Self-aggregation and antimicrobial activity of alkylguanidium salts

Two series of long chain guanidine surfactants, mono-alkylguanidine and N,N,N′-dimethylalkylguanidine were synthesized and the effect of the alkyl chain length and the nature of the cationic headgroup on aggregation and antimicrobial activity were investigated. Surface tension and conductivity were applied to study the aggregation of the amphiphilic molecules in aqueous solution. The antimicrobial activity was evaluated against Gram-negative, Gram-positive bacteria and fungi. The results showed that N,N,N′-dimethylalkylguanidine had much higher surface activity than those of mono-alkylguanidine with the hydrophobicity of the amphiphilic cation. Guanidine surfactants containing 8–12 carbon atoms in the alkyl chain showed antimicrobial activity at the concentration of 25–100 ppm, and their efficiency as antimicrobial agents increased with the chain length.