Synthesis and antibacterial activity of rhodanine-based azo dyes and their use as spectrophotometric chemosensor for Fe³⁺ Ions

This research includes the design and synthesis of new derivatives for rhodanine azo compounds (4a-c) containing a naphthalene ring. Physiochemical properties of the synthesized compounds were determined by their melting points, FTIR, ¹H-NMR, ¹³C-NMR, and elemental analysis spectroscopic techniques. The biological activities of the newly prepared azo rhodanine compounds were evaluated against some pathogenic bacteria using three different bacterial species including (Escherichia coli., Pseudomonas aeruginosa, Staphylococcus aureus) and compared with amoxicillin as a reference drug. The results showed that our compounds have moderate-to-good vital activity against the mentioned pathogenic bacteria. The selectivity and sensitivity of the newly prepared rhodanine azo compounds with transition metals Co²⁺, Cu²⁺, Zn²⁺, Ni²⁺, and Fe³⁺ were studied using UV-vis and fluorescence spectroscopy techniques. Among the synthesized azos, azo 4c showed affinity toward Fe³+ ions with an association constant of 4.63 x 10⁸ M^-1. Furthermore, this azo showed high sensitivity toward Fe³⁺ ions with detection limits of 5.14 μM. The molar ratio and Benesi-Hildebrand methods confirmed the formation of complexes between azo 4c and Fe³⁺ with 1:2 binding stoichiometry. Therefore, azo 4c showed excellent potential for developing efficient Fe3+ chemosensors.