Buildup of exponentially growing multilayer polypeptide films with internal secondary structure

The buildup and secondary structure of poly(L-glutamic acid)/poly(allylamine) (PGA/PAH) multilayer films were investigated by means of optical waveguide lightmode spectroscopy, quartz crystal microbalance, and Fourier transform infrared spectroscopy in attenuated total reflection mode. The thickness and the mass of these films grow exponentially with the number of deposited bilayers. Moreover, PGA undergoes a random/alpha-helix transition when interacting with PAH during the film buildup process. This structural transition leads to (PGA/PAH)(i) films with an alpha-helix content (contribution of the alpha-helices to the amide I band) that switches regularly between 30% and 40% during the film buildup, when the multilayer is alternatively brought into contact with the PAH and PGA solutions. The secondary structure of the film is thus entirely driven by the last deposited layer. The independence of the alpha-helix content with the number of deposited bilayers also strongly suggests that the film is structurally homogeneous over its whole thickness.