[25] Monte Carlo simulations of membranes: Phase transition of small unilamellar dipalmitoylphosphatidylcholine vesicles

Sugár, István P.; Biltonen, Rodney L.; Mitchard, Neil

doi:10.1016/s0076-6879(94)40064-4

Cited by 51 publications

(81 citation statements)

References 57 publications

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“…The simplest, Ising-like models assume that a lipid can be in two states -a gel state and a fluid state -with an interaction parameter indicating the balance between gelÀliquid, gelÀgel, and liquidÀliquid interactions. 35 This parameter can be optimized to reproduce the experimentally observed heat capacity curve. 36 There exist a host of refinements to this lattice-based approach, allowing for the description of the pretransition and the main transition as well as many-component bilayers.…”

Section: Articlementioning

confidence: 99%

Understanding the Phase Behavior of Coarse-Grained Model Lipid Bilayers through Computational Calorimetry

et al. 2012

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We study the phase behavior of saturated lipids as a function of temperature and tail length for two coarse-grained models: the soft-repulsive model typically employed with dissipative particle dynamics (DPD) and the MARTINI model. We characterize the simulated transitions through changes in structural properties, and we introduce a computational method to monitor changes in enthalpy, as is done experimentally with differential scanning calorimetry. The lipid system experimentally presents four different bilayer phasessubgel, gel, ripple, and fluidand the DPD model describes all of these phases structurally while MARTINI describes a single orderÀdisorder transition between the gel and the fluid phases. Given both models' varying degrees of success in displaying accurate structural and thermodynamic signatures, there is an overall satisfying extent of agreement for the coarse-grained models. We also study the lipid dynamics displayed by these models for the various phases, discussing this dynamics with relation to fidelity to experiment and computational efficiency.

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Section: Articlementioning

confidence: 99%

Understanding the Phase Behavior of Coarse-Grained Model Lipid Bilayers through Computational Calorimetry

et al. 2012

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“…5 a and c, Lower). The heat capacity profiles shown are actually calculated from a two-dimensional Ising model (30) involving two individual lipid states (ordered and fluid), with the melting process described by Monte-Carlo simulations (2,31). Curvature is introduced by constraining the relative populations of the two lipid states (which have different molecular areas) to Heat capacity traces of a 10 mM DMPG dispersion under various ionic strength conditions (in a 2 mM Hepes, 1 mM EDTA, pH 7.5 buffer; the top trace was measured in distilled water).…”

Section: Modeling the Transition Behavior Between Two Membrane Segmentsmentioning

confidence: 99%

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

Schneider

Marsh

Jahn

et al. 1999

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

120

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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“…If the cooperativity parameter is greater than zero, molecules tend to form clusters; when the cooperativity parameter is equal to zero, cooperativity between molecules vanishes. In the case where the cooperativity parameter is below zero, the system will tend to bring molecules of opposite states in contact [16]. Figure 1.…”

Section: Modeling Order-disorder Transition In Low-density Lipoproteinmentioning

confidence: 99%

“…This data collection entails recording the number of molecules in disordered state N i and the number of unlike nearest-neighbor contacts N si . Averaging N i and N si values and obtaining enthalpy from (3) allows us to calculate the heat capacity using fluctuation-dissipation theorem [16]:…”

Section: Modeling Order-disorder Transition In Low-density Lipoproteinmentioning

confidence: 99%

Modeling order-disorder transition in Low-Density Lipoprotein

Antonijevic

Lancaster

Starobin

2014

2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society

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Abstract-Low Density Lipoproteins (LDL) undergo a reversible order-disorder thermal transition close to biological temperature due to cooperative melting of the cholesteryl esters (CE) in the core of the LDL particle. We have noticed that chain-chain interactions between CE molecules are responsible for the stability of the ordered smectic phase; thus, we formulated a simple "coarse-grained" two-state model to describe the melting process. In this model only nearest neighbor interactions are allowed. On the basis of these assumptions we performed Metropolis Monte Carlo (MC) simulation in order to obtain the heat capacity curve. The resulting profile reveals well-known features of the systems with a finite size.

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[25] Monte Carlo simulations of membranes: Phase transition of small unilamellar dipalmitoylphosphatidylcholine vesicles

Cited by 51 publications

References 57 publications

Understanding the Phase Behavior of Coarse-Grained Model Lipid Bilayers through Computational Calorimetry

Understanding the Phase Behavior of Coarse-Grained Model Lipid Bilayers through Computational Calorimetry

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

Modeling order-disorder transition in Low-Density Lipoprotein

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