Anisotropic rotations of perylene in anisotropic media.
Item
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Title
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Anisotropic rotations of perylene in anisotropic media.
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Identifier
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AAI9908292
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identifier
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9908292
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Creator
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Atzeni, Salvatore Hauptmann.
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Contributor
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Adviser: Lesley Davenport
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Physical
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Abstract
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The anisotropic rotations of perylene labeled small unilamellar vesicles prepared from symmetric chain 1,2-ditetradecanoyl-sn-glycero-3-phosphocholine (DMPC) and asymmetric chain 1-stearoyl-2-caproyl-sn-glycero-3-phosphorycholine (C18:C10-PC) phospholipids have been studied using time-resolved emission anisotropy (TREA) measurements, as functions of temperature and excitation wavelength. Global analysis of the data was used, linking appropriate parameters according to photophysical and model constraints. Experimental temperatures included values below and above the phase transition of each phospholipid.;Perylene rotates anisotropically in isotropic solvents, and its rotational motions can be described using two rotational correlation times and two preexponential terms. Global analysis of TREA measurements of perylene in isotropic solvents recover constant values for preexponentials that are consistent with the photophysics of the molecule.;The phospholipid bilayers studied here present hindered, anisotropic environments, and the rotational motions of perylene become more complex, indicating possible lipid packing heterogeneity as well as heterogeneous distribution of perylene within the phospholipid bilayers. We eliminated the possibility of heterogeneous distribution of perylene by excluding the volume between the bilayer leaflets, using an asymmetric chain phospholipid that is known to interdigitate below the phase transition. With this approach, perylene may only be aligned along the acyl chains of the bilayer.;Global analysis of the TREA of perylene in phospholipid bilayers using conventional models do not properly describe the decay of the molecule: the recovered preexponentials do not sum to the limiting anisotropy (r{dollar}\sb0{dollar}) at each temperature; and magnitudes of recovered preexponentials is lower than those obtained using isotropic solvents. Since the magnitude of hindrance changes with the phospholipid state, a temperature dependent expression is required to describe the rotational behavior in a way that does not violate the photophysics of the molecule.;A new mathematical model, which accounts for the changes in the preexponential terms with temperature, has been developed and applied to the two phospholipid bilayer systems described above. The new model is tested by comparing the results of global data analysis with two conventional models. The goodness of fit is similar between models, but the new temperature dependent model represents a better description of the physical nature of phospholipid bilayers.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
