How does acyl chain length affect thermotropic phase behavior of saturated diacylphosphatidylcholine–cholesterol binary bilayers?

Abstract

Thermotropic phase behavior of diacylphosphatidylcholine (CnPC)-cholesterol binary bilayers (n=14-16) was examined by fluorescence spectroscopy using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and differential scanning calorimetry. The former technique can detect structural changes of the bilayer in response to the changes in polarity around Prodan molecules partitioned in a relatively hydrophilic region of the bilayer, while the latter is sensitive to the conformational changes of the acyl chains. On the basis of the data from both techniques, we propose possible temperature T-cholesterol composition Xch phase diagrams for these binary bilayers. A notable feature of our phase diagrams, including our previous results for diheptadecanoylphosphatidylcholine (C17PC) and distearoylphosphatidylcholine (C18PC), is that there is a peritectic-like point around Xch=0.15, which can be interpreted as indicating the formation of a 1:6-complex of cholesterol and CnPCs within the binary bilayer irrespective of the acyl chain length. We could give a reasonable explanation for such complex formation using the modified superlattice view. Our results also showed that the Xch value of the abolition of the main transition is almost constant for n=14-17 (ca. 0.33), while it increases to ca. 0.50 for n=18. By contrast, a biphasic n-dependence of Xch was observed for the abolition of the pretransition, suggesting that there are at least two antagonistic n-dependent factors. We speculate that this could be explained by the enhancement of the van der Waals interaction with increases in n and the weakening of the repulsion between the neighboring headgroups with decreases in n.

Thermodynamics of lipid multi-lamellar vesicles in presence of sterols at high hydrostatic pressure

“…The peak maxima correspond to 23.91 °C for 0 mol% of cholesterol, to 22.90 °C for 13 mol% and 28.27 °C at 25 mol%. These results are in agreement with 8 , 27 – 29 . In 8 , 27 it is also evidenced that no phase transition is detectable at 50 mol% cholesterol and in refs 27 , 29 it is shown that the phase transition becomes very broad at 25 mol% cholesterol.…”

“…These results are in agreement with 8 , 27 – 29 . In 8 , 27 it is also evidenced that no phase transition is detectable at 50 mol% cholesterol and in refs 27 , 29 it is shown that the phase transition becomes very broad at 25 mol% cholesterol.

Figure 1 Excess heat capacity profiles Δc p (solid lines) and volume expansion coefficients α V (open circles) for DMPC MLVs in the presence of 0 mol%, 13 mol%, 25 mol% and 50 mol% cholesterol (from bottom to top).

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“…These results are very similar to those given by Tamai et al . 27 . The values derived from neutron data are at the same order of magnitude at 25 mol%, but at 50 mol%, we find a similar value as at 25 mol% with neutrons, but nothing from calorimetry.…”

Communication: Rigidification of a lipid bilayer by an incorporated n-alkane

“…2, 3 The effect is bidirectional, so the difference in the molecular order between the two phases becomes smaller. The transition temperature (T M ) between these phases is lowered by incorporation of cholesterol.…”

“…Cholesterol affects the phase behavior to make the ordered gel phase more disordered (when the cholesterol concentration is higher than approximately 25 mol. %, the disordering effect results in the transition to the liquid-ordered L o phase 2,3 ) and the disordered liquid-crystalline phase more ordered (sometimes termed as the liquid-disordered L d phase, but it is essentially the same as the liquid-crystalline phase).…”