title: Designing ionic liquids: the chemical structure role in the toxicity.
abstract: Ionic liquids (ILs) are a novel class of solvents with interesting physicochemical properties. Many different applications have been reported for ILs as alternatives to organic solvents in chemical and bioprocesses. Despite the argued advantage of having low vapor pressure, even the most hydrophobic ILs show some degree of solubility in water, allowing their dispersion into aquatic systems and raising concerns on its pollutant potential. Moreover, nowadays most widespread notion concerning the ILs toxicity is that there is a direct relationship with their hydrophobicity/lipophilicity. This work aims at enlarging the currently limited knowledge on ILs toxicity by addressing negative impacts in aquatic ecosystems and investigating the possibility of designing hydrophobic ILs of low ecotoxicity, by the manipulation of their chemical structures. The impact of aromaticity on the toxicity of different cations (pyridinium, piperidinium, pyrrolidinium and imidazolium) and hydrophobic anions (bis(trifluoromethylsulfonyl)imide [NTf(2)] and hexafluorophosphate [PF(6)]) was analysed. Concomitantly, several imidazolium-based ILs of the type [C(                   n                 )C(                   m                 )C(                   j                 )im][NTf(2)] were also studied to evaluate the effects of the position of the alkyl chain on the ILs' toxicity. For that purpose, standard assays were performed using organisms of different trophic levels, Vibrio fischeri, Pseudokirchneriella subcapitata and Daphnia magna, allowing to evaluate the consistency of the structure-activity relationships across different biological targets. The results here reported suggest the possibility of designing ILs with an enhanced hydrophobic character and lower toxicity, by elimination of their aromatic nature.
authors.affiliation: Departamento de Química, CICECO, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal.
authors.forename: Sónia P M
authors.initials: SP
authors.lastname: Ventura
authors.forename: Ana M M
authors.initials: AM
authors.lastname: Gonçalves
authors.forename: Tânia
authors.initials: T
authors.lastname: Sintra
authors.forename: Joana L
authors.initials: JL
authors.lastname: Pereira
authors.forename: Fernando
authors.initials: F
authors.lastname: Gonçalves
authors.forename: João A P
authors.initials: JA
authors.lastname: Coutinho
mesh_terms: D048908:Aliivibrio fischeri / Q000187:drug effects; D000818:Animals; D000460:Chlorophyta / Q000187:drug effects; D003621:Daphnia / Q000187:drug effects; D057927:Hydrophobic and Hydrophilic Interactions; D052578:Ionic Liquids / Q000737:chemistry / Q000633:toxicity*; D012995:Solubility; D012997:Solvents / Q000737:chemistry / Q000633:toxicity*; D013329:Structure-Activity Relationship; D023382:Toxicity Tests, Acute; D036401:Toxicity Tests, Chronic; D055548:Vapor Pressure; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000633:toxicity*
chemical_list: D052578:Ionic Liquids; D012997:Solvents; D014874:Water Pollutants, Chemical