The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform

Virginie Coste - One of the best experts on this subject based on the ideXlab platform.

  • Raft-like domain formation in large unilamellar vesicles probed by the fluorescent phospholipid analogue, C12NBD-PC.
    Biochimica et Biophysica Acta, 2006
    Co-Authors: Virginie Coste, Nicolas Puff, Daniel Lockau, Peter J Quinn, Miglena I. Angelova
    Abstract:

    The liquid-ordered/Disordered-Phase domain co-existence in large unilamellar vesicle membranes consisting of phosphatidylcholine:sphingomyelin (2:1) with different amounts of cholesterol has been examined using a concentration-dependent self-quenching of a single reporter molecule, C12NBD-PC. A temperature-dependent decrease of fluorescence intensity was associated with the expected formation and increase of l o -Phase membrane fraction in the vesicles. The result is consistent with exclusion of the fluorescent probe from the liquid-ordered Phase which partitions preferentially into the liquid-Disordered Phase membrane domains. This leads to an increase of the local concentration of fluorophore in the liquid-Disordered Phase and a decrease of the quantum yield. This effect was used to obtain a quantitative estimation of the fraction of the vesicle membrane occupied by the liquid-ordered Phase, Φ o , as a function of temperature and cholesterol content between 0 and 45 mol%. The value of Φ o was related to the assumed partition coefficient k p of probe between liquid-ordered/Disordered Phases. For large unilamellar vesicles containing 20 and 4 mol% cholesterol and probe, respectively, with k p  = 0 (probe completely excluded from liquid-ordered Phase), Φ o  = 0.16 and with k p  = 0.2, Φ o  = 0.2. The results are relevant to the action of detergent in the fractionation of detergent-resistant membrane from living cells.

  • Ordering of lipid bilayer domains in large unilamellar vesicles probed by the fluorescent phospholipid analogue, C12NBD-PC
    Biochimica et Biophysica Acta:Biomembranes, 2006
    Co-Authors: Virginie Coste, Nicolas Puff, Daniel Lockau, Peter Quinn, Miglena Angelova
    Abstract:

    The liquid-ordered/Disordered-Phase domain co-existence in large unilamellar vesicle membranes consisting of phosphatidylcholine:sphingomyelin (2:1) with different amounts of cholesterol has been examined using a concentration-dependent self-quenching of a single reporter molecule, C12NBD-PC. A temperature-dependent decrease of fluorescence intensity was associated with the expected formation and increase of lo-Phase membrane fraction in the vesicles. The result is consistent with exclusion of the fluorescent probe from the liquid-ordered Phase which partitions preferentially into the liquid-Disordered Phase membrane domains. This leads to an increase of the local concentration of fluorophore in the liquid-Disordered Phase and a decrease of the quantum yield. This effect was used to obtain a quantitative estimation of the fraction of the vesicle membrane occupied by the liquid-ordered Phase, Φo, as a function of temperature and cholesterol content between 0 and 45 mol%. The value of Φo was related to the assumed partition coefficient kp of probe between liquid-ordered/Disordered Phases. For large unilamellar vesicles containing 20 and 4 mol% cholesterol and probe, respectively, with kp = 0 (probe completely excluded from liquid-ordered Phase), Φo = 0.16 and with kp = 0.2, Φo = 0.2. The results are relevant to the action of detergent in the fractionation of detergent-resistant membrane from living cells.

V. K. Malinovsky - One of the best experts on this subject based on the ideXlab platform.

A. Muramatsu - One of the best experts on this subject based on the ideXlab platform.

  • Quantum Disordered Phase in a Doped Antiferromagnet
    Europhysics Letters (EPL), 1995
    Co-Authors: C. Kübert, A. Muramatsu
    Abstract:

    A quantitative description of the transition to a quantum Disordered Phase in a doped antiferromagnet is obtained with a U(1) gauge theory, where the gap in the spin-wave spectrum determines the strength of the gauge fields. They mediate an attractive long-range interaction whose possible bound states correspond to charge-spin separation and pairing.

  • Quantum Disordered Phase in a doped antiferromagnet
    Journal of Low Temperature Physics, 1995
    Co-Authors: C. Kübert, A. Muramatsu
    Abstract:

    A quantitative description of the transition to a quantum Disordered Phase in a doped antiferromagnet is obtained for the long-wavelength limit of the spin-fermion model, which is given by the O(3) non-linear {sigma} model, a free fermionic part and current-current interactions. By choosing local spin quantization axes for the fermionic spinor we show that the low-energy limit of the model is equivalent to a U(1) gauge theory, where both the bosonic and fermionic degrees of freedom are minimally coupled to a vector gauge field. Within a large-N expansion, the strength of the gauge fields is found to be determined by the gap in the spin-wave spectrum, which is dynamically generated. The explicit doping dependence of the spin-gap is determined as a function of the parameters of the original model. As a consequence of the above, the gauge-fields mediate a long-range interaction among dopant holes and S-1/2 magnetic excitations only in the quantum Disordered Phase. The possible bound-states in this regime correspond to charge-spin separation and pairing.

