New mild amphoteric sulfohydroxybetaine-type surfactants containing different labile spacers: Synthesis, surface...

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.

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 C_nH_2n+1 and separated from the zwitterionic hydroxysulfobetaine headgroup by C₃H₆ or C₂H₄ linkers, i.e., [(3-alkanoyilomethyoamine)propyl] dimethylammonium 2-hydroxypropanesulfonates (C_nTMDAS) and [3-(alkylmetyloamino)-3-oxopropyl] dimethylammonium 2-hydroxypropanesulfonates (C_nDMPAS), respectively.

The C_nTMDAS surfactants showed slightly higher surface activity and lower CMC than the respective C_nDMPAS with the same number of carbon atoms. Moreover, the C_nTMDAS series exhibited significantly higher lime soap dispersing abilities and softer interactions with biological systems than C_nDMPAS. The molecular modeling computations revealed that the difference in surface activity originated from lower dipole moment of C_nTMDAS, hence, lower polarity, whereas higher free energy of dimerization of those surfactants with oleic acid may account for the favorable formation of mixed micelles.