NMR and dynamic light scattering studies of lipid membrane assemblies.
Item
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Title
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NMR and dynamic light scattering studies of lipid membrane assemblies.
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Identifier
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AAI9969745
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identifier
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9969745
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Creator
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Wu, Guohua.
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Contributor
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Adviser: Ruth E. Stark
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Date
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2000
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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, Polymer | Chemistry, Organic
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Abstract
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The combination of nuclear magnetic resonance (NMR) and quasielastic light scattering (QLS) offers a potent experimental strategy to determine three-dimensional structures of mixed micellar aggregates. It has been used in the study of C8-based model mixtures for fat digestion and C 18 fatty acid transport mixtures. Using high-resolution solution NMR experiments (COSY, TOCSY, and HMQC), all of the 1H resonances have been assigned in a model mixture. Then, intermolecular NOEs derived from 2D NOESY and ROESY spectra have revealed the molecular organization in mixed aggregates, and 1H line broadenings observed upon addition of paramagnetic Mn2+ ion have shown the distribution of polar groups at the aggregate surface. In a complementary fashion, QLS has been used to analyze the size, size distribution, and possible shape of the aggregates. Together, the NMR and QLS results argue for a rodlike model of the fat digestive aggregates and a (preliminary) discoid model for fatty acid transport aggregates. These models should advance a molecular-level understanding of the processes of fat digestion and fatty acid transport, respectively.;QLS methods have been applied to deduce the 2.5--9 nm hydrodynamic radii and discoid shape for mixed phospholipid bicelles with a ratio of dimyristoylphosphatidycholine (DMPC) to dihexanoylphosphatidylcholine (DHPC) of 0.167--2.0. This determination provides the first direct physical evidence indicating the retention of a bilayer structure in isotropic bicelle solutions, which have been proposed as membrane-mimetic media for structural studies of peptides and proteins.;Finally, the chain order and conformation of several phospholipid/cholesterol aqueous dispersions have been evaluated using magic angle spinning (MAS) NMR spectroscopy. A series of MAS semi-solid NMR measurements, including 1H sideband intensities, 13C chemical shift changes, and 2D spin-echo variable-amplitude cross polarization (SEVACP) were made in order to compare different phospholipids (DMPC, bovine sphingomyelin (BSM), and synthetic SM) and the effects of cholesterol on these membranes. Several conclusions emerge consistently from these experiments: the DMPC membrane is more rigid and ordered than SM; the addition of CHL makes each of the membranes more ordered, but DMPC is more sensitive than SM and the saturated acyl chain of BSM is more sensitive than the unsaturated acyl chain; a possible hydrogen bonding system exists in pure BSM membranes, but it may be disrupted in the presence of CHL.
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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.
