| Abstract: | Compression isotherms for 1-palmitoyl-2-6(pyren-1-yl)] hexanoyl-sn-glycero-3-phosphocholine (PPHPC), -ethanolamine (PPHPE), -glycerol (PPHPG), -serine (PPHPS) and -phosphatidic acid monomethylester (PPHPM) were recorded at an argon/water interface. Thereafter, the ratios of pyrene excimer to monomer fluorescence emission intensities (Ie/Im) were determined for liposomes of these lipids and were found to be 20.15, 12.30, 11.80, 10.15 and 6.95 for the ethanolamine, choline, monomethylester, glycerol and serine derivatives, respectively. Assuming Ie/Im to depend on the reciprocal of the mean molecular area of the pyrenelipids in liposomes, equilibrium surface pressure to be the same in liposomes of these lipids regardless of the head group structure and neglecting any possible influence due to differences in the orientation of the pyrene moiety, we sought for that surface pressure value in the compression isotherms where the correlation of the reciprocal of mean molecular area in monolayers to Ie/Im values observed in liposomes was maximal. This treatment results in a value of approximately 12 mN m-1 for the equilibrium surface pressure in 1-palmitoyl-2-6(pyren-1-yl)]hexanoyl-glycerophospholipid liposomes. |
