Fine tuning of physical properties of designed polypeptide multilayer films by control of pH.

Adjustment of pH can alter the ensemble of three-dimensional structures of a polypeptide in solution by changing the distribution of charge and Coulombic interactions. The role of pH in layer-by-layer self-assembly (LbL) of designed 32mer peptides containing the amino acid cysteine has been investigated using a combination of physical methods. Results show that pH can have a substantial influence on the mass of adsorbed peptide, surface roughness, and film density over a range of 1.5 pH units. Peptide film thickness depends on the number of layers, as with "conventional" polyelectrolytes. Film density and morphology, however, vary more with pH than does thickness, translating into a change in density on the order of 70% over the pH range 7.4-8.9. Results of this work provide insight on the physical basis of LbL and suggest that peptides are a promising class of polyelectrolytes for the creation of designer thin films for applications in biotechnology and other areas.