Deprotonation of para-sulphonatocalix[4]arene in water–methanol mixtures

Abstract

The deprotonation of para-sulphonatocalix[4]arene was investigated in some aqueous methanol solutions by spectrophotometric method. Principal component analysis was performed on the spectral data matrices in order to determine the number of light absorbing species which are involved in the deprotonation process. The equilibrium constant of the deprotonation reaction together with the pure spectrum and concentration profile of each species were extracted by STAR programme utilising the multivariate curve fitting. The effect of specific and non-specific solute–solvent interactions on the pK a values was examined upon the basis of the linear solvation energy relationship concept. Thus, a multiple linear regression analysis was used to correlate the pK a variation with the macroscopic (dielectric constant) and microscopic Kamlet–Taft parameters (α, β and π*) of binary mixtures. Results indicate that the deprotonation of para-sulphonatocalix[4]arene in water–methanol mixtures is highly related with the non-specific long-range electrostatic solute–solvent interactions.