Evaluation of the thermal coefficient of the resistance to fluorophore rotation in model membranes.
The thermal coefficient of the frictional resistance to fluorophore rotation (b), a parameter related to the change in the local viscosity with temperature, was determined for anthroyloxy-fatty acid probes in micelles and dimyristoyl lecithin (DMPC) and dioleoyl lecithin (DOPC) unilamellar and multilamellar vesicles. The value of b and the percent change in anisotropy with temperature (%dA/dT) remained constant with membrane depth and only depended on composition. These parameters were also the same when either in-plane, or in-plane and out-of-plane fluorophore motions were observed. This result indicates that the membranes expand isotropically. The magnitude of b was found to be primarily dependent on the packing of the hydrocarbon chains with higher b values relating to more closely-packed chains. b was responsive to the gel to liquid crystal phase transition of DMPC and the bilayer to hexagonal phase transition of egg-phosphatidylethanolamine. When the enthalpy values for the fluorophore transfer from one phase to another are calculated, the values are larger than those measured by calorimetry and reflect a discrepancy between the microscopic enthalpy experienced by the fluorophore due to a change in environment versus the macroscopic enthalpy of the system as a whole.
Scarlata
S F
SF
Cornell University Medical College, College of Medicine, New York 10021.
D004134:Dimyristoylphosphatidylcholine; D008081:Liposomes; D008433:Mathematics; D008962:Models, Theoretical; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D012997:Solvents; D013816:Thermodynamics
D008081:Liposomes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D012997:Solvents; C017251:1,2-oleoylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine