Use of bioenergetically active membranes for the study of green chemicals

Ionic liquids (ILs) represent promising, more sustainable substitutes for canonical volatile organic compounds in many industries. Yet, their toxicity is still debated. While their impact on ecotoxicological model organisms has been extensively studied, and though it is known how their ability to interact with biological membranes is the determining factor at the base of their toxicity, a detailed understanding of ILs interaction with native membranes is still missing. In this context, we investigated ILs effect on bioenergetically active membranes using chromatophores, photosynthetic vesicles isolated from the purple non-sulfur bacteria Rhodobacter capsulatus, and bovine-heart derived submitochondrial particles. Chromatophores bear carotenoids associated to the light-harvesting complex II whose visible spectrum of absorbance responds linearly to the membrane electrical potential (ΔΨ), acting as an intramembrane voltmeter. We utilised this carotenoid shift to obtain information on the ΔΨ dissipation in the presence of ILs. Moreover, we tested the compounds effect on the electron transfer reactions occuring within the cytochrome bc1 and the light-driven ATP synthesis of chromatophores, and in vivo on the photosynthetic growth of Rb. capsulatus. Subsequently, we tested ILs on submitochondrial particles, investigating their effect on the electron transport, and on the activity of complexes I, III and IV of the mitochondrial electron transport chain. ILs were able to collapse the ΔΨ at micromolar concentrations by increasing the ionic current across the chromatophores lipid bilayer, with bis(trifluoromethylsulfonyl)amide (Ntf2-) containing ILs being particularly effective. The compounds did not significantly inhibit cytochrome bc1 electron transfer reactions. Still, Ntf2 caused a drammatic decrease in light-driven ATP synthesis, and was able to inhibit the bacterium growth at millimolar concentrations. Finally, we found the ILs tested on submitochondrial particles to exert a primary effect of inhibition of the electron transport chain complexes at concentrations of tens of millimolar, with a secondary effect on the membrane electrochemical potential.