Degradable copper(ii)-doped starch-based biopolymeric films with antibacterial activity

Abstract

The search for new bioactive molecules and sustainable materials to address antimicrobial resistance continues to be of significant attention in many research areas. In this work, new copper(II) coordination polymers and complexes containing ammonia and aromatic carboxylate ligands were self-assembled, characterized, and applied as bioactive dopants to produce starch-based biopolymeric films. The structures of [Cu(NH₃)₂(nca)₂] (1) (Hnca = 2-naphthoic acid), [Cu(NH₃)₂(μ-ndca)]_n (2) (H₂ndca = 2,6-naphthalenedicarboxylic acid), and [Cu(NH₃)₂(μ-obba)]_n (3) (H₂obba = 4,4′-oxybis(benzoic acid)) reveal discrete monocopper(II) units in 1 or 1D coordination polymer chains in 2 and 3. In all compounds, the hexacoordinate Cu(II) centers feature an octahedral {CuN₂O₄} environment with mutually trans ammonia ligands. The compounds 1–3 were used as bioactive Cu-dopants (5%) to prepare biopolymeric films, 1–3@[PS]_n and 1–3@[PS-MCC]_n, based on sustainable and low-cost biofeedstocks such as potato starch (PS) or its mixture with microcrystalline cellulose (PS-MCC), respectively. Due to the importance in biomaterial-related infections, the growth inhibition of two clinically significant Gram-positive bacteria species, S. epidermidis and S. aureus, was studied in the presence of the prepared biopolymeric films. The Cu(NH₃)₂-carboxylates and derived biopolymeric materials showed a pronounced antibacterial activity, with doped films being able to inhibit the growth of 7 out of 8 strains tested, revealing a particularly high performance against the clinical isolates of S. epidermidis. By presenting these novel coordination compounds and biopolymeric films generated from sustainable biofeedstocks, this study combines several research approaches and broadens an antibacterial use of inorganic Cu-based derivatives and related biopolymer materials.