Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J21: Lipid and Insulating Bilayers |
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Sponsoring Units: DBP Chair: Jurgen Kurths, University of Potsdam Room: LACC 409A |
Tuesday, March 22, 2005 11:15AM - 11:27AM |
J21.00001: New Dendritic Lipids for Improved Gene Delivery by Cationic Liposome-DNA Complexes Kai Ewert, Heather M. Evans, Ayesha Ahmad, Nathan F. Bouxsein, Alexandra Zidovska, Cyrus R. Safinya Cationic Liposome-DNA (CL-DNA) complexes are widely used in non-viral gene delivery, including clinical trials, but their efficiency still requires optimization. Membrane charge density is a universal parameter for transfection with lamellar CL-DNA complexes (Lin AJ et al., \textit{Biophys. J.} 2003; \textbf{84}: 3307; Ahmad A et al., \textit{J. Gene Med.}, accepted). Newly synthesized lipids with dendritic headgroups, based on an ornithine scaffold, have headgroup charges of +4e to +16e. These lipids form lamellar complexes if the headgroup charge is small or the fraction of dendritic lipid in the membrane (in mixtures with DOPC) is low. Higher contents of highly charged lipids exhibit a novel phase of CL-DNA complexes, whose structure was determined by synchrotron x-ray diffraction. Cylindrical micelles of lipid are arranged on a hexagonal lattice, with DNA rods placed around them in the interstices. Complexes with this structure are highly transfecting, preventing the previously observed drop in transfection efficiency at very high membrane charge densities. Funded by NIH GM-59288. [Preview Abstract] |
Tuesday, March 22, 2005 11:27AM - 11:39AM |
J21.00002: Interaction Between Two Nonuniform and Flexible Bio-Interfaces Y.S. Jho, G. Park, C.S. Chang, M.W. Kim, P. Pincus One of fundamental interactions between charged bio-interfaces is the Coulomb interaction. The Coulomb interaction at nano- scale is different from that in a conventional scale due to proximity between charged particles. The attraction between two uniformly charged surfaces with same sign has been well known in a strongly coupled system. However surface charges in a real biological system are not uniformly distributed but rather discretely. We have found that the non-uniformity makes a stronger correlation of bulk counter ions to surface charges and induces stronger attractive pressure between two interfaces. Furthermore we have investigated the effect of the bio-interface flexibility on the pressure between two interfaces as a function of coupling parameter and distance for a large coupling parameter. Surface flexibility allows the surface ions to respond to counter ions. As a consequence, surface reforms to minimize total energy. Numerical simulations and theoretical analysis will be presented. [Preview Abstract] |
Tuesday, March 22, 2005 11:39AM - 11:51AM |
J21.00003: Fluctuations spectrum of passive and active giant vesicles measured by contour analysis. Jacques P\'ecr\'eaux, Hans-G\"unther D\"obereiner, Jacques Prost, Jean-Fran\c{c}ois Joanny, Patricia Bassereau We have developed a new method of contour analysis using phase contrast microscopy on giant vesicles [1]. Our set-up allows an accurate detection at video rate, and a direct comparison with theory in a planar geometry. We have been able to measure directly fluctuations spectra. For pure lipid vesicles, we measure bending rigidities corresponding to those of the literature. Our technique has also been extended to non-equilibrium membranes. We have set up a protocol to prepare giant vesicles containing bacteriorhodopsine[2], a light- activated protons pump. When the protein is pumping this system is a simple model of active membrane. We have measured the fluctuation spectra of these active liposomes. As a first analysis, our results cannot be explained by actual active membranes theory [4] and are not in agreement with micropipette experiments [3-4].\\[4pt] [1] J.P\'{e}cr\'{e}aux et al. (2004) Eur. Phys. J. E 13(3): 277-290.\\[0pt] [2] P. Girard, J.P\'{e}cr\'{e}aux et al (2004), Biophys. J. 87: 419-429.\\[0pt] [3] J.-B. Manneville et al. (1999), Phys. Rev. Lett. 82: 4356-4359.\\[0pt] [4] J.-B. Manneville et al. (2001), Phys. Rev. E 64(2): 021908. [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:03PM |
J21.00004: Small-angle neutron scattering study of lipid bilayers of magneto-vesicles Wilfred Ngwa, Kezheng Chen, Weili Luo, P. Thiyagarajan, A. Raghavan We present results from a small-angle neutron scattering (SANS) study of two types of magneto-vesicles (MVs): dioleoylphosphatidylcholine (DOPC) vesicles containing citrate-coated magnetic nanoparticles and those containing oleic-acid-coated magnetic particles. By using a polydisperse core shell model, these MVs were found to have similar sizes as their original vesicles without magnetic particles and their bilayer thicknesses to be consistent with unilamellar structure. [Preview Abstract] |
Tuesday, March 22, 2005 12:03PM - 12:15PM |
J21.00005: Shape Transformation of Fluctuating Vesicles Filled with a Ferrofluid Emulsion Zhang Tao, Wang Yafei, Hu Gang By transferring inverse double emulsion (O/W/O) droplets from an oil phase into a water phase we have assembled asymmetric vesicles containing monodisperse submicron-sized emulsion droplets, which are made of an oil-based ferrofluid. Under a magnetic field the submicron-sized ferrofluid droplets trapped inside flexible vesicles form chain structures, which depend on the size and the shape of vesicles. The formation of chains of trapped ferrofluid droplets can also induce shape changes in fluctuating vesicles. We examine the metastable shapes of lipid vesicles manipulated by an external magnetic field. The responsive vesicles provide a model system to study the topological and rheological properties of biological membranes. The equilibrium shapes and stability of the vesicles under various ionic strengths are also studied. [Preview Abstract] |
