Spectrofluorimetric study of the interaction of ciprofloxacin with amino acids in aqueous solution following solvatochromic studies

Complexation of a fluoroquinolone derivative (ciprofloxacin), L, and some amino acids has been studied using spectrofluorimetric method. Results indicated that ciprofloxacin have a greater tendency to form a 1:1 complex with aspartic acid and arginine than the other tested molecules. The fluorescence of ciprofloxacin exhibits quenching process while it has been titrated with these amino acids. Formation constant values (Kf) for complex formed between ciprofloxacin and amino acids were also calculated. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were studied too. Possible reasons for the observed stability sequence were discussed based on the structures proposed for the resulting complexes. Besides the solution studies, solvatochromic properties of the ciprofloxacin are discussed by studying its spectra in a selection of different solvents.

Graphical abstractEmission spectra of ciprofloxacin in twelve solvents with different polarity.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The fluorescence intensity was quenched by titrating CPF with amino acids. ► The results show that complex formation is less stable at higher temperatures. ► Fluorescence spectra of CPE was studied in twelve solvents with different polarities. ► A value of μe = 7.90 D was calculated for the excited singlet state dipole moment of CPE. ► The HOMO–LUMO gap values decrease with increasing dielectric constant of the solvents.