Adsorption of proteins onto film surfaces built up layer by layer from oppositely charged polyelectrolytes is a complex phenomenon, governed by electrostatic forces, hydrogen bonds, and hydrophobic interactions. The amounts of the interacting charges, however, both in polyelectrolytes and in proteins adsorbed on such films are a function of the pH of the solution. In addition, the number and the accessibility of free charges in proteins depend on the secondary structure of the protein. The subtle interplay of all these factors determines the adsorption of the proteins onto the polyelectrolyte film surfaces. We investigated the effect of these parameters for polyelectrolyte films built up from weak "protein-like" polyelectrolytes (i.e., polypeptides), poly(L-lysine) (PLL), and poly(glutamic acid) (PGA) and for the adsorption of human serum albumin (HSA) onto these films in the pH range 3.0-10.5. It was found that the buildup of the polyelectrolyte films is not a simple function of the pure charges of the individual polyelectrolytes, as estimated from their respective pKa values. The adsorption of HSA onto (PLL/PGA)n films depended strongly on the polyelectrolyte terminating the film. For PLL-terminated polyelectrolyte films, at low pH, repulsion, as expected, is limiting the adsorption of HSA (having net positive charge below pH 4.6) since PLL is also positively charged here. At high pH values, an unexpected HSA uptake was found on the PGA-ending films, even when both PGA and HSA were negatively charged. It is suggested that the higher surface rugosity and the decrease of the alpha-helix content at basic pH values (making accessible certain charged groups of the protein for interactions with the polyelectrolyte film) could explain this behavior.
One dimensional nanostructure materials have tremendous scope because of their important properties like high surface area to volume ratio, high porosity, high aspect ratio and reactivity. Rare earth ions are important because it possess high yield of luminescence and practical applications in modern lighting and display fields. In this paper, we report the synthesis of light emitting PMMA/Eu 3+ nanofibers by using electrospinning technique. The nanofibers are characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and photoluminescence (PL). The SEM image of PMMA/Eu 3+ nanofibers for weight composition (Eu(Cl)3:PMMA =1:9) as prepared by electrospinning reveals the diameter of the fibers less than 200 nm. FT-IR spectra of PMMA/Eu 3+ nanofibers indicated that upon addition of Eu 3+ ions, there appeared a higher frequency shoulder in the spectra due to the strong interaction between PMMA molecule chain and Eu 3+ ions. The intensity of emission could be controlled by the weight ratio of Eu 3+ ions to PMMA molecule chain at the weight ratio 1:9. The fluorescence enhancement of Eu 3+ ions in PMMA occurs because the PMMA keeps the donors and acceptors close, which results in the effective intermolecular energy transfer and consequently, the high enhancing efficiency. In our work the PMMA/Eu 3+ nanofibers showed excellent photoluminescence properties. It is expected that these materials would be applied in optoelectronic nanodevices.
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