and methylation of selenium oxyanions, then the final reduction step to dimethyl selenide and dimethyl diselenide may occur by chemical means via reduction by dimethyl sulfide and dimethyl disulfide.

Thomas G. Chasteen
Thesis Director

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