Understanding the Role of Complexation of Fluoroquinolone and β-Lactam Antibiotics with Iron (III) on the Photodegradation under Solar Light and UVC Light

Abstract

Antibiotics elimination by some photochemical processes involves ferric ions, but little is discussed about the fundamental aspects of complexation effects on their degradation. This study compares the photodegradation of two fluoroquinolones, three β-lactams, and their ferric complexes in deionized water. The complexed antibiotics were more recalcitrant than the free antibiotics to the solar light action (the photodegradation rate constants diminished by more than 50%). To better study the photodegradation, other experiments considering two representative cases (ciprofloxacin and dicloxacillin) were performed. For ciprofloxacin, as the iron amount was increased from 0 to 7.5 µmol L−1, its photodegradation rate constant decreased from 0.017 to 0.004 min−1. In contrast, for dicloxacillin, the increase in iron concentration (from 0 to 7.5 µmol L−1) accelerated its photodegradation (the rate constant augmented from 0 to 0.0026 min−1). When UVC light was used, the degradations of free and complexed antibiotics were very close, exhibiting values of degradation rate constants between 0.030 and 0.085 min−1. The antimicrobial activity (AA) was eliminated when 90% of ciprofloxacin and 90–95% of dicloxacillin were degraded. The AA removal was associated with structural changes in relevant moieties of antibiotics, such as fluorine and piperazyl ring for ciprofloxacin, or β-lactam ring for dicloxacillin.

Possibilities and Limitations of the Sono-Fenton Process Using Mid-High-Frequency Ultrasound for the Degradation of Organic Pollutants

“…Moreover, the mixture of the antibiotic and the ferric ions induced an intense yellow coloration of the solution. These results evidenced the formation of a CIP-Fe 3+ complex [ 33 ]. However, no interaction between ferrous ions and CIP was observed ( Figure S3 ).…”

“…However, no interaction between ferrous ions and CIP was observed ( Figure S3 ). Recent studies have also reported that the interaction between fluoroquinolones (CIP belongs to this antibiotics class) and ferric ions leads to the formation of stable complexes [ 33 , 34 ]. It can be noted that CIP has the keto-carbonyl moiety (structure with a higher number of lone electron pairs), which favors the interaction between this fluoroquinolone and ferric ion through chelation [ 35 , 36 , 37 ].…”

“…Subsequently, the ferric ions are complexed by the remaining molecules of CIP. The formed complex is a charged hydrophilic molecule [ 33 , 38 ] that is placed far away from the cavitation bubble and the hydroxyl radicals. Consequently, the complex is recalcitrant to the sonochemical action, and the CIP concentration remains constant, as observed in Figure 3 b.…”

“…the H 2 O 2 evolution presented in Figure 5 b also indicated a low consumption of hydrogen peroxide. The low photodegradation of the complexed CIP can be associated with the relocation of part of the electron density from the organic structure (i.e., CIP) on the metal ion [ 33 , 43 ]. Indeed, previous theoretical works have reported that the interaction of fluoroquinolones with the metal cations increases the activation energy for some photo-transformation pathways, thus making the complex more recalcitrant than the free antibiotic to the light action [ 43 , 44 , 45 ].…”

Use of Fluorescence Spectroscopy and Chemometrics to Visualise Fluoroquinolones Photodegradation Major Trends: A Confirmation Study with Mass Spectrometry

“…(F)Q photolytic rate constants and degradation pathways are highly pH and cation dependent. They exhibit the greatest photolysis rates at neutral pH, when the neutral form (and zwitterionic when also presenting amino groups) is the most abundant [ 8 , 9 ], whereas regarding the cations, it is variable, depending on the type of cation and (F)Q, respectively, forming diverse (F)Q–metal complexes with different stabilities, observing photolytic enhancement [ 10 ] or hindrance [ 11 ].…”