Master of Engineering Science
Chemical and Biochemical Engineering
Computational chemistry is a powerful tool to model different materials and predict their physical and chemical properties. The goal of this thesis was to apply different computational chemistry tools to model the properties of two classes of closely related organic compounds: formazans and tetrazolium salts for ionizing radiation dosimetry in water-based gels, whereby the absorbed dose is registered by optical detection of formazan formation from tetrazolium salts. The structural parameters of phenyl and benzothiazolyl-substituted tetrazolium salts and formazans were computed using the APFD density functional theory (DFT) model and 6-311+G(2d,p) basis set. Conformational searching of stereoisomers (TSCA and TATA structures) and tautomeric forms of formazans were analyzed in gaseous state, methanol, and chloroform solutions. It was found that formazans exist as a mixture of conformers. Two compounds, 2-(2-benzothiazolyl)-3-(4-nitrophenyl)-5-phenyltetrazolium and 1‑(2-benzothiazolyl)-5-(4-nitrophenyl)-3-phenylformazan were used as model molecules for frontier molecular orbital analysis (FMOA), charge distribution, IR and NMR (1H and 13C) spectra. The FMOA allowed for quantitative comparison of the reactivity of the tested molecules, while the spectrum modelling showed good agreement with experimental data. The UV-Visible spectra of tetrazolium salts and formazans was examined using seven select molecules and two models. Finally, the wavelengths of maximum absorbance for twelve formazans important for radiation dosimetry were calculated using multiple DFT models and compared with experimental data, obtained from in-gel dosimetry. In conclusion, DFT modelling showed excellent results and proved to be useful as a tool for predicting the properties of formazans and tetrazolium salts.
Summary for Lay Audience
The goal of this thesis is to apply different computational chemistry tools to model physical and chemical properties of two classes of closely related organic compounds: tetrazolium salts and formazan molecules. Up on radiation, tetrazolium salts convert to intensity colored formazan molecules. The observed color intensity helps to determine the amount of radiation. To mimic human body, water-based gels containing tetrazolium salts dosimetry device was selected. Its purpose is to study the amount and distribution of dose prescribed to radiotherapy patient as a quality assurance device. Several materials’ optical properties were investigated using Gaussian software. The model prediction showed a good agreement with experimental results. Therefore, it can be used to test similar potential materials. This reduces experimental cost to synthesize and test new materials for dosimetry application.
Bedada, Teshome G., "Characterization of Tetrazolium Salts and Formazans using Computational Chemistry for Radiochromic Dosimetry" (2019). Electronic Thesis and Dissertation Repository. 6458.