ESI-MS, UV-Vis, and Theoretical Investigation of Fe3+-Amoxicillin Complexation during Coagulation

Abstract

In this work, the complexation of the hazardous β-lactamic antibiotic amoxicillin (AMX) with Fe3+ ions during coagulation was investigated. New bands in the ultraviolet-visible (UV-vis) spectra suggested that AMX molecules bind to Feaq3+ and also displace ligands from a stable Fe thiocyanate complex. Electrospray ionization mass spectrometry (ESI-MS) showed strong signals at m/z=784 and 816, corresponding to the [Fe+(2AMX−2H)]+ and [Fe+(2AMX−2H)+CH3OH]+ species, respectively, also indicating the complexation of Fe3+ with AMX molecules. Density functional theory (DFT) calculations showed that among the different coordination modes of AMX to Fe3+, complexation via the carboxylate group is more stable and less sterically hindered. These results suggest that during coagulation, the Fe3+-AMX complexation-form stable intermediates are probably bound/trapped in the iron hydroxide precipitate. As a result of this process, significant amounts of AMX (approximately 69%) can be removed from aqueous solution. Experiments with heavily contaminated pharmaceutical industrial wastewaters showed very promising results with a strong decrease in AMX, TOC, and acute toxicity.