Interaction of 4-aminosalicylic acid and surfactants in aqueous solutions using UV-Vis spectra and steady-state fluorescence spectroscopy

Abstract

The interactions of 4-aminosalicylic acid (4-ASA) and surfactants in aqueous solutions were investigated by using UV-Vis spectra and steady-state fluorescence spectroscopy. The results showed that the strongest peak at UV-vis spectra of 4-ASA aqueous solution in the presence of cationic surfactant and cetyltrimethyl ammonium bromide (CTAB) appeared at 206 nm and took a red shift from 206 nm to 221 nm with the increase of 4-ASA concentrations from 0.8×10−5 to 4.4×10−4 mol/L. Similarly, the strongest peak at UV-vis spectra of 4-ASA aqueous solution in the presence of nonionic surfactant and polyvinylpyrrolidone (PVP) appeared at 206 nm and took a red shift from 206 nm to 219 nm with the increase of 4-ASA concentrations from 0.8×10−5 to 4.4×10−4 mol/L. However, the similar phenomena did not appeared in the presence of anion surfactant, sodium dodecyl sulfate (SDS), the UV-vis spectra of 4-ASA aqueous solution remained the same peak position and the peak value increased with the 4-ASA concentration increase. The results could be attributed to the electrostatic attraction between 4-ASA and CTAB or PVP, as well as the electrostatic repulsion between 4-ASA and SDS. Furthermore, the value of critical micelle concentration (CMC) of surfactants in the presence of 4-ASA was determined with Fluorescence method. The first and second CMC of CTAB was 1.2× 10−4 M and 2.4×10−4 M, respectively. The first and second CMC of PVP was 1.2×10−4 M and 2.8×10−4 M. SDS realized the multiple micellizations to form multiple CMC.