The Binding of Ciprofloxacin with Perfluorooctanesulfonic Acid (PFOS): Fluorescence and pH Studies

Antibiotics are considered emerging micropollutants. They are efficiently transmitted through wastewater treatment plants, leading to their widespread detection in rivers and streams. Ciprofloxacin (CPF) is an antibiotic that is extensively used and found throughout the world’s environment. Its structure and binding are heavily influenced by pH and interactions involving aquatic colloids (AC) such as perfluorooctanesulfonic acid (PFOS). This research reviews the relevant literature techniques and compares the experimental binding between CPF and PFOS when CPF is regarded as a tetraprotic or a triprotic acid using fluorescence spectroscopy. A binding equilibrium model is developed to calculate the binding constants between CPF and the PFOS monomer K11 and the CPF-(PFOS) pseudophase Kn1, from the fluorescence quenching of CPF by PFOS. It is determined that the binding between CPF and PFOS only occurs in the postaggregate pseudophase and differs in magnitude when CPF is considered a tetraprotic acid (438.2 ± 56 M−1) or a triprotic acid (175.7 ± 14 M−1). The binding is also weaker in comparison to other surfactants because of the low aggregation number and complex noncovalent interactions.