Adsorption properties of proteins at and near the air/water interface from IRRAS spectra of protein solutions.
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 beta-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, beta-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 subphase, while the thickness is about 30 nm.
Meinders
M B
MB
Department of Structure and Functionality, Wageningen Centre for Food Sciences, The Netherlands. marcel.meinders@chem.fdsci.wau.nl
van den Bosch
G G
GG
de Jongh
H H
HH
D000388:Air; D055592:Biophysical Phenomena; D001703:Biophysics; D002364:Caseins / Q000737:chemistry; D017666:Deuterium Oxide; D005504:Food Analysis; D011506:Proteins / Q000737:chemistry*; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods* / Q000706:statistics & numerical data; D014867:Water
D002364:Caseins; D011506:Proteins; D012996:Solutions; D014867:Water; D017666:Deuterium Oxide