Biological and physicochemical properties of gemini quaternary ammonium compounds in which the positions of a cross-linking sulfur in the spacer differ.

We synthesized two novel gemini quaternary ammonium compounds (gemini QACs), 4,4'-[1,6-(2,5-dithiahexane)]bis(1-alkylpyridinium bromide) and 4,4'-[1,6-(3,4-dithiahexane)]bis(1-alkylpyridinium bromide), which are essentially two dimerized pyridinium salts. Three gemini QACs in which the positions of a cross-linking sulfur in the spacer differ, in addition to the previously described 4,4'-[1,6-(1,6-dithiahexane)]bis(1-alkylpyridinium bromide) to both gemini compounds, were determined for their antimicrobial, hemolytic and surface activities and molecular hydrophobicity. Comparative biological and physicochemical studies concluded that the position of sulfur in the spacer chain for three gemini QAC series influences the surface activity, the hydrophobicity and the electron density of the ammonium nitrogen, and that their biological properties are ascribable to the variation of these parameters caused by the position of the sulfur.