Freeze fracture electron microscopy of dilute lamellar and anomalous isotropic (L3) phases

Strey, R.; Jahn, Werner; Porte, G.; Bassereau, Patricia

doi:10.1021/la00101a003

Cited by 141 publications

(118 citation statements)

References 3 publications

(5 reference statements)

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“…8b). Such defects have been widely experimentally [25][26][27] and theoretically [28][29][30][31] studied. In particular, they appear to be precursors of the lamellar-to-sponge phase transition as a probable consequence of the evolution of the membrane elastic constants.…”

Section: Analysis: a Porous L α Phasementioning

confidence: 99%

Swelling kinetics of a compressed lamellar phase

Leng

Nallet

Roux

2001

The European Physical Journal E

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Abstract. We investigate how multilamellar vesicles prepared in a compressed state under flow return to equilibrium. The kinetics is studied by following the temporal evolution of the viscoelasticity after the shear is stopped. It exhibits a two-step relaxation whose slower stage is strongly affected by temperature. According to a simple model, the temperature-dependent permeability of the lamellar phase is deduced from the measurements. We propose to attribute the permeability to handle-like defects, and its temperature dependence to an increase of the defect density when the lamellar-to-sponge phase transition is approached.

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Section: Analysis: a Porous L α Phasementioning

confidence: 99%

Swelling kinetics of a compressed lamellar phase

Leng

Nallet

Roux

2001

The European Physical Journal E

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“…For details see ref. 16. Cryo-transmission This paper was submitted directly (Track II) to the PNAS office.…”

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Network formation of lipid membranes: Triggering structural transitions by chain melting

Schneider

Marsh

Jahn

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

121

130

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Phospholipids when dispersed in excess water generally form vesicular membrane structures. Cryo-transmission and freeze-fracture electron microscopy are combined here with calorimetry and viscometry to demonstrate the reversible conversion of phosphatidylglycerol aqueous vesicle suspensions to a three-dimensional structure that consists of extended bilayer networks. Thermodynamic analysis indicates that the structural transitions arise from two effects: (i) the enhanced membrane elasticity accompanying the lipid state fluctuations on chain melting and (ii) solventassociated interactions (including electrostatics) that favor a change in membrane curvature. The material properties of the hydrogels and their reversible formation offer the possibility of future applications, for example in drug delivery, the design of structural switches, or for understanding vesicle fusion or fission processes. Lipids may undergo a cooperative melting reaction linked to the loss in conformational order of the lipid chains (1). This transition is accompanied by a large change of the internal energy (or enthalpy) that can be studied by calorimetry. It has long been known that the melting profiles are influenced by secondary components, e.g., proteins (2), cholesterol, or anesthetics (3, 4). Phase diagrams of lipid mixtures usually are constructed as a function of the chemical potential of the components and the temperature (5). Another kind of possible transition involves changes in vesicular shape. These transitions have been studied in some detail by theoretical means, resulting in phase diagrams for vesicle structure as a function of the elastic constants (6, 7). Changes in these constants can explain theoretically the wealth of shapes of erythrocytes (8). There are therefore two kinds of phase diagrams found for lipid systems: one describing the calorimetric features of chain melting, mainly dependent on short-range cooperative events within the membrane plane, and the other describing transitions in shape and long-range order influenced by changes in the elastic constants.Although seemingly different features of a lipid system, the elastic constants and the heat capacity of the lipid membrane are related because they are coupled to thermodynamic fluctuations in the membrane properties (9). Maximum elasticity is achieved in the regime of ordered (gel)-fluid phase coexistence (10), which implies that close to the heat capacity maximum the elastic constants change markedly and as a consequence the membranes become more flexible. From this it is expected that changes in structural equilibria may be found close to the chain-melting transition.We demonstrate here thermodynamically how the structural changes couple to the chain melting. Large viscosity changes of dimyristoyl phosphatidylglycerol (DMPG) dispersions close to the calorimetric melting transition have been reported that are accompanied by marked changes in heat capacity, light scattering, and electrical conductance (11,12). The changes in viscosity suggest a change in the l...

