Abstract
We investigated the toxicological effect of seven novel cholinium, guanidinium, and tetramethylguanidinium carboxylate ionic liquids (ILs) from an ecotoxicological point of view. The emphasis was on the potential structure-toxicity dependency of these surface-active ILs in aqueous environment. The median effective concentrations (EC50) were defined for each IL using Vibrio (Aliivibrio) fischeri marine bacteria. Dipalmitoylphosphatidylcholine (DPPC) liposomes were used as biomimetic lipid membranes to study the interactions between the surface-active ILs and the liposomes. The interactions were investigated by following the change in the DPPC phase transition behaviour using differential scanning calorimetry (DSC). Critical micelle concentrations for the ILs were determined to clarify the analysis of the toxicity and the interaction results. Increasing anion alkyl chain length increased the toxicity, whereas branching of the chain decreased the toxicity of the ILs. The toxicity of the ILs in this study was mainly determined by the surface-active anions, while cations induced a minor impact on the toxicity. In the DSC experiments the same trend was observed for all the studied anions, whereas the cations seemed to induce more variable impact on the phase transition behaviour. Toxicity measurements combined with liposome interaction studies can provide a valuable tool for assessing the mechanism of toxicity.
Highlights
The IL concentration range during the Differential scanning calorimetry (DSC) experiments was clearly below the critical micellar concentration (CMC) for the decanoates and neodecanoates, except for Na decanoate, which was used as a reference for the ILs
The cations did not have a significant impact on the toxicities of decananoates and isostearates, but the GND and TMG neodecanoates were surprisingly somewhat less toxic than their Ch equivalent
DSC experiments were utilised to investigate the potential effect of the surface-active ILs on DPPC liposomes
Summary
The IL concentration range during the DSC experiments was clearly below the CMCs for the decanoates and neodecanoates, except for Na decanoate, which was used as a reference for the ILs. excluding Na decanoate, the data clearly shows that singly dispersed IL molecules interact with the liposomes. DSC experiments were utilised to investigate the potential effect of the surface-active ILs on DPPC liposomes. These liposomes were used as biomimetic lipid bilayers and the Tm of the membrane was followed as a function of the IL concentration.
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