Impact of host-guest complexation between norfloxacin and β-cyclodextrin on fluorescence quenching: Steady-state and time resolved fluorescence study

The behaviour of host-guest interaction of the drug i.e. norfloxacin (NFX) with beta-cyclodextrin (beta-CD) has been investigated by the fluorescence quenching method in acidic and neutral pH using copper as a quencher at various temperatures. The stoichiometry of the host-guest complication has been estimated using the Benesi-Hildebrand relationship. The incorporation of NFX inside the cavity of beta-CD is revealed by fluorescence anisotropy and fluorescence lifetime measurements. The effect of temperature on the Stern-Volmer quenching constant (K-SV) and binding constant (K) has been analyzed, and the type of quenching was confirmed from the fluorescence lifetime measurement. Using van't-Hoff equation and Gibbs-Helmholtz equation, thermodynamic parameters like change of enthalpy (Delta H), entropy (Delta S) and free energy (Delta G) have been determined. The negative value of Delta H and the positive value of Delta S validate the hydrophobic interaction between drug and quencher, and the negative value of Delta G suggests that the complex is spontaneous in nature.