Supramolecular host-guest interaction of antibiotic drug ciprofloxacin with cucurbit[7]uril macrocycle: Modulations in photophysical properties and enhanced photostability

Abstract

Supramolecularly assisted modulations in the photophysical properties of the well known and practised antibiotic drug ciprofloxacin (Cpf) with versatile macrocyclic cavitand molecule cucurbit[7]uril (CB7) has been explored under different pH conditions. Both the cationic (Cpf-H+) and neutral (Cpf) forms of the drug exhibits strong binding interaction with CB7. Ground state absorption, steady-state fluorescence, time-resolved emission and fluorescence anisotropy decay measurements documented the host assisted intriguing changes in the photophysical properties of the drug, occurred through the successive formations of the 1:1 and 1:2 (drug to host) inclusion complexes, and thereby causing the intriguing small initial enhancement in fluorescence intensity at lower host concentrations and subsequently leading to a strong fluorescence quenching at higher CB7 concentration. Inferences drawn from the photophysical studies are nicely supported by the results obtained from the 1H NMR measurements. Investigations on the photodegradation studies involving the Cpf-H+ and Cpf forms of the drug, both in the absence and in the presence of CB7 host, revealed that there is a large enhancement in the photostability for both the prototropic forms of the drug, by about 3 times, on their inclusion complex formation with the CB7 host. Observed results from the supramolecular interactions of the ciprofloxacin drug with CB7 macrocycle are suggested to have implications in improving drug stability and in the possible deployments in drug formulations and drug delivery systems.