Alternative Strategy Property-based Approach

An alternate strategy is to predict membrane permeability by modeling the physics of membrane permeation. In principle, such models do not require training on existing experimental data and should have a broad domain of applicability. One approach is to model the process based on solubility-diffusion theory, in which the membrane permeability of the permeant is formulated as the reciprocal of the resistance experienced in the permeation process. With the assumption that diffiisional resistance is only contributed by the membrane and there is negligible resistance in the unstirred aqueous layer and the membrane interface, the permeation rate can be estimated from (l) the partition between the aqueous phase and the membrane, (2) the diffusion across the membrane, and (3) the distance of permeation. Common descriptors such as PSA and MW are reasonable surrogates for these properties, but it is possible to obtain more accurate estimates, as described below. 

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