Innovative synthesis of antimicrobial Biginelli compounds using a recyclable iron oxide-based magnetic nanocatalyst

The present study presents the synthesis and application of a new, magnetically separable nanocatalyst, Fe₃O₄@PEG@CPTMS@dithizone-Ag (FPCD-Ag), with a high stability and recyclability design. In the preparation of this catalyst through a core-shell approach, Fe₃O₄ acted as the magnetic core, modified by a coating of polyethylene glycol, functionalized with 3-chloropropyl-trimethoxysilane and dithizone for the immobilization of Ag metal on its surface. Comprehensive characterization was performed by SEM, FT-IR, BET, XRD, EDS-MAP, TEM, LSV, and TGA to confirm its structure and composition. The synthesized nanocatalyst was employed for the assessment of its catalytic efficiency in the one-pot synthesis of twenty-eight 3,4-dihydropyrimidin-2(1H)-ones/thiones through a multicomponent cyclo-condensation reaction involving various aldehydes, β-dicarbonyl compounds, and thiourea/urea. The structure of the resulting compounds was confirmed by IR, ¹H-, and ¹³C- NMR spectroscopy, and their antibacterial activity was determined against Staphylococcus aureus ATCC25923, Acinetobacter calcoaceticus ATCC23055, Escherichia coli ATCC25922, and Pseudomonas aeruginosa ATCC27853 with most of the compounds showing significant activities. The nanocatalyst showed excellent recyclability, maintaining high stability and catalytic efficiency for up to six cycles with minimal activity loss. In these cases, the optimization studies determined the best conditions of a 30 mg catalyst with a water-ethanol solvent system in a 1:1 mL ratio, providing a 97% yield in a very short period of 20 min. This paper outlines the following advantages of this catalyst, including ease of separation without centrifugation, readily available starting materials and cost-effective, environmentally benign, quick reaction, and excellent product yield, hence offering a green methodology for efficient synthesis of the antimicrobial compounds.