Iron complex facilitated copper redox cycling for nitric oxide generation as nontoxic nitrifying biofilm inhibitor

In this study, we developed poly(vinyl chloride) (PVC)-solvent casted mixed metal copper and iron complexes capable of catalytic generation of the antibiofilm nitric oxide (NO) from endogenous nitrite. In the absence of additional reducing agent, we demonstrated that the presence of iron complex facilitates a redox cycling, converting the copper(II) complex to active copper(I) species, which catalyzes the generation of NO from nitrite. Assessed by protein assay and surface coverage analyses, the presence of the mixed metal complexes in systems containing water industry-relevant nitrite-producing nitrifying biofilms was shown to result in a "nontoxic mode" of biofilm suppression, while confining the bacterial growth to the free-floating planktonic phase. Addition of an NO scavenger into the mixed metal system eliminated the antibiofilm effects, therefore validating first, the capability of the mixed metal complexes to catalytically generate NO from the endogenously produced nitrite and second, the antibiofilm effects of the generated NO. The work highlights the development of self-sustained antibiofilm materials that features potential for industrial applications. The novel NO-generating antibiofilm technology diverts from the unfavorable requirement of adding a reducing agent and importantly, the less tendency for development of bacterial resistance.