3B14
低濃度オゾン中における脂質単分子膜の構造と安定性（北海道大学 · 触媒化学研究センター） ○喬 琳，葛 愛民，大澤 雅俊，叶 深Structure and Stability Studies of Mixed Monolayers of Saturated andUnsaturated Phospholipids under Low-level Ozone(Hokkaido University, CRC)

○Lin QIAO, Aimin GE, Masatoshi OSAWA, Shen YE

1. Introduction
Cell membranes play crucial roles in the functionality of cells such as masstransport, metabolism, information exchange, and energy conversion. The
phospholipid bilayer, containing both saturated and unsaturated phospholipids,constructs the main frame structure for the cell membrane. The functionality of themembranes could be significantly affected by the stability of lipids, especially in anenvironment contaminated by oxidants such as ozone.1,2 The concentration of ozone
at the earth surface of troposphere are usually few tens of ppb, mainly formed upon
photochemical reaction of nitrogen oxide (NOx) and violated organic compounds(VOC) with UV light.3 However, the influence of ozone on the lipid molecules havebeen mainly investigated in high concentration range (0.3 ~ 10 ppm) in the previous
experiments.1,2 In the present study, the structure and stability of lipid monolayer
with both saturated and unsaturated lipids in low concentration of ozone (~20 ppb)
have been explored by π-A isotherm, atomic force microscopy (AFM) and sum
frequency generation (SFG) vibrational spectrscopy.4
2. Results and Discussions
The single or binary mixed monolayers ofan unsaturated lipid (DOPC) and a saturated
lipid (DPPC-d75) were made by LB methodon the water surface (22℃) in a chamber
under environment control. Figure 1 shows
the changes in the surface area as a functionof exposure time to N2 (0 ~ 60 min) andlow-level O3 (60 ~200 min) at a surfacepressure of 30 mN/m. All the monolayers
are stable in the nitrogen environment andshow only very small decreases in the initial

Figure 1. Stability of surface area for theDPPC-d75/DOPC mixed monolayers at 30mN/m exposed to N2 (0~60 min) and O3(60~200 min).

60 min. However, when a small amount of ozone (~20 ppb) is introduced into thechamber, all the monolayers, except for the pure DPPC-d75, show fast decays in thesurface area, and become almost constant after a certain period (ca. 1 hr). The
decrease in the surface area indicates the loss of molecules from the water surface
and implies that DOPC or DOPC-contained monolayers are partially decomposed by
the ozone exposure. Only a small surface area is remained for the pure DOPC
monolayer. More surface area is remained with increase of DPPC-d75 in the mixed
monolayer after exposure to O3. The instability of the mixed monolayer seems to berelated with the amount of the unsaturated DOPC in the monolayer. The origin forthis is further investigated based on AFM and SFG observations.
SFG observations demonstrated that the DPPC-d75 monolayer construct awell-ordered structure and are stable in ozone. The pure DOPC monolayer showed alarge amount of gauche defects in the monolayer and is unstable in ozone and most of
the reaction products are dissolved in water to form micelle structure or evaporated
into air, and only trace amount of oxidized phospholipid (oxPL) stay on the water
surface (Fig. 2, upper). When the mixed monolayers were exposed to low-level ozone,
DOPC molecules are also selectively oxidized but a small amount of DOPC isremained in the mixed monolayer (Fig. 2, lower), very different from the pure DOPC
monolayer.4 It is expected that the saturated DPPC components in the mixed
monolayer can partially inhibit theozone oxidation of unsaturated
DOPC molecules. The all-transhydrocarbon chains of DPPC canform a well-packed monolayer
and are stable to ozone oxidation.
On the other hand, by mixing
with DPPC molecules, the packing
density and orientation ordering
Figure 2. The schematic models for DOPC monolayerof DOPC are largely improved (upper) and DPPC-DOPC mixed monolayer (lower) on
and this can partially inhibit the a water surface before (left) and after (right) exposure
to a low-level ozone.
ozone attack on the defect sites.
Detailed results and discussion will be given in the presentation.
References:
1. Wadia, Y.; Tobias, D.; Stafford, R.; Finlayson-Pitts, B., Langmuir, 2000, 16, 9321
2. Thompson, K.; Jones, S.; Rennie, A.; King, M.; Ward, A.; Hughes, B.; Lucas, C.; Campbell, R.;
Hughes, A.; Langmuir, 2013, 29, 4594.
3. B. J. Finlayson-Pitts and J. N. P. Jr., Chemistry of the Upper and Lower Atmosphere: Theory,Experiments, and Applications, Academic Press, San Diego, 2000
4. Qiao, L.; Ge, A.; Osawa, M.;Ye, S. submitted to Phys. Chem. Chem. Phys.