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“…They contain structural defects that can be point-like or linear (dislocations). Unlike textural defects (e. g. focal conics), they are not visible in optical microscopy but they can be investigated using techniques such as FFEM (freeze-fracture electron microscopy) [1][2][3][4][5] For instance, in lamellar phases, three elementary point defects are possible: "pores", "necks", and "passages" [13]. Necks connect the non-polar medium (surfactant structure) ( fig.1a), pores (fig.1b) connect the polar medium (water), whereas passages join both media ( fig.1c).…”

mentioning

confidence: 99%

“…They contain structural defects that can be point-like or linear (dislocations). Unlike textural defects (e. g. focal conics), they are not visible in optical microscopy but they can be investigated using techniques such as FFEM (freeze-fracture electron microscopy) [1][2][3][4][5],SANS [6], spin-labeling [7], birefringence measurements [2,9], X-ray scattering [10,11], NMR [12], etc. However, these methods do not give much information about the defect topology.…”

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Diffusion Coefficients in a Lamellar Lyotropic Phase: Evidence for Defects Connecting the Surfactant Structure

Constantin

Oswald

2000

Phys. Rev. Lett.

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We measure diffusion coefficients in the lamellar phase of the nonionic binary system C12EO6/H2O using fluorescence recovery after photobleaching (FRAP). The diffusion coefficient across the lamellae shows an abrupt increase upon approaching the lamellar-isotropic phase transition. We interpret this feature in terms of defects connecting the surfactant structure. An estimation of the defect density and of the variation in defect energy close to the transition is given in terms of a simple model. PACS numbers: 61.30.Jf, 64.70.Md, 66.30.Jt Topological defects are very important in condensed matter. In solids, most of the defects are out of equilibrium and form during growth or plastic deformation. In soft matter, like liquid crystals, defects sometimes nucleate spontaneously in great number. In this case, they often announce the transition towards a phase of higher symmetry.Defective lamellar phases of lyotropic systems belong to this category. They contain structural defects that can be point-like or linear (dislocations). Unlike textural defects (e. g. focal conics), they are not visible in optical microscopy but they can be investigated using techniques such as FFEM (freeze-fracture electron microscopy) [1][2][3][4][5] For instance, in lamellar phases, three elementary point defects are possible: "pores", "necks", and "passages" [13]. Necks connect the non-polar medium (surfactant structure) ( fig.1a), pores (fig.1b) connect the polar medium (water), whereas passages join both media ( fig.1c). Screw dislocations are also frequent because their energy is low [14]. These defects also connect both media and their core may be filled with the polar or the non-polar medium.In this Letter we present a method of determining the topology of defects by monitoring the variation of the diffusion coefficients parallel D and perpendicularly D ⊥ to the director (normal to the layers) of fluorescent probes that are dissolved either in the polar medium or in the non-polar one.The system chosen is the lamellar phase of the lyotropic mixture of the non ionic surfactant C 12 EO 6 with water. Spin-labeling measurements [7] have shown the existence of highly curved defects, the density of which abruptly increases a few degrees before melting. Dislocation loops perpendicular to the layers have been observed in FFEM [1, 2] ,but they can only account for a small fraction of the total defect density. In the following we present experimental results showing the existence of point defects. We confirm the existence of pores [7], and we also show that necks appear close to the lamellarisotropic transition. We have first investigated the evolution of the diffusion coefficients for a fluorescent and hydrophobic dye. If D ⊥ (parallel to the layers) must not be significantly affected by the defects, D (across the layers), which is very small for a perfect structure (the molecule has to cross a water barrier), should dramatically increase if the defects connect the surfactant structure. We performed these measures on planar domains (director ...

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Freeze fracture electron microscopy of dilute lamellar and anomalous isotropic (L3) phases

Cited by 141 publications

References 3 publications

Swelling kinetics of a compressed lamellar phase

Swelling kinetics of a compressed lamellar phase

Network formation of lipid membranes: Triggering structural transitions by chain melting

Diffusion Coefficients in a Lamellar Lyotropic Phase: Evidence for Defects Connecting the Surfactant Structure

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