Herein, we synthesized two new phthalimide-functionalized benzoxazine monomers, pPP-BZ and oPP-BZ, through Mannich reactions of 2-(4-hydroxyphenyl)isoindoline-1,3-dione (pPP) and 2-(2-hydroxyphenyl)isoindoline-1,3-dione (oPP), respectively, with p-toluidine and paraformaldehyde. The structures of these two monomers were confirmed using Fourier transform infrared (FTIR) and nuclear magnetic resonance spectroscopy. We used differential scanning calorimetry, FTIR spectroscopy, and thermogravimetric analysis to study the polymerization behavior and thermal stability of the monomers and their corresponding polybenzoxazines. Poly(pPP-BZ) and poly(oPP-BZ) were formed on mild steel (MS) through spin-coating and subsequent thermal curing polymerization. We used various corrosion testing methods to examine the effect of the curing temperature on the corrosion resistance of the coated MS samples in 3.5 wt.% aqueous solution of NaCl. Among our tested systems, the corrosion rate reached a low of 2.78 µm·Y⁻¹ for the MS coated with poly(pPP-BZ)₁₈₀ (i.e., the coating that had been cured at 180 °C); this value is much lower than that (4.8 µm·Y⁻¹) reported for a maleimide-based benzoxazine compound (MI-Bz)/33 wt.% ACAT (amine-capped aniline trimer) blend. Thus, the incorporation of the imide functional group into the PBZ coatings is an effective strategy for affording high-performance corrosion resistance.

Two new Schiff base ligands (L1 and L2) were synthesized by condensing thiocarbohydrazide (TCH) with o-anisaldehyde or p-anisaldehyde in ethanol. Their mono- and bi-nuclear complexes with Sn(II), Zn(II), and Fe(II) were prepared for potential fluorescence and biological applications. Characterization was performed using FT-IR, NMR, UV-Vis spectroscopy, mass spectrometry, molar conductance, TGA, X-ray diffraction and SEM. XRD results indicated good crystallinity with crystallite sizes of 20–50 nm. Fluorescent intensity of free TCH ligands increased upon complexation with Sn, Zn, and Fe, suggesting their potential as fluorescence chemosensors. The compounds exhibited variable antimicrobial activities against Staphylococcus aureus, Escherichia coli, and Candida albicans, but lower than commercial drugs. L1Fe and L1Zn enhanced L1’s cytotoxicity in four colorectal malignancy cells and L1Zn in skin cancer cells (A375), lung cancer cells (A549), uterine cervix cells (HeLa), and glioblastoma cells (U87). L1Fe showed enhanced activity in mammary adenocarcinoma cells (T47D) and triple-negative breast cancer cells (MDA-MB-231). L2Sn exhibited 70fold increase in L2’s DPPH radical scavenging compared to the antioxidant ascorbic acid. L1Zn and L2Zn complexes outperformed indomethacin in reducing inflammation in RAW macrophages, enhancing the nanomolar efficacy of L1 and L2. These complexes have promising utility in cancer diagnosis, monitoring and highly selective duality of anti-inflammatory/cytotoxicity treatments.