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Mixed-chain phosphatidylcholine bilayers: structure and properties
J Mattai1, P K Sripada, G G Shipley
1Department of Medicine, Housman Medical Research Center, Boston University School of Medicine, Massachusetts 02118.
Biochemistry
|June 16, 1987
Summary
Saturated mixed-chain phosphatidylcholines exhibit distinct low-temperature bilayer phases, with shorter acyl chains promoting interdigitation and influencing phase transition temperatures. These structural changes are crucial for understanding lipid behavior.
Area of Science:
- Lipid bilayer thermodynamics and phase behavior
- Structural characterization of phospholipids
- Materials science of lipid-based systems
Background:
- Phosphatidylcholines (PCs) are key components of biological membranes.
- The physical properties of PCs are influenced by fatty acyl chain length and composition.
- Understanding lipid phase transitions is essential for membrane function and drug delivery systems.
Purpose of the Study:
- To investigate the effect of systematically varied saturated mixed-chain lengths on PC bilayer phases.
- To characterize the low-temperature crystalline and gel phases of phosphatidylcholines using calorimetry and X-ray diffraction.
- To elucidate the phase transition pathways and molecular packing in mixed-chain PCs.
Main Methods:
- Differential scanning calorimetry (DSC) to determine phase transition temperatures (Tm, Ts) and enthalpies (ΔHs).
- X-ray diffraction to characterize the structural organization of hydrated lipid multilamellar dispersions.
- Systematic variation of sn-1 and sn-2 fatty acyl chain lengths in saturated mixed-chain PCs (18:0/n:0-PC and n:0/18:0-PC, n=18-10).
Main Results:
- Mixed-chain PCs form low-temperature crystalline bilayer phases, except for 18:0/10:0-PC.
- Subtransition temperature (Ts) increases and approaches main transition temperature (Tm) with decreasing acyl chain length.
- Phase transition pathways from crystalline (Lc) to liquid-crystalline (Lα) phases are chain length dependent, with shorter chains favoring direct Lc→Lα transitions or interdigitated gel phases (Lβ).
Conclusions:
- Acyl chain length and positional asymmetry significantly influence the formation and stability of low-temperature lipid phases.
- Triple-chain interdigitated bilayer phases (Lβ) are favored in shorter or more asymmetric mixed-chain PCs to maximize chain-chain interactions.
- Despite varied transition pathways, the overall thermodynamic change (Lc→Lα) remains largely chain length independent.