DPPC vesicles

Eigure 4.36 shows a comparison of elution profiles of dipalmitoylphospha-tidylcholine (DPPC) vesicles on a TSK-GEL G6000PW column and a Sephacryl S-1000 column (25). 

Socaciu, C., C. Lausch, and H.A. Diehl. 1999. Carotenoids in DPPC vesicles Membrane dynamics. Spectrochim. Acta A Mol. Biomol. Spectrosc. 55 2289-2297. 

Fig. 4. Pressure dependence of the linewidths in DPPC vesicles for choline methyl groups (O) choline methylene groups ( ) palmitoyl methyl groups ( ) and carbonyl carbons ( ) at 52.7 °C (after Ref. 14).

For DMPC vesicles at 35°C, the ratio of 31P-NMR linewidths in the presence of calcium or magnesium is substantially less than 1 (0.82). This indicates that calcium binds more tightly than magnesium to DMPC. At 10° C, the linewidth ratio is further reduced (0.75), indicating that the selectivity of DMPC for calcium over magnesium is enhanced below the phase transition (Tc 22°C for sonicated vesicles (12)). Very similar results were obtained with DPPC vesicles. 

Steady-state illumination of hypericin effects a pH drop in its surroundings [110], When hypericin and an indicator dye, 3-hexadecanoyl-7-hydroxycoumarin, are both embedded in the DPPC vesicle, steady-state illumination causes hypericin to transfer a proton to the indicator within a time commensurate to its triplet-state lifetime. Triplet hypericin is seen to be a source, but not necessarily the only source of protons. 

The fact that no apparent fusion of the vesicles is revealed by the atomic force microscopy (AFM) does not prove the liposome structural integrity (Fig. 4c, d). Analysis of the profiles of the embedded vesicles show that they are immersed in the film, suggesting the immersion by two different modes of the capping film layers (1) exponential between the vesicles, and (2) linear on the vesicle top [82], Evidence of vesicle stability is proved by a direct release study of the vesicle-encapsulated CF marker, as shown in Fig. 4f [82]. Similar results were found for DPPC vesicles filled with ferrocyanide ions [77], No considerable release of the markers, at least during the first few hours after embedding, points to vesicle integrity. 

Using cholesterol as the basis, a theoretical model to explain the observed changes in lipid domain interfacial area has been derived. The model shows that enhancement of lateral density fluctuation and lipid domain interfacial area caused by cholesterol is stronger at temperatures further from the transition temperature [132]. A decrease in the phase transition temperature of DPPC vesicles upon addition of antidepressants and phase separation at increased concentrations has also been reported [133],... 

Figure 3.32 shows the 1H-NMR spectrum of DPPC vesicles in the presence of 5 mM Pr. It shows the separation of resonance signals of the inner (1) and outer (O) choline head groups and the proton resonance of the lipid acyl chains (H) and of the terminal methyl group (M) [121]. Lysed vesicles were obtained by cycling the DPPC... 

Fig. 3.33 1 H-NMR spectra showing the increase in the O/l ratio of DPPC vesicles in the presence of 50 mM decan-1 -ol. (a) After incubation, O/l ratio = 1.58. (b) After six cycles, O/l ratio = 1.92 (% lysis = 11.6). (c) After 10 cycles. O/l ratio = 2.25 % lysis = 20.6) (Reprinted from Fig. 3 of ref. 121 with permission from Elsevier Science.)...

DPPC vesicles (see Scheme 2.2) with an outer diameter of 22 nm show a total bilayer thickness of 3.5 nm, which is virtually identical to that of planar bilayers. 

With bilayer lipid membranes it is not possible to achieve a fully asymmetric arrangement of head groups or chains. There is no apparent reason why all the molecules of two independent layers should only concentrate in one layer. Nevertheless, a little asymmetric distribution is found in vesicles made of lipid mixtures. Cerebroside sulfate, an anionic monoglycosyl ceramide was, for example, added exclusively to the outer surface of a performed DPPC vesicle (see Scheme 2.2) which was quantitized by the metachromatic effect of acridine orange. 

Vesicles are ordered fluids or liquid crystals, a fact which reflects well in those photoreactivities that are particular to vesicle solutions. Fatty acid derivatives 24 and 25, for example, show low quantum yields of fluorescence ((j)f) and high quantum yields of cis-trans isomerization (< )c) as well as short fluorescence life times (tf) in both methylcyclohexane and micellar SDS solutions (Table 1). In DPPC vesicles, on the other hand, cis-trans isomerizations are cumbersome and much slower, and the fluorescence yield and lifetime rise considerably (Table 1). For those stilbene derivatives which are embedded in the middle of a fatty acid backbone, isomerization is virtually eliminated in the low-temperature or gel phase of the bilayer. The vesicle thus plays the role of stabilizing trans configurations which fit into the frozen oligomethylene chain matrix. 

Figure 5. Time-resolved fluorescence of pyranine at the wavelength of maximum

Zeaxanthin (C ) has been incorporated in DMPC and egg lecithin vesicles. This a,(D-bipolar carotenoid reinforces the DMPC vesicle with respect to mechanical stability and water permeability but has no effect on fluid egg lecithin membranes (Lazrak et al.,1987). Electron-poor derivatives with electron-withdrawing carboxyl or pyridinium end groups should reversibly take up electrons in a type of reversible Michael reaction and then act as organic wires. There are, however, no reports on stable anion radicals of such chro-mophores in the literature. Claims of electron transport through vesicle membranes are very probably erroneous. It has been shown by reduction of an entrapped indigo dye that bixin derivatives in DPPC vesicle membranes favor the transport of borohydride and dithionite ions through the membrane rather... 

When dimethyl viologen dication is entrapped in DPPC vesicles and irradiated in the presence of external K4[Fe(CN)g], the viologen is reduced to the radical monocation and iron is oxidized. Light-induced membrane potential is thus built up (Calvin, 1978). Electrons can be stored and released in viologen-benzoquinone polymers on electrode surfaces. At first the quinone is reduced to the hydroquinone at low pH. Two electrons are entrapped per hydroquinone monomer. Upon raising the pH to 6-9, the viologen becomes reduced by the hydroquinone anions and delivers the electrons to the electrode (Smith et al., 1989)... 

Increasing the temperature of liposomal systems causes a phase transition to occur in the lipid domains, but the effect of Choi and Card as monitored by HP and PP, can cause changes in transition temperatures. For example, Fig. 4 shows changes in the fluorescence polarization for HP as a function of increasing temperature in the presence of varying Choi concentrations (0-55%) in DPPC liposomes. A linear dependence of fluorescence polarization on temperature was observed in DPPC with 20% Choi, but at increasing Choi concentrations two transitions were observed. The first transition is typical of HP in DPPC vesicles, but the second transition at T = 45°C with 37% Choi and T = 49°C with Choi = 47% are not typical. At the highest concentration of Choi no phase transition occurs. 

PEAA in solution, in general, experiences a coil-to-globule transition at a pH of 6.2 (107). The conformational transition of PEAA in the presence of dipalmitoylphosphatidylcholine (DPPC) vesicles shifted to 6.5 (107). Chen and colleagues... 

Figure 11-14 H NMR spectrum of DPPC vesicles (lOmg/ml) in the presence of 5 mM...

A. H. de Vries, A. E. Mark, S. J. Marrink, Molecular dynamics simulation of the spontaneous formation of a small DPPC vesicle in water in atomistic detail, J. Am. Chem. Soc, 2004,126, 4488-4489. 

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