Abstract.
A detailed study is performed using infrared reflection absorption spectroscopy (IRRAS) to characterize the molecular behaviour of proteins at and near the air/water interface of protein solutions. IRRAS spectra of β-casein solutions in H2O and D2O show spectral shifts and derivative-like features not commonly observed in monomolecular layer systems. They can be fully understood using optical theory. Fair agreement between experimental and simulated IRRAS spectra over a broad spectral range (4000–1000 cm–1) is obtained using a stratified layer model. An attenuated total reflection and transmission spectrum is used to represent the protein extinction coefficient in H2O and D2O, respectively. It is shown that the derivative-like features observed result from the reflective properties of the proteins themselves. Furthermore, both concentration and film thickness could be fitted. At high protein concentrations (100 mg/mL) the spectrum is that of a single homogeneous protein solution. At 0.1 mg/mL, β-casein is accumulated at the surface in a thin layer of approximately 10 nm thickness, with a concentration about 2500 times higher than in the sub-phase. At an initial concentration of 10 mg/mL, the concentration in the surface layer is about 15 times higher than in the sub-phase, while the thickness is about 30 nm.
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Revised version: 2 November 2000
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Meinders, M.B., van den Bosch, G.G. & de Jongh, H.H. Adsorption properties of proteins at and near the air/water interface from IRRAS spectra of protein solutions. Eur Biophys J 30, 256–267 (2001). https://doi.org/10.1007/s002490000124
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DOI: https://doi.org/10.1007/s002490000124