DSPC

The presence of impurities like free fatty acids in egg or soybean phosphatidylcholine, or in the (semi)synthetic phosphatidylcholines (e.g., DMPC, DPPC, DSPC) can be detected by monitoring the electrophoretic behavior of liposome dispersions of these phospholipids in aqueous media with low ionic strength a negative charge will be found on these liposomes when free fatty acids are present in the bilayers. 

Liposomes DPPC/DPPG/chol (molar ratio 10 1 10) size about 0.7 um. PC/PS/chol (molar ratio 10 1 4) size about 0.3 ym. DSPC/ DPPG/chol (molar ratio 10 1 10) size about 0.7 ym. 

FIG. 10 Vibrational sum frequency spectrum of saturated monolayers of dilauroyl- (DLPQ, dimyristoyl- (DMPC), dipalmitoyl- (DPPC), and distearoyl-phosphatidylcholine (DSPC) at the D2O-CCI4 interface at ambient temperature in the region of the methylene and methyl symmetrical stretches. (From Ref 139, copyright American Chemical Society.)... 

After addition of lipid DSPC into the organic phase a monolayer is formed at the interface, and the steady-state current increased at all potentials. On expansion, the time constant of the charging current is reduced to ca. 5 ms and a shift of ca. 100 mV is observed in the potential of zero charge. From the video image of the droplet a highly distorted and heterogeneous interface is seen which relaxes after the fast stage (a few... 

Ruckenstein and Li proposed a relatively simple surface pressure-area equation of state for phospholipid monolayers at a water-oil interface [39]. The equation accounted for the clustering of the surfactant molecules, and led to second-order phase transitions. The monolayer was described as a 2D regular solution with three components singly dispersed phospholipid molecules, clusters of these molecules, and sites occupied by water and oil molecules. The effect of clusterng on the theoretical surface pressure-area isotherm was found to be crucial for the prediction of phase transitions. The model calculations fitted surprisingly well to the data of Taylor et al. [19] in the whole range of surface areas and the temperatures (Fig. 3). The number of molecules in a cluster was taken to be 150 due to an excellent agreement with an isotherm of DSPC when this... 

FIG. 4 ir—A isotherms measured for DSPC at water-1,2-DCE (O) and water-air ( ) interfaces from Ref. 41 and simulated with a real gas model [40] ideal gas with A = 0 and Ug = 0 (thin solid line), hard disks gas with A = 40 and ug = 0 (thick solid line), vdW gas with = 40 and Ug/kT = 3 (thin dashed line), and vdW gas with = 40 A and UgjkT = 7 (thick dashed line). The inset shows part of the thick dashed line. (Reproduced from Ref 40 with permission from Elsevier Science.)... 

FIG. 6 Enhancement factor observed in the forward rate constant for TEA+ ion transfer at the water-l,2-DCE interface due to the presence of PCs DLPC ( ), DMPC ( , DPPC (A), and DSPC ( ). (Experimental data are taken from Ref 12.)... 

More recently, Manzanares et al. [17] presented additional experimental evidence of the enhanced cation transfer across a hemispherical water-1,2-DCE interface covered with DSPC by using a syringe experimental set up described elsewhere [9,28]. Figure 7 shows the cyclic voltammograms measured in the cell [17],... 

FIG. 7 Comparison of cyclic voltammograms recorded at 1 mV/s before (a) and after addition (b) of 59 /xM DSPC to the organic phase. (Reproduced from Ref. 17 with permission from Elsevier Science.)... 

Effect of Cholesterol. Cholesterol inclusion into the lipid bilayers composed of DPPC or DSPC, eliminates apparent Tc and reduces permeability at and above the usual Tc. On the other hand, cholesterol inclusion increases packing of fluid bilayer composed of lipids with unsaturated fatty acyl chains. Since cholesterol rich liposomes are stable in plasma, cholesterol is commonly used as a liposomal component. 

Monte Carlo may be used to study the lateral distribution of lipid molecules in mixed bilayers. This of course is a very challenging problem, and, to date, the only way to obtain relevant information for this is to reduce the problem to a very simplistic two-dimensional lattice model. In this case, the lipid molecules occupy a given site and can be in one of the predefined number of different states. These pre-assigned states (usually about 10 are taken), are representative conformations of lipids in the gel or in the liquid state. Each state interacts in its own way with the neighbouring molecules (sitting on neighbouring sites). Typically, one is interested in the lateral phase behaviour near the gel-to-liquid phase transition of the bilayer [69,70]. For some recent simulations of mixtures of DMPC and DSPC, see the work of Sugar [71]. 

