Applicability Domain of Polyparameter Linear Free Energy Relationship Models for Predicting Equilibrium Partition Coefficients

Polyparameter linear free energy relationships (PP-LFERs) are accurate and robust models to predict equilibrium partition coefficients (K) of organic chemicals. The accuracy of predictions by a PP-LEFR depends on the composition of the respective calibration data set. It is generally expected that extrapolation outside the model calibration domain is less accurate than interpolation. In this study, the applicability domain (AD) of PP-LFERs is systematically evaluated by calculation of the leverage (h), a measure of distance from the calibration set in the descriptor space. Repeated simulations with experimental data show that the root mean squared error of predictions increases with h, and that large prediction errors (>3 SDtraining, the standard deviation of training data) occur more frequently when h exceeds the common threshold of 3 hmean, where hmean is the mean h of all training compounds. Nevetheless, analysis also shows that well-calibrated PP-LFERs with many (e.g., 100), diverse, and accurate training data are highly robust against extrapolation; extreme prediction errors (> 5 SDtraining) are rare. For such PP-LFERs, 3 hmean may be too strict as the cutoff for AD. Evaluation of published PP-LFERs in terms of their AD using 25 chemically diverse, environmentally relevant chemicals as AD probes indicated that many reported PP-LFERs do not cover organosiloxanes, per- and polyfluorinated alkylsubstances, highly polar chemicals, and/or highly hydrophobic chemicals in their AD. It is concluded that calculation of h is useful to identify model extrapolations as well as the strengths and weaknesses of the trained PP-LFERs.

Chiral torsional effects in anomalous fluids in thermal equilibrium

Using the similarity between spacetime torsion and axial gauge couplings, we study torsional contributions to the equilibrium partition function in a stationary background. In the case of a charged fluid minimally coupled to torsion, we spot the existence of linear torsional magnetic and vortical effects, while the axial-vector current and the spin energy potential do not receive corrections in the torsion at linear order. The covariant energy-momentum tensor, on the other hand, does contain terms linear in the torsion tensor. The case of a two-flavor hadronic superfluid is also analyzed, and the torsional contributions to the constitutive relations computed. Our results show the existence of a torsional electric chiral effect mediated by the charged pions.

The Relation Between Ejection Mechanism and Ion Abundance in the Electric Double Layer of Drops

The composition of outer drop layers has been associated with distinct chemical reactivity. We use atomistic modeling to examine how the composition of the surface excess charge layer (SECL) is related to the ejection mechanisms of ions. Even though the drop disintegration is inherently a non-equilibrium process we find that the equilibrium ion distribution in SECL predicts the ions that are ejected. The escape of the ions in aqueous drops takes place from conical protrusions that are global drop deformations and their appearance is independent of the location of a single ion. Our results are consistent with the equilibrium partition model, which associates the mass spectrum with the distribution of analytes in the drop’s double electric layer. We present evidence that atomistic simulations of minute nano-drops cannot distinguish Rayleigh fission from the ion evaporation mechanism.

The Relation Between Ejection Mechanism and Ion Abundance in the Electric Double Layer of Drops

The composition of outer drop layers has been associated with distinct chemical reactivity. We use atomistic modeling to examine how the composition of the surface excess charge layer (SECL) is related to the ejection mechanisms of ions. Even though the drop disintegration is inherently a non-equilibrium process we find that the equilibrium ion distribution in SECL predicts the ions that are ejected. The escape of the ions in aqueous drops takes place from conical protrusions that are global drop deformations and their appearance is independent of the location of a single ion. Our results are consistent with the equilibrium partition model, which associates the mass spectrum with the distribution of analytes in the drop’s double electric layer. We present evidence that atomistic simulations of minute nano-drops cannot distinguish Rayleigh fission from the ion evaporation mechanism.

The Relation Between Ejection Mechanism and Ion Abundance in the Electric Double Layer of Drops

The composition of outer drop layers has been associated with distinct chemical reactivity. We use atomistic modeling to examine how the composition of the surface excess charge layer (SECL) is related to the ejection mechanisms of ions. Even though the drop disintegration is inherently a non-equilibrium process we find that the equilibrium ion distribution in SECL predicts the ions that are ejected. The escape of the ions in aqueous drops takes place from conical protrusions that are global drop deformations and their appearance is independent of the location of a single ion. Our results agree with the equilibrium partition model, which associates the mass spectrum with the distribution of analytes in the drop’s double electric layer. We present evidence that atomistic simulations of minute nano-drops cannot distinguish Rayleigh fission from the ion evaporation mechanism.

Understanding interactions of organic nitrates with the surface and bulk of organic films: implications for particle growth in the atmosphere

Experiments, kinetics modeling and quantum chemical calculations are combined to probe both initial uptake and equilibrium partition coefficients for organic nitrates into various organic films.