Introduction of isothiuronium surfactant series: Synthesis, structure-dependent aggregation overview and biological activity

For a homologous series of isothiuronium surfactants (S-alkylisothiuronium bromides, CnSU, where n = 10, 12, 14, 16, 18), a synthesis procedure is described and aggregation properties are comprehensively characterized by a variety of techniques. Krafft temperature and critical micelle concentration (cmc) are obtained by methods of conductometry, tensiometry, spectrophotometry, fluorimetry. Using dynamic light scattering and NMR diffusometry, aggregate sizes in aqueous solutions were determined. The aggregation numbers of CnSU systems were estimated by alternative methods. An increase in the length of the alkyl tail from 10 to 16 carbon atoms leads to a decrease in cmc from 16 to 0.5 mM with a decrease in aggregation numbers. S-alkylisothiuronium bromides exhibit solubilization capacity toward a hydrophobic dye Orange OT which is 2–3 times higher than that of alkyltrimethylammonium analogues. Improved solubilization characteristics along with antimicrobial properties manifested at the concentrations of low hemolytic activity allow us to recommend these amphiphiles for the fabrication of soft nanocontainers for hydrophobic guests showing their own biological functionality.