Abstract
Vitamin E behaves as an antioxidant and is well known for its protective properties of the lipid membrane. The most biologically active form of vitamin E in the human organism is α-tocopherol (aToc). Very recently (Marquardt, D.; et al. J. Am. Chem. Soc. 2014, 136, 203-210) it has been shown that aToc resides near the center of dimyristoylphosphatidylcholine (DMPC) bilayer, which is in stark contrast with other PC membranes, where aToc is located near the lipid-water interface. Here we report an unusual effect of this exceptional location of aToc on the dynamical behavior of DMPC membrane probed by incoherent elastic and quasielastic neutron scattering. For pure DMPC vesicles, elastic scan data show two step-like drops in the elastic intensity at 288 and 297 K, which correspond to the pre- and main phase transitions, respectively. However, inclusion of aToc into DMPC membrane inhibits the step-like elastic intensity drops, indicating a significant impact of aToc on the phase behavior of the membrane. This observation is supported by our differential scanning calorimetry data, which shows that inclusion of aToc leads to a significant broadening of the main phase transition peak, whereas the peak corresponding to the pretransition disappears. We have performed quasielastic neutron scattering (QENS) measurements on DMPC vesicles with various concentrations of aToc at 280, 293, and 310 K. We have found that aToc affects both the lateral diffusion and the internal motions of the lipid molecules. Below the main phase transition temperature inclusion of aToc accelerates both the lateral and the internal lipid motions. On the other hand, above the main phase transition temperature the addition of aToc restricts only the internal motion, without a significant influence on the lateral motion. Our results support the finding that the location of aToc in DMPC membrane is deep within the bilayer.
| Original language | English |
|---|---|
| Pages (from-to) | 154-163 |
| Number of pages | 10 |
| Journal | Journal of Physical Chemistry B |
| Volume | 120 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 14 2016 |
Funding
Experiments on HFBS at NCNR are supported in part by the National Science Foundation under Agreement No. DMR-1508249. Research conducted at ORNL''s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. We acknowledge lab support of the Center for Structural Molecular Biology funded by the Office of Biological and Environmental Research (ERKP291). This manuscript has been authored by UT-Battelle, LLC under Contract No. DEAC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). Certain commercial material suppliers are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.
| Funders | Funder number |
|---|---|
| DOE Public Access Plan | |
| Office of Basic Energy Sciences | |
| Office of Biological and Environmental Research | ERKP291, DEAC05-00OR22725 |
| Scientific User Facilities Division | |
| United States Government | |
| National Science Foundation | DMR-1508249 |
| U.S. Department of Energy | |
| National Institute of Standards and Technology | |
| NIST Center for Neutron Research |