Protonation of quinoline yellow WS in aqueous solutions: Spectroscopic and DFT theoretical studies

In the current work, the protolytic and some spectrophotometric characteristics of the food coloring Quinoline Yellow WS are studied in detail. Using DFT calculations, a probable pathway for dye protonation is proposed. Ionization constants were determined by spectrophotometry and tristimulus colorimetry methods, which were assigned to the corresponding functional groups of the dye. The obtained values of the ionization constants form the basis for calculating the distribution diagram of the coexisting acid-base forms of the Quinoline Yellow WS. For the dominant equilibrium form of the dye, the effect of the nature of the solvent was studied and it was shown that the molar absorptivity increases with an increase in the dielectric permittivity of the solvent. (C) 2020 Elsevier B.V. All rights reserved.