Phase separation in short-chain lecithin/gel-state long chain lecithin aggregates

Abstract

Small bilayer particles form spontaneously from gel-state long-chain phospholipids such as dipalmitoylphosphatidylcholine and 0.2 mol fraction short-chain lecithins (e.g., diheptanoyl-phosphatidylcholine). When the particles are incubated at temperatures greater than the Tm of the long-chain phosphatidylcholine (PC), the particles rapidly fuse (from 90-A to greater than or equal to 5000-A radius); this transition is reversible. A possible explanation for this behavior involves patching or phase separation of the short-chain component within the gel-state particle and randomization of both lipid species above Tm. Differential scanning calorimetry, 1H T1 values of proteodiheptanoyl-PC in diheptanoyl-PC-d26/dipalmitoyl-PC-d62 matrices of varying deuterium content, solid-state 2H NMR spectroscopy as a function of temperature, and fluorescence pyrene excimer-to-monomer ratios as a function of mole fraction diheptanoyl-PC provide evidence that such phase separation must occur. These results are used to construct a phase diagram for the diheptanoyl-PC/dipalmitoyl-PC system, to propose detailed geometric models for the different lipid particles involved, and to understand phospholipase kinetics toward the different aggregates.

Solid‐state NMR analysis of the orientation and dynamics of epigallocatechin gallate, a green tea polyphenol, incorporated into lipid bilayers

“…At T c , the interactions of short-chain phosphatidylcholine (dihexanoyl or diheptanoyl) with long-chain (dimyristoyl, dipalmitoyl, or distearoyl) phosphatidylcholine would predominantly have characteristics of the long-chained component. [23,24] Thus, mixtures of DHPC and DMPC in water would be expected to form discoidal aggregates in which a flat DMPC bilayer is stabilized by the DHPC rim. [25] Using solid-state 31 P NMR spectrometry, we confirmed that the surfaces of bicelles orient parallel to the magnetic field (data not shown).…”

Structural and morphological transition of long-chain phospholipid vesicles induced by mixing with short-chain phospholipid

“…Since various assemblies are expected, depending on the states of DMPC vesicle membrane (gel and liquid crystalline) and on the DHPC concentrations, in the present system, the tran- sition process may be more complicated than that explained by three-stage model [20][21][22][23]. It is demonstrated that the vesicle to micelle transition takes place through the formation of thread-like intermediate structure under the experimental condition of this study, and the possible mechanism of the transition process will be discussed.…”

A time-resolved study on the interaction of oppositely charged bicelles – implications on the charged lipid exchange kinetics

“…[27][28][29][30][31]35 The typical bicelle diameter was around 20 nm with a bilayer thickness of about 6 nm at room temperature. The disc-like bicelles were formed by mixing the zwitterionic long-chain lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and the short-chain lipid 1,2-diheptanoylsn-glycero-3-phosphocholine (diC7PC) in aqueous solution.…”