The two leaflets of the DMPC bilayer may be spectroscopically distinguished
when per-deuterated phospholipids are introduced into one leaflet. Garcia-Areaz
et al. [31] studied the orientation of the hydrocarbon chains in transverse asymmetric
h-DMPC and d 54 -DMPC bilayers in which either the inner (electrode facing) or
outer (electrolyte facing) leaflet contained h-DMPC molecules. The PM IRRA
spectra in the CH stretching modes region of the h-DMPC molecules show differences between the two leaflets. The tilt angle of the hydrocarbon chains in DMPC
molecules depends on the potential applied to the Au(111) electrode (Fig. 3.9). In
both leaflets the hydrocarbon chains have different orientation. In the inner electrode
facing leaflet in the DMPC bilayer adsorbed on the Au(111) surface the average tilt
of the hydrocarbon chains is close to 24
–25
versus surface normal (filled squares in
Fig. 3.9) [31]. Desorption of the bilayer leads to a small decrease in the tilt of
hydrocarbon chains. Significantly larger changes are observed in the outer leaflet. In
the adsorbed state, the hydrocarbon chains in DMPC molecules of the outer leaflet
have in average 10
larger tilt than in the inner leaflet (opened squares in Fig. 3.9).
In the inner leaflet of the bilayer adsorbed on the Au(111) electrode surface the tilt
of the hydrocarbon chains is equal to 35
–37
versus surface normal (Fig. 3.9).
Desorption leads to a decrease in the tilt angle of the chains to ca. 27
[31]. These
results indicate that even in a single-component bilayer the lipid molecules have a
distinct orientation in the two leaflets.
Two-component, asymmetric lipid bilayers composed of PE in the inner and
phosphatidylglycerol (PG) in the outer leaflet were prepared on the Au(111) electrode surface. In these transverse asymmetric lipid bilayers the composition of the
Fig. 3.9 The tilt of the hydrocarbon chains in DMPC molecules in the lipid bilayer adsorbed on the
Au(111) electrode in the inner, electrode facing (filled squares) and outer, electrolyte facing (open
squares) leaflets as a function of potential applied to the electrode. Copied with permission from
[31]. Inset: Orientation of DMPC molecules in the bilayer adsorbed on the Au(111) surface
62
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .
when per-deuterated phospholipids are introduced into one leaflet. Garcia-Areaz
et al. [31] studied the orientation of the hydrocarbon chains in transverse asymmetric
h-DMPC and d 54 -DMPC bilayers in which either the inner (electrode facing) or
outer (electrolyte facing) leaflet contained h-DMPC molecules. The PM IRRA
spectra in the CH stretching modes region of the h-DMPC molecules show differences between the two leaflets. The tilt angle of the hydrocarbon chains in DMPC
molecules depends on the potential applied to the Au(111) electrode (Fig. 3.9). In
both leaflets the hydrocarbon chains have different orientation. In the inner electrode
facing leaflet in the DMPC bilayer adsorbed on the Au(111) surface the average tilt
of the hydrocarbon chains is close to 24
–25
versus surface normal (filled squares in
Fig. 3.9) [31]. Desorption of the bilayer leads to a small decrease in the tilt of
hydrocarbon chains. Significantly larger changes are observed in the outer leaflet. In
the adsorbed state, the hydrocarbon chains in DMPC molecules of the outer leaflet
have in average 10
larger tilt than in the inner leaflet (opened squares in Fig. 3.9).
In the inner leaflet of the bilayer adsorbed on the Au(111) electrode surface the tilt
of the hydrocarbon chains is equal to 35
–37
versus surface normal (Fig. 3.9).
Desorption leads to a decrease in the tilt angle of the chains to ca. 27
[31]. These
results indicate that even in a single-component bilayer the lipid molecules have a
distinct orientation in the two leaflets.
Two-component, asymmetric lipid bilayers composed of PE in the inner and
phosphatidylglycerol (PG) in the outer leaflet were prepared on the Au(111) electrode surface. In these transverse asymmetric lipid bilayers the composition of the
Fig. 3.9 The tilt of the hydrocarbon chains in DMPC molecules in the lipid bilayer adsorbed on the
Au(111) electrode in the inner, electrode facing (filled squares) and outer, electrolyte facing (open
squares) leaflets as a function of potential applied to the electrode. Copied with permission from
[31]. Inset: Orientation of DMPC molecules in the bilayer adsorbed on the Au(111) surface
62
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .