Reversible peptide oligomerization over nanoscale gold surfaces

A selective oligomeric formation of amyloid beta 1-40 (A beta(1- 40)) monomers over a nanogold colloidal surface was investigated. An unfolded A beta(1- 40) monomer is considered to construct a dimer or trimer based oligomeric form with its hydrophobic segment placing outward under an acidic condition. Under a basic condition, a conformation of A beta is expected to take a folded monomeric form with its hydrophilic segment folded inward, avoiding the networking with residual colloidal particles. The most probable oligomeric form constructed over a 20 nm gold colloidal surface within a 25 degrees C to 65 degrees C temperature range is a dimer based unit and that over 30 or 40 nm gold colloidal surface below 15 degrees C is concluded to be a trimer based unit. However, selective oligomerization was not successfully reproduced under the rest of the conditions. A dipole-induced dipole interaction must cause a flexible structural change between folded and unfolded forms.