Zein monolayers. Unusual liquid-liquid phase transition and interaction with (bio)surfactants

Zein is a major water-insoluble protein of corn seeds. Bearing some structural similarity with keratin proteins, zein gains popularity as a convenient model of skin/hair proteins in studies on possible effects of surfactants on human skin and hair. Zein monolayers display interesting compression behaviour, with an indication of an unusual liquid expanded-liquid expanded (LE-LE) type at surface pressure ~20 mN/m, which has not been discussed in the literature (previously interpreted as a collapse). In the course of the current proposal we plan to verify the hypothesis of the phase transition being related to formation of a comb-like structure within the zein monolayer. For this purpose the monolayer will be compressed and decompressed stepwise with NR measurements at several characteristic surface pressure values along the compression isotherm (5, 15, 20, 30, 40 and 48 mN/m). In the next step, the effect of a model anionic surfactant (SDS) and a biosurfactant (saponin) on the pre-compressed zein monolayer (30 mN/m) will be investigated to complement our recent Langmuir trough experiments. The latter clearly pointed to important differences between the synthetic and natural surfactants but their interpretation requires a more thorough understanding of the structural details accompanying the interaction which could be provided by the present proposal.