supported directly on the Au surface. To distinguish between the CH stretching
modes in thioglucose and in DMPC molecules, perdeuterated DMPC (d-DMPC)
was used [78]. The ν as (CD 2 ) and ν s (CD 2 ) modes are centered at 2194 and 2095 cm
À1 ,
respectively. The wavenumbers of the maxima of absorption of the CD 2 stretching
modes indicate that the hydrocarbon chains in d 54 -DMPC molecules exist in a gel
state. The average tilt angles of the hydrocarbon chains in the floating and supported
DMPC bilayers are shown in Fig. 3.13. The open symbols show the average tilt angle
of the hydrocarbon chains in the floating d 54 -DMPC bilayer. It is almost independent
of the electrode potential. In the adsorbed state of the bilayer the hydrocarbon chains
make a tilt of 18
to the surface normal. Desorption of the floating d 54 -DMPC bilayers
leads to a small decrease in the chain tilt angle (Fig. 3.13). A tight packing of the
hydrocarbon chains is associated with the adaptation of the zig-zag orientation of the
polar head groups (see inset to Fig. 3.13). This space saving packing of the DMPC
molecules is also observed in the desorbed LB-LS bilayers (inset to Fig. 3.13)
[37]. This is an important result demonstrating that in the floating lipid bilayer on
the Au surface water is present on both sides of the membrane.
In a floating lipid bilayer composed of DMPC, polyethylene glycol lipid (DMPEPEG350) and cholesterol was assembled on the thioglucose monolayer adsorbed
previously on the Au surface. The packing of the lipid molecules is similar to that
found in pure DMPC floating lipid bilayer [79]. The hydrocarbon chains in the d 54 -
DMPC molecules have an average tilt of ~5
with respect to the surface normal. The
position of the maximum of absorption of the ν(C¼O) mode at 1725 cm
À1 indicates a
good hydration of ester group. This result is in agreement with the presence of the
aqueous environment on both sides of the membrane [72]. For example, in DMPC
bilayers adsorbed directly on the Au surface the maximum of absorption of the
ν(C¼O) mode is located at 1731 cm
À1 [30, 39]. The analysis of the PM IRRA spectra
indicates that the polyethylene glycol residues present in the spacer jointing the gold
surface with the lipid membrane exist in an amorphous state [79]. In contrast to the
helical conformation, the amorphous polyethylene glycol chain is well hydrated,
ensuring hydrophilic environment in the polar head group region of the inner leaflet
of the floating lipid bilayer. Described above results show that floating lipid bilayers
are stable on the gold electrode surface and that indeed water is present on both sides,
making them attractive models for the incorporation of transmembrane proteins.
3.3.2 Determination of Potential-Driven Structural Changes
in Models of Cell Membranes Interacting with Small
Molecules: In Situ PM IRRAS
Perfluorinated organic compounds find numerous industrial applications. Due to
their chemical stability they are resistant to microbial degradation and metabolism
by animals and humans [80]. Perfluorooctanesulfonic acid (PFOS) and
perfluorooctanoic acid (PFOA) are the main final products of the environmental
degradation of fluorinated organic compounds. They accumulate in wildlife and
68
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .
modes in thioglucose and in DMPC molecules, perdeuterated DMPC (d-DMPC)
was used [78]. The ν as (CD 2 ) and ν s (CD 2 ) modes are centered at 2194 and 2095 cm
À1 ,
respectively. The wavenumbers of the maxima of absorption of the CD 2 stretching
modes indicate that the hydrocarbon chains in d 54 -DMPC molecules exist in a gel
state. The average tilt angles of the hydrocarbon chains in the floating and supported
DMPC bilayers are shown in Fig. 3.13. The open symbols show the average tilt angle
of the hydrocarbon chains in the floating d 54 -DMPC bilayer. It is almost independent
of the electrode potential. In the adsorbed state of the bilayer the hydrocarbon chains
make a tilt of 18
to the surface normal. Desorption of the floating d 54 -DMPC bilayers
leads to a small decrease in the chain tilt angle (Fig. 3.13). A tight packing of the
hydrocarbon chains is associated with the adaptation of the zig-zag orientation of the
polar head groups (see inset to Fig. 3.13). This space saving packing of the DMPC
molecules is also observed in the desorbed LB-LS bilayers (inset to Fig. 3.13)
[37]. This is an important result demonstrating that in the floating lipid bilayer on
the Au surface water is present on both sides of the membrane.
In a floating lipid bilayer composed of DMPC, polyethylene glycol lipid (DMPEPEG350) and cholesterol was assembled on the thioglucose monolayer adsorbed
previously on the Au surface. The packing of the lipid molecules is similar to that
found in pure DMPC floating lipid bilayer [79]. The hydrocarbon chains in the d 54 -
DMPC molecules have an average tilt of ~5
with respect to the surface normal. The
position of the maximum of absorption of the ν(C¼O) mode at 1725 cm
À1 indicates a
good hydration of ester group. This result is in agreement with the presence of the
aqueous environment on both sides of the membrane [72]. For example, in DMPC
bilayers adsorbed directly on the Au surface the maximum of absorption of the
ν(C¼O) mode is located at 1731 cm
À1 [30, 39]. The analysis of the PM IRRA spectra
indicates that the polyethylene glycol residues present in the spacer jointing the gold
surface with the lipid membrane exist in an amorphous state [79]. In contrast to the
helical conformation, the amorphous polyethylene glycol chain is well hydrated,
ensuring hydrophilic environment in the polar head group region of the inner leaflet
of the floating lipid bilayer. Described above results show that floating lipid bilayers
are stable on the gold electrode surface and that indeed water is present on both sides,
making them attractive models for the incorporation of transmembrane proteins.
3.3.2 Determination of Potential-Driven Structural Changes
in Models of Cell Membranes Interacting with Small
Molecules: In Situ PM IRRAS
Perfluorinated organic compounds find numerous industrial applications. Due to
their chemical stability they are resistant to microbial degradation and metabolism
by animals and humans [80]. Perfluorooctanesulfonic acid (PFOS) and
perfluorooctanoic acid (PFOA) are the main final products of the environmental
degradation of fluorinated organic compounds. They accumulate in wildlife and
68
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .