Gel-liquid crystal phase transition

The results of differential scanning calorimetry(DSC) indicate the change in aggregation state. The trans micelle showed a main endothermic peak at 14 2°C(A H =1.0 kcal/mol), corresponding to a gel-liquid crystal phase transition, whereas the transition temperature for the cis micelle appeared at 11.9°C( AH = 0.8 kcal/mol). This is unequivocal evidence that the trans-cis photoisomerization is a sufficient perturbation to alter the state of molecular aggregation. 

The rate and character of the molecular motions of both the molecules embedded in the lipid bilayer and lipid molecules themselves are strongly dependent on the temperature [19, 203], At a certain temperature tm, the gel-liquid crystal phase transition is known to occur for the membrane made of a synthetic lipid. For example, tm = 41.5 °C for the membranes from DPL. In the vesicles formed by a mixture of lipids, e.g. egg lecithin, the phase transition occurs smoothly rather than jumpwise and starts below 0 °C. Note that the permeability of lipid membranes increases notably upon transition from the liquid crystal state to the gel state [204]. 

The DSC thermogram of the liposome-embedded heme was measured to estimate the phase transition of the lipid bilayer of the liposome-embedded heme . The DMPC-liposome showed the endothermic peak at 24 °C, which was corresponding to the gel-liquid crystal phase transition temperature (T,) of the liposome . But for the liposome in which a simple heme such as I was embedded, the phase transition peak was broadened and shifted to lower temperature (22 °C). On the other hand, the peak was also observed at 24 °C for the DMPC liposome/lipid-heme. This suggests that the orientation of the phospholipid in the liposome is equivalent for the DMPC-liposome and the DMPC liposome/lipid-heme and that the compatibility of the lipid-heme with the phospholipid is large enough to form a stable liposome. 

K.-I., and Kambara, T. (1993) A model for self-sustained potential oscillation of lipid bilayer membranes induced by the gel-liquid crystal phase transitions. Biophys.]., 64, 1461-1475. 

With the aim to develop a drug delivery system with thermal stimuli respons-ing, Nozawa et al. have been investigated liquid crystal (LC)-entrapped membranes, polymer alloyed membranes and LC-adsorbed membranes for the transport and release of indomethacin. Polymer alloyed membranes were obtained by polymerizing aaylic monomers in presence of LC and LC-adsorbed membrane were obtained by adsorbing LC into porous hydrophobic polymer membrane. Permeation experiments showed that below and above the gel-liquid crystal phase transition tanperature of the LC, the extent of thermo-sensitivity for LC-adsorbed... 

A2 has been found to be particularly useful in characterizing phase transitions. For example, the gel-liquid crystal phase transition of a biomembrane is manifest by a sharp increase in A2> Figure 8, corresponding to an increase in the distribution of order parameters or quadrupole splittings. The maximum in A2 occurs close to the centre of the phase transition. 

The gel to liquid crystal phase transition temperature of DHPC bilayers containing 5-oxo KSA or 12-oxo KSA, at the concentrations used here, is around 46 C (data not shown). 

DHPC l -dihexadecyl-sn-glycero-3-phosphocholine KSA potassium stearate 5-oxo KSA 5-oxo potassium stearate 12-oxo KSA 12-oxo potassium stearate 9HP 9-heptadecanone Tc temperature of the gel-to-liquid crystal phase transition of DHPC bilayers 43.41C... 

Figure 9. NMR spectra of the plasma membranes of Acholeplasma laidlawii enriched in palmitic acid labeled at the 13-position (I3-Ai 16 0) and in oleic acid labeled at the 12-position (12-d2 18 1). Spectra were obtained at the growth temperature, 37°C. The temperatures of optimal growth, To, and the calorimetric gel to liquid crystal phase transition of the lipids in the membranes, T, are indicated. Details of sample preparation and spectral acquisition are given in Ref. 23 and 24.

Evidence for surfactant aggregation into bilayers in protein-surfactant films was obtained by observing gel-to-liquid crystal-phase transitions by differential scanning calorimetry (DSC). This phase transition is related to the onset of fluidity of the hydrocarbon tails for surfactants arranged in bilayers [5-7]. Phase transition temperatures (T ) of Mb-surfactant films [19,24,25] were observed for all the surfactants in Fig. 2. For a given surfactant, values of films were within several °C of values for the corresponding vesicle dispersions. These results indicate that all of the surfactants are arranged in bilayers in the films. The presence of the protein does not seem to influence Tc in any consistent manner. 

Lipid-water systems usually exist in either a gel or a liquid crystal phase depending on temperature. In this case, the gel-to-liquid crystal phase transition of... 

Figure 7 shows a series of typical DSC curves for samples of the DPPC-water mixture with increasing wato content expressed as [(g water)/(g lipid + g wato )] X 100 and designated as The ice-melting peaks are followed by two lipid transition peaks of the gel (Lp-)-to-gel (Fp ) and subsequent gel (Fp )-to-liquid crystal phase transitions, generally called the Tp and transitions, respectively. 

Finally, we discuss the role of interlamellar water in lipid phase transitions. As shown in Fig. 36, the phase behavior of the lipid in the DMPE-water system is complex in the absence of freezable interlamellar water [21], Presumably, in a region of such low water content, the lipid bilayers exist as hydrated crystals containing only nonfreezable interlamellar water. However, with the appearance of freezable interlamellar water (curves d-m), the lipid phase transition comes to be characterized by a certain peak that is gradually shifted to lower temperatures with increasing water content and finally converges to a fixed temperature, generally ascribed to the gel-to-liquid crystal phase transition. Such phase behavior suggests that freezable interlamellar water is absolutely necessary for the formation of the gel phase of lipid-water systems. In this respect, another noticeable point is that the fixed peak of the gel-to-liquid crystal transition is obtained above a certain water content where a maximum uptake of the freezable interlamellar... 

The incorporated SP exhibited photochromism in both of the immobilized bilayer complexes with montmorillonite and PSS. Kinetic measurements of the thermal isomerization (decoloration) were carried out for the annealed film. The decoloration reaction rate is dependent on the mobility of the surroundings and, in polymer matrices, is influenced by the glass transition. It was found that the reaction rates abruptly increased near the gel-to-liquid-crystal phase-transition temperature (54°C) of the immobilized bilayer due to increased matrix mobility in this system. The film prepared with montmorillonite gives more homogeneous reaction environments for the chromophore than those with the linear polymer (PSS). This leads to drastic changes in the reaction rate at the crystal-to-liquid-crystal phase transition of the bilayer, showing the effect of the phase transition of immobilized bilayers to be more pronounced than that of the glass transition of amorphous polymer matrices. 

Even this is not the entire story, however. The properties of the bilayer, and hence the diffusion rates, also depend on the composition and physical state of the bilayer. For example, in the studies of benzene diffusion in a dimyristolylphosphatidyl-choline (DMPC) bilayer mentioned above, temperature was varied in a controlled manner. As the temperature varied, so did the distribution of free volume. At low temperatures (still above the gel to liquid-crystal phase transition) the free volume was largely localized in large voids in the center of the... 

---