Tuesday, March 22, 2005 12:15PM - 12:27PM |
J21.00006: Electrostatically driven spatial patterns at supported lipid membrane junctions Raghuveer Parthasarathy, Paul A. Cripe, Jay T. Groves We have recently shown that mobile, membrane-bound proteins sandwiched at simple, cell-free junctions between lipid bilayers can organize themselves into micron-scale spatial patterns. This pattern formation is mechanical in origin, a consequence of the coupling of the lateral mobility of the proteins and inter-membrane adhesion forces. We find that these mechanically driven protein patterns can electrostatically generate patterns of charged membrane lipids. Measuring the magnitude of the electrostatic interaction as a function of lipid composition and ionic strength, and quantitatively analyzing the interplay between thermodynamics and electrostatics via a Poisson-Boltzmann approach, we are able to determine the charge densities and surface potentials of the components of our junctions -- properties that are difficult or impossible to measure by other means. Surprisingly, the electrostatic potential of the proteins is a minor factor in the lipid reorganization; the protein size and its modulation of the junction topography play the dominant role in driving the electrostatic patterns. [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 12:39PM |
J21.00007: Thermotropic liquid crystalline properties of amphotropic branched glycolipids Guangxun Liao, Kelly Zewe, Jessica Hagerty, Rauzah Hashim, Antal Jakli Glycolipids are amphotropic liquid crystals forming lyotropic liquid crystals in aqueous solutions and thermotropic liquid crystals in their dry form. We report studies of six different branched glycolipids: four maltoside and two glucoside lipids in their dry form. Optical birefringence, electrical conductivity, DSC, and dielectric spectroscopy measurements were employed to characterize the phase structures of the materials. In general they exhibit a wide ($>$100$^{o}$C) mesophase (smectic, columnar) range with low (0.01-0.04) birefringence. They have large (60-120) dielectric susceptibility mainly proportional to the number of polar sugar heads. Depending on the temperature the relaxation frequency of the susceptibility varies from $<$100Hz to $>$1MHz, mainly determined by the hydrogen bonding between the polar sugar heads. Interestingly in heating the materials with long hydrophobic chains show optically isotropic phase between the smectic and columnar phases. Such a situation when more phases appear in heating than cooling has never been observed in other thermotropic liquid crystals. [Preview Abstract] |
Tuesday, March 22, 2005 12:39PM - 12:51PM |
J21.00008: Membrane Simulations Over Long Length and Time Scales Lawrence Lin, Frank Brown We present a simulation algorithm for the dynamical evolution of lipid bilayers over long length and time scales. The membrane is treated as an elastic sheet with bending energy and surface tension and includes hydrodynamic coupling to the surrounding solvent and thermal fluctuations. The method we have developed allows for arbitrary external forces acting on the membrane and is particularly useful for studying many biological processes inaccessible to detailed atomistic simulations. Using this method, we have studied the repulsive interaction between the cytoskeleton and the membrane and its effect on thermal height fluctuations. We present results on the above application, but focus on recent work involving nonthermal fluctuations in membranes due to the activity of protein pumps embedded in the surface. We quantify the influence of these pumps on the height fluctuations in the membrane and discuss the results. [Preview Abstract] |
Tuesday, March 22, 2005 12:51PM - 1:03PM |
J21.00009: Kinetics of rupture of a lipid bilayer under tension, with and without peptides in solution Pierre-Alexandre Boucher, Bela Joos, Martin Zuckermann The rupture of fluid membrane vesicles with a steady ramp of micropipette suction has been shown to produce a distribution of breakage tensions. The width and mean of the distribution increases significantly with tension rate (E. Evans et al. Biophys. J. vol. 85, p. 2342 (2003)). Starting from a lattice model which incorporates the essential features of the lipid bilayers held together with hydrophobic forces (Phys. Rev. E vol. 67, no. 051908 (2003)), and developing it to handle varying tension rates, we reproduce the essential features of the experimental results. In essence we show that the rupture kinetics are driven for all tension rates by the nucleation and growth of pores. The role of peptides in solution that can adsorb and insert themselves into the bilayer is also considered. Parameters relevant to various peptides and bilayers are used to explore the different possible scenarios that can occur, including recent experiments. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:15PM |
