Self-assembly of polypeptide molecules on charged surfaces. 1. Effect of polydispersity

Atomic force microscopy and dynamic light scattering were used to study the effect of polydispersity on surface-generated fiber formation of poly[(gamma)-benzyl-L-glutamate] (PBLG) from solutions in dioxane. Polydispersity was modeled by mixing at varying weight ratios of PBLG samples with essentially different molecular weights. We found three distinctive regimes of fibrogenesis of PBLG determined by the ratio of shorter-to-longer polymer in the solution. At equal weight concentrations of longer and shorter molecules, the shorter molecules irreversibly attach to the surface, while the longer polymer assembles on the top of the primary layer. A reduction of the weight ratio to ca. 1:20, produces large, distorted fibers consisting of a mixture of long and short polymers. A further decrease of the ratio shorter-to-longer macrochains to the value as small as 1:200 induces lateral association of the surface-attached fibers formed mostly from a longer polymer.