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

Abstract

The behaviour of host-guest interaction of the drug i.e. norfloxacin (NFX) with β-cyclodextrin (β-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 β-CD is revealed by fluorescence anisotropy and fluorescence lifetime measurements. The effect of temperature on the Stern-Volmer quenching constant (KSV) 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 (ΔH), entropy (ΔS) and free energy (ΔG) have been determined. The negative value of ΔH and the positive value of ΔS validate the hydrophobic interaction between drug and quencher, and the negative value of ΔG suggests that the complex is spontaneous in nature.