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- Hydration, Structure, and Molecular Interactions in the Head...Hydration, Structure, and Molecular Interactions in the Headgroup Region of Dioleoylphosphatidylcholine Bilayers: An Electron Spin Resonance Study
Biophysical Journal, Volume 85, Issue 6, 1 December 2003, Pages 4023-4040
Mingtao Ge and Jack H. Freed
AbstractThe relationship between bilayer hydration and the dynamic structure of headgroups and interbilayer water in multilamellar vesicles is investigated by electron spin resonance methods. Temperature variations of the order parameter of a headgroup spin label DPP-Tempo in DOPC in excess water and partially dehydrated (10wt % water) show a cusp-like pattern around the main phase transition, . This pattern is similar to those of temperature variations of the quadrupolar splitting of interbilayer DO in PC and PE bilayers previously measured by H NMR, indicating that the ordering of the headgroup and the interbilayer water are correlated. The cusp-like pattern of these and other physical properties around are suggestive of quasicritical fluctuations. Also, an increase (a decrease) in ordering of DPP-Tempo is correlated with water moving out of (into) interbilayer region into (from) the bulk water phase near the freezing point, . Addition of cholesterol lowers , which remains the point of increasing headgroup ordering. Using the small water-soluble spin probe 4-PT, it is shown that the ordering of interbilayer water increases with bilayer dehydration. It is suggested that increased ordering in the interbilayer region, implying a lowering of entropy, will itself lead to further dehydration of the interbilayer region until its lowered pressure resists further flow, i.e., an osmotic phenomenon.
Abstract | Full Text | PDF (259 kb) - Structure and Interactions of Fully Hydrated Dioleoylphospha...Structure and Interactions of Fully Hydrated Dioleoylphosphatidylcholine Bilayers
Biophysical Journal, Volume 75, Issue 2, 1 August 1998, Pages 917-925
Stephanie Tristram-Nagle, Horia I. Petrache and John F. Nagle
AbstractThis study focuses on dioleoylphosphatidylcholine (DOPC) bilayers near full hydration. Volumetric data and high-resolution synchrotron x-ray data are used in a method that compares DOPC with well determined gel phase dipalmitoylphosphatidylcholine (DPPC). The key structural quantity obtained is fully hydrated area/lipid =72.2±1.1Å at 30°C, from which other quantities such as thickness of the bilayer are obtained. Data for samples over osmotic pressures from 0 to 56 atmospheres give an estimate for the area compressibility of =188dyn/cm. Obtaining the continuous scattering transform and electron density profiles requires correction for liquid crystal fluctuations. Quantitation of these fluctuations opens an experimental window on the fluctuation pressure, the primary repulsive interaction near full hydration. The fluctuation pressure decays exponentially with water spacing, in agreement with analytical results for soft confinement. However, the ratio of decay length =5.8Å to hydration pressure decay length =2.2Å is significantly larger than the value of 2 predicted by analytical theory and close to the ratio obtained in recent simulations. We also obtain the traditional osmotic pressure versus water spacing data. Our analysis of these data shows that estimates of the Hamaker parameter and the bending modulus are strongly coupled.
Abstract | Full Text | PDF (165 kb) - Studies of Phospholipid Hydration by High-Resolution Magic-A...Studies of Phospholipid Hydration by High-Resolution Magic-Angle Spinning Nuclear Magnetic Resonance
Biophysical Journal, Volume 76, Issue 1, 1 January 1999, Pages 387-399
Zhe Zhou, Brian G. Sayer, Donald W. Hughes, Ruth E. Stark and Richard M. Epand
AbstractA sample preparation method using spherical glass ampoules has been used to achieve 1.5-Hz resolution in H magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of aqueous multilamellar dispersions of 1,2-dioleoyl--glycero-3-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl--glycero-3-phosphocholine (POPC), serving to differentiate between slowly exchanging interlamellar and bulk water and to reveal new molecular-level information about hydration phenomena in these model biological membranes. The average numbers of interlamellar water molecules in multilamellar vesicles (MLVs) of DOPC and POPC were found to be 37.5±1 and 37.2±1, respectively, at a spinning speed of 3kHz. Even at speeds as high as 9kHz, the number of interlamellar waters remained as high as 31, arguing against dehydration effects for DOPC and POPC. Both homonuclear and heteronuclear nuclear Overhauser enhancement spectroscopy (NOESY and HOESY) were used to establish the location of water near the headgroup of a PC bilayer. H NMR comparisons of DOPC with a lipid that can hydrogen bond (monomethyldioleoylphosphatidylethanolamine, MeDOPE) showed the following trends: 1) the interlamellar water resonance was shifted to lower frequency for DOPC but to higher frequency for MeDOPE, 2) the chemical shift variation with temperature for interlamellar water was less than that of bulk water for MeDOPE MLVs, 3) water exchange between the two lipids was rapid on the NMR time scale if they were mixed in the same bilayer, 4) water exchange was slow if they were present in separate MLVs, and 5) exchange between bulk and interlamellar water was found by two-dimensional exchange experiments to be slow, and the exchange rate should be less than 157Hz. These results illustrate the utility of ultra-high-resolution H MAS NMR for determining the nature and extent of lipid hydration as well as the arrangement of nuclei at the membrane/water interface.
Abstract | Full Text | PDF (199 kb) - …more
Copyright © 1985 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 47, Issue 2, 203-209, 1 February 1985
doi:10.1016/S0006-3495(85)83892-3
Research Article
Phospholipid surface bilayers at the air-water interface. I. Thermodynamic properties
K. Tajima and N.L. Gershfeld
Abstract
Dispersions of dimyristoylphosphatidylcholine (DMPC) in water spontaneously form a surface bilayer at the equilibrium air/water surface (Gershfeld, N. L., and K. Tajima, 1979, Nature [Lond.]. 279: 708–709). This phenomenon has now been demonstrated with dispersions of dioleoylphosphatidylcholine (DOPC), dipalmitoylphosphatidylcholine (DPPC), and with a mixture of DMPC and DOPC. Each of these dispersions forms a surface bilayer at a singularity in temperature that is a characteristic of the phospholipid. The surface bilayer formed by the lipid mixture is shown to have the same composition as the bulk liquid-crystal phase of the dispersion, and the surface components have identical partial molar entropies as the bulk lipid components. These properties indicate that the surface bilayer has the same structure as the bilayer in the liquid-crystal phase of the bulk dispersion.
