Reliable Prediction of the Octanol–Air Partition Ratio

Abstract

The octanol-air equilibrium partition ratio, K OA , is frequently used to describe the volatility of organic chemicals, whereby n-octanol serves as a substitute for a variety of organic phases ranging from organic matter in atmospheric particles and soils, to biological tissues such as plant foliage, fat, blood and milk, and to polymeric sorbents.Because measured K OA values exist for just over 500 compounds, most of which are nonpolar halogenated aromatics, there is a need for tools that can reliably predict this parameter for a wide range of organic molecules, ideally at different temperatures. The ability of five techniques, specifically poly-parameter linear free energy relationships (ppLFERs) with either experimental or predicted solute descriptors, EPISuite's This article is protected by copyright. All rights reserved. Accepted ArticleKOAWIN, COSMOtherm, and OPERA, to predict the K OA of organic substances, either at 25 °C or at any temperature, was assessed by comparison with all K OA values measured to date. In addition, three different ppLFER equations for K OA were evaluated and a new modified equation is proposed. A technique's performance was quantified with the mean absolute error (MAE), the root mean square error (RMSE), and the estimated uncertainty of future predicted values, i.e. the prediction interval. We also considered each model's applicability domain and accessibility. With an RMSE of 0.37 and a MAE of 0.23 for predictions of log K OA at 25 °C and RMSE of 0.32 and MAE of 0.21 for predictions made at any temperature, the ppLFER equation using experimental solute descriptors predicted the K OA the best. Even if solute descriptors must be predicted in the absence of experimental values, ppLFERs are the preferred method, also because they are easy to use and freely available.

Density Functional Theory with Implicit Solvents for Accurate Estimation of Aqueous and Organic Solvation Free Energies of Lignin Fragments

“…As regards solvent purity, experimental organic phases are usually referred to as wet solvents since they can contain considerable amounts of water . An interesting example is 1-octanol, whose hydrated phase (“wet-octanol”) presents considerably different solvation properties such as the increase in the solubility of polar solutes (and decrease of apolar ones) due to its stronger hydrogen-bond acidity. , …”

“…72 An interesting example is 1-octanol, whose hydrated phase ("wet-octanol") presents considerably different solvation properties such as the increase in the solubility of polar solutes (and decrease of apolar ones) due to its stronger hydrogenbond acidity. 72,73 As reported by Bannan et al, 20 the consideration of total immiscibility between water and the organic solvents will worsen the results of log P calculations. Results will be more affected as the polarity of the organic solvent increases since it will also increase the mutual miscibility with water.…”

Retrieval, Selection, and Evaluation of Chemical Property Data for Assessments of Chemical Emissions, Fate, Hazard, Exposure, and Risks

“…To address this limitation, property prediction techniques based on quantum chemistry and statistical thermodynamics, e.g., COSMOtherm, serve as an ideal complement because they rarely, or to a very limited extent, rely on experimentally derived data. Recent studies have demonstrated that COSMOtherm performed almost as well as QSARs/QSPRs based on training sets in predicting partition ratios and internal energies, with the exception of the internal energy change for dissolution in water. ,, Nevertheless, COSMOtherm calculations usually require a long time and intensive computational power because they rely on 3D geometry optimization of the molecular structure, which limits the use of this approach in high-throughput chemical screening.…”

A holistic modeling framework for estimating the influence of climate change on indoor air quality

“…Usually, values for 298 K are available. Factors and enthalpies for conversion to other temperatures have been published for various substances 29,122,123 …”

“…Factors and enthalpies for conversion to other temperatures have been published for various substances. 29,122,123 Liu et al ( 2013) 124 pointed out that the assumption of instantaneous gas/particle equilibrium can lead to large errors in the estimation of indoor SVOC concentrations. Therefore, in this work, the estimation of SVOC concentration is treated as a post-processing module, that is, first the indoor TSP is quantified and then the sorbed SVOC on the particles is estimated using Equation (3)…”