1-2-oleoylphosphatidylcholine and n-tetradecane

The properties of n-tetradecane emulsions with dipalmitoylphosphatidylcholine (DPPC) or dioleoylphosphatidylcholine (DOPC) in 1M ethanol were investigated at 20 and 37°C. The zwitterionic phospholipids having the same headgroup bound to the apolar tail composed of two saturated or unsaturated chains were used as stabilizing agents. Both phospholipids may self-organize into aggregates, which possess different sizes and surface affinities. Electrokinetic properties of the systems at natural pH or pH 8 were investigated taking into account the effective diameter of the droplets as well as the zeta potentials using the dynamic light scattering technique. The effect of both phospholipids decreases the initially negative zeta potential of the n-tetradecane emulsion and is more evident in the case of DPPC especially at a physiological temperature near its main temperature transition. The change of zeta potential by DOPC is visible at both temperatures probably as an effect of a loose packing of this phospholipid on n-tetradecane droplets, because of the presence of double bonds in its molecule. Also, the role of ethanol dipoles on the stability of oil/phospholipid emulsions is obvious. The other aim of paper was the characterization of the phospholipase A(2) influence on DOPC hydrolysis in the emulsion environment in order to emphasize the importance of such methodology. The present work is the first study that explores the effects of both electrolyte ions and ethanol molecules on DOPC hydrolysis by phospholipase. The effect of enzyme on the n-tetradecane/DOPC emulsions was investigated at pH 8 with Na(+) or Ca(2+) ions, which occur in the physiological fluids. The effective diameters do not always correlate with the zeta potentials. A possible reason of such behavior might a mechanism different from the electrostatic stabilization. The particular role of Ca(2+) ions in the emulsions with phospholipids was confirmed. Those investigations provide insight into the properties of the PLA(2) hydrolysis process enhanced by added ethanol. It is believed that the enzyme effect on the phospholipid aggregation behavior at the oil-water interface will be helpful for understanding other biological phenomena.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Alkanes; Electrolytes; Emulsions; Ethanol; Hydrogen-Ion Concentration; Hydrolysis; Models, Molecular; Molecular Structure; Osmolar Concentration; Particle Size; Phosphatidylcholines; Phospholipases A2; Sodium Chloride; Surface Properties; Temperature

The behavior of dioleoylphosphatidylethanolamine (DOPE)/cholesterol/tetradecane and dioleoylphosphatidylcholine (DOPC)/cholesterol/tetradecane were examined using x-ray diffraction and the osmotic stress method. DOPE/tetradecane, with or without cholesterol, forms inverted hexagonal (HII) phases in excess water. DOPC/tetradecane forms lamellar phases without cholesterol at lower temperatures. With tetradecane, as little as 5 mol% cholesterol in DOPC induced the formation of HII phases of very large dimension. Increasing levels of cholesterol result in a systematic decrease in the HII lattice dimension for both DOPE and DOPC in excess water. Using osmotic pressure to control hydration, we applied a recent prescription to estimate the intrinsic curvature and bending modulus of the HII monolayers. The radii of the intrinsic curvature, RPO, at a pivotal plane of constant area within the monolayer were determined to be 29.4 A for DOPE/tetradecane at 22 degrees C, decreasing to 27 A at 30 mol% cholesterol. For DOPC/tetradecane at 32 degrees C, RPO decreased from 62.5 A to 40 A as its cholesterol content increased from 30 to 50 mol%. These data yielded an estimate of the intrinsic radius of curvature for pure DOPC of 87.3 A. The bending moduli kc of DOPE/tetradecane and DOPC/tetradecane, each with 30 mol% cholesterol, are 15 and 9 kT, respectively. Tetradecane itself was shown to have little effect on the bending modulus in the cases of DOPE and cholesterol/DOPE. Surprisingly, cholesterol effected only a modest increase in the kc of these monolayers, which is much smaller than estimated from its effect on the area compressibility modulus in bilayers. We discuss possible reasons for this difference.

Topics: Alkanes; Cholesterol; Elasticity; Liposomes; Models, Chemical; Models, Structural; Molecular Conformation; Osmolar Concentration; Phosphatidylcholines; Phosphatidylethanolamines; Stress, Mechanical; X-Ray Diffraction