Abstract


Akpolat, Osman M., Following the headspace production of dimethyl telluride produced by Pseudomonas fluorescens amended with sodium tellurate or sodium tellurite. Master of Science (Chemistry), August, 1999, Sam Houston State University, Huntsville, Texas, 84 pp. (pdf version of this thesis)

Purpose

The purpose of this study was to determine whether a facultative anaerobe, Pseudomonas fluorescens K27, would produce volatile organometalloids when amended with sodium tellurate or sodium tellurite.
Methods
Batch bacterial bioreactor experiments were undertaken in order to observe the changes in the headspace of a growth media solution inoculated with Pseudomonas fluorescens and amended with tellurium salts. Gas samples were taken from the bioreactor every hour and were analyzed by gas chromatography to determine the composition of the headspace. Liquid samples were analyzed by a spectrometer to determine their optical densities which were used as an indicator of cell growth. Different concentrations of tellurate and tellurite amendments were tested. As a further verification of the identity of the peak appearing around 7.3 minutes in the gas chromatography, headspace above a tellurate amended culture was analyzed by gas chromatography/mass spectrometry.

Filtration of the bioreactorís solution at the end of the experiments was carried out to determine the amounts of Te present in the bioreactor when cultures of P. fluorescens had reached stationary phase. Both solid particles of Te and Te dissolved in solution were sampled. These filtration samples were analyzed by atomic absorption spectrometry.

In addition, the synthesis of dimethyl tellurone, a Te analog of the well-known sulfones, was tried by oxidation of dimethyl telluride. For this purpose two approaches were utilized; a microwave-induced oxidation and a conventional wet oxidation of dimethyl telluride were attempted.
 

Findings
The production of dimethyl telluride was observed in the batch bioreactor experiments using Pseudomonas fluorescens. Analyzed headspace gases above the solutions amended with tellurium salts gave increasing concentrations of dimethyl telluride as the cell population increased.

The chromatographic peak for dimethyl telluride was identified by using standard gas chromatography and gas chromatography/mass spectrometry. The retention time in our chromatographic temperature program for the dimethyl telluride peak was reported and fragmentation pattern for dimethyl telluride was shown.

The concentration of Te left in the solution after the experiments were over was calculated by filtering out the solid and dissolved Te from the solution and measuring the concentration by AAS. The % conversion to gas and % Te that had been biomethylated were calculated. For K27 cultures with either 0.2 or 2.0 mM mixed amendments grown into stationary phase in large volume 2.7 L bioreactor experiments, approximately 80% of the added Te was converted to compounds that were volatilized either into culture headspace or lost in subsequent sample handling to determine tellurium in solid or liquid phase.

Two different pathways to oxidation of dimethyl telluride were followed in an attempt to synthesize dimethyl tellurone. No product was obtained when microwave-induced oxidation technique was used as measured by thin layer chromatography. The product obtained from classical oxidation of dimethyl telluride was sent for elemental analysis. Percent compositions of possible products were calculated and the results from elemental analysis were compared with the calculated percentages. Apparently dimethyl tellurone was not successfully synthesized. Based on elemental analysis, the most likely product isolated was either CH3-Te(OH)2-OCH3 or CH3-Te(O)(OH)-OCH3. This product was not soluble in any common solvent nor did it melt below 300oC.
 

Thomas G. Chasteen
Thesis Director

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