The purpose of this study was to investigate the biological reduction and methylation of antimony compounds by living organisms and to determine whether or not this process occurs in the cultures and soils examined.Methods
Experiments were carried out in which different bacteria (a culture of Pseudomonas fluorescens, bacterial mixed cultures isolated from soil samples from different places including an arsenic polluted site in Switzerland and a waste water plant and various places in Huntsville) were amended with different antimony compounds in various growth media. The bacteria were allowed to grow anaerobically in test tubes in the presence of various antimony compounds and the headspaces above the bacteria were then analyzed for reduced and methylated antimony compounds using a fluorine-induced chemiluminescence detector after separation by gas chromatography. A mass selective detector was also used to identify these compounds. Time course experiments were carried out to relate the production of the reduced and methylated compounds produced to the rate of bacterial growth. The growth of the bacteria was monitored by changes in the culturesı optical density.Findings
Trimethyldibromoantimony, one of the antimony compounds used for amending the bacteria, was synthesized by bromination of Trimethylstibine which was obtained by reacting antimony(III) chloride with a Grignard reagent, methyl magnesium iodide.
In addition, calibration curves and Henry's Law constants for four volatile sulfur and selenium compounds were determined in order to quantitate the total production of these compounds by bacteria.
Trimethyldibromoantimony was successfully synthesized. The compound was identified by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and elemental analysis.
Reduction of trimethyldibromoantimony to trimethylstibine was easily achieved by P. fluorescens K27 in anaerobic cultures grown in a defined medium. This bacterium started producing detectable amounts of trimethylstibine during the lag phase of growth but the production increased almost exponentially when the culture went into the stationary phase after about 30 hours.
This thesis is the first unambiguous report of biological methylation of antimony compounds. In the headspace of the soil samples amended with potassium antimonyl tartrate and potassium hexahydroxo antimonate(V), trimethylstibine was found and identified by both its retention time compared to a standard detected by a chemiluminescence detector and its mass spectrum acquired by a mass selective detector. On the other hand, the blanks that contained no antimony compounds and the ones that were sterilized and yet had amended antimony did not produce any detectable trimethylstibine (detection limit = 2.1 parts per billion by volume).
The amounts of trimethylstibine found in the headspace above soils amended with potassium antimonyl tartrate and potassium hexahydroxo antimonate(V) ranged from low parts per billion to low parts per million by volume within two weeks of amendment.
This thesis also reports Henryıs Law constants of methyl sulfides and selenides in a biological defined medium. The Henryıs Law constants of dimethyl sulfide, dimethyl disulfide, dimethyl selenide, and dimethyl diselenide in a well defined medium were calculated at 25 °C.
Thomas G. Chasteen