title: The activation energy of incorporation of extrinsic probes in model vesicles.
abstract: Time dependence of fluorescence enhancement of probes after addition to lipid vesicles has been used to investigate the position of chromophores in the lipid bilayer. Incorporation studies of a series of n-(9-anthroyloxy) fatty acids (n = 2, 2, 12 and 16) and 1,6-diphenylhexatriene in dipalmitoyl phosphatidylcholine vesicles are described. The activation energies for incorporation of these several lipid-mimic type fluorescent probes have been measured. Results show that the activation energy is a function of the distance of the anthracene moiety (chromophore) from the polar end of the probe and the length of the acyl portion of the probe. An average insertion energy of 0.6 kcal/carbon is seen for these fatty acid probes. The activation energy of 1,6-diphenylhexatriene, a factor of 2 greater than that of 16-(9-anthroyloxy)palmitic acid, is consistent with locating 1,6-diphenylhexatriene in the middle of the bilayer.
mesh_terms: D002151:Calorimetry; D005227:Fatty Acids; D005456:Fluorescent Dyes; D007700:Kinetics; D008051:Lipid Bilayers; D008954:Models, Biological; D008968:Molecular Conformation; D011663:Pulmonary Surfactants; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013696:Temperature
chemical_list: D005227:Fatty Acids; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D011663:Pulmonary Surfactants