Molecular studies on protein conformations at polymer/liquid interfaces using sum frequency generation vibrational spectroscopy

Sum frequency generation (SFG) vibrational spectroscopy has been applied to examine the molecular structures of proteins adsorbed at various interfaces, especially polymer/protein solution interfaces in situ. A thin film model was adopted to interpret interfacial protein SFG spectra. A polarization mapping method was developed that can help to analyze complicated protein SFG spectra more reliably, from which more structural information of various interfacial proteins can be deduced. SFG signals in different frequency ranges, including C-H, N-H, O-H stretching and amide I ranges, can be collected from proteins at interfaces. Different proteins, including bovine serum albumin, ubiquitin, fibrinogen, factor XII, and some selectively or randomly deuterated proteins, have been examined in SFG studies. Our research shows that proteins can have different conformations at various interfaces, and also that time-dependent structural changes of proteins after adsorption can be varied. SFG can be developed into a powerful and unique technique to elucidate interfacial protein structures at the molecular level in situ after continued success in the application of SFG to examine interfacial protein structures.