Cu(II) complexes using acylhydrazones or cyclen for biocidal antifouling coatings

Copper and copper-based compounds have broad spectrum antimicrobial activity, but concerns about leaching into the environment and toxicity on non-target organisms is leading the use of copper-based coatings being restricted. Our objective was to develop coatings that used the biocidal activity of copper, but with low negative impacts by reducing its leaching into the environment. This study reports the synthesis and characterisation of copper coordinating ligands, their formulation into coatings and testing of their antibacterial activity. A polyacylhydrazone and a series of simple acylhydrazones were synthesised and coordinated to Cu(II), but were considered unsuitable due to either their poor water-solubility or high levels of copper leaching. In an alternative approach, copper was successfully chelated to the tetraazamacrocycle, cyclen, and used to synthesise Cu(II)-cyclen functionalised silica particles, which were successfully combined with commercial paint formulations. These functionalised products showed poor antibacterial activity when incorporated into epoxy coatings, probably due to the low copper content of the formulations. However, these ligands may have other applications, such as removal of heavy metals from contaminated effluent steams.