Enzymatic Oligomerization of Ampyrone- and Phenylhydrazine-Based Monomers: Structural, Thermal, and Antioxidant Functional Analysis

In this study, 2,4-dihydroxybenzaldehyde was subjected to separate condensation reactions with phenylhydrazine and ampyrone (4‑amino antipyrine), yielding a hydrazine‑based monomer (M‑PHy) and an azomethine monomer (M‑Amp), respectively. Both monomers were subsequently polymerized via horseradish peroxidase/hydrogen peroxide (HRP/H₂O₂)–mediated enzymatic oxidative oligomerization, affording two novel oligomeric products, O‑PHy and O‑Amy. The chemical structures of all synthesized compounds were confirmed by FT‑IR, UV‑Vis, and ¹H NMR spectroscopic analyses. Molecular weight distributions of the oligomers were determined using gel permeation chromatography (GPC). Thermal properties were evaluated by thermogravimetric analysis (TGA), revealing initial decomposition temperatures of 178 °C for O‑PHy and 192 °C for O‑Amy, with residual masses of 16.5% and 15.6% at 1000 °C, respectively. Surface morphologies of the oligomers were examined by scanning electron microscopy (SEM), demonstrating distinct microstructural features associated with their molecular architectures. These findings highlight the successful synthesis, structural verification, and physicochemical characterization of two new enzymatically derived oligomers.