The formation of associates between single- or double-charged anions of bromocresol purple (3,3'-dimethyl-5,5'-dibromophenolsulfonephthalein) and single-charged cations of cyanines (quinaldine blue, quinaldine red) has been investigated. The equilibrium constants of the association have been determined on the basis of UV-Vis spectroscopy data. The energy of the cation-anion interaction (the standard enthalpy of formation of ions and associates), as well as the probable structure of associates, were established using the PM7 semiempirical method. The presented results can be useful in the development of new spectroscopic methods for the detection of organic additives in water (e.g. acetone) due to the spectral properties of dissimilar associates.
Keywords: Bromocresol purple; Dissimilar association; Enthalpy of formation; Semiempirical method; UV–Vis spectroscopy.
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