Computational permeability models

Factors Influencing the Accuracy of Computational Permeability Models... 

Hamlen R.C. 1991. Paper Structure, Mechanics, and Permeability Computer-Aided Modeling. [LES]... 

CHEOPS is based on the method of atomic constants, which uses atom contributions and an anharmonic oscillator model. Unlike other similar programs, this allows the prediction of polymer network and copolymer properties. A list of 39 properties could be computed. These include permeability, solubility, thermodynamic, microscopic, physical and optical properties. It also predicts the temperature dependence of some of the properties. The program supports common organic functionality as well as halides. As, B, P, Pb, S, Si, and Sn. Files can be saved with individual structures or a database of structures. 

In Sec. 3 our presentation is focused on the most important results obtained by different authors in the framework of the rephca Ornstein-Zernike (ROZ) integral equations and by simulations of simple fluids in microporous matrices. For illustrative purposes, we discuss some original results obtained recently in our laboratory. Those allow us to show the application of the ROZ equations to the structure and thermodynamics of fluids adsorbed in disordered porous media. In particular, we present a solution of the ROZ equations for a hard sphere mixture that is highly asymmetric by size, adsorbed in a matrix of hard spheres. This example is relevant in describing the structure of colloidal dispersions in a disordered microporous medium. On the other hand, we present some of the results for the adsorption of a hard sphere fluid in a disordered medium of spherical permeable membranes. The theory developed for the description of this model agrees well with computer simulation data. Finally, in this section we demonstrate the applications of the ROZ theory and present simulation data for adsorption of a hard sphere fluid in a matrix of short chain molecules. This example serves to show the relevance of the theory of Wertheim to chemical association for a set of problems focused on adsorption of fluids and mixtures in disordered microporous matrices prepared by polymerization of species. 

Our main focus in this chapter has been on the applications of the replica Ornstein-Zernike equations designed by Given and Stell [17-19] for quenched-annealed systems. This theory has been shown to yield interesting results for adsorption of a hard sphere fluid mimicking colloidal suspension, for a system of multiple permeable membranes and for a hard sphere fluid in a matrix of chain molecules. Much room remains to explore even simple quenched-annealed models either in the framework of theoretical approaches or by computer simulation. 

Figure 22.1 A. Schema for a physiologically based pharmacokinetic model incorporating absorption in the stomach and intestines and distribntion to various tissues. B. Each organ or tissue type includes representation of perfusion (Q) and drug concentrations entering and leaving the tissue. Fluxes are computed by the product of an appropriate rate law, and permeable surface area accounts for the affinity (e.g., lipophilic drugs absorbing more readily into adipose tissue). Clearance is computed for each tissue based on physiology and is often assumed to be zero for tissues other than the gut, the liver, and the kidneys.

Bergstrom, C. A. S. Computational models to predict aqueous drug solubility, permeability and intestinal absorption. Exp. Opin. Drug Metab. Toxicol. 2005, 1, 513-527. 

As expected, the estimated values were found to be closer to the correct ones compared with the estimated values when the water-oil ratios are only matched. In the 2nd run, the horizontal permeabilities of layers 5 to 10 (6 zones) were estimated using the value of 200 md as initial guess. It was found necessary to use the pseudo-inverse option in this case to ensure convergence of the computations. The initial and converged profiles generated by the model are compared to the observed data in Figures 18.25a and 18.25b. 

The determination of the evolution of the permeability of these rocks during acidizing is necessary when attempting to predict the evolution of the skin (Equation 2). Previous studies (6) have tried to model the shift of the pore size distribution due to acid attack. Then, permeability profiles were computed by integrating the contributions to the overall flow of each of the rock pores, all over the considered volume of rock. The main limitation of this method lies in the disregarding of the spatial correlation between rock pores. 

Theory and computational aspects of intestinal permeability have been reviewed in detail by Egan and Lauri [27], Briefly, a drug must be somewhat permeable through the membrane of the intestinal tract if it is to be administered orally and achieve systemic exposure. The rate of membrane permeability is strongly related to the lipophilicity and hydrophilicity of the molecule. Thus, models with a small number of descriptors related to those two properties can provide useful predictions of drug absorption. 

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