Regioselective design of spiroisoxazoline as a dual steel corrosion inhibitor: electrochemical performance, molecular-level insight, and POM toxicity evaluation
摘要
We report the regioselective synthesis of a spiroisoxazoline (SIO) via a 1,3-dipolar cycloaddition of an aza-aurone dipolarophile with an in situ generated arylnitriloxide. Spiroisoxazolines have scarcely been explored as corrosion inhibitors, and our study highlights their potential as a new class of heterocyclic protective agents. The structure of SIO was confirmed by IR and NMR (1H, 13C) analyses, while hemolysis assays demonstrated favorable hemocompatibility at concentrations ≤ 10−2 mg/mL, indicating low toxicity. The corrosion inhibition performance of SIO was evaluated on mild steel (MS) and the rarely studied H13 tool steel in 1.0 M HCl using OCP, EIS, and PDP techniques. Remarkably, SIO displayed distinct inhibitory modes—cathodic on MS and anodic on H13—achieving efficiencies of 93.8% and 91.2%, respectively, at 10−5 M. Adsorption followed the Langmuir model with high equilibrium constants and negative Gibbs free energies (− 49 and − 46 kJ/mol), consistent with strong chemisorption. The experimental findings were supported by computational studies. DFT calculations revealed high reactivity (Egap = 2.368 eV), while ESP, ELF/LOL, and RDG/NCI analyses identified key interaction sites and stabilizing noncovalent interactions. MD simulations on Fe(110) confirmed strong and spontaneous adsorption of SIO with a binding energy of − 160.22 kcal/mol, indicating formation of a stable protective layer. Toxicity (POM) and charge analyses highlighted reactive heteroatoms and pharmacophore sites, suggesting potential bioactivity in addition to corrosion inhibition. Overall, these results support spiroisoxazolines as efficient and multifunctional corrosion inhibitors and provide an integrated experimental–theoretical framework for designing advanced protective agents for steel surfaces.