Dipalmitoyl-phosphatidylcholine bilayers

The model reproduces the most prominent phase transitions of phospholipid monolayers [78] and bilayers [80]. In particular, it reproduces a main transitirm from a fluid membrane phase (L to a tilted gel phase Lpi) with an intermediate ripple phase Pp ), in agreement with experiments. The elastic parameters have been studied in the fluid phase and are in reasonable agreement with those of saturated DPPC (dipalmitoyl-phosphatidylcholine) bilayers. Recently, the Lenz model has been supplemented with a simple cholesterol model [81]. Cholesterol molecules are taken to be shorter and stiffer than lipids, and they have a slight affinity to lipids. Mixtures of lipids and cholesterol were found to develop nanoscale raft domains... 

Cordomi A, Edholm O, Perez JJ (2008) Effect of ions on a dipalmitoyl phosphatidylcholine bilayer. A molecular dynamics simulation study. J Phys Chem B 112 1397-1408... 

Fig. 2.3. Differential scanning calorimeter trace of dipalmitoyl phosphatidylcholine bilayers dispersed in water. The reference pan contained distilled water.

Figure 5 shows the transmembrane profiles of D2O penetration, for dipalmitoyl phosphatidylcholine bilayers with and without 50 mol% cholesterol, which are determined by three-pulse H-ESEEM spectroscopy. Earlier studies that employed two-pulse echoes are given in ref. 23-25. The amplitude, /tot, of the D2O signal decreases with depth into the membrane, with a sharp change at an intermediate chain position... 

Figure Bl.20.11. Force curves of DMPC/DPPE (dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylethanolainine) bilayers across a solution of PEG at different concentrations. Clearly visible is a concentration-dependent depletion attraction, with pennission from [17],...

Fig. 2. Phase diagram describing lateral phase separations in the plane of bilayer membranes for binary mixtures of dielaidoylphosphatidylcholine (DEPC) and dipalmitoyl-phosphatidylcholine (DPPC). The two-phase region (F+S) represents an equilibrium between a homogeneous fluid solution F (La phase) and a solid solution phase S presumably having monoclinic symmetry (P(J. phase) in multilayers. This phase diagram is discussed in Refs. 19, 18, 4. The phase diagram was derived from studies of spin-label binding to the membranes.

Liposomes were first proposed for drug topical administration to the skin more than 25 years ago by Mezei and Gulusekharam [1,2]. The basic components of liposomes are phospholipids (phosphatidylcholine, phophatidylethanolamine, phophatidylserine, dipalmitoyl phosphatidylcholine, and others), cholesterol, and water. Liposomes may vary significantly in terms of size (from tens of nm to microns) and structure. In liposomes, one or more concentric bilayers surround an aqueous core generating small or large unilamellar vesicles (SUV, LUV) or multilamellar vesicles (MLV), respectively [3]. 

Lipids are building blocks of model and real membranes, which can be combined with proteins and some other important biomolecules to simulate real membranes. The simplest model is hence the self-assembly of only one component of the complex membrane, in this case the lipids. These mono-component lipidic models are often employed in studies as their interaction with small molecules mimics the actual relationship between the cell membrane and a substrate. A commonly employed amphiphatic lipid, dipalmitoyl phosphatidylcholine (DPPC) (Figure 4.6.2), has been widely used to construct these cell membrane motifs, due to its high content in animal cells, and thus its tendency to mimic a valid animal ceU. The supramolecular organization of these (a) DPPC amphiphatic molecules lead to a (b) Langmuir monolayer, (c) bilayer, (d) micelle, and (e) vesicle, which are the available levels of modeling to mimic the cellnlar membrane. 

Since DAGs with diC are the most effective activators of protein kinase C it was concluded that the activation of the enzyme occurs via a transverse perturbation of the lipid bilayer structure [72]. H-NMR spectra of dipalmitoyl-phosphatidylcholine (DPPC) in the absence and presence of DAGs of various chain lengths are depicted in Figure 11-7. 

Fig. 6. The bilayer as a temperature-sensing selector of fatty acids, a is a DSC scan of membranes from A. laidlawii grown at 37°C in tryptose. The ratio of palmitate to oleate (P/0) taken up from the medium and esterified into membrane lipids after short-time incubation at various temperatures is shown in b. Physical binding of palmitate and oleate to protein-free lipids is shown in c. A mixture of dipalmitoyl phosphatidylcholine and egg phosphatidylcholine (25%) produced the DSC scan in d and the fatty acid binding curve in e.

The bilayer thinning is accompanied by an expansion of the bilayer area. For dipalmitoyl phosphatidylcholine it is found that AE /F +14%, the expansion in membrane area more than compensating for the 10% decrease in bilayer thickness to give the +4%... 

Such calibration measurements were made for water penetrating dipalmitoyl phosphatidylcholine (DPPC) phospholipid model membranes. It was concluded that the concentration of free water near the spin-labelled 4th carbon atom along the lipid chain is 5.2 M for cholesterol-free, and 7.2 M for cholesterol-containing membranes, respectively. Another example is a study of the penetration of glycerol-ds across model membranes quantitative assessment of the glycerol concentration at the middle of the bilayer resulted in a value of 0.4 M ( 3% v/v). 

Hg. 5 Dependence on spin-label position, n, of the H-ESEEM spectral amplitudes from DOXYL chain-labelled phosphatidylcholines in dipalmitoyl phosphatidylcholine (DPPC) bilayers with (solid squares) and without (open circles) 50 mol% cholesterol, at 77 K. Solid lines are non-linear, least-squares fits with eqn 9. Data from ref. 11 amplitudes are normalised as defined in ref. 32, giving values with units of time. 

Fig. 6 Location of TOAC-substituted alamethicin peptide in phospholipid membranes. D2O-ESEEM amplitudes of alamethicin-TOAC -TOAC and -TOAC in dioleoyl PC bilayers (solid horizontal lines), relative to the profile of D20-arriplitudes for DOXYL phosphatidylcholines n-PC in dipalmitoyl PC bilayers (solid circles). ...

We report here the results of a study of the adsorption of the alkaline earth cations to bilayer membranes formed from phosphatidylcholines with saturated chains dipalmitoyl phosphatidyl choline (DPPC) and dimyristoyl phosphatidyl choline (DMPC). Our salient result is that the adsorption of calcium is distinct from the other alkaline earth cations in two respects. First, only calcium adsorbs significantly more strongly to PCs with saturated chains than to phosphatidyl cholines with unsaturated chains, even when all lipids are present in the liquid crystalline state. Second, when the membranes are present in the frozen or gel state, the binding of calcium is significantly enhanced. We used two independent techniques to demonstrate this unique behavior of calcium. 

Acetylcholineesterase Bilayer lipid membranes were prepared by adding a solution of egg phosphatidylcholine and dipalmi-toyl phosphatidic acid dropwise into the surface of aqueous 0.1 M KC1/10 mM HEPES, near the Saran Wrap partition of a two compartment plexiglass cell. A portion of AChE solution in 10 mM Tris hydrochloride buffer solution of pH 7.4 was applied. The electrolyte level was momentarily dropped below the orifice and raised to form a membrane. The membranes were used as transducers for the reaction of AChE with ACh. An external voltage (25 mV) was applied across the membrane between two Ag/AgCl reference electrodes. Enzymatically generated hydronium ion causes transient current due to alteration of the electrostatic field by the ionization of dipalmitoyl phosphatidic acid. The response delay time was directly related to the substrate concentration where acetylcholine can be determined from 1 pM upto mM level. [113]... 

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