Urea-based gemini surfactants: Synthesis, aggregation behaviour and biological activity

Synthesis, aggregation properties in aqueous solution and antimicrobial activity of novel urea-based cationic gemini surfactants N,N'-bis{2-[(undecylcarbamoyl)amino]ethyl}-N,N,N',N'-tetramethylalkanece-alpha,omega-diammoniumdibromides of variable spacer length are presented as a function of surfactant molecular structure. Utilizing the experimental methods of tensiometry, dynamic light scattering, time-resolved fluorescence quenching, neutron scattering, and zeta potential, the obtained data indicate a stronger aggregation tendency of urea-based surfactants with a short spacer composed of 2 CH2 groups which was confirmed by all applied experimental methods. As results from the comparison with the gemini surfactants without urea groups in the alkyl tails and polymethylene spacer, the presence of urea groups enhances the aggregation properties of gemini molecules through additional hydrogen bonding interactions. A simple molecular model of the hydrogen bonding interaction between neighbouring urea-based gemini molecules is provided. For longer spacers of 4-10 CH2 groups, the existence of monodisperse spherical micelles has been confirmed. The dependence of antimicrobial activity vs. spacer length shows nonlinear parabolic behaviour with the maximum antimicrobial activity found at the spacer length of 6 CH2 groups for bacteria and 8 CH2 groups for fungi. This is related to a different composition of cell membrane of the used microorganisms. (C) 2016 Elsevier B.V. All rights reserved.