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Antifungal studies were made of mixtures of minimal inhibitory concentrations (MICs) of 8-quinolinol and its bischelates with copper(II), zinc(II), and manganese(II) and with mixed ligand chelates composed of 8-quinolinol, copper(II) and a second ligand including salicylic acid, 3-hydroxy-2-naphthoic acid, 3,5-diiodosalicylic acid, and 4-bromo-3-hydroxy-2-naphthoic acid. Mixtures of the MICs of the bischelates of 8-quinolinol with copper(II) and zinc(II) and copper(II) and manganese(II), as well as 7-iodo-8-quinolinol and its bischelate with copper(II), and 8-quinolinol and 5-iodo-8-quinolinol were also studied against six fungi: Aspergillus niger, Aspergillus oryzae, Trichoderma viride, Myrothecium verrucaria, Mucor cirinelloides, and Trichophyton mentagrophytes. With the exceptions of the mixtures of 8-quinolinol and (8-quinolinolato )(3,5-diiodosalicylato )copper(II) and (8-quinolinolato)(4- bromo-3-hydroxy-2-naphthoato)copper(II) against M. cirinelloides, all of the test organisms were inhibited by 40% or less of each mixture containing 8-quinolinol. Bischelates of 8-quinolinol with copper(II) and zinc(II) and copper(II) and manganese(II) inhibited five fungi at 50% of the mixtures of the MICs. Mucor cirinelloides was not inhibited by bis(8-quinolinolato)copper(II), bis(8-quinolinolato)zinc(II), or by bis(7- iodo-8-quinolinolato)copper(II). The following conclusions were drawn: (1) there is synergism between 8-quinolinols and their metal chelates; (2) the mechanisms of fungitoxicity of 8-quinolinols and their metal chelates are different; (3) the fungitoxic actions of the chelates of 8-quinolinols with different metals appear to be additive; (4) the mechanisms of fungitoxicity of 8-quinolinol and 5-iodo-8-quinolinol are different; (5) the toxicity of 8-quinolinols is due to the concerted action of the ligands and their metal chelates, whereas when the toxicant is the preformed metal chelate, toxicity is due to the chelate alone

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American pharmaceutical association 78 no. 11:975-978. 0022-3549/89/1100-0975$01.00/0

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