Dichroic ATR-FTIR spectroscopy on oriented α-helical poly(l-lysine) multilayered with polyanions

The preparation and spectroscopic and microscopic characterization of oriented polyelectrolyte multilayers (PEM) interesting for defined nanostructured functional materials and surfaces are reviewed. Oriented PEM were generated by consecutively adsorbing α-helical poly(l-lysine) (PLL) and oppositely charged polyanions like poly(vinylsulfate) (PVS) or poly(styrene sulfonate) (PSS) at silicon substrates texturized by parallel nanoscopic surface grooves, respectively. Dichroic Attenuated Total Reflexion Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to study the conformation and macromolecular order of stiff polyelectrolytes within PEM. High order parameters up to S=0.82 (S=1 for high, S=0 for low order) were obtained from the dichroic ratios of the Amide I and Amide II bands suggesting a significant alignment of charged α-helical polypeptides in PEM. For PEM consisting of PLL/polyanion the S values significantly increased with increasing molecular weight of PLL and with decreasing molecular weight of the polyanion. These spectroscopic findings were supported by SFM images on PEM-PLL/PVS with high molecular PLL and PEM-PLL/PSS with low molecular PSS, which both showed anisotropically oriented worm-like structures, while PEM-PLL/PVS with low molecular PLL and PEM-PLL/PSS with high molecular PSS showed no orientation features.