Assessment of bromide-based ionic liquid toxicity toward aquatic organisms and QSAR analysis

The toxicities of 24 bromide-based ionic liquids (Br-ILs) towards Vibrio fischeri (V. fischeri) and Daphnia magna (D. magna) were determined. These Br-ILs are composed of a bromide ion and a generic cation (i.e., pyrrolidinium, piperidinium, pyridinium or imidazolium) with different alkyl side chains. QSAR models with relatively high correlation coefficients, R2, of 0.954 and 0.895 were developed for V. fischeri and D. magna. The model for V. fischeri indicated that the Br-IL toxicity towards V. fischeri was negatively correlated with the energy of the lowest unoccupied molecular orbitals (ELUMO) which reflects the electron affinities (EAs) and positively correlated with the volumes of Br-IL cations. For the D. magna model, the Br-IL toxicity was positively correlated with the dipole moment (μ) and negatively correlated with the total energy (TE) that is highly correlated with the molecular volume (V). For Br-ILs with the same cation ring, the toxicity increased as the length of the alkyl chains increased. For the same alkyl chain length, the toxicity order for V. fischeri was pyridinium>imidazolium>piperidinium>pyrrolidinium, except for those containing octyl side chains, while the toxicity ranking for D. magna was imidazolium~pyridinium>piperidinium>pyrrolidinium.