Abstract
Novel bis-quaternary ammonium compounds (bis-QACs), 5, 5'- [2, 2'-(tetramethylenedicarbonyldioxy) diethyl] bis (3-alkyl-4-methylthiazolium iodide) s (5DEBT-4, n: alkyl chain length, n=8, 10, 12, 14, 16 or 18) were synthesized and characterized. The chemical structure of 5DEBT-4, n is a symmetrical dimer which is composed of two N-alkyl-5-(2-hydroxyethyl)-4- methylthiazolium iodides (T-n) connected by a tetramethylene chain. Both the bacteriostatic activity and the bactericidal activity of 5DEBT-4, n were higher than those of T-n and were scarcely affected by the length of the alkyl chain unlike general mono-QACs. 5DEBT-4, n exhibited a wide-ranging and effective antimicrobial activity against both bacteria and fungi, compared with a bactericide, benzyldimethyldodecylammonium chloride (BAC), and a fungicide, 2-(4-thiazolyl) benzimidazole (TBZ), both of which are widely used. The bacteriostatic activity of 5DEBT-4, n was reduced with the increase in molecular hydrophobicity, while the bactericidal activity was not influenced by that. This result suggests that the hydrophobic materials in the medium interacts with 5DEBT-4, n, especially when possessing longer alkyl chains, and covers the active moiety of the agents. Furthermore, it was implied that properties other than the molecular hydrophobicity contribute to the bactericidal action. 5DEBT-4, n showed a higher bactericidal activity in the ranges of pH 5 to 8.5 and 10 to 40°C than T-n and was little influenced by pH and temperature.
