The behavior of amphiphilic molecules such as lipids, peptides and theirmixtures at the air/water interface allow us to evaluate and visualize thearrangement formed in a confined and controlled surface area. We have studiedthe surface properties of the zwitterionic DPPC lipid and Aβ(1-40)peptide in mixed film at different temperatures (15 ֯C to 40 ֯C). Inthis range of temperature the surface properties of pure Aβ(1-40)peptide remained unchanged, whereas DPPC undergoes its characteristicliquid-expanded→liquid-condensed phase transition that depends on thetemperature and lateral pressure. This particular property of DPPC makes itpossible to study the influence of the phase state of the lipid on amyloidstructure formation at the interface in a continuous, isothermal, dynamic andabrupt change on the environmental condition. As the mixed film is compressedthe fibril-like structure of Aβ(1-40) is triggered specifically in the liquid-expanded region,independently of temperature, and it is selectively excluded from thewell-visible liquid condensed domains of DPPC. The Aβ amyloidfibers were Thio T positive and were visualized by using BAM and AFM. In mixedDPPC/Aβ(1-40)  films the condensed domains (in between 11 mN/m to 20 mN/m)become irregular probably due to the fibril-like structures imposing additionallateral stress sequestering lipid molecules in the surrounding liquid-expandedphase to self-organize into amyloids.

We conclude an important molecular aspect of interfacial Aβ amyloidfibrillation with DPPC monolayers. The interfacial fibrillation transition frommonomer to fibers it is a selective process since it discriminates between theliquid-expanded character from the liquid-condensed phase ones. If the aboveaspects figure out combined at the neuron membrane interface it may triggersupramolecular cytotoxic arrangements leading to membrane leakage withsubsequent cell death.