Multilayered Polypeptide Films: Secondary Structures and Effect of Various Stresses

Abstract

Polyelectrolyte multilayers constructed from polypeptides present secondary structures similar to those found in proteins (R-helices and β-sheets). These secondary structures are used as a tool to investigate the buildup and internal stability of multilayer films by means of Fourier transform infrared spectroscopy. Special attention is focused on the β-sheet contribution to the amide I band. Two main problems are addressed: (i) Does there exist a correlation between the local structure of the polypeptide multilayers and their corresponding polyanion/polycation complexes in solution? (ii) How stable is the local structure of these multilayers toward external stresses such as pH jumps, temperature rise, and changes of the nature of the outer layers of the film? Four different polypeptide multilayers, poly(L-glutamic acid)/poly(Llysine) (PGA/PLL), poly(L-aspartic acid)/poly(L-lysine), poly(L-glutamic acid)/poly(D-lysine), and poly(Lglutamic acid)/poly(L-ornithine), are studied. It is shown that the film secondary structures always closely resemble those of their corresponding complexes in solution. For example, the absence of β-sheet structures in the films correlates with their absence in solution. This shows the strong similarity between the physical processes leading to the formation of polypeptide complexes in solution and those involved in the multilayer formation. The secondary structures of (PGA/PLL)n films appear very stable against pH jumps for pH values ranging between 4 and 10.5. On the other hand, the sudden contact of a film constructed at pH 7.4 with a solution at pH 1.5 or 13.5 leads to a strong reduction of its β-sheet content together with a partial or total dissolution of the film. The structural response of a (PGA/PLL) n film to a temperature rise up to 89 °C depends on the way in which the temperature increase is performed: a slow temperature increase induces a reversible decrease of the β-sheet content at the expense of the R-helices. On the contrary, when the film is heated rapidly, the β-sheet content increases and a further increase is observed during cooling to room temperature. Finally, the deposition of poly(styrene sulfonate)/poly(allylamine) (PSS/PAH) bilayers on top of (PLL/PGA) n films leads to the total disappearance of the β-sheets. This seems to be related to the diffusion of PSS chains into the film during the first PSS deposition steps and an exchange of PGA molecules of the film by PSS ones deep in the architecture. Such an exchange process between two polyelectrolytes of different nature inside a multilayer architecture was, to the authors' knowledge, never observed before.

Multiple Functionalities of Polyelectrolyte Multilayer Films: New Biomedical Applications

“…Exchange can be followed easily using FTIR spectroscopy due to the specific chemical signature of each polyelectrolyte. This was first evidenced by Boulmedais et al [79] who showed that PSS chains could diffuse within a PLL/PGA film and exchange with PGA chains. These observations were corroborated by further experiments using PAH in solution on PGA/PAH films containing multivalent ions [80] and on PLL/HA films.…”

“…Several parameters will affect the secondary structure of the film's constituents, including the structural properties of the polyelectrolytes used for assembly [63][64][65] as well as solvent properties. As previously mentioned, this includes ionic strength, [61,66] pH, [61,66,67] type of solvent, [68] hydration, [69] and temperature. [67] Boulmedais et al [63] and Haynie and co-workers [64] showed, for example, that adding a (PSS/PAH) layer on top of a [PLL/poly(L-glutamic)acid; PLL/PGA) film significantly changed the secondary structure of the film.…”

Controlled Electrodissolution of Polyelectrolyte Multilayers: A Platform Technology Towards the Surface‐Initiated Delivery of Drugs

“…Polyelectrolyte multilayers can be considered as "layered complexes" held together by the same interactions as soluble complexes, [5,[62][63][64][65] but exhibiting a higher segment density. [66] Owing to their high hydration and their swelling properties, they can be viewed as dense hydrogels, [67] in which the crosslinking density is controlled by the charge distribution along the chain.…”

Polyelectrolyte Multilayer Films as Substrates for Photoreceptor Cells

“…Cell number that the nature of the terminating layer affected cells greatly in terms of viability and attachment, which is in good agreement with the literature. 39,40,64 From the physicochemical characterization it was concluded that glass slides were not totally covered by (PLL/CSA) 10 multilayers (Figures 4a and 5a). The build-up of 20 bilayers of (PLL/CSA) 20 resulted in a homogenous film covering the entire surface (Figures 4b, 5b).…”