  • Quantum Disordered Phase in an antiferromagnet via doping
    Physica C: Superconductivity, 1994
    Co-Authors: C. Kübert, A. Muramatsu
    Abstract:

    Abstract A quantitative description of the transition to a quantum Disordered Phase in a doped antiferromagnet is obtained for the long-wavelength limit of the spin-fermion model, which is given by the O(3) nonlinear σ model, a free fermionic part and current-current interactions as obtained by Shraiman and Siggia for the t − J model. By choosing local spin quantization axes for the fermions we show that the low-energy limit of the model is equivalent to a U(1) gauge theory, where both the bosonic and fermionic degrees of freedom are coupled minimally to a vector gauge field. Within a large-N expansion, the strength of the gauge fields is found to be determined by the gap in the spin-wave spectrum, which is dynamically generated. The explicit doping dependence of the spin-gap is determined as a function of the parameters of the original model. As a consequence of the above, the gauge-fields mediate a confining interaction among dopant holes and S - 1 2 magnetic excitations only in the quantum Disordered Phase. The possible bound-states in this regime correspond to charge-spin separation and pairing.

Luis A. Bagatolli - One of the best experts on this subject based on the ideXlab platform.

  • Direct Visualization of the Lateral Structure of Porcine Brain Cerebrosides/POPC Mixtures in Presence and Absence of Cholesterol
    Biophysical Journal, 2009
    Co-Authors: Matthias Fidorra, Thomas Heimburg, Luis A. Bagatolli
    Abstract:

    We studied the thermal behavior of membranes composed of mixtures of natural cerebrosides (from porcine brain) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with and without cholesterol, using differential scanning calorimetry, Fourier transform infrared spectroscopy, and confocal/multiphoton fluorescence microscopy. The POPC/cerebroside mixture display solid ordered/liquid Disordered Phase coexistence in a broad range of compositions and temperatures in agreement with previous results reported for POPC/(bovine brain)cerebrosides. The observed Phase coexistence scenario consists of elongated, micrometer-sized cerebroside-rich solid ordered domains that span the bilayer, embedded in a POPC-rich liquid Disordered Phase. The data obtained from differential scanning calorimetry and Fourier transform infrared spectroscopy was in line with that obtained in the microscopy experiments for the binary mixture, except at very high cerebroside molar fractions (0.8–0.9) were some differences are observed. Cholesterol incorporation exerts strong changes on the lateral organization of POPC/porcine brain cerebroside membranes. At intermediate cholesterol concentrations (10–25 mol %) the solid ordered/liquid Disordered Phase coexistence scenario gradually transform to a solid ordered/liquid ordered one. Above 25 mol % of cholesterol two distinct regions with liquid ordered Phase character are visualized in the membrane until a single liquid ordered Phase forms at 40 mol % cholesterol. The observed cholesterol effect largely differs from that reported for POPC/porcine brain ceramide, reflecting the impact of the sphingolipids polar headgroup on the membrane lateral organization.

  • direct visualization of the lateral structure of porcine brain cerebrosides popc mixtures in presence and absence of cholesterol
    Biophysical Journal, 2009
    Co-Authors: Matthias Fidorra, Thomas Heimburg, Luis A. Bagatolli
    Abstract:

    We studied the thermal behavior of membranes composed of mixtures of natural cerebrosides (from porcine brain) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with and without cholesterol, using differential scanning calorimetry, Fourier transform infrared spectroscopy, and confocal/multiphoton fluorescence microscopy. The POPC/cerebroside mixture display solid ordered/liquid Disordered Phase coexistence in a broad range of compositions and temperatures in agreement with previous results reported for POPC/(bovine brain)cerebrosides. The observed Phase coexistence scenario consists of elongated, micrometer-sized cerebroside-rich solid ordered domains that span the bilayer, embedded in a POPC-rich liquid Disordered Phase. The data obtained from differential scanning calorimetry and Fourier transform infrared spectroscopy was in line with that obtained in the microscopy experiments for the binary mixture, except at very high cerebroside molar fractions (0.8–0.9) were some differences are observed. Cholesterol incorporation exerts strong changes on the lateral organization of POPC/porcine brain cerebroside membranes. At intermediate cholesterol concentrations (10–25 mol %) the solid ordered/liquid Disordered Phase coexistence scenario gradually transform to a solid ordered/liquid ordered one. Above 25 mol % of cholesterol two distinct regions with liquid ordered Phase character are visualized in the membrane until a single liquid ordered Phase forms at 40 mol % cholesterol. The observed cholesterol effect largely differs from that reported for POPC/porcine brain ceramide, reflecting the impact of the sphingolipids polar headgroup on the membrane lateral organization.

