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1.
C.W. Maier A. Behrisch A. Kloboucek D.A. Simson R. Merkel 《The European physical journal. E, Soft matter》2001,6(4):273-276
We studied biomembrane adhesion using the micropipet aspiration technique. Adhesion was caused by contact site A, a laterally
mobile and highly specific cell adhesion molecule from Dictyostelium discoideum, reconstituted in lipid vesicles of DOPC (L-α-dioleoylphosphatidylcholine) with an addition of 5 mol % DOPE-PEG2000 (1,2-diacyl-sn-glycero-3-phosphatidylethanolamine-N-[poly(ethyleneglycol) 2000]). The “fuzzy” membrane mimics the cellular
plasma membrane including the glycocalyx. We found adhesion and subsequent receptor migration into the contact zone. Using
membrane tension jumps to probe the equation of state of the two-dimensional “gas” of bound receptor pairs within the contact
zone, we found strong, attractive lateral interactions.
Received 16 February 2001 相似文献
2.
Highly oriented solid-supported lipid membranes in stacks of controlled number N ≃ 16 (oligo-membranes) have been prepared by spin-coating using the uncharged lipid model system 1,2-dimyristoyl-sn-glycero-3-phosphocholine
(DMPC). The samples have been immersed in aqueous polymer solutions for control of osmotic pressure and have been studied
by X-ray reflectivity. The bilayer structure and fluctuations have been determined by modelling the data over the full q-range. Thermal fluctuations are described using the continuous smectic Hamiltonian with the appropriate boundary conditions
at the substrate and at the free surface of the stack. The resulting fluctuation amplitudes and the pressure-distance relation
are discussed in view of the inter-bilayer potential. 相似文献
3.
We consider surfaces with disordered charge distribution. The disorder can be caused by mobile charges, as for example in
mixed lipid bilayers, or by weakly charged surfaces where charge regulation takes place (e.g. carboxyl groups). Using Monte-Carlo
simulation methods we find for quenched as well as annealed disordered charge distributions counterion densities close to
the surface that are significantly larger than for ordered regularly spaced surface ions. Our field-theoretic results agree
well with results obtained from Monte-Carlo simulations of the system. Furthermore, we obtain expressions for the effective
interaction between charged colloids and charged rods close to a charged surface and discuss the effect of the surface-ion
mobility and polarization charges on the interaction. In general, polarization effects as well as surface-ion mobility lead
to a weakening of the effective interaction between charged objects. 相似文献
4.
We present here a neutron reflectivity study of the influence of an alternative electric field on a supported phospholipid
double bilayer. We report for the first time a reproducible increase of the fluctuation amplitude leading to the complete
unbinding of the floating bilayer. Results are in good agreement with a semi-quantitative interpretation in terms of negative
electrostatic surface tension. 相似文献
5.
We present a phase field model on buckling membranes to analyze phase separation and budding on soft membranes. By numerically
integrating dynamic equations, it turns out that the formation of caps is greatly influenced by the presence of a little excess
area due to the surface area constraint. When cap-shaped domains are created, domain coalescence is mainly observed not between
domains with same budding directions, but between domains with opposite budding directions, because the bending energy between
two domains is larger in the former case. Although we do not introduce spontaneous curvature like Helfrich model, we obtain
some suggestions related to the slow dynamics of the phase separation on vesicles. 相似文献
6.
The density of the elastic energy of a deformed membrane in a liquid state is calculated. The thermodynamic equilibrium of
its different parts is taken into account. The shape equation of a closed membrane is deduced. The quantity which keeps its
value, when the variations of the energy of the system are calculated, is not the area of the deformed membrane, but its area
in the flat tension free state. Because of this, additional terms appear in the second variation around the stable state.
The case of a lipid bilayer and its fluctuations is examined for both free and blocked exchange of molecules between the monolayers,
comprising the bilayer.
Received 4 February 2002 / Received in final form 15 April 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: bivas@issp.bas.bg 相似文献
7.
