Aggregation of amphiphilic compounds in dimethyl sulfoxide: example of non-ionic alkyl–fluoroalkyl lipopeptides

Abstract

The surface-active properties and association in dimethyl sulfoxide (DMSO) of two non-ionic alkyl–fluoroalkyl lipopeptides have been studied up to the limit of solubility (0.15–0.25) mol dm^–3) by combined use of surface tension, ¹⁹F NMR, and small-angle neutron scattering (SANS) experiments. Various models of aggregation have been tested using least-squares procedures on both NMR and SANS data. The conclusion is a progressive and very limited aggregation of these surfactants in DMSO with a structure where the hydrophobic chains tend to gather together. Equilibrium constants for a multistep equilibrium are clearly weaker for the primary step of dimerization, thus showing the existence of weak cooperative solvophobic effects in higher aggregates.