“Organic counterion” modified quaternary ammonium salt: Impact on antibacterial activity & application properties

Quaternary ammonium salts (QAS) with organic counterion (QAS-OC) impact on surface tension, micelle aggregation, antibacterial activity and three application properties were investigated by surface tension, steady-state fluorescence, bacteriostatic assay, foaming property, contact angle and emulsifying performance measurements. Besides the alkyl-chain-length of its cationic part on antibacterial activity was also investigated. It is demonstrates that micellization and surface adsorption first decreasing and then increasing as the alkyl-chain-length of organic counterion exceed 2, i.e. C16NC2 (cetyltrimethylammonium acetate). The number of aggregates (Nagg) also follow this law as the change of counterion at a same concentration of 5 mM. Antibacterial test reveals that the increasing counterion length moderately impairs antibacterial activity, and there is a slight influence for the dealing time of antibacterial agent on antibacterial activity. The minimum concentration of C16NCx for bacterial rate of 99.9% is 40 mg/L. It shows the antimicrobial activity for different bacteria strain follow this order: Staphylococcus aureus (S. A.) = Monilia albican (M. A.) > Escherichia coli (E. coli) > Bacillus subtilis (B. S.) > Pseudomonas aeruginosa (P. A.). Bactericidal activity result indicates a fine sterilizing rate of 99% can be obtained at concentration of 40 mg/L. On the other hand, the alkyl chain length of cationic part has significant impact on antibacterial activity, and only when single alkyl-chain-length beyond C12 dose the QAS has an effective antibacterial rate (> 50%). The application property of foam height and its stability only build up as the alkyl-chain-length of counterion beyond 6 (C16NC6). Both the wetting ability and emulsion stability have a similar variation law as the former.