Calixarenes and cyclodextrins as off- and on-fluorescence probes for carbazole

Abstract

Absorption and fluorescence spectra of the nitrogen polycyclic aromatic hydrocarbon carbazole (CZL) were analyzed with native cyclodextrins (CD; α,β,γ); derivatized CD (hydroxypropyl-β-cyclodextrin, HPCD; methyl-β-cyclodextrin, MeCD) and p-sulfonated calixarenes (SCAn, with n= 6 and 8) macrocycles. The results showed a slight increase in the absorbance of CZL with CD, but the mixture of CZL with SCA showed lower absorption than the sum of the individual spectra. Also, changes in fluorescence were observed by adding the macrocycles, quenching with SCA, and significant increases with CD. The higher fluorescence enhancement was with HPCD rationalized as a complex formation with 1:1 stoichiometry, with an average value for the association constant (KA) of (12 ± 1) x 102 M-1, and a quantum yield ratio between the complexed CZL and free CZL (ΦCZL-HPCD/ΦCZL) of (1.56 ± 0.02) at neutral pH and 25.0 °C. These increases in fluorescence were used as an on-fluorescence switch to develop a supramolecular analytical method for CZL in aqueous samples. The best analytical parameters were in HPCD (LOD= 1.41±0.01 ng/mL). The method was validated in aqueous samples of river and tap water with recoveries between 96-104%. The proposed supramolecular method is quick, direct, selective and represents an alternative and low-cost analysis method.