FR between the fundamental ν s (CH 2 ) and the overtones of the methylene bending
modes while the shoulder around 2900 cm
À1 from the FR between the fundamental
ν s (CH 3 ) and the overtone of the methyl asymmetric bending modes [58, 59]. Large
differences between the PM IRRA spectra of DMPC, DMPS and DMPE are
observed (Fig. 3.7). In Table 3.1 the positions of the ν as (CH 2 ) and ν s (CH 2 ) in the
three bilayers are listed.
The wavenumber of the absorption maximum of the methylene stretching modes
is sensitive to the conformation of the hydrocarbon chain [58–60]. In a hydrocarbon
chain having a fully stretched all-trans conformation the ν as (CH 2 ) mode appears
3000
x3
x3
x3
2950
0.005
Wavenumber / cm
–1
2900
2850
3000
2950
0.002
Wavenumber / cm
–1
2900
2850
Random
Random
Random
0.002
a
b
c
0.2 V
–0.2 V
–0.6 V
–0.8 V
–1.0 V
–1.0 V
–0.7 V
–0.3 V
0.0 V
0.4 V
3000
2950
Wavenumber / cm
–1
2900
2850
–1.0 V
–0.7 V
–0.4 V
0.0 V
0.4 V
Fig. 3.7 PM IRRA spectra
in the CH stretching modes
region of LB-LS transferred
single-component (a)
DMPC, (b) DMPS (Copied
with permission from [35])
and (c) DMPE (Copied with
permission from [34])
bilayers on the Au(111)
electrode surface in 0.05 M
NaF in D 2 O at potentials
marked in the figure
3.3 In Situ PM IRRAS Studies of Films of Biomolecules Adsorbed on Electrode Surfaces 57