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Title: Water and Lipid Bilayers

 [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
DOE Contract Number:
Resource Type:
Country of Publication:
United States

Citation Formats

Nickels, Jonathan D, and Katsaras, John. Water and Lipid Bilayers. United States: N. p., 2015. Web. doi:10.1007/978-3-319-19060-0_3.
Nickels, Jonathan D, & Katsaras, John. Water and Lipid Bilayers. United States. doi:10.1007/978-3-319-19060-0_3.
Nickels, Jonathan D, and Katsaras, John. 2015. "Water and Lipid Bilayers". United States. doi:10.1007/978-3-319-19060-0_3.
title = {Water and Lipid Bilayers},
author = {Nickels, Jonathan D and Katsaras, John},
abstractNote = {},
doi = {10.1007/978-3-319-19060-0_3},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2015,
month = 1

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  • Using neutron diffraction the authors studied the incorporation of small hydrophobic compounds into bilayers consisting of phosphatidylcholine (PC) and cholesterol. They were found to be localized in a narrow band at the center of the hydrocarbon region, between the two halves of the bilayer. The structures formed by introduction of the compounds are therefore intercalated structures with the long axis of the intercalated molecules lying in the plane of the bilayer. The authors worked with several bilayers which differed by the length of the hydrocarbon chain of the PC. The quality of the localization depended on the presence of cholesterol,more » the water content and the PC chain length.« less
  • Our goal is to understand the structure and dynamics of water, in its different phases, at the interfaces between these phases, and in confined and heterogeneous environments. To this end, linear and nonlinear vibrational spectroscopy is playing a very important role. We have developed techniques for calculating spectroscopic observables, and then used our results to analyze and interpret experiment.
  • A study was undertaken of the effect of monovalent cations (Li/sup +/, Na/sup +/, K/sup +/) on the dielectric constant (epsilon) of the water-lipid interface of unilamellar phosphatidylcholine (PC) vesicles, i.e., the ester carbonyl oxygen region of the PC molecules or the neighborhood of the oxygen atoms of the phosphorylcholine moiety. epsilon was determined by reacting the free radical 1,1-diphenyl-2-picrylhydrazyl with ..cap alpha..-tocopherol incorporated in the lipid vesicles. The results are consistent with a decrease of epsilon (LiCl: 35.5 to 29.5; NaCl: 34 to 29; KCl: 33 to 29) as the concentration of the salts in the solvent media increasesmore » from 0.025 to 0.5 M. These effects can be rationalized in terms of dielectric saturation at the water-lipid interface brought about by ion-induced local electric fields. In the unilamellar PC vesicles the effect of the ions on epsilon follows the sequence K/sup +/ > Na/sup +/ > Li/sup +/ which contrasts strikingly with what happens in the liquid state where this is Li/sup +/ > Na/sup +/ > K/sup +/. These effects are related to the degree of hydration of the dissociated ions at the water-lipid interface which must differ in a considerable way from that in the liquid state. 43 references, 5 figures, 2 tables.« less
  • Potential of mean force (PMF) profiles and position-dependent diffusion coefficients of Na + and K + are calculated to elucidate the translocation of ions through a cyclic peptide nanotube, composed of 8 × cyclo[-(D-Leu-Trp) 4-] rings, in water and in hydrated DMPC bilayers. The PMF profiles and PMF decomposition analysis for the monovalent cations show that favorable interactions of the cations with the CPN as well as the lipid bilayer and dehydration free energy penalties are two major competing factors which determine the free energy surface for ion transport through CPNs both in water and lipid bilayers, and that themore » selectivity of CPNs to cations mainly arises from favorable interaction energies of cations with CPNs and lipid bilayers that are more dominant than the dehydration penalties. Calculations of the position-dependent diffusion coefficients and dynamic friction kernels of the cations indicate that the dehydration process along with the molecular rearrangements occurring outside the channel and the coupling of the ion motions with the chain-structured water movements inside the channel lead to decrease of the diffusion coefficients far away from the channel entrance and also reduced coefficients inside the channel. Here the PMF and diffusivity profiles for Na + and K + reveal that the energetics of ion transport through the CPN are governed by global interactions of ions with all the components in the system while the diffusivity of ions through the channel is mostly determined by local interactions of ions with the confined water molecules inside the channel. Comparison of Na + and K + ion distributions based on overdamped Brownian dynamics simulations based on the PMF and diffusivity profiles with the corresponding results from molecular dynamics shows good agreement, indicating accuracy of the Bayesian inference method for determining diffusion coefficients in this application. In addition this work shows that position-dependent diffusion coefficients of ions are required to explain the dynamics and conductance of ions through the CPN properly.« less