Investigation of the inclusion behavior between p-sulfoniccalix[8]arene and norfloxacin by fluorescence spectroscopy

The host-guest complexation between p-sulfoniccalix8]arene (SC₈A) and norfloxacin (NFLX) in aqueous solution was investigated by fluorescence spectroscopy. Strong fluorescence intensity of the NFLX aqueous solution alone and obvious fluorescence quenching of NFLX solution in the presence of SC₈A were observed. The fluorescence lifetimes of NFLX and SC₈A-NFLX inclusion complex were determined and the effect of temperature on SC₈A-NFLX inclusion complex was studied. The static quenching of the inclusion was obtained, that is the SC₈A can form a nonfluorescent ground-state inclusion complex with NFLX. As the results show, the combined ratio (n) was 1:1 and association constant K was 1.17×10⁵ L/mol. Based on the experimental results, the mechanism of the inclusion complex was explored. The space matching, electrostatic force and hydrogen bond play important effects in the inclusion process. Subsequently, the addition of bovine serum albumin (BSA) solution led to the recovery of fluorescence intensity. It is indicated that BSA can liberate the NFLX into the solution by destructing the SC₈A-NFLX inclusion complex. Hence SC₈A may be used for controlled-release drug delivery in the pharmaceutical industry.