Pure DPPC

The electrostatic potential profile is rather complex. In the hydrophobic region, the features are similar to those discussed above for the pure DPPC layer cf. Figure 15. The electrostatic potential profile in the PE layer is parabolic, and outside the PE layer the potential is very low, but decays according to the classical Gouy-Chapmann theory, i.e. exponential decay towards zero. 

Fig. 17. NMR spectrum obtained using a single 90° pulse without H decoupling in pure DPPC bilayers at 50 °C and 1 bar (a) and P NMR spectra obtained using a fully phase-cycled Hahn echo sequence with inversely gated H decoupling in pure DPPC bilayers at 50 °C and 1 bar in the LC phase (b), 1 kbar in the GI phase (c), 1.75 kbar in the interdigitated Gi gel phase (d), 2.5 kbar in the GII gel phase (e), 3.7 kbar in the GUI gel phase (f), and 5.1 kbar in the GX gel phase (g) (after Refs. 4, 18).

The calculated Aa values of pure DPPC bilayers are plotted as a function of pressure in Fig. 18. Only the absolute value of Aa can be determined from Eq. (7), but in view of the fact that Aa is negative for the LC phase and the temperature-induced gel phases (GI, GII), it is expected that Aa will also be negative for the high pressure gel phases of DPPC. The absolute value of Aa increases slightly with pressure in the LC phase in the pressure range from 1 to 500 bar. The transition from the LC phase to the GI phase is accompanied by a... 

Table III Comparison of Percent of Total Gauche Conformers for Pure DPPC, 2 1 DPPC/Cholesterol, and DPPC/Gramicidin Mixtures.

In the simulation of Tu et al. [72] with 12.5 mol% cholesterol, the starting configuration was obtained from a simulation of a pure DPPC bilayer composed of 64 DPPC molecules. Four DPPC molecules per leaflet were replaced by cholesterol to generate the DPPC-cholesterol system. The system was simulated for 1.4 ns the area per phosholipid decreased during the first 700 ps of the simulation but then remained stable for the rest of the simulation. As pointed out by the authors, the decrease in the surface area was due to the replacement of the phospholipids by the thinner cholesterol and not to an ordering effect of cholesterol. Accordingly, little effect of cholesterol on the order of the alkyl chains was observed in this simulation, in contradiction to the results of a cholesterol-DPPC simulation performed by Smondyrev and Berkowitz that is described below. 

Smondyrev and Berkowitz [73] performed a rather long simulation (2 ns) of a system with a low cholesterol content (ratio of 1 8 or 11 mol%) and of two systems that contained cholesterol at 1 1 molar ratio and differed in the arrangement of the cholesterol molecules (Figure 6.11). In the simulation with low cholesterol content, the area per lipid was about 62 A2, close to that found in a simulation of pure DPPC for the first approximately 800 ps. However, after this time it started to decrease and reached a value of 58.3 A2 after an additional 500 ps, where it remained for the last 750 ps of the simulation. In the simulation with high cholesterol content, the area per DPPC-cholesterol heterodimer surface area showed also a decrease over the simulation time that was approximately exponential (Table 6.7). In system A (Figure 6.11), with a more uniform distribution of cholesterol, the surface area tended to decrease over the full simulation time of 2 ns, whereas for system B a stable and somewhat lower value was obtained after 1 ns. Although the authors concluded that system A, with more uniformly distributed cholesterol, might be trapped in a metastable state, this system was used in a later publication for comparison of the effects caused by cholesterol sulfate (see below). 

Fig. 6.12 Change in distribution of phosphorus (a), nitrogen (b), and carbonyl oxygen (c) positions along the bilayer normal in pure DPPC and in membranes with 11 and 50 mol% cholesterol.

Fig. 6.13 Distribution of the angle between P-N vector and bilayer normal in pure DPPC membrane (solid line) and in membranes containing cholesterol 11 mol% (dotted line), 50 mol% structure A (dash dot line), and structure B (dashed line). When cosine is positive, the P—N vector points into the water layer.

Oxygens Pure DPPC DPPC-cholesterol 11 mol% 50 mol%a DPPC-cholesterol sulfate 50 mol% Pure DM PC DM PC cholesterol 22 mol%... 

