Antibacterial Activities of Five Cationic Gemini Surfactants with Ethylene Glycol Bisacetyl Spacers

A series of cationic gemini surfactants containing two dimethylalkylammonium chains linked by ethylene glycol bisacetyl spacers were synthesized [G m -A n A- m , G = gemini surfactant, m  = 12 (–C 12 H 25 ), 14 (–C 14 H 29 ), or 16 (–C 16 H 33 ), A = acetyl, and n  = 2, 3, or 4 is the number of ethylene glycol units in the spacers]. Because of the inductive effect of the oxygen atom in the spacer, acylation can take place using chloroacetyl chloride instead of bromoacetyl bromide which helps to limit the use of environmentally harmful reagents. Critical micelle concentrations were determined using conductivity measurements. The antibacterial activities of the surfactants against Gram-positive bacterium Staphylococcus aureus and Gram-negative bacterium Escherichia coli were evaluated from the minimum inhibitory concentration (MIC), minimum bacterial concentration, a time–kill study, and the inhibitory zone. Increasing the length of the spacer did not result in an obvious change of antibacterial activity. However, increasing the length of the alkyl chain apparently increased the antibacterial activity against S. aureus but decreased the antibacterial activity against E. coli . The G 12-A2A-12 surfactant had the lowest CMC of 1.26 mmol L −1 and exhibited the best antibacterial activity with a MIC of 32 μg mL −1 toward S. aureus and 64 μg mL −1 toward E. coli in the presence of 10 5  CFU of bacteria. This work indicated that these cationic gemini surfactants have potential applications as antibacterial agents and emulsifiers.