Transformation Diagrams for the Collapse of a Phospholipid Monolayer

Rugonyi, Sandra; Smith, Ethan C.; Hall, Stephen B.

doi:10.1021/la049081t

Cited by 18 publications

(15 citation statements)

References 35 publications

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“…[43][44][45] Access to high π requires compression faster than the maximum rate of collapse. 46 More graduated effects on the kinetics of collapse, such as the dispersion of coexisting phases, may therefore determine which films with fluid regions can reach the high π where they become metastable.…”

Section: Discussionmentioning

confidence: 99%

Distribution of Coexisting Solid and Fluid Phases Alters the Kinetics of Collapse from Phospholipid Monolayers

Yan

Hall

2006

J. Phys. Chem. B

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To determine how coexistence of liquid-expanded (LE) and tilted-condensed (TC) phases in phospholipid monolayers affects collapse from the air/water interface, we studied binary films containing dioleoyl phosphatidylcholine-dipalmitoyl phosphatidylcholine (DPPC) mixtures between 10 and 100% DPPC. Previously published results established that this range of compositions represents the LE-TC coexistence region at the equilibrium spreading pressure of 47 mN/m. When held at 49.5 mN/m on a captive bubble, the extent of total collapse fit with the LE area predicted by the phase diagram. The kinetics of collapse, however, when normalized for changes in the LE area, slowed with increasing mole fraction of DPPC. Surface area expressed as stretched exponential functions of time yielded an Avrami exponent that decreased from 1 for the homogeneously LE film to 0.3 for DPPC ≥ 70%. Microscopic studies showed that the largest changes in kinetics occurred when either alterations of the initial composition or the process of collapse induced the films to cross the percolation threshold, so that the LE phase became divided into isolated domains. Our results show that although coexisting solid and fluid phases collapse to extents that are independent, the kinetics of collapse, corrected for differences in LE area, depend on the distribution of the two phases.

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Section: Discussionmentioning

confidence: 99%

Distribution of Coexisting Solid and Fluid Phases Alters the Kinetics of Collapse from Phospholipid Monolayers

Yan

Hall

2006

J. Phys. Chem. B

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“…Following any dynamic compression, including those at surface tensions above σ e where collapse does not occur, viscoelastic relaxation produces a decaying change in area. 35 That process, however, usually lasts less than tens of minutes 2,4 and produces changes in area that are quite limited. Experimental results for DPPC-dchol monolayers at constant σ show an initial rapid decrease in area, followed by a slower decrease at rates that diminish for more than 12 h (Figure 2).…”

Section: Discussionmentioning

confidence: 99%

Kinetics for the Collapse of Trilayer Liquid-Crystalline Disks from a Monolayer at an Air−Water Interface

2005

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Unlike surfactants considered in previous studies, when phosphatidylcholine (PC) monolayers collapse at constant surface tension to form a 3D bulk phase, surface area decreases at rates that slow. The different kinetics could result from collapse by a distinct mechanism. Rather than the transfer of molecules all along the interface between the monolayer and bulk phase, PC films can collapse by the folding and subsequent sliding of a bilayer over the monolayer. By this mechanism, molecules can transfer to collapsed trilayers through a locus of constant size. In this article, we use the theory of nucleation and growth to show analytically that during collapse, the area can decrease at rates that decelerate when each individual structure grows through a region of fixed dimensions. We also show that binary films of 30% dihydrocholesterol (dchol) and dipalmitoyl phosphatidylcholine (DPPC), which have previously been shown to form a homogeneous monolayer from which trilayer disks grow through a point, collapse with rates of area decay that slow, in agreement with our analytical expressions.

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“…If these aggregates can readily respread at the interface upon decrease of the monolayer surface density, then the collapse is reversible; otherwise, it leads to irreversible loss of material from the interface. Interestingly, the mechanism of monolayer collapse and the collapse surface tension also depend on the rate of increase of the monolayer surface density (15), which reflects the speed of lateral compression. At high rates, a monolayer in a liquid state can be supercompressed (14) into a metastable state and thus achieve a low surface tension.…”

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The molecular mechanism of lipid monolayer collapse

Baoukina

Monticelli

Risselada

et al. 2008

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

255

253

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Lipid monolayers at an air-water interface can be compressed laterally and reach high surface density. Beyond a certain threshold, they become unstable and collapse. Lipid monolayer collapse plays an important role in the regulation of surface tension at the air-liquid interface in the lungs. Although the structures of lipid aggregates formed upon collapse can be characterized experimentally, the mechanism leading to these structures is not fully understood. We investigate the molecular mechanism of monolayer collapse using molecular dynamics simulations. Upon lateral compression, the collapse begins with buckling of the monolayer, followed by folding of the buckle into a bilayer in the water phase. Folding leads to an increase in the monolayer surface tension, which reaches the equilibrium spreading value. Immediately after their formation, the bilayer folds have a flat semielliptical shape, in agreement with theoretical predictions. The folds undergo further transformation and form either flat circular bilayers or vesicles. The transformation pathway depends on macroscopic parameters of the system: the bending modulus, the line tension at the monolayer-bilayer connection, and the line tension at the bilayer perimeter. These parameters are determined by the system composition and temperature. Coexistence of the monolayer with lipid aggregates is favorable at lower tensions of the monolayerbilayer connection. Transformation into a vesicle reduces the energy of the fold perimeter and is facilitated for softer bilayers, e.g., those with a higher content of unsaturated lipids, or at higher temperatures.lung surfactant ͉ bilayer reservoir ͉ course grain ͉ vesicle budding ͉ molecular dynamics L ipid molecules are insoluble in both polar and apolar media because of their amphipathic nature. At polar-apolar interfaces, they form monomolecular films that reduce the surface tension. Lipid monolayers form the main structural component (Ϸ97% by weight) of lung surfactant at the gas-exchange interface in the lung alveoli (1) and constitute the outer layer of tear film in the eyes (2). The properties of lipid monolayers vary with their surface density (3). For example, the higher the density, the lower is the resulting surface tension at the interface. At a certain very high surface density, however, a further reduction of the surface tension is not possible: the monolayers become unstable at the interface and collapse (4) (see scheme in Fig. 1). Besides being of fundamental interest for surface science, lipid monolayer collapse is crucial for maintaining low surface tension at the gas-exchange interface in the lungs during breathing (5).Collapse is characterized by loss of material from the interface and can proceed through different pathways. The modes of collapse and the surface tension at which collapse occurs depend on the molecular composition of the monolayer and on temperature (6-13), which determine the morphology and material properties of the monolayer. Although lipid monolayers in the liquid state do not usually ...

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Transformation Diagrams for the Collapse of a Phospholipid Monolayer

Cited by 18 publications

References 35 publications

Distribution of Coexisting Solid and Fluid Phases Alters the Kinetics of Collapse from Phospholipid Monolayers

Distribution of Coexisting Solid and Fluid Phases Alters the Kinetics of Collapse from Phospholipid Monolayers

Kinetics for the Collapse of Trilayer Liquid-Crystalline Disks from a Monolayer at an Air−Water Interface

The molecular mechanism of lipid monolayer collapse

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