Evaluation of the Ability of PAMPA Membranes to Emulate Biological Processes through the Abraham Solvation Parameter Model

Two parallel artificial membrane permeability assay (PAMPA) systems intended for emulating skin permeability have been characterized through the solvation parameter model of Abraham using multilinear regression analysis. The coefficients of the obtained equations have been compared to the ones already established for other PAMPA membranes using statistical tools. The results indicate that both skin membranes are similar to each other in their physicochemical properties. However, they are different from other PAMPA membranes (e.g., intestinal absorption and blood-brain PAMPAs), mainly in terms of hydrophobicity and hydrogen bonding properties. Next, all PAMPA membranes have been compared to relevant biological processes also characterized through the solvation parameter model. The results highlight that skin-PAMPA membranes are a very good choice to emulate skin permeability.

Sorption of pyrene to dissolved humic substances and related model polymers. 1. Structure--property correlation

Solid-phase microextraction (SPME) was employed to determine sorption coefficients for pyrene on dissolved humic substances (DHS) of various origins and also on model polymers to gain a better understanding of the relationships between sorption potential and sorbent structures. The sorption potential of DHS from very different sources is described by an empirical two-parameter correlation involving the polarity (O/H atomic ratio) and the aromaticity (epsilon 280 nm) as descriptors. On the other hand, sorption experiments with well-defined model polymers, poly(acrylic acid) esters, led to the conclusion that aliphatic chains may be more effective than aromatic moieties in binding PAHs. The molecular weight of the model sorbents was found to have a significant influence on the sorption potential.

Chromatographic models for the sorption of neutral organic compounds by soil from water and air

The solvation parameter model is used to construct models for the estimation of the soil-water and soil-air distribution constants and to characterize the contribution of fundamental intermolecular interactions to the underlying sorption processes. Wet soil is shown to be quite cohesive and polar but relatively non-selective for dipole-type, lone-pair electron and hydrogen-bond interactions. Using a comparison of system constant ratios chromatographic systems employing reversed-phase liquid chromatography on polar bonded phases are shown to provide suitable models for estimating soil-water distribution constants. No suitable gas chromatographic models were found for the soil-air distribution constant but the requirements for such a system are indicated. Models are also provided for adsorption at the air-water interface. Estimation methods based on either the solvation parameter model or chromatographic model reproduce experimental distribution constants for a wide variety of compounds with a similar error (0.2-0.3 log units) to that expected in the experimental data.