| Abstract
| - The structural changes in fibrinogen as a consequence of its adsorption onto the surface of or its embeddinginto the interior of poly(allylamine hydrochloride) (PAH) or poly(styrenesulfonate) (PSS) multilayers areinvestigated by means of attenuated total reflection Fourier transform infrared (ATR−FTIR) spectroscopy. Itis found that both adsorption and embedding preserve the secondary structure of the fibrinogen molecules.Furthermore, the interactions of the polyelectrolytes with the protein molecules prevent their aggregation,especially in the embedded state, at room temperature. Thus, it seems that the structure and the biologicalactivity of proteins adsorbed on or embedded in polyelectrolyte multilayers could largely be preserved, whichopens up great perspectives in the design of new bioactive surfaces. The nature and the extent of thepolyelectrolyte−protein interactions are further studied via analysis of the thermotropic responses of the differentarchitectures. It is found that both PAH- and PSS-terminated polyelectrolyte multilayers can elevate the onsettemperature of the structural changes in adsorbed/embedded fibrinogen molecules by about 5 °C as comparedwith that for fibrinogen in solution. These polyelectrolytes also broaden the thermally induced structuraltransitions in the adsorbed/embedded fibrinogen molecules. The magnitude of these thermally induced structuralchanges is polyelectrolyte- and architecture-dependent. Whereas multilayer PAH−fibrinogen and multilayerPSS−fibrinogen constructions exhibit roughly the same large-scale thermally induced structural changes, inall architectures where fibrinogen is embedded the scale of these structural changes is restricted. The restrictionbecomes stronger as the presence of PSS at the polyelectrolyte−fibrinogen interfaces increases (PAH−fib−PAH < PAH−fib−PSS ≈ PSS−fib−PAH < PSS−fib−PSS). In the PSS−fib−PSS arrangement, thesecondary structure of fibrinogen as determined from its infrared spectrum changes only slightly up to 90 °C.The underlying processes of the thermally induced structural changes is, in addition, different for fibrinogenmolecules adsorbed onto or embedded into PAH-terminated polyelectrolyte multilayers. A tentative modelbased on “encapsulation” of the embedded protein by the polyelectrolytes is proposed to explain the observedfeatures.
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