Temperature and pressure dependent growth and morphology of DMPC/DSPC domains studied by Brewster angle microscopy

Arnold, Alexandre A.; Cloutier, Isabelle; Ritcey, Anna M.; Auger, Michèle

doi:10.1016/j.chemphyslip.2004.09.020

Cited by 15 publications

(8 citation statements)

References 60 publications

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“…Electrostatic repulsions cause formation of elongated structures that are often branched or dendritic in shape. A lower line tension causes an increased number of domains of smaller size to form [65]. The higher number of smaller sized domains observed in the presence of monovalent cations stems from increased disorder in the monolayer (i.e.…”

Section: Cation Identity and Salt Concentration Effects On The Surfacmentioning

confidence: 97%

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

Adams

Casper

Allen

2016

Journal of Colloid and Interface Science

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The effect of highly concentrated salt solutions of marine-relevant cations (Na(+), K(+), Mg(2+), and Ca(2+)) on Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC) was investigated by means of surface pressure-area isotherms, Brewster angle microscopy (BAM), and infrared reflection-absorption spectroscopy (IRRAS). It was found that monovalent cations and Mg(2+) have similar phase behavior, causing DPPC monolayers to expand, while Ca(2+) induces condensation. All cations disrupted the surface morphology at high cation concentration, resulting in decreased reflectivity from the monolayer. Monolayer refractive index was calculated from BAM image intensity in the liquid condensed phase and decreased with increasing cation concentration, which suggests that orientation of the alkyl chains change. Monovalent ions increase ordering of the alkyl chains, more than divalents, yet have little interaction with the DPPC headgroup. Mg(2+) induces gauche defects in the alkyl chain and increases headgroup hydration at low lipid coverage but increases chain ordering and dehydrates the headgroup at high lipid coverage. Ca(2+) orders alkyl chains and dehydrates the phosphate moiety, independent of lipid phase. At the highest salt concentration investigated, significant narrowing of the asymmetric PO2(-) vibrational mode occurs and is attributed to considerable dehydration of the DPPC headgroup.

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Section: Cation Identity and Salt Concentration Effects On The Surfacmentioning

confidence: 97%

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

Adams

Casper

Allen

2016

Journal of Colloid and Interface Science

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“…Equation 6 also indicates that nucleation and growth of domains are opposed by linear tension, being necessarily the formation of a nucleus of n large enough to overcome the second unfavorable term of the equation. This effect adds extra energy requirements for the enlargement of the lateral interface and the formation of a stable nucleus (29,31). The occurrence of compositional fluctuations necessary to form droplets of the new phase, large enough to overcome line tension, is a kinetically dependent process.…”

Section: Perimeter-activated Versus Area-activated Mechanism Of Actiomentioning

confidence: 99%

Sphingomyelinase acts by an area-activated mechanism on the liquid-expanded phase of sphingomyelin monolayers

Tullio

Maggio

Fanani

2008

Journal of Lipid Research

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We describe the localization of Alexa-488-labeled SMase in SM/ceramide (Cer) lipid monolayers containing segregated liquid-condensed (LC) Cer-enriched domains surrounded by a continuous liquid-expanded (LE) SMenriched phase. Langmuir-Schaefer films were made in order to visualize the labeled enzyme. Independently of initial conditions Alexa-SMase is preferably localized in the SMenriched LE phase and it is not enriched at the domain boundaries. A novel mechanism is proposed for the action of SMase, which can also explain the regulatory effect of the surface topography on the enzyme activity. The homogeneous enzymatic generation of Cer in the LE phase leads to a meta-stable, kinetically trapped, supersaturated mixed monolayer. This effect acts as driving force for the segregation of the Cer-enriched domain following classical nucleation mechanisms. Accordingly, the number and size of Cer-enriched domains are determined by the extent of Cer supersaturation in the LE phase rather than by the SMase local activity. The kinetic barrier for nucleation, for which a compositional gap of at least 53 mol% of Cer is necessary to reach a thermodynamically stable LC phase, can explain the lag time to reaching full catalytic activity. Altogether, the data support an "area-activated mechanism," in which the enzyme is homogeneously active over the LE surface. Phospholipases are a group of mostly water-soluble enzymes, widely spread in nature, that perform their catalytic activity at an interface, owing to the insoluble nature of their substrates (1). Several studies have equated "membrane defects," such as those arising from the coexistence of lipid domains in different physical states, with enhanced catalytic activity (2-8). In 1990, it was reported that the liquidexpanded (LE), liquid-condensed (LC) lateral interfaces (lipid domain borders) in a one-component monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) act as starting points for Naja naja phospholipase A 2 (PLA 2 ) catalytic activity (9). Dahmen-Levison, Brezesinski, and Mohwald (10) showed in lipid monolayers that the fluorescent-labeled PLA 2 preferably accumulates at the LC-LE interface of domains. Those results support the socalled perimeter-activated or border-activated mechanism, in which the enzyme must have physical contact with the domain boundary/membrane defect in order to become fully active and exerts its major catalytic action adsorbed to these linear interfaces (11). However, more recent studies (12) have demonstrated that fluorescein-labeled PLA 2 from Crotalus atrox was homogeneously distributed in 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and DPPC giant unilamellar vesicles when the lipids were in the LE state and preferentially localized in the LE phase at temperatures corresponding to the gel-fluid phase coexistence. The homogeneous distribution of PLA 2 on the membrane surface would support a mechanism by which the enzyme is fully active over the whole fluid surface (area-activated mechanism) but cannot adequately explain...

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“…Monolayers and bilayers of the binary mixture of dimyristoylphosphatidylcholine (DMPC) and distearoylphosphatidylcholine (DSPC) have been widely studied. − The lateral pressure−molecular area compression isotherm of DMPC at 23 °C shows a behavior expected for a liquid-expanded film while DSPC forms liquid-condensed films with a solid−solid phase transition at 25 mN m −1 . Mixed DSPC/DMPC monolayers and bilayers show nonideal behavior. − …”

Section: Introductionmentioning

confidence: 99%

Rheological Properties of a Two Phase Lipid Monolayer at the Air/Water Interface: Effect of the Composition of the Mixture

2010

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Many biologically relevant monolayers show coexistence of discrete domains of a long-range ordered condensed phase dispersed in a continuous, disordered, liquid-expanded phase. In this work, we determined the viscous and elastic components of the compressibility modulus and the shear viscosity of monolayers exhibiting phase coexistence with the aim at elucidating the contribution of each phase to the observed monolayer mechanical properties. To this purpose, mixed monolayers with different proportions of distearoylphosphatidylcholine (DSPC) and dimyristoylphosphatidylcholine (DMPC) were prepared and their rheological properties were analyzed. The relationship between the phase diagram of the mixture at 10 mN m(-1) and the rheological properties was studied. We found that the monolayer shear viscosity is highly dependent on the presence of domains and on the domain density. In turn, the monolayer compressibility is only influenced by the presence of domains for high domain densities. For monolayers that look homogeneous on the micrometer scale (DSPC amount lower that 23 mol %), all the analyzed rheological properties remain similar to those observed for pure DMPC monolayers, indicating that in this proportion range the DSPC molecules contribute as DMPC to the surface rheology in spite of having hydrocarbon chains four carbons longer.

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Temperature and pressure dependent growth and morphology of DMPC/DSPC domains studied by Brewster angle microscopy

Cited by 15 publications

References 60 publications

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

Sphingomyelinase acts by an area-activated mechanism on the liquid-expanded phase of sphingomyelin monolayers

Rheological Properties of a Two Phase Lipid Monolayer at the Air/Water Interface: Effect of the Composition of the Mixture

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