Sugar, I. P., Thompson, T. E. and Biltonen, R. L. (1999). Monte Carlo simulation of two-component bilayers DMPC/DSPC mixtures, Biophys. J., 76, 2099-2110. 

DSPc Dual specificity phosphatase, catalytic domain E(MFP)B 5(5) 10(10) 1VHR... 

Remote Loading of Doxorubicin into DSPC Cholesterol (55 45) Large Unilamellar Vesicle... 

DSPC/Chol (55 45) LUVs (diameter = 100 nm) are prepared as described in section Preparation of Sphingomyelin/Cholesterol (55 45) Large Unilamellar Vesicle by Extrusion [(Lipid) = 20 mM, volume = 5mL], using 350 mM citrate pH 4.0 as the hydration buffer, and 20 mM HEPES 1.50 mM NaCl pH 7.5 (HEPES-buffered saline) as the external buffer. In this case, the pH gradient is formed during the final dialysis step. It would also be possible to omit the final dialysis step and form the pH gradient by one of two common column methods. This could be desirable if the LUV... 

The initial mixture and each time point are then assayed for doxorubicin and lipid. Lipid concentrations can be quantified by the phosphate assay (see above) or by liquid scintillation counting of an appropriate radiolabel. Doxorubicin is quantified by an absorbance assay (see below). The percent uptake at any time point (e.g., t = 30 minutes) is determined by %-uptake = [(D/L), =30minutes] x 100/[(D/L) inuiai]. Doxorubicin can be assayed by both a fluorescence assay and an absorbance assay, but we find the latter to be more accurate. The standard curve consists of four to five cuvettes containing 0 to 150 nmol doxorubicin in a volume of 0.1 mL samples to be assayed are of the same volume. To each tube is added 0.9 mL of 1% (v/v) Triton X-100 (in water) solution. For saturated lipid systems such as DSPC/Chol, the tubes should be heated in a boiling water bath for 10 to 15 seconds, until the detergent turns cloudy. Samples are allowed to cool, and absorbance is read at 480 nm on a UV/Visible spectrophotometer. 

The experimental procedure below describes the uptake of ciprofloxacin into sphingomyelin (SPM)/Chol LUVs. Drug delivery vehicles prepared from SPM/Chol often exhibit greater efficacy than those prepared from DSPC/Chol (13). Included is a description of the Bligh-Dyer extraction procedure (78), which involves partitioning the lipid and water-soluble drug into organic solvent and aqueous layers, respectively. This is necessary because lipid interferes with the ciprofloxacin assay. 

The initial mixture and each time point are then assayed for ciprofloxacin and lipid. Lipid can be quantified using the phosphate assay (64,65) or by liquid scintillation counting. Ciprofloxacin is quantified by an absorbance assay following removal of drug from lipid by a Bligh-Dyer extraction procedure (78) (see below). The percent uptake is determined as described in the section Remote Loading of Doxorubicin into DSPC/Cholesterol (55 45) Large Unilamellar Vesicle. ... 

LEH is primarily composed of a combination of saturated high-carbon phospholipids and cholesterol. Synthetic phospholipids replaced hydrogenated soy lecithin when the latter was found to induce several untoward biological responses (40). Current choice of a saturated high-carbon phospholipid is mostly between distearoyl phosphatidylcholine (DSPC, 55°C) and... 

The preformed vesicle (PFV) approach involves incubation of liposomes containing a cationic lipid and a PEG coating with polynucleotides in the presence of ethanol. Typically, LUV composed of distearoyl-phosphatidyl-choline (DSPC), cholesterol (Choi), l-0-(2 -(oi-methoxy-polyethylene-glycol)... 

Ethanol is required for entrapment to occur. Addition of increasing amounts of ethanol to 100 nm DSPC/Chol/DODAP liposomes leads to the formation of large lipid structures following oligonucleotide addition and a concomitant increase in oligonucleotide entrapment levels (Table 1). The... 

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