A Density Functional Theory Study on the Ozone Oxidation of Sulfonamide Antibiotics

The electronic structures of sulfonamide antibiotics (the ground state and the lowest singlet excited-state geometries) have been investigated by using density functional theory (DFT) simulations. Experimental studies on the removal of sulfamethazine, sulfathiazole and sulfamethoxazole by ozone have also been conducted by using liquid chromatography with tandem mass spectrometric detection (LC/MS/MS). The calculated ground and excited state geometries exhibited low energy of the inter-ring bonds, which suggests the weakest bonds that can be broken during the ozone oxidation process. The orbital energy calculations (HOMO-LUMO and its energy gap) demonstrate that the smaller HOMO-LUMO energy gap, the higher reactivity toward ozone oxidation. Additionally, the current study suggests potential products of the three pharmaceutical compounds based on their electronic properties, which may help better understand the unknown reaction pathways of the pharmaceutical compounds.