Mixed 2D molecular systems: Mechanic, thermodynamic and dielectric properties

Beňo, Juraj; Weis, Martin; Dobročka, Edmund; Haško, Daniel

doi:10.1016/j.apsusc.2008.03.176

Cited by 4 publications

(11 citation statements)

References 20 publications

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“…Structural information about monolayers can be supplied by various experimental methods − ,− or extracted from molecular simulations on monolayers or bilayers. The latter procedures are more often coarse-grained − because this approach allows investigations of larger systems at a lower computational price.…”

Section: Introductionmentioning

confidence: 99%

Structural Aspects of Lipid Monolayers: Computer Simulation Analyses

et al. 2010

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Extensive molecular dynamics simulations at room temperature were carried out for model films of two dissimilar lipids (DPPC and dicaprin) at the air/water interface. To study the peculiarities of the organization patterns at different average areas per molecule, surface concentrations corresponding to five almost equally spaced points along the isotherms of the two surfactants were considered. A variable of prime interest was the density distribution in a direction normal to the interface of the monolayer components: interfacial water and surfactant on one hand and the separate moieties of the lipids on the other hand. The packing pattern and cluster size dispersion were studied by means of Voronoi tessellation and radial distribution functions. Speculations regarding structural changes upon phase-state changes during film compression were made. Individual characteristics for surfactant heads and tails as well as for interfacial water were outlined and related to the available experimental data. An analysis of the diffusion coefficients revealed the limiting factors for lipid lateral and normal diffusion. Structural arguments in support of changes in monolayer dielectric properties with the area per molecule were provided.

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Section: Introductionmentioning

confidence: 99%

Structural Aspects of Lipid Monolayers: Computer Simulation Analyses

et al. 2010

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“…On the other hand, the respective part of the tangential dipoles has not been discussed. It is noteworthy that the dipole moment curves in refs and are characterized by a minimum in the region of LE/LC phase coexistence. However, its origin has not been commented by the authors.…”

Section: Introductionmentioning

confidence: 89%

“…It has been used for structural and rheological studies almost from the beginning of Langmuir monolayer investigations. Lately, its evolution upon monolayer compression has been used to extract the elasticity of monolayers (from the first derivatives with respect to area) , or the free energy of mixing with other surfactants (through integration) . Dipole−dipole interactions have been suggested as the driving force for the mixing …”

Section: Introductionmentioning

confidence: 99%

“…Two methods for such evaluation dominate in the literature. The first one is based on the classical Helmholtz equation, while the more modern approach relies on Maxwell displacement current measurements. , Using the latter, the profile of the normal dipole moment along the entire surface/pressure area isotherm has been determined. , In ref , the authors have suggested dipole moments compensation as a possible reason for favorable mixing of DPPC with a second surfactant. Then, this contribution has been ruled out as the dominating factor due to its negligible magnitude.…”

Section: Introductionmentioning

confidence: 99%

“…Another indirect relation of the dipole moment to the thickness of DPPC monolayers has been the hypothesis that the pH dependence of the latter is defined by the orientation of the P−N vector of the choline group. From mechanistic point of view, control of the monolayer dipole moment has been deemed as a factor facilitating Langmuir−Blodgett film deposition …”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Study of the Electric and Dielectric Properties of Model DPPC and Dicaprin Insoluble Monolayers: Size Effect

et al. 2010

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Atomistic modeling of insoluble monolayers is currently used to inspect their organization and electric characteristics, providing a link between theory and experiment. Extensive molecular dynamics simulations at 300 K were carried out for model films of the lipids dipalmitoylphosphatidylcholine (DPPC) and dicaprin (DC) at the air/water interface. Surface concentrations corresponding to a set of points along the surface pressure/area isotherms of the surfactants were considered. The models contained 25 or 81 lipid molecules in hexagonal arrangement and explicit aqueous media (TIP3P) treated in periodic boundary conditions. Molecular dynamics simulations based on a classical force field (CHARMM27) were carried out and key characteristics of the studied films were estimated. The dielectric properties of the films in normal and tangential direction were quantified by means of dipole moment magnitude and orientation analysis and by monolayer dielectric permittivity. The contributions of lipids and interfacial water to each component of the considered characteristics were assessed and their variations upon film compression were discussed and compared for the two monolayers and to earlier results. The dielectric permittivity tensors were analyzed. Electrostatic potential profiles across the layers and surface pressure values were used for more detailed clarification of experimental measurements. The results show dissimilar behavior of the two lipids at the air-water interface. While the average electric and dielectric properties of DPPC monolayers result from opposite surfactant and water contributions, the two subsystems are synergetic in the DC films. The anisotropy of the monolayer dipole moment and dielectric permittivity is explained by domination of a different subsystem in the various components. Tangential characteristics turn out to be more sensitive to the size of the model and to the degree of film compression.

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