Inclusions embedded in lipid membranes undergo a mediated force, due to the tendency of the membrane to relax its excess of
elastic energy. In this paper we determine the exact shape of a two-dimensional vesicle hosting two different inclusions,
and we analyse how the inclusion conformation influences the mediated interaction. We find non-trivial equilibrium configurations
for the inclusions along the hosting membrane, and we derive the complete phase diagram of the mediated interaction. In particular,
we find a non-vanishing mediated force even when the distance between the inclusions is much greater than their size. Our
model can be applied to describe the mediated interactions of parallel, elongated inclusions embedded in three-dimensional
membranes.
Received 22 October 2001 and Received in final form 8 March 2002 相似文献
8.
Giahi A El Alaoui Faris M Bassereau P Salditt T 《The European physical journal. E, Soft matter》2007,23(4):431-437
In view of recent theories of “active” membranes, we have studied multilamellar phospholipid membrane stacks with reconstituted
transmembrane protein bacteriorhodopsin (BR) under different illumination conditions by X-ray scattering. The light-active
protein is considered as an active constituent which drives the system out of equilibrium and is predicted to change the collective
fluctuation properties of the membranes. Using X-ray reflectivity, X-ray non-specular (diffuse) scattering, and grazing incidence
scattering, we find no detectable change in the scattering curves when changing the illumination condition. In particular
the intermembrane spacing d remains constant, after eliminating hydration-related artifacts by design of a suitable sample environment. The absence of
any observable non-equilibrium effects in the experimental window is discussed in view of the relevant parameters and recent
theories. 相似文献
9.
Sabín J Prieto G Ruso JM Sarmiento F 《The European physical journal. E, Soft matter》2007,24(2):201-210
We present a study of the fractal dimension of clusters of large unilamellar vesicles (LUVs) formed by egg yolk phosphatidylcholine
(EYPC), dimyristoylphosphocholine (DMPC) and dipalmitoylphosphocholine (DPPC) induced by Ca2+ . Fractal dimensions were calculated by application of two methods, measuring the angular dependency of the light scattered
by the clusters and following the evolution of the cluster size. In all cases, the fractal dimensions fell in the range from
2.1 to 1.8, corresponding to two regimes: diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation
(RLCA). Whereas DMPC clusters showed a typical transition from the RLCA to the DLCA aggregation, EYPC exhibited an unusual
behaviour, since the aggregation was limited for a higher concentration than the critical aggregation concentration. The behaviour
of DPPC was intermediate, with a transition from the RLCA to the DLCA regimes with cluster sizes depending on Ca2+ concentration. Studies on the reversibility of the aggregates show that EYPC and DPPC clusters can be re-dispersed by dilution
with water. DMPC does not present reversibility. Reversibility is evidence of the existence of secondary minima in the DLVO
potential between two liposomes. To predict these secondary minima, a correction of the DLVO model was necessary taking into
account a repulsive force of hydration. 相似文献
10.
Conditions for self-reproduction are sought for a growing vesicle with its growth defined by an exponential increase of vesicle
membrane area and by adequate flow of the solution across the membrane. In the first step of the presumed vesicle self-reproduction
process, the initially spherical vesicle must double its volume in the doubling time of the membrane area and, through the
appropriate shape transformations, attain the shape of two equal spheres connected by an infinitesimally thin neck. The second
step involves separation of the two spheres and relies on conditions that cause the neck to be broken. In this paper we consider
the first step of this self-reproduction process for a vesicle suspended in a solution whose solute can permeate the vesicle
membrane. It is shown that vesicle self-reproduction occurs only for certain combinations of the values of membrane hydraulic
and solute permeabilities and the external solute concentration, these quantities being related to the mechanical properties
of the membrane and the membrane area doubling time. The analysis includes also the relaxation of a perturbed system towards
stationary self-reproduction behavior and the case where the final shape consists of two connected spheres of different radii. 相似文献
11.
In this paper, we study the equilibrium properties of polymer chains end-tethered to a fluid membrane. The loss of conformational
entropy of the polymer results in an inhomogeneous pressure field that we calculate for Gaussian chains. We estimate the effects
of excluded volume through a relation between pressure and concentration. Under the polymer pressure, a soft surface will
deform. We calculate the deformation profile for a fluid membrane and show that close to the grafting point, this profile
assumes a cone-like shape, independently of the boundary conditions. Interactions between different polymers are also mediated
by the membrane deformation. This pair-additive potential is attractive for chains grafted on the same side of the membrane
and repulsive otherwise.
