Self-aggregation and antimicrobial activity of cationic benzimidazolium surfactants: Electrolyte effect on the Krafft temperature

In the present work, biomimetic approach was implemented using benzimidazole as a biofragment for the synthesis of amphiphilic compounds. A homologous series of cationic surfactants with a benzimidazolium head group and different lengths of the alkyl tail (BI-n, n = 10, 12, 14, 16) was obtained. The influence of the surfactant structure on aggregation, functional and biological properties was studied. In particular, the self-association of surfactants in aqueous solutions, solubilizing ability, antimicrobial and hemolytic activity, and cytotoxic effect were studied. For higher homologues, the effect of salt additives (NaCl) of various concentrations on the Krafft temperature and aggregation activity of surfactants were studied. It was shown that with an increase in the length of the hydrophobic tail of the amphiphile, a decrease in the aggregation thresholds and an increase in the Krafft temperature occurred (from 17.5 °C for BI-10 to 48 °C for BI-16). Benzimidazolium surfactants exhibit high bacteriostatic and bactericidal activity, as well as low hemolytic activity. In addition, the BI-n series showed a selective cytotoxic effect on cancer cells. The surfactants also turned out to be effective solubilizers for the hydrophobic substrate. Addition of salt to solutions of higher surfactants homologues (BI-14 and BI-16) made it possible to achieve a significant decrease in the Krafft temperature (by 8 degrees), as well as aggregation thresholds by 6 times. This study is expected to improve the understanding of the influence of structural parameters of surfactants on their aggregation and biological activity.