pH influence on the complexation site of Al(III) with protocatechuic acid. A spectroscopic and theoretical approach

► Al(III) forms a monodentate complex with the carboxylate function of protocatechuic acid, at pH = 6.5. ► Al(III) changes binding site according to the pH. ► The structure of the complex was elucidated by combined UV-vis spectroscopy and TD-DFT calculations.