Miscibility and phase behaviour of binary mixtures of N-palmitoylethanolamine and dipalmitoylphosphatidylcholine.
The content of N-acylethanolamines (NAEs) increases dramatically in cell membranes when the parent organism is subjected to injury or stress. This increase has been attributed to stress-combating mechanisms of the organism. In this study, a binary phase diagram of hydrated mixtures of N-palmitoylethanolamine (NP-E)--an endogenous ligand for the peripheral cannabinoid receptor (CB-2)--with dipalmitoylphosphatidylcholine (DPPC) is established by high-sensitivity differential scanning calorimetry (DSC). The structures of the phases involved were determined by using 31P-NMR spectroscopy and low-angle X-ray scattering. DSC studies show that NP-E and DPPC mix well in the composition range DPPC/NP-E=100:0 to 40:60 (mol/mol). At higher contents of NP-E, phase separation is indicated by the presence of additional transitions in the thermograms. Characterization of the structures formed by the mixtures with 31P-NMR shows that, up to 80 mol% NP-E, DPPC remains in the lamellar phase. The low-angle X-ray diffraction data are also consistent with a lamellar gel-phase structure for DPPC/NP-E mixtures up to 60 mol% NP-E. Above 70 mol% NP-E, NP-E phase separates in the gel-phase region, while complete miscibility is observed in the fluid phase. These results provide a structural basis for understanding the membrane interactions of NAEs, which is necessary for understanding the mechanism of their putative stress-combating role in the parent organisms.
Swamy
Musti J
MJ
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India. mjssc@uohyd.ernet.in
Ramakrishnan
M
M
Marsh
D
D
Würz
U
U
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D000577:Amides; D002152:Calorimetry, Differential Scanning; D063388:Endocannabinoids; D004983:Ethanolamines; D009682:Magnetic Resonance Spectroscopy; D010169:Palmitic Acids / Q000737:chemistry*; D012542:Scattering, Radiation; D014961:X-Ray Diffraction
D000577:Amides; D063388:Endocannabinoids; D004983:Ethanolamines; D010169:Palmitic Acids; D015060:1,2-Dipalmitoylphosphatidylcholine; C005958:palmidrol