Water Soluble EDTA and DTPA Ligands Functionalized With 2‐Aminobenzothiazole: Synthesis and Aqueous Metal Ion Equilibrium Studies

Water pollution by toxic metals remains a persistent challenge due to their persistence and substantial risk to the environment. The development of water‐soluble ligands for metal‐ion detection is key for enabling effective sensing in aqueous environments. In this work, two water‐soluble receptors were synthesized by coupling 2‐aminobenzothiazole (ABT) with polyaminopolycarboxylic acid backbones derived from ethylenediaminetetraacetic acid (EDTA, R1) and diethylenetriaminepentaacetic acid (DTPA, R2). The resulting ligands integrate strong metal‐binding sites with chromophoric ABT units, enabling simultaneous coordination and optical transduction. Protonation studies in aqueous media revealed three acid–base equilibria for R1 and four for R2, reflecting the increased denticity and basicity of the DTPA scaffold. UV–Vis titrations were performed to examine interactions with Cu 2+ , Ni 2+ , Pb 2+ , and As(V) ions at neutral and basic pH. Distinct spectral responses and binding affinities were observed, with log K values of 4.8–4.9 for divalent metals and enhanced Pb 2+ stabilization by R2 (log K ≈ 6.3). These findings demonstrate that incorporating ABT into polyaminocarboxylate frameworks yields water‐soluble receptors with tunable optical behavior. The dual chelating and chromogenic character of these ligands highlight their potential as optical recognition motifs for environmentally relevant metal ions.