Sustainable extraction of ciprofloxacin using deep eutectic solvents: Molecular dynamics insights under hospital...

This study investigates the molecular-level extraction behavior of ciprofloxacin (CIP), a widely used antibiotic and prominent pharmaceutical pollutant, using green hydrophobic deep eutectic solvents (HDESs). We evaluated three HDES systems: thymol-hexanoic acid (THY-HEX, DES1), thymol-nonanoic acid (THY-NON, DES2), and thymol-dodecanoic acid (THY-DOD, DES3). We conducted classical molecular dynamics (MD) simulations using GROMACS to model the interactions between CIP and each HDES under varying physicochemical conditions, specifically at pH 4 (acidic), pH 7 (neutral), and pH 10 (basic). The protonation state of CIP was adjusted accordingly, protonated at pH 4, zwitterionic at pH 7, and anionic at pH 10significantly affecting its interaction behavior. Simulations were also performed at three HDES-to-water dilution levels (1:1, 1:5, and 1:10 v/v) to emulate realistic extraction environments. Structural and dynamic analyses, including radial distribution functions (RDFs), mean square displacement (MSD), and hydrogen bonding assessments, revealed that CIP exhibited the strongest affinity for DES3 under acidic conditions (pH 4) and at the highest dilution level (1:10). Key indicators of this interaction include a high coordination number (CN = 1.87), a reduced MSD slope (β ≈ 1.16), and stable hydrogen bonding, all of which suggest enhanced stabilization of the protonated CIP species within the HDES matrix. These findings highlight the potential of THY-based HDESs as tunable, sustainable solvents for antibiotic removal from wastewater. The results support the application of HDESs in environmental remediation and offer valuable molecular insights to guide the design of next-generation green solvents.