Abstract
Phenylene-bis-quaternary ammonium compounds (Ph-bis-QACs), 4, 4'-(p-xylylenedithio) bis (1-alkylpyridinium iodide) s, N, N'-p-phenylenebis (1-alkyl-4-carbamoylpyridinium bromide) s and 4, 4'-(terephthaloylamino) bis (1-alkylpyridinium bromide) s composed of two pyridinium salt groups linked by a p-phenylene spacer chain were evaluated for their antimicrobial characteristics. We also compared the activities of these compounds with those of Methylene-bisquaternary ammonium compounds (M-bis-QACs), 4, 4% (1, 6-hexamethylenedithio) bis (1- alkylpyridinium iodide) s, N, N'-hexamethylenebis (4-carbamoyl-1-alkylpyridinium iodide) s and 4, 4% (tetramethylenedicarbonyldiamino) bis (1-alkylpyridinium iodide) s connected by a methylene spacer chain, and investigated the structure-activity relationship in a bis-QAC. Three Ph-bis-QACs exhibited a high and constant bactericidal activity with a carbon number from n = 8 to n =18, and a wide-ranging and effective antimicrobial activity against both bacteria and fungi. The antibacterial activities of Ph-bis-QACs were higher than those of M-bis-QACs by converting the methylene spacer chain of M-bis-QACs to a p-phenylene spacer chain. Moreover, while the activities of M-bis-QACs were influenced by the electron density of ammonium nitrogen, the activities of Ph-bis-QACs were not dependent on that. Therefore, these results suggested that the antibacterial activity of a bis-quaternary ammonium compound (bis- QAC) was strengthened more by decreasing the number of rotation axes in the spacer chain rather than changing the electron density of ammonium nitrogen and by increasing the rigid property of molecule structure, and that the steric structure of a bis-QAC is a significant factor influencing the antimicrobial activity of a bis-QAC.
