Lipid concentration

The actual characteristics of REV produced depend on a number of factors such as choice of lipids (% cholesterol and charged lipids), lipid concentration used in the organic solvent, rate of evaporation, and ionic strength of the aqueous phase (Szoka and Papahadjopoulos, 1980). Modifications of this REV technique were proposed by several groups. The SPLV (stable plurilamellar vesicles) method consists of bath-sonicating an emulsion of the aqueous phase in an ether solution of lipid while evaporating the ether (Griiner et al., 1985). 

A disadvantage of the ethanol injection method to produce SUV is the need to use a low lipid concentration, resulting in a low encapsulation efficiency of the aqueous phase. The dispersions can be concentrated by ultracentrifugation, ultrafiltration, or removal of water by evaporation. 

Depending on the lipid concentration, vesicles with different particle sizes can be prepared (Kremer et al., 1977). At a low Upid concentration (3 mM), vesicles with a diameter of 30 nm are formed, whereas 110-nm vesicles are formed at higher concentrations... 

An analogous apparatus to that of Ref. 9 was used to follow the effect of the lipid monolayer on the rate of electron transfer (ET). In this setup [47], an organic phase droplet (1,2-DCE) is continuously expanded into the aqueous phase, and the resulting current transient was monitored in the absence and presence of the adsorbed lipid mono-layer. The rate of ET was decreased as a function of the lipid concentration. 

Perhaps the most important experimental progress made recently in electrochemistry was the introduction of a scanning electrochemical microscope (SECM). Tsionsky et al. have used SECM to study also the rate of ET across a lipid monolayer at the water-benzene interface [48,49]. The presence of the monolayer decreased the rate of ET, being the decrease more significant for longer hydrocarbon chains and larger lipid concentration in solution. It was thus concluded that the ET reaction does not occur at defect sites in the lipid monolayer. 

Forde, O. H., Knutsen, S.F., Arnesen, E., Thelle, D. S., The Tromso heart study Coffee consumption and serum lipid concentrations in men with hypercholesterolemia A randomized intervention study, BrMedJ, 290, 893, 1985... 

Since there would be increased overall lipid concentration in the dodecane solution, we decided to create a sink condition in the acceptor wells, to lower the membrane retention. We discovered that the pH 7.4 buffer saturated with sodium laurel sulfate serves as an excellent artificial sink-forming medium. Since the new PAMPA membranes would possess substantial negative charge, the negatively charged micellar system was not expected to act as an aggressive detergent to the two-component artificial membrane infused in the microfilter. 

Table 10.4 Amounts of dye bonded to wool using LUV and MLV liposomes at different lipid concentrations with Cl Acid Blue 90 [57]...

Figure 10.13 Exhaustion rates of Cl Disperse Violet 1 on untreated wool in dyeing using liposomes at different lipid concentrations and constant dye concentration [58]...

Flavell DM, Pineda Torra I, Jamshidi Y, Evans D, Diamond JR, Elkeles RS, et al. Variation in the PPARalpha gene is associated with altered function in vitro and plasma lipid concentrations in Type 2 diabetic subjects. Diabetologia 2000 43 673-680. 

Prepare a liposome suspension, containing PE, at a total-lipid concentration of 5mg/ml in 0.1M sodium phosphate, 0.15M NaCl, pH 6.8. Maintain all lipid-containing solutions under an inert gas atmosphere. Degas all buffers and bubble them with nitrogen or argon prior to use. 

Increases in serum lipids and glucose appear to be transient and of little clinical importance. /J- Blockers increase serum triglyceride levels and decrease high-density lipoprotein cholesterol levels slightly. /1-Blockers with -blocking properties (carvedilol and labetalol) do not affect serum lipid concentrations. 

Figure 4. Half-life Ti/2of pH gradient decay in the dark as a function of lipid concentration for Mab(Phyt)2 or EPC vesicles after light-induced proton translocation by BR at 2S°C,...

Figure 5.28 Circular dichroism spectra of DC8 9PC tubules prepared in (a) ethanol-water (7 3), (b) methanol-ethanol-water (35 35 20), and (c) methanol-water (70 30) and (d) DCj PC liposomes above melting temperature. All samples were prepared at lipid concentration of 2.0 mg/ml and spectra for tubules were recorded at 25°C. Liposome spectrum was recorded at 40°C and peak intensity is about 104 smaller than that from tubules.

Figure 5.29 Negative-stained electron micrograph of DCs,9 PC tubule from 5-mg/ml sample in methanol-water (85 15). Solvent conditions and lipid concentration were adjusted to obtain sample of two-bilayer tubules as shown in enlargement of tubule edge in bottom panel. Bar = 200 nm (top) 50 nm (bottom). Reprinted with permission from Ref. 125. Copyright 1998 by the American Chemical Society.

Figure 5.31 Concentration dependence of CD spectra at 205 nm (top) and specific heat (bottom) of DCg.gPC tubules prepared in ethanol-water (70 30) at lipid concentrations of (a) 0.2, (b) 0.5, (c) 1.0, (d) 2.0, and (e) 5.0 mg/ml. These results show crossover from continuous to discontinuous melting as lipid concentration is increased. Reprinted with permission from Ref. 137. Copyright 1997 by the American Chemical Society.

Figure 5.38 (a) Negative-stained transmission electron micrograph of nanotubules formed from equimolar mixture of DCg PC and DNPC (2 mM total lipid concentration) stored at 4°C just prior to deposition, (b) Freeze-fracture electron micrograph of twisted ribbons at 27°C. Bars = 100 nm. Reprinted with permission from Ref. 153. Copyright 2001 by the American Chemical Society. 

Figure 5.43 Phase contrast optical micrographs of typical helical structures in chemically defined lipid concentrate system, (a) Low-pitch helical ribbon with pitch angle i r = 11 2°. (b) High-pitch helical ribbons with pitch angle t t = 54 2°. (c) Intermediate-pitch helical ribbons with pitch angle i r = 40.8 3.8°. Reprinted with permission from Ref. 162. Copyright 1999 by the National Academy of Sciences, U.S.A.

There are two reasons to think this situation might occur. The first reason is experimental. As discussed in Sections 2-5, in most experiments on chiral materials, tubules and helical ribbons are observed with only one sense of handedness. However, there are a few exceptions in experiments on diacetylenic phospholipids,144 diacetylenic phosphonate lipids,145 146 and bile.162 In these exceptional cases, some helices are observed with the opposite sense of handedness from the majority. In the work on diacetylenic phospholipids, the minority handedness was observed only during the kinetic process of tubule formation at high lipid concentration,144 which is a condition that should promote metastable states. Hence, these experiments may indeed show a case of biased chiral symmetry-breaking in which the molecular chirality favors a state of one handedness and disfavors a mirror image state. 

Fig. 3.20. Retention of CF as function of the trehalose/lipid concentration with varied dextran additions. I, no dextran 2, 0.08g dextran/g lipid . 3, 1.2 g dextran/g lipid, 4, 2.0 g dextran/g lipid (Fig. 9 from [3.37]).

---