Methylene stretching vibrations

The recrystallization of S-layer proteins at phosphoethanolamine monolayers on aqueous subphases has been also studied on a mesoscopic scale by dual label fluorescence microscopy andFourier transform infrared spectroscopy (FTIR) [110]. It has been shown that the phase state of the lipid exerts a marked influence on the protein crystallization. When the surface monolayer is in the phase separated state between fluid and crystalline phase, the S-layer protein is preferentially adsorbed at the boundary line between the two coexisting phases and crystallization proceeded underneath the crystalline phase. Crystal growth is much slower under the fluid lipid and the entire interface is overgrown only after prolonged protein incubation. In turn, as indicated by characteristic frequency shifts of the methylene stretch vibrations on the lipids, protein crystallization affects the order of the alkane chains and drives the fluid lipid into a state of higher order. However, the protein does not interpenetrate the lipid monolayer as confirmed by x-ray reflectivity studies [105-107]. 

There are two C H oscillators and two methylene stretching vibrations. The antisynunetric methylene C—H stretching mode is assigned to the higher of the two peaks based on mechanical analysis, and the lower wavenumber band is assigned to the symmetric methylene stretch. 

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