FORMATION OF POLYPEPTIDE-DYE MULTILAYERS BY AN ELECTROSTATIC SELF-ASSEMBLY TECHNIQUE

To demonstrate the feasibility of preparing ordered multilayers composed of charged macromolecule/dye bilayers, we used an electrostatic self-assembly technique to prepare polypeptide/dye multilayers. We immersed previously protonated silanized glass slides in aqueous solutions (1 mM) of two representative anionic dyes: rod-shaped congo red or plate-shaped copper phthalocyanine tetrasulfonic acid sodium salt and cationic polypeptide poly(L-lysine) solutions (15 mM monomer). Films resulting from up to 100 dipping cycles were characterized by UV-vis absorption spectra, ellipsometry, CD, and FT IR. FT IR spectra of film material embedded in KBr pelf ets showed an amide I band at 1654 cm(-1), suggesting thin film alpha-helical conformation. In both systems, the dye absorbance increased with the number of layers. In the copper phthalocyanine system, the absorption spectrum was a combination of phthalocyanine monomer and dimer contributions, with no evidence of higher aggregates. The congo red film dye absorption maximum was a function of the number of bilayers, suggesting congo red resided in a polar, hydrophilic environment that became less polar with increasing bilayer number. From ellipsometry measurements, the bilayer thickness in both films was determined to be 20 Angstrom. The phthalocyanine Q band showed negative-induced CD, while the congo red pi pi* band exhibited positive-induced CD The CD measurements gave evidence for ordered dye-polypeptide complexes in films greater than 100-Angstrom thickness. The current work suggested a bilayer structure where monomeric congo red or dimeric copper phthalocyanine tetrasulfonate were randomly distributed among excess poly(K) monomer bindings sites, giving clear films with no scattering centers.