Effect of lipid admixtures on the L-dipalmitoylphosphatidylcholine subtransition

Effect of the chirality of the glycerol backbone on the bilayer and nonbilayer phase transitions in the diastereomers of di-dodecyl-beta-D-glucopyranosyl glycerol

“…Within each of these lipid groups the chain-melting phase transition temperatures are very similar, whereas the temperatures of transitions involving solid-state transformations, if multiple gel phases are formed, vary significantly with the lipid headgroup and the chirality of the backbone molecule. For example, although the subgel phases of L-DPPC have been extensively investigated (2,(5)(6)(7)(8), it is still not clear whether such phases exist in the racemic mixture (6,7), and this is also true of the DPPGs (51,52). However, with the L-and DL-DPPEs, while the Lc/La phase transition temperatures are very different (66°C versus 82°C, respectively), the first-order spacings for the L, phases are similar, showing only slight differences in the packing of their hydrocarbon chains ( 14).…”

“…Most studies of the thermotropic phase behavior of aqueous dispersions of membrane lipids have dealt with the 1,2-diacylphosphatides, particularly the phosphatidylcholines (PCs)' (1)(2)(3)(4)(5)(6)(7)(8) and phosphatidylethanolamines (PEs) (5,(9)(10)(11)(12)(13)(14)(15)(16)(17), which are known to occur naturally in a wide range of eukaryotic cells ( 18). Although the effect of varying the length and structure of the hydrocarbon chain and the structure of the polar headgroup has been extensively investigated (1)(2)(3)(4)19), stud-ies on the effect of variations in the stereochemical conformation of these glycerophospholipids on their thermotropic phase behavior are less common.…”

“…Although the effect of varying the length and structure of the hydrocarbon chain and the structure of the polar headgroup has been extensively investigated (1)(2)(3)(4)19), stud-ies on the effect of variations in the stereochemical conformation of these glycerophospholipids on their thermotropic phase behavior are less common. While it has been established that there are marked differences in the lamellar gel-state polymorphism of the 1,2-sn (L) isomers and the racemic (DL) mixtures of both dipalmitoylphosphatidylcholine (DPPC) (2,(5)(6)(7)(8)20) and dipalmitoylphosphatidylethanolamine (DPPE) (5, 9-13, 17, 21), there have been very few studies of the lamellar phases of the 1,2-sn and 2,3-sn isomers (22), which are often assumed to exhibit identical physical properties. Even though this has not been verified experimentally, it seems a reasonable assumption, since these phospholipid molecules contain only a single chiral center (at C2 of glycerol) and thus the 1,2-sn-and 2,3-sn isomers are mirror images (enantiomers).…”

Scanning calorimetry reveals a new phase transition in L-alpha-dipalmitoylphosphatidylcholine

“…Binary mixtures of phosphatidylcholines differing in chain length by a single methylene unit exhibit a much slower rate of SGI phase formation than what is observed in the pure components (Finegold and Singer, 1984), even though ideal mixing is expected in both the gel and liquid crystalline phase. Similarly, binary mixtures containing a small amount of the opposite headgroup stereoisomer (5% D-DPPC) or cholesterol are unable to form the SGI phase (Boyanov et al, 1986). Clearly, the behavior of the SGI phase in mixtures emphasizes that its formation is sensitive to the ability of the system to attain long range order in both the acyl chain region and the polar headgroup/ interface region.…”

DSC Analysis of Surfactant-Based Microstructures

“…These temperatures correspond to the two eutectic mixtures of enantiomeric and racemic crystals, and the shape of the (pseudo) binary phase diagram indicates that the crystal of the racemate is a racemic compound, as in the case of the bulk compound. Chiral discrimination has been found in a number of DSC studies of phospholipid bilayers [120][121][122][123][124][125][126]. 14) when equimolar solutions of the R and S isomers were mixed.…”