Photosensitisers offer a potential efficient way to kill bacteria in water under visible light by producing reactive oxygen species. However, the majority of photosensitising metal complexes are based on rare transition metals. Often the efficiency of most solution-based photosensitisers is greatly compromised upon immobilisation on a solid support, which is essential for safe treatment. Photosensitisers based on inexpensive metal complexes, such as those of Cu, Ni or Fe, usually have too short excited state lifetime to react efficiently with oxygen and are ineffective in production of reactive oxygen species. Here I show a complex of (Cu(1) [Cu(I)(xantphos)(dmp)]tfpb (1) [tfpb = tetrakis(3,5-bis-(trifluoromethyl)phenyl)borate] immobilised on silica, 1-silica which demonstrates efficient killing of bacteria through ROS production. This complex has a sterically-hindered coordination-centre leading to an excited state lifetime of &gt;200ns, which enables 1 to efficiently photosensitise singlet oxygen (29%). Upon irradiation with 400nm, 17.5 mW cm-2, 1-silica (55 mM) shows 99.99% killing of a Gram-positive bacterium Staphylococcus aureus (the Methicillin Resistant strain MRSA 315) after 15 minutes and complete inhibition after 2 hours (&gt;99.9999%). 1-silica also demonstrated significant killing of Gram-negative E. Coli; 99.99% killing was achieved after 2 hrs, and 99.9999% after 3 hrs of irradiation under the same conditions. Thus 1-silica is orders of magnitude more efficient than many immobilised photosensitisers, is similar in activity to immobilised porphyrin derivatives, and exceeds the &gt;= 99.99% threshold by WHO for the “highly protective” antibacterial agents. This first example of an immobilised Cu(I) complex used for light-driven bacterial killing demonstrates the potential of Earth-abundant transition metal complexes as low-cost efficient photo-antibacterial agents.

Immobilised complexes of Earth-abundant copper(I) as antibacterial photosensitisers for water treatment

ACS Fall 2021

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