Antimicrobial activity of supramolecular salts of gallium(III) and proflavine and the intriguing case of a trioxalate complex

The use of the gallium oxalate complex [Ga(ox)(3)](3−) as a building block in the formation of a drug-drug salt with the antimicrobial agent proflavine (PF) as its proflavinium cation (HPF(+)), namely [HPF](3)[Ga(ox)(3)]·4H(2)O, is reported together with the preparation of the potassium salt K(3)[Ga(ox)(3)] and the novel dimeric gallium(III) salt K(4)[Ga(2)(ox)(4)(μ-OH)(2)]·2H(2)O. All compounds have been characterized by solid state methods, and their performance as antimicrobial agents has been evaluated by disk diffusion assay against the bacteria strains Pseudomonas aeruginosa ATCC27853, Staphylococcus aureus ATCC25923, and Escherichia coli ATCC25922. While the [HPF](3)[Ga(ox)(3)]·4H(2)O drug-drug salt is effective against all three strains, the gallium oxalate salt K(3)[Ga(ox)(3)] showed impressive selectivity towards P. aeruginosa, with little to no antimicrobial activity against the other two organisms. This work presents novel breakthroughs towards Ga based antimicrobial agents.