Molecular properties of proteins at and near the air/water interface from IRRAS spectra of protein solutions.

M.B.J. Meinders, G.G.M. van den Bosch, H.H.J. de Jongh

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42 Citations (Scopus)


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 #-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, #-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.
Original languageEnglish
Pages (from-to)256-267
JournalEuropean Biophysics Journal
Issue number4
Publication statusPublished - 2001


  • Air/water interface
  • Infrared reflection absorption spectroscopy
  • Protein solutions
  • Spectral simulation
  • β-Casein


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