  • absence of fluid ordered fluid Disordered Phase coexistence in ceramide popc mixtures containing cholesterol
    Biophysical Journal, 2006
    Co-Authors: Matthias Fidorra, Lars Duelund, Chad Leidy, Adam Cohen Simonsen, Luis A. Bagatolli
    Abstract:

    The effect of temperature on the lateral structure of lipid bilayers composed of porcine brain ceramide and 1-palmitoyl 2-oleoyl-phosphatidylcholine (POPC), with and without addition of cholesterol, were studied using differential scanning calorimetry, Fourier transformed infrared spectroscopy, atomic force microscopy, and confocal/two-photon excitation fluorescence microscopy (which included LAURDAN generalized polarization function images). A broad gel/fluid Phase coexistence temperature regime, characterized by the presence of micrometer-sized gel-Phase domains with stripe and flowerlike shapes, was observed for different POPC/ceramide mixtures (up to ∼25 mol % ceramide). This observed Phase coexistence scenario is in contrast to that reported previously for this mixture, where absence of gel/fluid Phase coexistence was claimed using bulk LAURDAN generalized polarization (GP) measurements. We demonstrate that this apparent discrepancy (based on the direct comparison between the LAURDAN GP data obtained in the microscope and the fluorometer) disappears when the additive property of the LAURDAN GP function is taken into account to examine the data obtained using bulk fluorescence measurements. Addition of cholesterol to the POPC/ceramide mixtures shows a gradual transition from a gel/fluid to gel/liquid-ordered Phase coexistence scenario as indicated by the different experimental techniques used in our experiments. This last result suggests the absence of fluid-ordered/fluid-Disordered Phase coexistence in the ternary mixtures studied in contrast to that observed at similar molar concentrations with other ceramide-base-containing lipid mixtures (such as POPC/sphingomyelin/cholesterol, which is used as a canonical raft model membrane). Additionally, we observe a critical cholesterol concentration in the ternary mixtures that generates a peculiar lateral pattern characterized by the observation of three distinct regions in the membrane.

Martin J Zuckermann - One of the best experts on this subject based on the ideXlab platform.

  • A triangular lattice model for binary and ternary mixtures containing surfactants
    Journal of Physics: Condensed Matter, 1994
    Co-Authors: Mohamed Laradji, Hong Guo, Martin J Zuckermann
    Abstract:

    The Phase equilibria of ternary mixtures of water, oil and surfactants and binary mixtures of water and surfactants are studied using a triangular lattice-gas model that is an extension of the spin-1 Blume-Capel model with the addition of the orientational degrees of freedom for surfactants. The Phase diagram of the model is investigated via Monte Carlo simulations in conjunction with the extrapolation technique of Ferrenberg and Swendsen combined with the finite-size scaling method of Lee and Kosterlitz. Five Phases are found for ternary mixtures in the case of equal water and oil concentrations: a water-oil coexistence region, a lamellar Phase, a liquid crystalline Phase, which has the symmetry of a rhombic lattice, and an extended Disordered Phase, which is divided by a Lifshitz line into Disordered fluid and microemulsion regions. In the limiting case of a binary mixture of water and surfactants, we found a rich Phase diagram corresponding to a lamellar Phase, a hexagonal Phase and a Disordered Phase. which is again divided by a Lifshitz line into Disordered fluid and structured fluid regions. The latter can be considered as the analogue of the microemulsion found for the ternary systems.

  • Ordering dynamics of microscopic models with nonconserved order parameter of continuous symmetry
    Physical Review A, 1993
    Co-Authors: Zhengping Zhang, Ole G Mouritsen, Martin J Zuckermann
    Abstract:

    Numerical Monte Carlo temperature-quenching experiments have been performed on two threedimensional classical lattice models with continuous ordering symmetry: the Lebwohl-Lasher model [Phys. Rev. A 6, 426 (1972)] and the ferromagnetic isotropic Heisenberg model. Both models describe a transition from a Disordered Phase to an orientationally ordered Phase of continuous symmetry. The Lebwohl-Lasher model accounts for the orientational ordering properties of the nematic-isotropic transition in liquid crystals and the Heisenberg model for the ferromagnetic-paramagnetic transition in magnetic crystals