QASs with a short substituent (butyl or 2-hydroxyethyl) in the quinine-derived cation, on the other hand, exhibited low antagonistic activity towards the tested microorganisms (MIC and MBC/MFC up to above 1000 mg dm -3 ), comparable to that of pure quinine. On the other hand, 2Br, 2Asp and 2Ala comprising a medium-length substituent (octyl) in the cation showed noticeable levels of activity toward most of the microorganisms tested, although they were less active compared to their counterparts with a dodecyl substituent.