Radi, Sahar (2025) An investigation of the products formed through oxidative transformations of some antibiotics using Nuclear Magnetic Resonance spectroscopic and chromatographic/mass spectrometric techniques. PhD thesis, Victoria University.

Abstract

Antibiotics are increasingly recognized as emerging pollutants due to their continual release into aquatic environments, where they contribute to antimicrobial resistance and generate transformation products with uncertain toxicity. This study investigated the degradation behaviour of three representative antibiotics, Penicillin G, Amoxicillin, and Ciprofloxacin, under an oxidative treatment, with an initial assessment of UV irradiation and a detailed investigation of treatment sodium hypochlorite solution, a widely used water disinfectant. Preliminary experiments tested UV irradiation on both solid and solution forms of the antibiotics using spectroscopic means (FTIR and NMR), but no measurable structural changes were observed under the experimental conditions. Based on these findings, the study focused on oxidation using sodium hypochlorite solution, which showed clear and measurable degradation for the target antibiotics. A dual analytical approach combined 1H, 13Cand 19F Nuclear Magnetic Resonance (NMR) spectroscopy with High-performance liquid chromatography/ Mass spectrometry (HPLC/MS) to provide complementary insights into the degradation process. Initially, FTIR spectroscopy (ATR mode) was also employed as a supporting technique to characterise the pristine antibiotics and their oxidised forms after UV and sodium hypochlorite solution treatment. The FTIR spectra revealed notable band shifts and intensity changes, suggesting functional group modifications in case of modified versions through sodium hypochlorite solution treatment, though the information was limited and could not conclusively resolve specific degradation pathways. The NMR spectroscopic analyses revealed real-time functional group changes, including β-lactam ring opening, side-chain rearrangements, and piperazine ring oxidation, while HPLC/MS identified and tracked the parent compounds and their key transformation products over time. For the β-lactam antibiotics, Penicillin G and Amoxicillin, NMR and HPLC/MS together confirmed rapid and extensive degradation, with the parent ions (m/z 365 and m/z 364) disappearing quickly and products such as penicilloic acid, penilloic acid, and other lower-mass fragments forming sequentially. In contrast, Ciprofloxacin showed partial, slower degradation, where the piperazine ring was oxidised (producing m/z 306 and 362), but the parent ion (m/z 332) persisted after 24 hours, and the cyclopropyl ring remained intact.By correlating NMR and LC/MS data, this thesis provides a detailed picture of antibiotic behaviour under sodium hypochlorite solution treatment, demonstrating that β-lactams degrade readily, while fluoroquinolones are more resistant. These findings have important implications for water disinfection strategies, highlighting both the effectiveness of sodium hypochlorite solution for some antibiotic classes and the need for further treatment processes for more persistent compounds.

Search Google Scholar

Repository staff login