Copper complexation inhibits fluoroquinolone photodegradation: An overlooked factor enhancing environmental...

Area of Science:

• Environmental Chemistry
• Photochemistry
• Aquatic Toxicology

Background:

• Fluoroquinolones (FQs) and copper ions (Cu²⁺) are common contaminants in wastewater from aquaculture and livestock.
• The photochemical interactions between FQs and Cu²⁺ and their impact on FQ environmental fate are not well understood.

Purpose of the Study:

• To investigate the photochemical interactions between 12 different FQs and Cu²⁺.
• To elucidate the mechanism by which Cu²⁺ affects FQ photodegradation.
• To assess the implications of these interactions on the environmental persistence of FQs.

Main Methods:

• Photodegradation experiments with 12 different FQs in the presence of Cu²⁺.
• Steady-state quenching experiments and transient absorption spectroscopy to study quenching mechanisms.
• Density functional theory (DFT) calculations to model FQ-copper complexation and excited states.

Main Results:

• Cu²⁺ significantly inhibited the photodegradation of all 12 FQs studied.
• The inhibition efficiency showed a strong linear correlation (R²=0.95) with FQ-copper complexation constants.
• A static quenching mechanism was proposed, where excited FQ-Cu complexes undergo non-radiative decay, suppressing reactive oxygen species formation.

Conclusions:

• Metal complexation, specifically with Cu²⁺, plays a critical role in reducing the photodegradation rates of fluoroquinolones.
• This complexation pathway leads to enhanced environmental persistence of FQs by suppressing photochemical degradation.
• Understanding these interactions is crucial for assessing the environmental fate and risk of fluoroquinolone antibiotics in aquatic ecosystems.