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

Abstract

The deprotonation of para-sulfonatocalix[4]arene was studied by a combination of spectrophotometric and potentiometric methods at 25 °C. The ionic strength of the solutions was kept constant by sodium perchlorate as a background electrolyte at 0.10-4.0 mol dm-3. The spectral changes evidenced proton dissociation of only one hydroxyl group of calixarene in the studied pH range of 2-10. The pKa values were calculated using the STAR program by multivariate curve resolution of the absorbance data. The results indicated that the acid-base behavior of para-sulfonatocalix[4]arene varied strongly with increasing ionic strength of the solution. The dependence of the deprotonation constant on ionic strength was explained by means of the Specific Ion Interaction Theory (SIT). The activity coefficients of the species were modeled using a modified SIT approach. The extracted specific ion interaction parameters were associated with the thermodynamic deprotonation constant of para-sulfonatocalix[4]arene. Copyright (C)2013 SCS.