Reinvestigation on the Buildup Mechanism of Alternate Multilayers Consisting of Poly(l-glutamic acid) and Poly(l-, d-, and dl-lysines)

Abstract

The buildup mechanism of polypeptide multilayers prepared by the layer-by-layer deposition of a polyanion (poly(L-glutamic acid) (PGA)) and polycations (poly(L-lysine) (PLL), poly(D-lysine) (PDL), and copoly(DL-lysine)(PDLL)) was reinvestigated by using in situ ATR-IR spectroscopy. A difference spectral technique applied to analyze the spectra indicated that the deposition of both the PGA and PLL (PDL) layers accompanies the formation of secondary structures consisting mainly of the antiparallel pleated sheet (the beta-sheet) structure, and that the formation of the beta-sheet structure cannot always be explained in terms of polyanion/polycation complex formation or charge compensation between the polyanion and polycations, although it has been considered as a major process in the multilayer buildup process. Instead, the present paper proposes the following mechanism. During the deposition of the polyelectrolyte, a small amount of the beta-sheet structures are produced at the interface as a result of charge compensation between a polyelectrolyte and an oppositely charged polyelectrolyte in the multilayer. The beta-sheets act as nuclei from which further propagation of the structure takes place at the solution/multilayer interfaces. The driving force of the buildup process in the new mechanism is a kinetically favorable insolubilization of each polyelectrolyte in solution at the interfaces.

Branched polymer models and the mechanism of multilayer film buildup

“…All of the CD spectra have a roughly similar shape. This implies that the peptides in all six films had approximately the same backbone structure and that all contained a significant proportion of residues in the same conformation, ␤ sheet [25,31,33,40], consistent with interpretation of Fourier-transform infrared spectra of polypeptide multilayer films [22,31,32].…”

“…S2). The signal shape throughout the far-UV range, and particularly the broad band with a minimum near 217 nm, reflects a large percentage of residues in a ␤ sheet conformation, as found in previous studies by Fourier-transform infrared spectroscopy and CD [22,23,25,28,31,32]. "Random coil" peptides in solution, by contrast, show a deep minimum near 200 nm [33].…”

“…Dendrimeric polycations in this work made a larger contribution than linear polyanions to the optical density increment, as in film systems consisting of linear PLL and linear PLGA [31]; see Fig. 2.…”

Covalent Defects Restrict Supramolecular Self-Assembly of Homopolypeptides: Case Study of β2-Fibrils of Poly-L-Glutamic Acid

“…Non-covalent binding and inclusion of molecules sterically incompatible with this type of PLGA self-assembly could prove yet another way of disrupting the β 2 -architecture. We have tested this hypothesis using PLL and PDL as model disruptors, since polylysine is known to form stable β-pleated electrostatic complex with PLGA [31]–[32]. Figure 5 shows FT-IR spectra of PLGA doped with either PLL or PDL at different molar ratios (expressed as Glu:Lys side chains).…”

Biomimetic assembly of polyelectrolyte multilayers containing phosvitin monitored with reflectometric interference spectroscopy

“…Consequently, a careful online monitoring of PEM film growth with a high temporal resolution is of fundamental importance for generating biomimetic material coatings. Surface analytical measurement techniques employed to monitor PEM film growth comprise the following: optical waveguide light microscopy, 13,14 quartz microbalance 15,16 ͑QCM-D͒, ellipsometry, 17,18 surface plasmon resonance ͑SPR͒, 19 absorption measurements ͑vis and near UV͒, 20 and infrared spectroscopy. 20,21 This is the first study on the analysis of PEM film growth in situ using reflectometric interference spectroscopy ͑RIfS͒.…”