Orientation of alpha-helical poly(L-lysine) in consecutively adsorbed polyelectrolyte multilayers on texturized...

Alternate polyelectrolyte multilayers composed of poly(L-lysine) (PLL) in the alpha-helical state and poly(maleic acid-co-alpha-methylstyrene) (PMA-MS) were deposited by consecutively adsorbing from aqueous solutions on both unmodified and unidirectionally scratched silicon substrates. Thereby, the alpha-helical PLL rods formed in the presence of NaClO(4) were found to be significantly aligned along the scratching direction of the substrate. From the dichroic ratios of the amide I and amide II band, obtained by ATR-FTIR spectroscopy, order parameters with respect to uniaxial orientation were determined using a cone distribution model and the known angles of the transition dipole moments relative to the helix axis. They ranged from S = 0.5-0.7 for the PLL rods oriented on the texturized Si substrate and S = 0.0-0.2 (S = 1 for perfect ordering) for the unoriented PLL rods in the dry and wet states, respectively. Additionally, multilayers composed of PLL and poly(vinyl sulfate) showed similar uniaxial alignment on texturized Si substrates (S = 0.6). Generally, drying the multilayers caused a certain loss of order. Surfaces of anisotropically oriented alpha-helical polypeptides could be interesting for biomimetic purposes.