Received 20 April 2000 相似文献
12.
Mader MA Ez-Zahraouy H Misbah C Podgorski T 《The European physical journal. E, Soft matter》2007,22(4):275-280
A simple 2D model of deformable vesicles tumbling in a shear under flow is introduced in order to
account for the main qualitative features observed experimentally as shear rates are increased.
The simplicity of the model allows for a full analytical
tractability while retaining the essential physical ingredients. The model reveals that the main axes of the vesicle
undergo oscillations which are coupled to the vesicle orientation in
the flow. The model reproduces and sheds light on the main novel features reported in
recent experiments [M. Mader et al., Eur. Phys. J. E. 19, 389
(2006)], namely that both coefficients A and B that enter the
Keller-Skalak equation, dψ/dt = A+Bcos(2 ψ) (ψ is
the vesicle orientation angle in the shear flow), undergo a collapse
upon increasing shear rate. 相似文献
13.
14.
Tilt of hydrocarbon chains of lipid molecules with respect to membrane plane is commonly considered to characterize the internal
structure of a membrane in the crystalline state. However, membranes in the liquid state can also exhibit tilt resulting from
packing constraints imposed on the lipid molecules in diverse biologically relevant structures such as intermediates of membrane
fusion, pores in lipid bilayers and others. We analyze the energetics of tilt in liquid membranes and its coupling with membrane
bending. We consider three contributions to the elastic energy: constant tilt, variation of tilt along the membrane surface
and membrane bending. The major assumption of the model is that the core of a liquid membrane has the common properties of
an elastic continuum. We show that the variation of tilt and membrane bending are additive and that their energy contributions
are determined by the same elastic coefficient: the Helfrich bending modulus, the modulus of Gaussian curvature and the spontaneous
curvature known from previous studies of pure bending. The energy of a combined deformation of bending and varying tilt is
determined by an effective tensor accounting for the two factors. In contrast, the deformation of constant tilt does not couple
with bending and its contribution to the elastic energy is determined by an independent elastic constant. While accurate determination
of this constant requires additional measurements, we estimate its value using a simplified approach. We discuss the relationships
between the obtained elastic Hamiltonian of a membrane and the previous models of membrane elasticity.
Received 10 February 2000 and Received in final form 19 June 2000 相似文献
15.
J. Nissen S. Gritsch G. Wiegand J.O. Rädler 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):335-344
We report on the wetting behavior of phospholipid membranes on solid surfaces immersed in aqueous solution. Using fluorescence
microscopy, the spreading velocity of fluid bilayers advancing from a lipid source is investigated. The kinetic spreading
coefficient was measured as a function of temperature for pure DMPC membranes and as a function of charge density and cholesterol
content for binary membranes. A theoretical model for the membrane flow is presented, which takes into account the liquid
crystalline bilayer architecture of the lipid membrane. The spreading power results from the membrane-solid VdW interaction
and is dissipated in hydrodynamic shear flow as well as by inter-monolayer friction within the bilayer. The frictional drag
causes a dynamic tension gradient in the spreading membrane, which is manifested by a single exponential decay of the fluorescence
intensity profile along the spreading direction. Obstacles are shown to act as pinning centers deforming the advancing line
interface. However, no depinning was observed, since the centers are circumflown without abrupt relaxation.
Received 6 November 1998 相似文献
16.
F. Pincet S. Cribier E. Perez 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):127-130
Many experiments done on neutral lipid bilayers in pure water show weak repulsions. These weak forces prevent vesicles from
adhering and are generally overcome by adding some salt in the aqueous medium. They also appear as stray repulsions in surface
forces measurements made on lipid bilayers. Using a surface forces apparatus in pure water and in salt solution, we have measured
the forces between two stearoyl-oleoyl-phosphatidyl-choline (SOPC) bilayers and between two dimiristoyl-phosphatidyl-ethanolamine
(DMPE) bilayers. The results show that the repulsions are due to a small amount of negative charges coming from impurities
in SOPC. This was quantitatively confirmed by electrophoretic measurements. There are 3 times less charges in the case of
DMPE layers. The effect of these charges which is negligible at high salt concentration may significantly affect the adhesion
energy and behaviour of neutral lipid bilayers between 0 and salt.
