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Oak Ridge, TN, United States

Marquardt D.,Brock University | Williams J.A.,Indiana University - Purdue University Indianapolis | Kucerka N.,National Research Council Canada | Atkinson J.,Brock University | And 6 more authors.
Journal of the American Chemical Society | Year: 2013

We show evidence of an antioxidant mechanism for vitamin E which correlates strongly with its physical location in a model lipid bilayer. These data address the overlooked problem of the physical distance between the vitamin's reducing hydrogen and lipid acyl chain radicals. Our combined data from neutron diffraction, NMR, and UV spectroscopy experiments all suggest that reduction of reactive oxygen species and lipid radicals occurs specifically at the membrane's hydrophobic-hydrophilic interface. The latter is possible when the acyl chain "snorkels" to the interface from the hydrocarbon matrix. Moreover, not all model lipids are equal in this regard, as indicated by the small differences in vitamin's location. The present result is a clear example of the importance of lipid diversity in controlling the dynamic structural properties of biological membranes. Importantly, our results suggest that measurements of aToc oxidation kinetics, and its products, should be revisited by taking into consideration the physical properties of the membrane in which the vitamin resides. © 2013 American Chemical Society.

Armstrong C.L.,McMaster University | Haussler W.,TU Munich | Seydel T.,Laue Langevin Institute | Katsaras J.,Oak Ridge National Laboratory | And 4 more authors.
Soft Matter | Year: 2014

Lipid dynamics in the cholesterol-rich (40 mol%) liquid-ordered (l o) phase of dimyristoylphosphatidylcholine membranes were studied using neutron spin-echo and neutron backscattering. Recent theoretical and experimental evidence supports the notion of the liquid-ordered phase in phospholipid membranes as a locally structured liquid, with small ordered 'domains' of a highly dynamic nature in equilibrium with a disordered matrix [S. Meinhardt, R. L. C. Vink and F. Schmid, Proc. Natl. Acad. Sci. U. S. A., 2013, 110(12), 4476-4481, C. L. Armstrong et al., PLoS One, 2013, 8(6), e66162]. This local structure was found to have a pronounced impact on the membranes' dynamical properties. We found that the long-wavelength dynamics in the liquid-ordered phase, associated with the elastic properties of the membranes, were faster by two orders of magnitude as compared to the liquid disordered phase. At the same time, collective nanoscale diffusion was significantly slower. The presence of a soft-mode (a slowing down) in the long-wavelength dispersion relationship suggests an upper size limit for the ordered lipid domain of ≈220 Å. Moreover, from the relaxation rate of the collective lipid diffusion of lipid-lipid distances, the lifetime of these domains was estimated to be about 100 nanoseconds. © 2014 the Partner Organisations.

Marquardt D.,Brock University | Williams J.A.,Indiana University - Purdue University Indianapolis | Kinnun J.J.,Indiana University - Purdue University Indianapolis | Kucerka N.,National Research Council Canada | And 7 more authors.
Journal of the American Chemical Society | Year: 2014

Using data obtained from different physical techniques (i.e., neutron diffraction, NMR and UV spectroscopy), we present evidence which explains some of the conflicting and inexplicable data found in the literature regarding α-tocopherol's (aToc's) behavior in dimyristoyl phosphatidylcholine (di-14:0PC) bilayers. Without exception, the data point to aToc's active chromanol moiety residing deep in the hydrophobic core of di-14:0PC bilayers, a location that is in stark contrast to aToc's location in other PC bilayers. Our result is a clear example of the importance of lipid species diversity in biological membranes and importantly, it suggests that measurements of aToc's oxidation kinetics, and its associated byproducts observed in di-14:0PC bilayers, should be reexamined, this time taking into account its noncanonical location in this bilayer. © 2013 American Chemical Society.

Marquardt D.,University of Graz | Kucerka N.,Joint Institute for Nuclear Research | Kucerka N.,Comenius University | Wassall S.R.,Indiana University - Purdue University Indianapolis | And 5 more authors.
Chemistry and Physics of Lipids | Year: 2016

It is well known that cholesterol modifies the physical properties of lipid bilayers. For example, the much studied liquid-ordered L o phase contains rapidly diffusing lipids with their acyl chains in the all trans configuration, similar to gel phase bilayers. Moreover, the L o phase is commonly associated with cholesterol-enriched lipid rafts, which are thought to serve as platforms for signaling proteins in the plasma membrane. Cholesterol's location in lipid bilayers has been studied extensively, and it has been shown - at least in some bilayers - to align differently from its canonical upright orientation, where its hydroxyl group is in the vicinity of the lipid-water interface. In this article we review recent works describing cholesterol's location in different model membrane systems with emphasis on results obtained from scattering, spectroscopic and molecular dynamics studies. © 2016 Elsevier Ireland Ltd.

Egami T.,Joint Institute for Neutron science | Egami T.,University of Tennessee at Knoxville | Egami T.,Oak Ridge National Laboratory
JOM | Year: 2010

Liquids and glasses have been well known to human kind for millennia. And yet major mysteries remain in the behavior of glasses and liquids at the atomic level, and identifying the microscopic mechanisms that control the properties of glasses is one of the most challenging unsolved problems in physical sciences. For this reason, applying simplistic approaches to explain the behavior of metallic glasses can lead to serious errors. On the other hand because metallic glasses are atomic glasses with relatively simple structure, they may offer better opportunities to advance our fundamental understanding on the nature of the glass. The difficulties inherent to the problem and some recent advances are reviewed here. © 2010 TMS.

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