RESUMO
HYPOTHESIS: The excellent performance of zwitterionic alkylamide-type surfactants may be tuned by slight modifications of their structures, especially concerning linking groups between hydrophilic and hydrophobic moieties and the moderation of strong NH hydrogen bonds via the introduction of a methyl group attached to the nitrogen. EXPERIMENTS: The influence of the structure of alkylamidehydroxysulfobetaine-type surfactants on their adsorption and micellization, lime soap dispersing ability, wettability, as well as antimicrobial and hemolytic activities was studied in this work. We synthesized a series of novel surfactants with labile CON(Me)CH2 or CH2N(Me) CO spacers that were adjacent to the hydrophobic tail CnH2n+1 and separated from the zwitterionic hydroxysulfobetaine headgroup by C3H6 or C2H4 linkers, i.e., [(3-alkanoyilomethyoamine)propyl] dimethylammonium 2-hydroxypropanesulfonates (CnTMDAS) and [3-(alkylmetyloamino)-3-oxopropyl] dimethylammonium 2-hydroxypropanesulfonates (CnDMPAS), respectively. FINDINGS: The CnTMDAS surfactants showed slightly higher surface activity and lower CMC than the respective CnDMPAS with the same number of carbon atoms. Moreover, the CnTMDAS series exhibited significantly higher lime soap dispersing abilities and softer interactions with biological systems than CnDMPAS. The molecular modeling computations revealed that the difference in surface activity originated from lower dipole moment of CnTMDAS, hence, lower polarity, whereas higher free energy of dimerization of those surfactants with oleic acid may account for the favorable formation of mixed micelles.