Fandom

VroniPlag Wiki

Ry/048

< Ry

31.385Seiten in
diesem Wiki
Seite hinzufügen
Diskussion0 Teilen

Störung durch Adblocker erkannt!


Wikia ist eine gebührenfreie Seite, die sich durch Werbung finanziert. Benutzer, die Adblocker einsetzen, haben eine modifizierte Ansicht der Seite.

Wikia ist nicht verfügbar, wenn du weitere Modifikationen in dem Adblocker-Programm gemacht hast. Wenn du sie entfernst, dann wird die Seite ohne Probleme geladen.

Permeation of Organometallic Compounds through Phospholipid Membranes

von Dr. Raycho Yonchev

vorherige Seite | zur Übersichtsseite | folgende Seite
Statistik und Sichtungsnachweis dieser Seite findet sich am Artikelende
[1.] Ry/Fragment 048 01 - Diskussion
Zuletzt bearbeitet: 2016-03-04 17:25:08 WiseWoman
Anézo 2003, Fragment, Gesichtet, KomplettPlagiat, Ry, SMWFragment, Schutzlevel sysop

Typus
KomplettPlagiat
Bearbeiter
Klgn
Gesichtet
Yes.png
Untersuchte Arbeit:
Seite: 48, Zeilen: 1 ff. (entire page)
Quelle: Anézo 2003
Seite(n): 64, 65, Zeilen: 64, 65
II.2.4 Macroscopic ensembles

The sensitivity of lipid bilayers to the macroscopic boundary conditions applied in a simulation has been shown in several studies [52,53]. Several macroscopic ensembles can be distinguished and the choice of a specific ensemble may influence the results obtained from the simulation. While the temperature T and the number of atoms N are generally kept constant, the volume V of the simulation box, the external pressure P, or the applied surface tension may be kept constant or not. The most commonly ensembles applied to lipid bilayer simulations are described and commented below.

NVT ensemble. A certain number of membrane simulations have been performed with the so-called canonical ensemble NVT, in which the volume of the unit cell is kept constant. Assumptions about the total molecular density of the simulated system have to be made in order to be able to fix the volume of the unit cell. Experimental values for the area per lipid and the bilayer lamellar spacing (i.e. bilayer repeat distance) are usually used to determine the box size. Depending on the accuracy of the available experimental data, the model system will restore with more or less success the features of membrane structure and properties. The density of the system is directly related to the physical state of the membrane and has to be finely adjusted so as to reproduce a liquid crystalline state. If the density is too high, the chain packing becomes too tight, the global ordering increases, and a gel-like state may be simulated. If the density is too low, a gap might be observed between the two monolayers. If the estimation of the density is correct, the main membrane properties will be well replicated. The principal danger of the NVT ensemble is that the results might look promising even if there are underlying flaws in the calculation procedure or in the force field. As long as the system density is right, the simulation will produce a rather good looking fluid phase membrane irrespective of the quality of the force field or other computational parameters, since the constraints applied on the box volume prevent the system from going to an incorrect density. Furthermore, accurate experimental data about structural membrane parameters are often limited to a few single lipid component bilayers and, in the case of membranes made up of mixture of lipids, experiments provide only indirect guidance for assigning the appropriate [simulation cell dimensions, making membrane simulations using constant volume algorithms difficult.]


52. Feller, S. E.; Pastor, R. W. J. Chem. Phys. 1999, 111, 1281.

53. Tieleman, D. P.; Berendsen, H. J. C. J. Chem. Phys. 1996, 105, 4871.

[page 64]

3.2.2.3 Macroscopic ensembles

The sensitivity of lipid bilayers to the macroscopic boundary conditions applied in a simulation has been shown in several studies [98,99]. Several macroscopic ensembles can be distinguished and the choice of a specific ensemble may influence the results obtained from the simulation. While the temperature T and the number N of atoms are generally kept constant, the volume V of the simulation box, the external pressure P, or the applied sur-

[page 65]

face tension γ may be kept constant or not. The most commonly ensembles applied to lipid bilayer simulations are described and commented below.

NVT ensemble A certain number of membrane simulations have been performed with the so-called canonical ensemble NVT, in which the volume of the unit cell is kept constant [100,101]. Assumptions about the total molecular density of the simulated system have to be made in order to be able to fix the volume of the unit cell. Experimental values for the area per lipid and the bilayer lamellar spacing (i.e. bilayer repeat distance) are usually used to determine the box size. Depending on the accuracy of the available experimental data, the model system will restore with more or less success the features of membrane structure and properties. The density of the system is directly related to the physical state of the membrane and has to be finely adjusted so as to reproduce a liquid crystalline state. If the density is too high, the chain packing becomes too tight, the global ordering increases, and a gel-like state may be simulated. If the density is too low, a gap might be observed between the two monolayers. If the estimation of the density is correct, the main membrane properties will be well replicated. The principal danger of the NVT ensemble is that the results might look promising even if there are underlying flaws in the calculation procedure or in the force field. As long as the system density is right, the simulation will produce a rather good looking fluid phase membrane irrespective of the quality of the force field or other computational parameters, since the constraints applied on the box volume prevent the system from going to an incorrect density. Furthermore, accurate experimental data about structural membrane parameters are often limited to a few single lipid component bilayers and, in the case of membranes made up of mixture of lipids, experiments provide only indirect guidance for assigning the appropriate simulation cell dimensions, making membrane simulations using constant volume algorithms difficult.


[98] D. P. Tieleman and H. J. C. Berendsen. J. Chem. Phys., 105:4871–4880, 1996.

[99] S. E. Feller and R. W. Pastor. J. Chem. Phys., 111:1281–1287, 1999.

[100] U. Essmann, L. Perera, and M. L. Berkowitz. Langmuir, 11:4519–4531, 1995.

[101] U. Essmann and M. L. Berkowitz. Biophys. J., 76:2081–2089, 1999.

Anmerkungen

The source is not given. References 100 and 101 in the source are not included.

Sichter
(Klgn), WiseWoman


vorherige Seite | zur Übersichtsseite | folgende Seite
Letzte Bearbeitung dieser Seite: durch Benutzer:WiseWoman, Zeitstempel: 20160304172613

Auch bei Fandom

Zufälliges Wiki