Effect of lipid ozonation products on liposomal membranes detected by Laurdan fluorescence

We report here the influence of the lipid ozonation products, 1-palmitoyl-2-(9-oxononanoyl)-sn-glycero-3-phosphocholine (PC-aldehyde) and 1-palmitoyl-2[8-(5-octyl-1, 2, 4-trioxolan-3-yl)-octanoyl]-sn-glycero-3-phosphocholine (PC-Criegee ozonide), on the phase domains of small unilamellar vesicles. (See Scheme 1 for structures.) 6-Lauroyl-2-dimethylaminonaphtalene (Laurdan) fluorescence excitation and emission spectra and generalized polarization measurements allowed us to study how lipid ozonation products affect the phase components of phospholipid membranes. A shift of excitation and emission spectra and a decrease in generalized polarization reveal the presence of a more polar environment surrounding the probe. We find that when either PC-aldehyde or PC-Criegee ozonide are incorporated into a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane, or when the POPC membrane is directly ozonated, a change in polarity of the phospholipid environment occurs that changes the properties of the bilayer. The introduction of more oxygenated and more polar phospholipids creates a more polar environment allowing the deeper penetration of water molecules into the membrane. Water penetration also is facilitated by the membrane disorder-producing effect of the ozonation products. The presence of an increased number of water molecules in the membrane effects the bilayer, altering packing order and cooperativity among fatty acyl chains as well as enhancing membrane fluidity.