Phases of phosphatidyl ethanolamine monolayers studied by synchrotron x-ray scattering

Helm, C. A.; Tippmann-Krayer, P.; Möhwald, Helmuth; Als‐Nielsen, J.; Kjær, Kristian

doi:10.1016/s0006-3495(91)82182-8

Cited by 152 publications

(148 citation statements)

References 32 publications

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“…This stretching results in a greater thickness of the hydrocarbon region of the lipid. A similar increase of thickness has been observed for the LE phase of the DMPE lipid with compression of the monolayer, [22] as well as with the incorporation of saturated alkanes into DPPC and DPPE monolayers. [23] Estrela-Lopis et al have reported on a similar significant reduction of the tilt angle in mixed DPPC monolayers, being this tilting decrease attributed to significant changes in the conformation of the head group of the lipids.…”

supporting

confidence: 76%

Mechanism of Action of Cyclic Oligosquaramides on DPPC Phospholipid Monolayers

et al. 2011

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supporting

confidence: 76%

Mechanism of Action of Cyclic Oligosquaramides on DPPC Phospholipid Monolayers

et al. 2011

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“…As is described for many isotherms, e.g. for DMPE (see [52]), the kink in the isotherm in the film pressure range of 25-30 mN m −1 is referred to as the transition between a coexistence region and a homogeneous solid phase. We therefore conclude that in dynamic surface elasticity measurements ε P is constant over the full range of the coexistence region of crystalline DPPC domains embedded in fluid monolayer phase.…”

Section: Discussionmentioning

confidence: 99%

Surface rheology of monolayers of phospholipids and cholesterol measured with axisymmetric drop shape analysis

Vrânceanu

Winkler

Nirschl

et al. 2007

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Surface rheology of monolayers of a saturated phospholipid (dipalmitoylphosphatidylcholine, DPPC), an unsaturated phospholipid (dioleoylphosphatidylcholine, DOPC) and cholesterol is studied with axisymmetric drop shape analysis at the argon/water interface. Measurement techniques for lipids are described in detail. Profile analysis tensiometry (PAT) is used to determine the film pressure Π, surface elasticity and surface dilational viscosity of monolayers upon sinusoidal oscillations of the drop surface for various amplitudes a and frequencies f to assess their dependence on these dynamic parameters. It is shown that surface dilational viscosity strongly depends on the frequency and decreases by a factor 2-5 with increasing f in the considered range. Dilational viscosity is higher the more the monolayer approaches a relaxed state. Thus, the molecular interactions are stronger in the relaxed than in the stressed state. Surface elasticity is much less dependent on dynamic conditions. For DPPC a minimum of the dynamic surface elasticity is found for f = 12.5 mHz (at Π = 17.5 mN m −1 ) which coincides well with the relaxation frequencies measured in stress relaxation experiments. The dynamic surface elasticity of DPPC exhibits a plateau in the range 13.5 mN m −1 ≤ Π ≤ 27 mN m −1 in good coincidence with the phase boundaries of the coexistence region of micron-sized liquid crystalline domains surrounded by a fluid monolayer phase. In equilibrium measurements (Π/A-isotherms) a plateau of the film pressure is seen at the lower bound and a break at the upper bound of the coexistence region. Film pressure/area isotherms produced by PAT and a Langmuir film balance closely coincide as is shown in a comparison to literature values. However, the surface elasticities measured dynamically with oscillating surfaces widely deviate from those derived from isotherms in the case of DPPC and cholesterol, whereas for DOPC very good agreement can be found.

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“…Possibly, the DODAB : DOPE layer contains more water because both the amino and phosphate groups of the DOPE are able to establish bonding with water. When in the expanded phase, monolayers of pure phosphatidylethanolamines (PE) that have the same head group but different lengths of chains and degree of unsaturation were found to have relatively high levels of hydration of 14-19 and 8-10 H 2 O/PE molecule, by X-ray diffraction and reflection [48] and X-ray diffraction [49], respectively. Water vapour uptake studies have shown that a 1 : 1 molar mixture of egg phosphatidylcholine and egg phosphatidylethanolamine has an average hydration of 14 H 2 O molecules compared with just nine H 2 O molecules per lipid in pure phosphatidylethanolamine films [50], which is consistent with the higher hydration value for DODAB : DOPE monolayers compared with the DODAB monolayers shown here.…”

mentioning

confidence: 99%

The effect of neutral helper lipids on the structure of cationic lipid monolayers

Dabkowska

Barlow

Hughes

et al. 2011

J. R. Soc. Interface.

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Successful drug delivery via lipid-based systems has often been aided by the incorporation of 'helper lipids'. While these neutral lipids enhance the effectiveness of cationic lipid-based delivery formulations, many questions remain about the nature of their beneficial effects. The structure of monolayers of the cationic lipid dimethyldioctadecylammonium bromide (DODAB) alone, and mixed with a neutral helper lipid, either diolelyphosphatidylethanolamine or cholesterol at a 1 : 1 molar ratio was investigated at the air -water interface using a combination of surface pressure -area isotherms, Brewster angle microscopy (BAM) and specular neutron reflectivity in combination with contrast variation. BAM studies showed that while pure DODAB and DODAB with cholesterol monolayers showed fairly homogeneous surfaces, except in the regions of phase transition, monolayers of DODAB with diolelyphosphatidylethanolamine were, in contrast, inhomogeneous exhibiting irregular bean-shaped domains throughout. Neutron reflectivity data showed that while the thickness of the DODAB monolayer increased from 17 to 24 Å as it was compressed from a surface pressure of 5 -40 mN m 21, the thickness of the helper lipid-containing monolayers, over the same range of surface pressures, was relatively invariant at between 25 and 27 Å . In addition, the monolayers containing diolelyphosphatidylethanolamine were found to be more heavily hydrated than the monolayers of cationic lipid, alone or in combination with cholesterol, with hydration levels of 18 molecules of water per molecule of lipid being recorded for the diolelyphosphatidylethanolamine-containing monolayers at a surface pressure of 30 mN m 21 compared with only six and eight molecules of water per molecule of lipid for the pure DODAB monolayer and the cholesterol-containing DODAB monolayer, respectively.

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Phases of phosphatidyl ethanolamine monolayers studied by synchrotron x-ray scattering

Cited by 152 publications

References 32 publications

Mechanism of Action of Cyclic Oligosquaramides on DPPC Phospholipid Monolayers

Mechanism of Action of Cyclic Oligosquaramides on DPPC Phospholipid Monolayers

Surface rheology of monolayers of phospholipids and cholesterol measured with axisymmetric drop shape analysis

The effect of neutral helper lipids on the structure of cationic lipid monolayers

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