Thad Harroun

Publications (66) View all

• Article: The location and behavior of α‐tocopherol in membranes

  Jeffrey Atkinson, Thad Harroun, Stephen R. Wassall, William Stillwell, John Katsaras
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  ABSTRACT: Vitamin E (α-tocopherol) has long been recognized as the major antioxidant in biological membranes, and yet many structurally related questions persist of how the vitamin functions. For example, the very low levels of α-tocopherol reported for whole cell extracts question how this molecule can successfully protect the comparatively enormous quantities of PUFA-containing phospholipids found in membranes that are highly susceptible to oxidative attack. The contemporary realization that membranes laterally segregate into regions of distinct lipid composition (domains), we propose, provides the answer. We hypothesize α-tocopherol partitions into domains that are enriched in polyunsaturated phospholipids, amplifying the concentration of the vitamin in the place where it is most needed. These highly disordered domains depleted in cholesterol are analogous, but organizationally antithetical, to the well-studied lipid rafts. We review here the ideas that led to our hypothesis. Experimental evidence in support of the formation of PUFA-rich domains in model membranes is presented, focusing upon docosahexaenoic acid that is the most unsaturated fatty acid commonly found. Physical methodologies are then described to elucidate the nature of the interaction of α-tocopherol with PUFA and to establish that the vitamin and PUFA-containing phospholipids co-localize in non-raft domains.
  Molecular Nutrition & Food Research 04/2010; 54(5):641 - 651. · 4.30 Impact Factor
• Source

  Available from: John Katsaras

  Article: Ion distribution in multilayers of weak polyelectrolytes: A neutron reflectometry study.

  Oleh M Tanchak, Kevin G Yager, Helmut Fritzsche, Thad Harroun, John Katsaras, Christopher J Barrett
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  ABSTRACT: Neutron reflectometry was used to determine the distribution of salt ions and water in thin poly(acrylic acid) and poly(allylamine hydrochloride) polyelectrolyte multilayers assembled with and without salt. Increasing salt concentration reverses the exclusion of water from the substrate region, eventually leading to an asymmetric segregation of water near the substrate at high salt concentration. The counterions were found to localize near the substrate in films that were either assembled with salt or were exposed to salt solutions. In addition, the capping layer of the film was found to greatly influence the counterion distribution in the multilayer.
  The Journal of chemical physics 09/2008; 129(8):084901. · 3.09 Impact Factor
• Source

  Available from: John Katsaras

  Article: Effect of cations on the structure of bilayers formed by lipopolysaccharides isolated from Pseudomonas aeruginosa PAO1.

  Norbert Kucerka, Erzsebet Papp-Szabo, Mu-Ping Nieh, Thad A Harroun, Sarah R Schooling, Jeremy Pencer, Eric A Nicholson, Terry J Beveridge, John Katsaras
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  ABSTRACT: The asymmetric outer membrane of Gram-negative bacteria contains lipopolysaccharides (LPSs) which contribute significantly to the bacterium's surface properties and play a crucial role in regulating membrane permeability. We report on neutron diffraction studies performed on aligned, self-assembled bilayers of Na-, Ca-, and Mg-salt forms of LPS isolated from Pseudomonas aeruginosa PAO1. From the one-dimensional neutron scattering length density profiles we find that water penetrates Ca2+-LPS bilayers to a lesser extent than either Na+- or Mg2+-LPS bilayers. This differential water penetration could have implications as to how small molecules permeate the outer membrane of Gram-negative bacteria and, possibly, how nonlamellar phases are formed.
  The Journal of Physical Chemistry B 08/2008; 112(27):8057-62. · 3.70 Impact Factor
• Source

  Available from: John Katsaras

  Article: Water distribution in multilayers of weak polyelectrolytes.

  Oleh M Tanchak, Kevin G Yager, Helmut Fritzsche, Thad Harroun, John Katsaras, Christopher J Barrett
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  ABSTRACT: The water localization in thin polyelectrolyte multilayers assembled from poly(acrylic acid) and poly(allylamine hydrochloride) was investigated with neutron reflectivity in an atmosphere of controlled humidity and with bulk water. Water was found to be distributed asymmetrically within the multilayer and to localize preferentially at the polymer surface. The diffusion of water into the multilayer did not completely penetrate to the substrate, but instead there appeared to be an exclusion zone near the Si substrate. These results help to explain previous observations of anomalous water transport kinetics in weak polyelectrolyte systems.
  Langmuir 06/2006; 22(11):5137-43. · 4.19 Impact Factor
• Article: Vitamin E Responds to its Lipid Environment

  Justin A. Williams, Drew Marquardt, William Stillwell, Jeffrey Atkinson, Thad A. Harroun, Stephen R. Wassall
  Biophysical Journal 01/2011; 100:493. · 3.65 Impact Factor