Exploring the Speciation of trans-Aconitic Acid in Aqueous Solution: Interactions with Divalent Metal Cations of...

Trans-aconitic acid is a naturally occurring, biodegradable, unsaturated tricarboxylic acid that represents a promising sustainable alternative to conventional, poorly degradable chelating agents used in metal ion remediation. In this study, its acid-base behavior and chelating properties toward environmentally relevant divalent metal cations (Ca²⁺, Mg²⁺, Cu²⁺, Co²⁺, and Zn²⁺) were systematically investigated in an aqueous solution of potassium chloride (I = 0.10-1.00 mol dm^-3) and at T = 298.15 K. A combined experimental and computational approach, including potentiometry, UV-vis and NMR spectroscopy, and Density Functional Theory (DFT) calculations, was employed to achieve a molecular-level thermodynamic characterization. The results indicate that trans-aconitic acid exhibits good sequestration efficiency, with a marked affinity toward Cu²⁺ and Mg²⁺ cations, as confirmed by pL_0.5 and pM parameters as well as binding energy analyses. DFT calculations elucidated the microscopic acidities of the three carboxylic groups and rationalized the different interaction modes of Ca²⁺ and Mg²⁺. Overall, this study provides a comprehensive thermodynamic framework for trans-aconitic acid-metal interactions, supporting its potential application as an ecofriendly ligand for metal ion remediation and scale prevention in natural and industrial waters.