Poly(isobutylene- alt -maleic anhydride)–Zinc Tetraphenylporphyrin Conjugates as Photodynamic Antimicrobial Materials with Plasmid DNA Degradation Properties

The emergence of multidrug-resistant (MDR) bacteria underscores the urgent need for alternative antimicrobial strategies. In this study, we report the synthesis and characterization of poly(isobutylene-alt-maleic anhydride) (PMAL) functionalized with amino tetraphenylporphyrin (TPP) and subsequent zinc metalation (PMAL-ZnTPP) as a photodynamic antimicrobial material. The potential of PMAL-ZnTPP to eradicate a wide range of pathogenic MDR bacteria and degrade the plasmid vectors that frequently carry antimicrobial resistance (AMR) genes is evaluated. Amino porphyrin was covalently grafted onto PMAL through a nucleophilic acyl substitution (aminolysis) reaction, resulting in ring opening of the anhydride and formation of amide and carboxylic acid groups. The conjugates were characterized, confirming successful grafting and zinc coordination. Nanosecond transient absorption spectroscopy (ns-TAS) revealed the formation of a long-lived triplet excited state, with lifetimes of 245 μs in toluene and 360 μs in DMSO, which is essential for the generation of reactive oxygen species and underpins the antimicrobial photodynamic activity of photosensitizing polymers. PMAL-ZnTPP generates singlet oxygen with a quantum yield of 0.59 under visible-light irradiation. Antimicrobial evaluation against 14 bacterial strains, including clinically and environmentally relevant Gram-positive and Gram-negative species, demonstrated broad-spectrum activity, achieving log reductions in colony-forming units/mL (CFU/mL) ranging from 0.36 to 5.8 upon light exposure for 1 h compared to the controls. Plasmid DNA integrity analysis indicated that PMAL-ZnTPP-mediated photodynamic treatment induced plasmid damage both in isolated DNA and within bacterial cells. The non-water-soluble nature of PMAL-ZnTPP makes it well-suited for immobilized or dispersed decontamination applications. Its broad-spectrum antimicrobial activity and plasmid degradation properties make this an attractive material for further development where mitigation of AMR transmission is a priority.