Ry/Fragment 060 01

Typus KomplettPlagiat

Bearbeiter WiseWoman

Gesichtet

Untersuchte Arbeit: Seite: 60, Zeilen: 1 ff. (entire page)

Quelle: Anézo 2003 Seite(n): 140, 141, Zeilen: 140: 29 ff.; 141 1 ff.

[In this model, the diffuse interfaces] between the lipid headgroups and water are included in the description of the permeation process, and the anisotropic and inhomogeneous character of the membrane interior is now taken into consideration. For a structurally heterogeneous membrane, both the partition and diffusion coefficients of the solute and, hence, its permeability coefficient exhibit spatial variations within the membrane. Equation (2.15) can be thus generalized to express the overall membrane resistance R as the integral over the local resistances across the membrane and to relate it to spatially dependent solute partition and diffusion coefficients: $R = \frac{1}{P}=\int_0^d \frac{dz}{K_{z/w} (z) D(z)} (2.16)$ Kz/w(z) and D(z) are the depth dependent partition coefficient of the solute between water and the membrane and the solute diffusion coefficient within the membrane, respectively, at a position z along the bilayer normal. d is now the entire membrane thickness, including the water/membrane interfaces. The critical parameter in Equation (2.16) is the partition coefficient Kz/w, which does not only reflect the solute distribution between the aqueous phase and the membrane, but also all possible molecular interactions between the solute and both environments. Kz/w can be calculated from the Gibbs free energy ΔG, required to transfer the solute from aqueous to the hydrophobic phase as follows: $K_{z/w}(z) = \exp (-\Delta G(z) / R_c T) (2.17)$ where Rc is the ideal gas constant and T, the temperature. In essence, water/membrane partitioning cannot be predicted reliably and accurately without the ability to determine the associated free energy changes. Thus, the permeation resistance can be expressed in terms of free energy:

In this model, the diffuse interfaces between the lipid headgroups and water are included in the description of the permeation process, and the anisotropic and inhomogeneous character of the membrane interior is now taken into consideration. [page 141] For a structurally heterogeneous membrane, both the partition and diffusion coefficients of the solute and, hence, its permeability coefficient exhibit spatial variations within the membrane. Equation 5.1 can be thus generalized to express the overall membrane resistance R as the integral over the local resistances across the membrane and to relate it to spatially-dependent solute partition and diffusion coefficients: $R = \frac{1}{P}= \int_0^d R(z) \cdot \mathrm{d}z = \int_0^d \frac{\mathrm{d}z}{K_{z/w} (z) \cdot D(z)} (5.2)$ Kz/w and Dz are the depth-dependent partition coefficient of the solute between water and the membrane and the solute diffusion coefficient within the membrane, respectively, at a position z along the bilayer normal. d is now the entire membrane thickness, including the water/membrane interfaces. The critical parameter in Equation 5.2 is the partition coefficient Kz/w which does not only reflect the solute distribution between the aqueous phase and the membrane, but also all possible molecular interactions between the solute and both environments. Kz/w can be calculated from the Gibbs free energy ΔG required to transfer the solute from the aqueous to the hydrophobic phase as follows: $K_{z/w}(z) = \exp (-\Delta G(z) / R_c T) (5.3)$ where Rc is the ideal gas constant and T, the temperature. In essence, water/membrane partitioning cannot be predicted reliably and accurately without the ability to determine the associated free energy changes. Thus, the permeation resistance can be also expressed in terms of free energy:

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