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

To demonstrate the feasibility of preparing ordered multilayers compos ed of charged macromolecule/dye bilayers, we used an electrostatic sel f-assembly technique to prepare polypeptide/dye multilayers. We immers ed previously protonated silanized glass slides in aqueous solutions ( 1 mM) of two representative anionic dyes: rod-shaped congo red or plat e-shaped copper phthalocyanine tetrasulfonic acid sodium salt and cati onic polypeptide poly(L-lysine) solutions (15 mM monomer). Films resul ting from up to 100 dipping cycles were characterized by UV-vis absorp tion spectra, ellipsometry, CD, and FT IR. FT IR spectra of film mater ial embedded in KBr pelf ets showed an amide I band at 1654 cm(-1), su ggesting thin film alpha-helical conformation. In both systems, the dy e absorbance increased with the number of layers. In the copper phthal ocyanine system, the absorption spectrum was a combination of phthaloc yanine monomer and dimer contributions, with no evidence of higher agg regates. The congo red film dye absorption maximum was a function of t he number of bilayers, suggesting congo red resided in a polar, hydrop hilic environment that became less polar with increasing bilayer numbe r. From ellipsometry measurements, the bilayer thickness in both films was determined to be 20 Angstrom. The phthalocyanine Q band showed ne gative-induced CD, while the congo red pi pi band exhibited positive- induced CD The CD measurements gave evidence for ordered dye-polypepti de complexes in films greater than 100-Angstrom thickness. The current work suggested a bilayer structure where monomeric congo red or dimer ic copper phthalocyanine tetrasulfonate were randomly distributed amon g excess poly(K) monomer bindings sites, giving clear films with no sc attering centers.