title: Automated carboxylesterase assay for the evaluation of ionic liquids' human toxicity.
abstract: Aiming the prediction of ionic liquids' (ILs) human toxicity, an automated carboxylesterase activity assay was developed. The method was implemented on a sequential injection analysis (SIA) system and relied on the hydrolysis of 4-methylumbelliferyl acetate by the enzyme, to produce the fluorescent compound 4-methylumbelliferone (λ(exc)=365 nm; λ(em)=460 nm). The adopted approach was based on activity/inhibition assays in which the reduction of enzyme activity was denoted by a decrease of fluorescence. The activity assays were performed in aqueous media and in the presence of increasing concentrations of seven commercially available ILs and sodium bis(p-nitrophenyl) phosphate, a strong inhibitor of carboxylesterase. The inhibitory effects were quantified by means of the calculation of half maximal inhibitory effective concentration (EC(50)) values that were between 38 and 134 μmol L(-1). This allowed us to perform some considerations about the toxicity of the compounds. The less and more toxic ILs found in this study were emim [Ms] and tbph [Ms], respectively. The developed SIA methodology is robust and exhibits good repeatability in all the tested conditions (rsd<5.0%, n=10). At the same time a reduction of costs was attained by reduced consumption of reagents and minimal effluent production (2 mL per cycle).
authors.affiliation: REQUIMTE, Departamento de Química, Faculdade de Farmácia, Universidade do Porto, Rua Jorge Viterbo Ferreira n° 228, 4050-313 Porto, Portugal.
authors.forename: Edite
authors.initials: E
authors.lastname: Cunha
authors.forename: Paula C A G
authors.initials: PC
authors.lastname: Pinto
authors.forename: José P S
authors.initials: JP
authors.lastname: Carvalho
authors.forename: M Lúcia M F S
authors.initials: ML
authors.lastname: Saraiva
mesh_terms: D001331:Automation; D001681:Biological Assay / Q000379:methods*; D043182:Carboxylesterase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D052578:Ionic Liquids / Q000633:toxicity*; D014468:Umbelliferones / Q000378:metabolism*
chemical_list: D052578:Ionic Liquids; D014468:Umbelliferones; C032078:4-methylumbelliferyl acetate; D043182:Carboxylesterase