Quantitative Analysis of Molecular Interaction Potentials of Ionic Liquid Anions Using Multi-Functionalized Stationary Phases in HPLC

In vitro methods for predicting the bioconcentration of xenobiotics in aquatic organisms

The accumulation of anthropogenic chemical substances in aquatic organisms is an immensely important issue from the point of view of environmental protection. In the context of the increasing number and variety of compounds that may potentially enter the environment, there is a need for efficient and reliable solutions to assess the risks. However, the classic approach of testing with fish or other animals is not sufficient. Due to very high costs, significant time and labour intensity, as well as ethical concerns, in vivo methods need to be replaced by new laboratory-based tools. So far, many models have been developed to estimate the bioconcentration potential of chemicals. However, most of them are not sufficiently reliable and their predictions are based on limited input data, often obtained with doubtful quality. The octanol-water partition coefficient is still often used as the main laboratory tool for estimating bioconcentration. However, according to current knowledge, this method can lead to very unreliable results, both for neutral species and, above all, for ionic compounds. It is therefore essential to start using new, more advanced and credible solutions on a large scale. Over the last years, many in vitro methods have been newly developed or improved, allowing for a much more adequate estimation of the bioconcentration potential. Therefore, the aim of this work was to review the most recent laboratory methods for assessing the bioconcentration potential and to evaluate their applicability in further research.

Validation and updating of QSAR models for partitioning coefficients of ionic liquids in octanol-water and development of a new LFER model

Since estimating the octanol-water partitioning coefficients (log P) of numerous ionic liquids (ILs) is tedious, time & material consuming and labor intensive, predicting by quantitative structure-activity relationship (QSAR) approach is necessary. Although several researchers presented the QSAR models for the property, validation assessment of the models were not sufficiently performed due to lack of log P dataset. In this study, the log P values of external ILs were measured by a shaking-flask method or collected from literatures. The newly obtained external log P values were applied for the validation study of previous models. In results, it was found that previous models showed rather low predictabilities and/or non-ignorable prediction limits to some IL structures whose anions were not involved in the previous studies. Accordingly, to achieve better predictability, the parameters used for previous modeling were re-selected and also their coefficients were re-calculated by multiple linear regression analysis with an inclusion of the external validation set to previous training set. Moreover, for reasonable understanding of chemical meanings in octanol-water partitioning behavior of ILs, we developed a new prediction model with a few number of descriptors, which has a good accuracy of R² = 0.862 and standard error = 0.564 log units.

Membrane partitioning of ionic liquid cations, anions and ion pairs - Estimating the bioconcentration potential of organic ions

Recent efforts have been directed towards better understanding the persistency and toxicity of ionic liquids (ILs) in the context of the "benign-by-design" approach, but the assessment of their bioaccumulation potential remains neglected. This paper reports the experimental membrane partitioning of IL cations (imidazolium, pyridinium, pyrrolidinium, phosphonium), anions ([C(CN)₃]^-, [B(CN)₄]^-, [FSO₂)₂N]^-, [(C₂F₅)₃PF₃]^-, [(CF₃SO₂)₂N]^-) and their combinations as a measure for estimating the bioconcentration factor (BCF). Both cations and anions can have a strong affinity for phosphatidylcholine bilayers, which is mainly driven by the hydrophobicity of the ions. This affinity is often reflected in the ecotoxicological impact. Our data revealed that the bioconcentration potential of IL cations and anions is much higher than expected from octanol-water-partitioning based estimations that have recently been presented. For some ILs, the membrane-water partition coefficient reached levels corresponding to BCFs that might become relevant in terms of the "B" (bioaccumulation potential) classification under REACH. However, this preliminary estimation need to be confirmed by in vivo bioconcentration studies.

In silico prediction of linear free energy relationship descriptors of neutral and ionic compounds

Prediction models for LFER descriptors – excess molar refraction (E), dipolarity/polarizability (S), H-bonding acidity (A) & basicity (B), McGowan volume (V), and interaction of cations (J⁺) and anions (J⁻) – of both ionic and neutral compounds.