Spectrofluorometric study on the inclusion behavior of p-(p-carboxyl benzeneazo) calix[4]arene with norfloxacin

Spectrofluorometric titrations have been performed to investigate the inclusion behavior of p-(p-carboxyl benzeneazo) calix[4]arene (CBC4A) with norfloxacin (NFLX) in NaAc–HAc buffer solution (pH = 5.0). It was found that the fluorescence intensity of NFLX quenched regularly upon the addition of CBC4A. The results indicated 1:1 complex stoichiometry and an association constant of 8.21 × 105 L mol−1 at 20.0 °C were calculated by applying a deduced equation. Job's plot also verified the existence of 1:1 inclusion complex. The proposed interaction mechanism indicates that NFLX goes into (or partially goes into) the cavity of CBC4A with the help of hydrogen bonding and other forces. The various factors (pH value, ionic strength, and surfactants) affecting the inclusion process were examined in details.