A conformational investigation of zwitterionic surfactants in the micelle via 13C chemical shift measurements and 2D NOESY spectroscopy

Abstract

The conformation and orientation of a series of zwitterionic surfactants (the alkyl-N,N-dimethylammoniopropanesulfonates, or Zwittergent® Detergents) has been studied via 13C chemical shift measurements and 2D NOESY spectroscopy. Chemical shift changes (Δδ values) support the tendency for the intercharge arm to adopt a ring-like orientation as the alkyl chain length increases. Protons of the headgroup regions for both the 8 carbon and the 10 carbon Zwittergent® appear to form a greater number of intermolecular interactions with headgroups of neighboring monomers in the micelle. Interactions between the end of the alkyl chain and the headgroup region of the 12 carbon Zwittergent® are also apparent from examination of the NOESY spectrum indicating that the tail folds back towards the surface of the micelle. These results indicate that a combination of the ring-like conformation of the intercharge arm along with crowding in the vicinity of the sulfonate group could explain why ZW3-12 appears to behave more as a cationic surfactant in previously studied mixed micellar systems.