Temperature effects vesicle phase transition

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Papahadjopoulos, D., Jacobson, K., Nir, S. and Isac, T. (1973). Phase transitions in phospholipid vesicles fluorescence polarization and permeability measurements concerning the effect of temperature and cholesterol, Biophys. Biochim. Acta, 311, 330-348. 

Pyrene has been used to investigate the extent of water penetration into micelles and to accurately determine critical micellar concentrations (Kalyanasundaram, 1987). Polarity studies of silica or alumina surfaces have also been reported. In lipid vesicles, measurement of the ratio Ii/Iui provides a simple tool for determination of phase transition temperatures and also the effect of cholesterol addition. 

A similar study by O Brien and coworkers utilized bilayers composed of a shorter chain diacetylenicPC (9) and DSPC or DOPC [37]. Phase separation was demonstrated in bilayers by calorimetry and photopolymerization behavior. DSC of the 9/DSPC (1 1) bilayers exhibited transitions at 40 °C and 55 °C, which were attributed to domains of the individual lipids. Polymerization at 20 °C proceeded at similar rates in the mixed bilayers and pure 9 bilayers. A dramatic hysteresis effect was observed for this system, if the bilayers were first incubated at T > 55 °C then cooled back to 20 °C, the DSC peak for the diacetylenicPC at 40 °C disappeared and the bilayers could no longer be photopolymerized. The phase transition and polymerizability of the vesicles could be restored simply by cooling to ca. 10 °C. A similar hysteretic behavior was also observed for pure diacetylenicPC bilayers. Mixtures of 9 and DOPC exhibited phase transitions for both lipids (T = — 18 °C and 39 °C) plus a small peak at intermediate temperatures. Photopolymerization at 20 °C initially proceeded at a similar rate as observed for pure 9 but slowed after 10% conversion. These results were attributed to the presence of mixed lipid domains... 

The chemical compositions and isomeric structures of the fatty acid chains of phospholipids is well known to have large effects on the physical properties of lipid bilayers, such as the temperatures of endothermic chain melting phase transitions. Lipid vesicles sensitized with lipid haptens can be agglutinated with specific antibodies directed against the haptens (see Fig. 1). 

Predict the effects of the following operations on the phase-transition temperature and on phospholipid mobility in vesicles made from dipalmitoylphosphatidylcholine ... 

Helmkamp (1980a) studied the effect of the fatty acid composition of the acceptor lipid on the stimulation of phosphatidylinositol transfer from rat liver microsomes to phosphatidylcholine vesicles by bovine brain exchange protein. Acceptor vesicles containing egg phosphatidylcholine or dioleoyl phosphatidylcholine gave approximately the same transfer activity, whereas dielaidoyl phosphatidylcholine or dimyristoyl phosphatidylcholine vesicles produced lower transfer rates. Zborowski and Demel (1982) used the same protein and measured the rate of transfer of phosphatidylinositol from a monolayer to phosphatidylcholine vesicles. Vesicles of egg, dioleoyl, dielaidoyl, and dipalmitoyl phosphatidylcholine, even below its phase transition temperature, all gave equivalent transfer rates. However, a reduced rate was found when dimyristoyl and dilin-oleoyl phosphatidylcholine, and other phosphatidylcholines with two polyunsaturated fatty acids, were used. Table IV shows a comparison of the transfer activities measured in the two assays. The transfer rates are expressed as a percent of the transfer rate obtained with egg phosphatidylcholine acceptor vesicles. 

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. 

The ratio can be used to calculate the percentage of lysed vesicles. The authors have studied the effect of normal alcohols on the vesicular permeability induced at the phase transition temperature. The incorporation of alcohols in the vesicles increased the degree of lysis on cycling through T,. Compared to the control, an increase in the 0 1 ratio is observed after cycling ftirough T, (Figure 11-15). 

Cationic vesicles, for example those formed from di-n-hexadecyldimelhylammonium bromide (DHAB) accelerate the decarboxylation by a factor of about 1000 relative to pure water. Dehydration of the carboxylate group at the binding sites is most likely the main factor behind the catalysis. Different isokinetic temperatures (obtained from linear plots of enthalpies v.y. entropies of activation) have been observed above and below the main phase transition temperature. These excellent isokinetic relationships indicate that the catalytic effects are caused by a single important interaction mechanism. ... 

D. Papahadjopoulos, K. Jacobson, S. Nir, and T. Isac, Phase Transitions in Phospholipid Vesicles. Fluorescence Polarization and Permeability Measurements Concerning the Effect of Temperature and Cholesterol, Biochim. Biophys. Acta 311, 330-348 (1973). 

Danger and Sekwen (20) investigated the effect of free fatty acids on the permeability of the 1,2-dimyristoyl-5 >72-glycero-3-phosphotidylcholine (DMPC) bilayer at the main phase transition. When vesicles were formed between DMPC and oleic acid, the phase transition temperature was reduced drastically, but at the phase transition from the gel to liquid crystalline phase, membrane permeability reaches a maximum. Saturated fatty acids did not have the same effect on the bilayer as unsaturated fatty acids, in that there was a reduced effect on the phase transition temperature. They also concluded that -bilayer flip-flop is at a maximum at the phase transition temperature of DMPC being in the millisecond range for oleic acid. DMPC was found to have a flip-flop rate of 4 h at the phase transition and even longer rates at other temperatures. 

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