Cu(II)-phenanthroline coordination complex-functionalized polymeric films: physicochemical characterization, antibacterial assay and computational modelling of predictive complex diffusion

Abstract This study describes the development and characterization of novel polymeric films based on sodium alginate (SA) and bovine gelatin (BG) functionalized with a copper(II)-1,10-phenanthroline (Cu(II)-phen) coordination complex for potential antibacterial applications. The Cu(II)-phen-functionalized films were prepared by solvent evaporation and comprehensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled to energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FT-IR) spectroscopy, and thermogravimetric and differential thermal analyses (TG-DTA). Antibacterial susceptibility assays were done against Gram-negative and Gram-positive strains, and computational modeling was used to interpret the diffusion-related antibacterial response of the complex-functionalized films against the tested strains. XRD analysis revealed that the incorporation of the Cu(II)-phen complex modified the films’ crystalline profile, indicating intermolecular interactions between the polymeric network and the coordination complex. SEM-EDS analyses revealed a more homogeneous, compact morphology of the functionalized films, with copper distributed within the SABG blend, suggesting successful matrix restructuring upon loading with the metal complex at two different concentrations (SABG3 and SABG5). FT-IR spectroscopy confirmed intermolecular interactions between SA, BG, and the Cu(II)-phen complex via characteristic band shifts. Thermal analysis showed that incorporating the complex alters the degradation profile of SABG films, with the SABG3 formulation exhibiting greater thermal stability than SABG5. Disc diffusion assays confirmed measurable antibacterial activity of the functionalized films against both Gram-negative ( Klebsiella pneumoniae and Escherichia coli ) and Gram-positive ( Staphylococcus aureus and Enterococcus faecalis ) bacteria, with performance superior to that of the reference antibiotic gentamicin, particularly for films containing 5 wt% of the Cu(II)-phen complex. Diffusion-based modeling was employed to interpret disk diffusion assays, revealing that the antimicrobial response is governed by diffusion-limited transport and bacterial susceptibility rather than by a linear dependence on complex loading.