Critical mixing in monomolecular films : pressure-composition phase diagram of a two-dimensional binary mixture

Hirshfeld, C.L.; Seul, Michael

doi:10.1051/jphys:0199000510140153700

Cited by 68 publications

(73 citation statements)

References 30 publications

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“…The DMPC/cholesterol monolayer (1:1 mol ratio) adopts a uniformly liquid-condensed phase,29 giving rise to the steep π – A isotherm shown in Figure 7A (solid isotherm on the right). The effect of incorporating 3 within the monolayer, however, is dramatic.…”

Section: Resultsmentioning

confidence: 99%

Self-Assembly and Lipid Interactions of Diacylglycerol Lactone Derivatives Studied at the Air/Water Interface

et al. 2008

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Synthetic diacylglycerol lactones (DAG-lactones) have been shown to be effective modulators of critical cellular signaling pathways. The biological activity of these amphiphilic molecules depends in part upon their lipid interactions within the cellular plasma membrane. This study explores the thermodynamic and structural features of DAG-lactone derivatives and their lipid interactions at the air/water interface. Surface-pressure/area isotherms and Brewster angle microscopy revealed the significance of specific side-groups attached to the terminus of a very rigid 4-(2-phenylethynyl) benzoyl chain of the DAG-lactones, which affected both the self-assembly of the molecules and their interactions with phospholipids. The experimental data highlight the formation of different phases within mixed DAG-lactone/phospholipid monolayers and underscore the relationship between the two components in binary mixtures of different mole ratios. Importantly, the results suggest that DAG-lactones are predominantly incorporated within fluid phospholipid phases rather than in the condensed phases that form, for example, by cholesterol. Moreover, the size and charge of the phospholipid headgroups do not seem to affect DAG-lactone interactions with lipids.

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Section: Resultsmentioning

confidence: 99%

Self-Assembly and Lipid Interactions of Diacylglycerol Lactone Derivatives Studied at the Air/Water Interface

et al. 2008

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“…Appropriate mixtures of dimyristoyl phosphatidylcholine (DMPC) and cholesterol (30)(31)(32) and DPPC-cholesterol (34,35) exhibit the same characteristics of a critical point, although at pressures well below the values at which remixing occurs here. Surfactant preparations, however, that contain the complete set of phospholipids are far from binary mixtures.…”

Section: Discussionmentioning

confidence: 99%

Neutral Lipids Induce Critical Behavior in Interfacial Monolayers of Pulmonary Surfactant

et al. 1998

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We have shown previously that lateral compression of pulmonary surfactant monolayers initially induces separation of two phases but that these remix when the films become more dense (1). In the studies reported here, we used fluorescence microscopy to examine the role of the different surfactant constituents in the remixing of the separated phases. Subfractions containing only the purified phospholipids (PPL), the surfactant proteins and phospholipids (SP&PL), and the neutral and phospholipids (N&PL) were obtained by chromatographic separation of the components in extracted calf surfactant (calf lung surfactant extract, CLSE). Compression of the different monolayers produced nonfluorescent domains that emerged for temperatures between 20 and 41°C at similar surface pressures 6-8 mN/m higher than values observed for dipalmitoyl phosphatidylcholine (DPPC), the most prevalent component of pulmonary surfactant. Comparison of the different preparations showed that the neutral lipid increased the total nonfluorescent area at surface pressures up to 25 mN/m but dispersed that total area among a larger number of smaller domains. The surfactant proteins also produced smaller domains, but they had the opposite effect of decreasing the total nonfluorescent area. Only the neutral lipids caused remixing. In images from static monolayers, the domains for N&PL dropped from a maximum of 26 ± 3% of the interface at 25 mN/m to 4 ± 2% at 30 mN/m, similar to the previously reported behavior for CLSE. During continuous compression through a narrow range of pressure and molecular area, in N&PL, CLSE, and mixtures of PPL with 10% cholesterol, domains became highly distorted immediately prior to remixing. The characteristic transition in shape and abrupt termination of phase coexistence indicate that the remixing caused by the neutral lipids occurs at or close to a critical point. † © 1999 American Chemical Society * To whom correspondence should be addressed at Mail Code OHSU, Portland,.. NIH Public Access Author ManuscriptBiochemistry. Author manuscript; available in PMC 2012 December 08. The phase behavior of biological phospholipid films and membranes may be important in at least two respects. First, the different physical characteristics of the different phases can alter processes such as lateral diffusion. Second, phase separation can maintain components in distinct compartments and provide a means of organizing biological processes (2). Both of these issues may be important for the function of pulmonary surfactant. This complex mix of lipids and proteins coats the thin liquid layer that lines the lung's alveolar air spaces. When compressed by decreasing alveolar surface areas during normal exhalation, the surfactant film achieves very high densities, well above equilibrium values. Measurements in situ show that the surfactant films lower the surface tension of the air-liquid interface to very low levels (3) and in doing so stabilize the alveoli. Only films with the physical characteristics of a highly ordered phase se...

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“…Epifluorescence microscopy and methods described previously (13,14) were used to observe coexisting liquid phases in the presence and absence of a field.…”

Section: Methodsmentioning

confidence: 99%

Electric field effect on cholesterol–phospholipid complexes

Radhakrishnan

McConnell

2000

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

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Monolayer mixtures of dihydrocholesterol and phospholipids at the air-water interface are used to model membranes containing cholesterol and phospholipids. Specific, stoichiometric interactions between cholesterol and some but not all phospholipids have been proposed to lead to the formation of condensed complexes. It is reported here that an externally applied electric field of the appropriate sign can destabilize these complexes, resulting in their dissociation. This is demonstrated through the application of an electric field gradient that leads to phase separations in otherwise homogeneous monolayers. This is observed only when the monolayer composition is close to the stoichiometry of the complex. The electric field effect is analyzed with the same mean field thermodynamic model as that used previously to account for pairs of upper miscibility critical points in these mixtures. The concentrations of dihydrocholesterol, phospholipid, and complex vary strongly and sometimes discontinuously in the monolayer membrane in the field gradient. The model is an approximation to a two-dimensional liquid in which molecules freely exchange between free and complexed form so that the chemical potentials are constant throughout the membrane. The calculations are illustrated for a complex of about 15 molecules, composed of 5 cholesterol molecules and 10 phospholipid molecules.monolayers ͉ membranes ͉ chemical activity ͉ phase separations ͉ sphingomyelin

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Critical mixing in monomolecular films : pressure-composition phase diagram of a two-dimensional binary mixture

Cited by 68 publications

References 30 publications

Self-Assembly and Lipid Interactions of Diacylglycerol Lactone Derivatives Studied at the Air/Water Interface

Self-Assembly and Lipid Interactions of Diacylglycerol Lactone Derivatives Studied at the Air/Water Interface

Neutral Lipids Induce Critical Behavior in Interfacial Monolayers of Pulmonary Surfactant

Electric field effect on cholesterol–phospholipid complexes

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