Reference : Properties of mixed monolayers of lecithin and spin probe. II Analysis of the molecul...
Scientific journals : Article
Life sciences : Biochemistry, biophysics & molecular biology
Properties of mixed monolayers of lecithin and spin probe. II Analysis of the molecular organization
Chatelain, P. [ > > ]
Brasseur, Robert mailto [Université de Liège - ULiège > Chimie et bio-industries > Centre de Bio. Fond. - Section de Biophysique moléc. numér. >]
Ruysschaert, J. M. [ > > ]
Delmelle, M. [ > > ]
Journal of Colloid & Interface Science
Academic Press
Yes (verified by ORBi)
[en] This paper seeks to investigate the molecular organization of fatty acid spin label (4-palmitamido-2,2,6,6-tetramethylpiperidine-1-oxyl) and dipalmitoylphosphatidylcholine molecules in monolayer vesicles. The molar ratio of the spin probe was varied from 1 to 22% and the corresponding electron spin resonance spectra were measured at 25 and 48°C. These spectra were analysed in terms of the dipole-dipole and exchange interactions occuring between the radicals. From a computer simulation, a quantitative analysis of these interactions could be made. Comparison of these data with theoretical models indicate that above the lipid phase transition, i.e., at 48°C, the membrane is homogeneous and the label molecules diffuse randomly in the lecithin bulk phase (D = 3.8 X 10-8 cm2/sec). At 25°C, the membrane model can be viewed as a mosaic structure composed of spin probe clusters (7.9 X 1011 clusters/cm2). The size of the clusters as well as the minimal mean distance between two cluster edges could be calculated as a function of the spin label molar ratio. These results are used to interpret the observations made in the first paper of this series [Chatelain et ak., J. Colloid Interface Sci. 72, 287 (1979)] concerning the surface viscosity of the mixed monolayer and the kinetics of the enzymatic activity of phospholipase A2. It can be concluded that above a critical spin label concentration (10-15%) the properties of the entire lecithin phase are influenced by the presence of the spin probe clusters.

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