POPC

F. Volke, A. Pampel 1995, (Membrane hydration and structure on a subnanometer scale as seen by high resolution solid state nuclear magnetic resonance POPC and P0PC/C12E04 model membranes), Biophys.J. 68, 1960-1965. 

DGDG digalactosyl diacylglycerol DHPC dihexadecyl phosphatidylcholine DMPC dimyristoyl phosphatidylcholine DOPC dioleoyl phosphatidylcholine DPPC dipalmitoyl phosphatidylcholine EYPC egg yolk phosphatidylcholine POPC 1-palmitoyl 2-oleoyl-phosphatidylcholine SBPC soya bean phosphatidylcholine... 

LUT 14NC5 15NC16 CHOL DMPC 4NC7 15NC16 DMPC POPC... 

LUT DMPC 14NC10 1sNC18 DMPC CHOL, 4NC16 15NC18 POPC... 

Observed collisions between 14N 15N spin-label pairs are indicated. DMPC and POPC molecules are also shown. POPC represents the major component (70%) of the EYPC mixture, (b) Bimolecular collision rate for a nitroxide moiety at the C16 position of the stearic acid alkyl chain with other SASLs in the DMPC alone and the DMPC with 10mol% lutein at 27°C. (From Yin, J.J. and Subczynski, W.K., Biophys../., 71, 832,1996. With permission.)... 

Figure 5.30 Temperature dependence of molar ellipticity at 218 nm for liposomes prepared from L-DMPC, L-DPPC (39), and L-POPC (40). Reprinted with permission from Ref. 134. Copyright 1997 by the American Chemical Society.

In order to verify that the adsorbed lipid membrane indeed forms a bilayer film, another experiment is conducted with an aim to detect the formation of a monolayer lipid. It starts with a piranha-cleaned micro-tube treated with silane to render its inner surface hydrophobic. POPC liposome is then injected into the microtube. It is known that POPC lipid will form a monolayer to such a surface by orienting their hydrophobic tails toward the hydrophobic wall. The experimental results using a mode with similar sensitivity as the previous experiment are shown in Fig. 8.39. The resonance shift in this case is 22 pm, which is about half of that observed for the adsorption of a lipid bilayer. These two experiments suggest that the microtube resonator is capable of accurately determining an adsorbed biomolecular layer down to a few nm thicknesses. 

Abbreviations DOPS, dioleoylphosphatidylserine DLPE, dilauroylphosphatidylethanolamine POPC, palmitoyloleoylphosphatidylcholine DOPG, dioleoyl phosphatidylglycerol SM, sphingomyeline. 

In order to provide quantitative information on the elfeets of pressure on eross-peak intensities, we earned out 2D-NOESY experiments on pure POPC (l-palmitoyl-2-oleoyl-x -glyeero-3-phosphatidylcholine (Ci6 o, Cig c )) and DMPC (l,2-dimyristoyl-OT-glyeero-3-phosphatidylcholine (di-Ci4 o)) lipid bilayers.As an example, we present data on POPC, a phospholipid which is also a very important eomponent of animal cell membranes. It has an... 

HIGH PRESSURE NMR STUDIES 175 Table 2. Assignment of H NMR resonances in POPC vesicles " ... 

Fig. 10. High-pressure ID H-NMR spectra of sonicated POPC—TTC vesicles (25 mol% TTC) at room temperature (T=22°C) and pD = 5.5 (after Ref 49).

Figure 10 shows the NMR spectrum of sonicated POPC-TTC vesicles at room temperature and selected pressures. Already the one-dimensional NMR spectra exhibit some interesting features. With increasing pressure, the signal intensity of the acyl-chain protons at 0.85 and 1.24 ppm decrease due to the pressure-induced rigidization of the acyl-chains, as it is also observed for pure phospholipid samples. At pressures above the fluid-gel main transition, which is detected at a pressure of about 1200 bar at 20 °C in pure POPC dispersions, the acyl-chain signals of pure lipid samples disappear completely, whereas in the spectra of the POPC-TTC system considerable signal intensities remain even up to pressures of 2800 bar. Furthermore, we observe for the... 

Jonas et al. measured the proton rotating frame spin-lattice relaxation time (Tip) at pressures from 1 bar to 5000 bar and at temperatures of 50 to 70 °C for DPPC and at 5 to 35 °C for POPC. If intermolecular dipolar interactions modulated by translational motion contribute significantly to the proton relaxation, the rotating frame spin-lattice relaxation rate (1/Tip) is a function of the square root of the spin-locking field angular frequency... 

Figure 19 shows the pressure effeets on the lateral self diffusion eoeffieient of sonicated DPPC and POPC vesicles. The lateral diffusion coefficient of DPPC in the LC phase decreases with increasing pressure from 1 to 300 bar at 50 °C. A sharp decrease in the D-value occurs at the LC to GI phase transition pressure. From 500 bar to 800 bar in the GI phase, the values of the lateral diffusion coefficient 1 x 10 cm /s) are approximately constant. There is another sharp decrease in the value of the lateral diffusion coefficient at the... 

Fig. 19. Lateral self-diffusion constant D of DPPC (top) and POPC (bottom) in sonicated vesicles as a function of pressure at 50 °C and 35 °C, respectively (after Ref 62).

MD simulations have provided a unique molecular description of cholesterol-phospholipid interactions [31]. Atomistic simulations have succeeded in reproducing the condensing effect of cholesterol on phospholipid bilayers [32-34], With atomistic detail, many properties can be determined, such as the effect of cholesterol on lipid chain ordering or on hydrogen bond formation. Other simulations have focused on the interaction of cholesterol and SM [35-37], Aittoniemi et al. [38] showed that hydrogen bonding alone cannot explain the preferential interaction between cholesterol and SM compared to cholesterol and POPC. 

Figure 2 PMFs and density profiles for cholesterol in a SSM and POPC bilayer, a, b Partial density profiles for the two bilayer systems. The cholesterol density was multiplied by a factor of 20 for visualization, c, d PMFs for cholesterol transfer from equilibrium of the respective bilayer to bulk water. The center of mass of the cholesterol molecule was restrained with respect to the center of the bilayer. Reprinted with permission from ref. 46. Copyright 2009 American Chemical Society.

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