J21.00010: Microtubule – Cationic Liposomes Assemblies: Pathways to the Formation of Lipid-Protein Tubular Complexes Uri Raviv, Daniel Needleman, Kai Ewert, Youli Li, Herbert Miller, Leslie Wilson, Cyrus Safinya The self-assembly of microtubules and charged membranes has been studied, using X-ray diffraction and electron microscopy. Polyelectrolyte lipid complexes (PLC) usually form structures where the lipid phase acts as the template, when the polyelectrolyte curvature (Cp) is much larger than the membrane spontaneous curvature (Co). When Cp approaches Co, as in microtubules, two new structures emerge. Depending on conditions, vesicles either adsorb onto the microtubule, forming a ‘beads on a rod’ structure, or undergo a wetting transition, coating the microtubule, which now forms the template. Tubulin rings next coat the microtubule-lipid assembly, forming a lipid protein tubular complex (LPTC). The ‘beads on a rod’ structure is a non-templated, kinetically trapped assembly state. The kinetic energy barrier between the two states depends on the membrane bending rigidity and charge density. The LPTC is the ground state of the system. Finally we make a connection to earlier studies and describe the assembly pathways of PLC as a function of polyelectrolyte curvature, membrane bending rigidity and charge density. This project is supported by NIH GM-59288, NSF DMR- 0203755, CTS-0404444. U.R. is supported by the HFSPO fellowship. [Preview Abstract] |
Tuesday, March 22, 2005 1:15PM - 1:27PM |
J21.00011: Temperature Effect on Transport Dynamics of a Cationic Molecule across an anionic Liposome Joon Heon Kim, Mahn Won Kim By using second harmonic generation (SHG), we have studied the transport dynamics of cationic triphenylmethane dyes across anionic liposome bilayers. Because the square root of SH signal is proportional to the difference between the surface density of dye molecules on both sides of the bilayers, the time dependence of the SH signal provides nondestructive and in-situ information on the transport of these dyes across liposome bilayers. In this experiment, we measured the time dependence of SH signal as a function of temperature and dye concentration. The temperature dependence of the transport rate follows the Arrhenius equation. We found that activation energy is about 1 eV and independent of dye concentration. This indicates that the charge interaction plays an important role for the transport. Furthermore, we observed some interesting phenomena related with dye concentration dependence of the transport dynamics. [Preview Abstract] |
Tuesday, March 22, 2005 1:27PM - 1:39PM |
J21.00012: Oxygen Transport Across Space-Filling Biological Membranes Chen Hou, Peter Pfeifer Space-filling fractal surfaces play a fundamental role in how organisms function and in how structure determines function at various levels. In this project we developed an efficient and powerful algorithm, rope-walk algorithm, for solving diffusion equations of transport of species across the space-filling fractal surface. We performed analytic computations of the oxygen current across the alveolar membranes in the lung, as a function of diffusion coefficient and membrane permeability, using the rope-walk algorithm, without adjustable parameters. The analytic calculation identifies the four cases as sharply delineated screening regimes and finds that the lung operates in the partial-screening regime, close to the transition to no screening, and in the no-screening regime, for respiration at rest and in exercise respectively. The gas exchange satisfies six criteria of optimal design: maximum current; minimum waste of surface area; minimum permeability; maximum fault tolerance; minimum waiting time and maximum current increase when going from rest to exercise. This extraordinary, multiply optimized performance is a direct consequence of the space-filling membrane architecture. [Preview Abstract] |
Tuesday, March 22, 2005 1:39PM - 1:51PM |
J21.00013: Dielectric behaviors of polydisperse cell suspensions C.T. Yam, J.P. Huang, K.W. Yu It is of technological importance to separate various cells which differ from one another in their dielectric properties. For instance, living cells have different conductivity from that of dead cells resulting in polydisperse cell suspensions. As a theoretical model, we consider a bidisperse suspension in which two different types of spherical biological cells are dispersed in a host medium, subject to an external ac electric field. The Clausius-Mossotti factors of the cells with isotropic, lossless dielectric membrane and with an intrinsic dispersion due to the presence of mobile hydrophobic ions within the plasma membrane have been given by Roth and Dignam [1]. A dielectric dispersion spectral representation (DDSR) is employed to express the Clausius-Mossotti factors of the two types of spherical particles as a series of sub-dispersions [2]. With DDSR, the characteristic frequencies and the corresponding dispersion magnitudes of the various sub-dispersions are determined for the individual particles in suspension [3,4]. We will report the effects of medium conductivity and volume fraction on the dielectric dispersion spectra. [1]. J. Roth and M. J. Dignam, J. Opt. Soc. Am. 63, 308 (1973). [2]. J. Lei, J. T. K. Wan, K. W. Yu, H. Sun, Phys. Rev. E 64, 012903 (2001). [3]. J. P. Huang, K. W. Yu, G. Q. Gu, Phys. Rev. E 65, 021401 (2002). [4]. L. Gao, J. P. Huang, K. W. Yu, Phys. Rev. E 67, 021910 (2003). [Preview Abstract] |
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