The interaction of soluble cations with the phospholipid phosphate groups has been investigated on a mixture of DPPC and 1,2-dipalmitoyl-sn-glycero-3-phosphoserine DPPS as a function of surface pressure and Ca2+ ion presence [51], The presence of Ca2+ in the subphase induce an acyl chain ordering at all surface pressures in both components of the binary mixture that was not observed in the case of pure DPPC alone. Unlike the bulk phase mixture of... 

Figure 1 Compression isotherm of pure DPPC monolayer.

We note here that systematic studies of the melting transition of dry or nearly dry phospholipids bilayers (e.g., vesicles) have been scarce. While there is an abundant experimental and theoretical literature concerning the structure and properties of bilayers in water, less is known about their behavior when water is removed. We have therefore initiated a systematic experimental study of the gel-liquid crystal transition of pure DPPC and DPPC-cholesterol vesicles freeze-dried with and without disaccharides and oxyanion-disaccharide complexes. Some of our results to date are shown in Figure 9.3. 

A much more complex behaviour is observed for the process of penetration of various proteins into phospholipid monolayers. This behaviour depends strongly on the protein and the solution properties although some common features are observed. Fainerman et al. [116] studied the P-lactoglobulin penetration dynamics into DPPC monolayers. For a (i-lactoglobulin bulk concentration of 510 mol/l and molar areas of the lipid larger than the critical value, A > A, first order phase transitions are observed. Thus, two-dimensional condensed phase are formed although at these molar area values the pure DPPC monolayer exists only in the fluid-like state and does not form any domains. The first-order phase transition in the DPPC monolayer becomes visible by the characteristic break point in the dynamic surface pressure curve Fl(t) (see Fig. 4.50). 

Beyond this phase transition point, the creation and growth of condensed phase domains is observed. The shape of these domains is very similar to those of pure DPPC domains, as one can see from the images given in Fig. 4.51. The BAM images were taken at different times after the start of the penetration experiments and the letters correspond to the respective moments in the rt(t) curve. The aggregation of DPPC into condensed phase domains is induced even if the initial surface DPPC concentration is less than 50% of the critical adsorption T. ... 

GlvcoDhorin-Lioid Monolayers at the Air-Water Interface. Further to the study of pure glycophorin monolayers we investigated the interaction between the glycophorin and dipalmitoyl-phosphatidylcholine (DPPC) in mixed monolayers at the air-water interface (27). Pure DPPC undergoes the characteristic liquid expanded (L ) to intermediate state (I) transition in monolayers at temperatures below the chain-melting temperature (- 42 C) of... 

Figure 4.4. In this phase diagram we find the Lp-, Pp-, Lp and phases that have already been described, plus a few new ones, namely Iv, Lo and L p. W (denoted c in the figure) is the pure DPPC crystalline or subgel phase, that is only observed in annealed (i.e. kept at 4 °C for several days) aqueous multilamellar dispersions of DPPC. A thermotropic transition, the subtransition , converts the Lc- into the Lp- phase at ca. 18 °C. Lo and Lop are two different hquid ordered (Lo) regions, respectively called liquid-crystalUne-like liquid ordered (Loo) and gel-like liquid ordered (Lop). The latter two phases differ in the orientational order of the hydrocarbon chains, and in the relative position of the cholesterol molecule in the host PC bUayer.

The surface pressure (7i )-area (A) isotherms for pure CiiCONH-j6-CD and its mixed monolayers with DPPC are illustrated in Fig. 4, and those for pure PEO-lipid (12,13) and its monolayers with DMPC are shown in Fig. 5. From Fig. 4 it is apparent that while at all studied surface concentrations of CnCONH-j8-CD the two components behave independently of each other, as indicated by the location of all isotherms of mixed films falling between those corresponding to pure components, their collapse pressures gradually increased with the increase in the DPPC surface concentration. From Fig. 4 it is also apparent that the presence of CuCONH-j9-CD led to the disappearance of the liquid-expanded (LE) to the liquid-condensed (LC) phase transition characteristic of pure DPPC. 

The bilayer morphology of hydrocarbon SLBs composed of increasing amounts of fluorinated lipid was examined using atomic force microscopy (AFM). SLBs of pure DPPC appeared uniform and planar by AFM (Figure 9), with a maximum thickness of 5mn. SLBs containing... 

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