Received 18 December 1998 相似文献
17.
T. Salditt C. Li A. Spaar U. Mennicke 《The European physical journal. E, Soft matter》2002,7(2):105-116
We have investigated the structure of solid-supported, multilamellar membranes by X-ray reflectivity. The density profile
is obtained by fitting the full q-range to a model using the bilayer Fourier coefficients as fitting parameters. The effect of hydration and the substrate
boundary condition are discussed in view of the well-known Landau-Peierls effect and its implications for structure determination.
The resulting bilayer density profile agrees remarkably well with previously published data of a molecular dynamics (MD) simulation
for 1,2-oleoyl-palmitoyl-sn-glycero-3-phosphocholine (OPPC).
Received 1 October 2001 and Received in final form 21 December 2001 相似文献
18.
Fluctuation spectra of fluid compound membrane systems are calculated. The systems addressed contain two (or more) almost
parallel membranes that are connected by harmonic tethers or by a continuous, harmonic confining potential. Additionally,
such a compound system can be attached to a supporting substrate. We compare quasi-analytical results for tethers with analytical
results for corresponding continuous models and investigate under what circumstances the discrete nature of the tethers actually
influences the fluctuations. A tethered, supported membrane pair with similar bending rigidities and stiff tethers can possess
a nonmonotonic fluctuation spectrum with a maximum. A nonmonotonic spectrum with a maximum and a minimum can occur for an
either free or supported membrane pair of rather different bending rigidities and for stiff tethers. Typical membrane displacements
are calculated for supported membrane pairs with discrete or continuous interacting potentials. Thereby an estimate of how
close the constituent two membranes and the substrate typically approach each other is given. For a supported membrane pair
with discrete or continuous interactions, the typical displacements of each membrane are altered with respect to a single
supported membrane, where those of the membrane near the substrate are diminished and those of the membrane further away are
enhanced. 相似文献
19.
Mader MA Vitkova V Abkarian M Viallat A Podgorski T 《The European physical journal. E, Soft matter》2006,19(4):389-397
The dynamics of giant lipid vesicles under shear flow is experimentally investigated. Consistent with previous theoretical
and numerical studies, two flow regimes are identified depending on the viscosity ratio between the interior and the exterior
of the vesicle, and its reduced volume or excess surface. At low viscosity ratios, a tank-treading motion of the membrane
takes place, the vesicle assuming a constant orientation with respect to the flow direction. At higher viscosity ratios, a
tumbling motion is observed in which the whole vesicle rotates with a periodically modulated velocity. When the shear rate
increases, this tumbling motion becomes increasingly sensitive to vesicle deformation due to the elongational component of
the flow and significant deviations from simpler models are observed. A good characterization of these various flow regimes
is essential for the validation of analytical and numerical models, and to relate microscopic dynamics to macroscopic rheology
of suspensions of deformable particles, such as blood. 相似文献
20.
R. Capovilla C. Chryssomalakos J. Guven 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):163-166
We examine the equilibria of a rigid loop in the plane, characterized by an energy functional quadratic in the curvature,
subject to the constraints of fixed length and fixed enclosed area. Whereas the only non self-intersecting equilibrium corresponding
to the fixed length constraint is the circle, the area constraint gives rise to distinct equilibria labeled by an integer.
These configurations exhibit self-intersections and bifurcations as the area is reduced. In addition, not only can the Euler-Lagrange
equation be integrated to provide a quadrature for the curvature but the embedding itself can be expressed as a local function
of the curvature. Perturbations connecting equilibria are shown to satisfy a first order ODE which is readily solved. Analytical
expressions for the energy as a function of the area are obtained in the limiting regimes.
Received 18 October 2001 / Received in final form 31 May 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: capo@fis.cinvestav.mx
RID="b"
ID="b"e-mail: chryss@nuclecu.unam.mx
RID="c"
ID="c"e-mail: jemal@nuclecu.unam.mx 相似文献