Temperature-dependent permeability of liposome membrane incorporated with Mg-chlorophyll a

The permeability was examined for the liposome membrane composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and various mole fractions f(c) of Mg-chlorophyll a (Chla). The permeability coefficient P-CF, was determined at 35-55 degrees C with respect to the liposome-encapsulated 5(6)-carboxyfluorescein (CF) by analyzing kinetics of its release into the bulk solution. The POPC/Chla liposomes containing CF (Chla-CFL) with f(c) of 0.018 were monodisperse and 134.1 +/- 1.6 nm in mean diameter. The Chla-CFL membrane showed the P-CF value of 9.15 +/- 0.24 x 10(-10) cm/s at 55 degrees C which was 42 times larger than that at 35 degrees C. The size distribution of Chla-CFL was practically unchanged by the incubation at 55 degrees C. The CF-release was thus resulted from permeabilization of the membrane while maintaining vesicular structure. The activation energy determined for the Chla-CFL membrane (164 kJ/mol) was much larger than that for the intact POPC one (85.0 kJ/mol). The Chla-CFL membranes with f(c) of 0.008 and 0.038 were less permeable than that with f(c) of 0.018. The results obtained indicate that the Chla molecules can form the domain of their aggregates within the POPC membrane, which provides a local route for the permeation of CF with significantly high activation energy being estimated as 243 kJ/mol. (C) 2011 Elsevier B.V. All rights reserved.