Distearoyl phosphatidylcholine

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.)... 

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... 

Maruyama K, Yuda T, Okamoto A, et al. Prolonged circulation time in vivo of large unilamelar liposomes composed of distearoyl phosphatidylcholine and cholesterol containing amphipathic poly(ethylene glycol). Biochim Biophys Acta 1992 1128 44. 

DSPC distearoyl phosphatidylcholine DPPG dipalmitoyl phosphatidylglycerol MI mechanical index... 

Liquid crystals, liposomes, and artificial membranes. Phospholipids dissolve in water to form true solutions only at very low concentrations ( 10-10 M for distearoyl phosphatidylcholine). At higher concentrations they exist in liquid crystalline phases in which the molecules are partially oriented. Phosphatidylcholines (lecithins) exist almost exclusively in a lamellar (smectic) phase in which the molecules form bilayers. In a warm phosphatidylcholine-water mixture containing at least 30% water by weight the phospholipid forms multilamellar vesicles, one lipid bilayer surrounding another in an "onion skin" structure. When such vesicles are subjected to ultrasonic vibration they break up, forming some very small vesicles of diameter down to 25 nm which are surrounded by a single bilayer. These unilamellar vesicles are often used for study of the properties of bilayers. Vesicles of both types are often called liposomes.75-77... 

Because the dynamics of phospholipid membranes have been well characterized using AF probes [8-13], fluorescence results obtained with hydrated human SC were compared to aqueous suspensions of unilamellar distearoyl-phosphatidylcholine (DSPC) vesicles. DSPC was also used because its phase transition temperature (55°C) is close to that of SC lipids (65 C). The microenvironment inside DSPC and SC membranes was studied by measuring fluorescence lifetimes, and shifts in emission maxima were compared to excitation maxima (Stokes shifts), along with quenching of a series of AF probes by iodide. Stokes shifts (Av) [6] were calculated as ... 

Fig. 4 Separation of dipalmitoyl phosphatidylcholine and distearoyl phosphatidylcholine. The solvent system used for the TC-CCC was hexane/ethyl acetate/ethanol/1% trifluoroacetic acid (5 5 5 4). The upper phase (organic phase) was mobile. The rotational speed was maintained at 1500-700 rpm. The highest column pressure was 360 psi. Amounts (100 pg each) of phosphatidylcholine dipalmitoyl and phosphatidylcholine distearoyl were loaded. Each fraction was spotted and developed on the HPTLC using chloroform/methanol/ 0.2% CaCl2 (60 32 4). Distearoyl phosphatidylcholine contains 2 mol of esterified stearic acids and dipalmitoyl phosphatidylcholine contains 2 mol of esterified palmitic acids. PC C16 0, dipalmitoyl phosphatidylcholine PC C18 0, distearoyl phosphatidylcholine. SF, solvent front.

To assess the ability of the TC-CCC molecular species, two molecular species of phosphatidylcholine, which were synthesized, were subjected to TC-CCC. Dipalmi-toyl phosphatidylcholine (PC C16 0) and distearoyl phosphatidylcholine (PC C18 0), two of the major molecular species of phosphatidylcholine, were completely separated as shown in Fig. 4. Distearoyl phosphatidylcholine contains 2 mol of esterified stearic acids and dipal-mitoyl phosphatidylcholine contains 2 mol of esterified palmitic acid. The structures of these compounds are shown in Fig. 4. These two compounds were completely separated. This result indicates that the TC-CCC system can separate molecular species in both phospholipids and glycolipids categories. 

Figure 19.1. The general structures of some phospholipids, distearoyl-phosphatidylcholine (DSPC), 1, and distearoylphosphatidylethanolamine (DSPE), 2.

The polyhedral borane ion [n-B2oH,8] reacts with liquid ammonia in the presence of a suitable base to produce an apical-equatorial isomer of the [B2oH,7NH3] ion. This species undergoes acid-catalyzed rearrangement to an apical-apical isomer. The sodium salts of both isomers were encapsulated in unilamellar liposomes, composed of distearoyl phosphatidylcholine/cholesterol, and investigated as boron delivery agents for BNCT (Feakes et al. 1994 Shelly et al. 1992). 

Abbreviations DMPC, DPPC, DSPC, dimyristoyl-, dipalmitoyl-,distearoyl-phosphatidylcholine DPPA, dipalmitoylphosphatidic acid PE, phosphatidylethanolamine PS, phosphatidylserine (U) and (M), unilamellar and multilamellar liposomes temperature of crystal liquid-crystal transition Diff. spectr., difference spectroscopy. 

Egg phosphatidylcholine (PC), distearoyl phosphatidylcholine (DSPC), phospha-tidic acid (PA), and phosphatidyl glycerol (PG) (more than 99% pure) were from Lipid Products Nutfield. All other phospholipids (more than 98% pure), cholesterol, triolein (TO), stearylamine (SA), fluorescein isothiocyanate (FITC), and oil red O were from Sigma Chemical Company. Sepharose CL-4B and polyethylene glycol 6000 were obtained from Pharmacia. All other reagents were of analytical grade. 

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