Ionic strength effect on deprotonation of para-sulfonatocalix[4]arene

The deprotonation of para-sulfonatocalix[4]arene were studied by a combination of spectrophotometric and potentiometric methods at 25°C. The ionic strength of solutions was kept constant by sodium perchlorate as background electrolyte at 0.10 to 4.0 mol dm-3. Potentiometer was calibrated according to Gran method for each ionic strength. Spectral changes show evidence for proton dissociation of only one hydroxyl group of calixarene in the studied pH range of 2-10. The pKa values were calculated using STAR program by multivariate curve resolution of absorbance data. Results indicate that the acid-base behavior of para-sulfonatocalix[4]arene varies strongly with increasing ionic strength of solution. The dependence of deprotonation constants on ionic strength were explained by means of Specific ion Interaction Theory (SIT). Activity coefficients of species were modeled by a modified SIT approach. The specific ion interaction parameters were extracted associated with thermodynamic deprotonation constant of para-sulfonatocalix[4]arene