Evaluating the Toxicity of Ionic Liquids on Shewanella sp. for Designing Sustainable Bioprocesses

Abstract

Ionic liquids (ILs) are widely used as reaction and separation media in many technologies due to their unique and advantageous physicochemical properties. Thus, further studies approaching the study of the toxicity of these materials are required. Moreover, they are utilized in devices in which microorganisms such as Shewanella sp. act as biocatalysts. Thus, in this work, the toxicity of 69 ILs on the marine bacterium Shewanella sp. was tested. Specifically, the ILs analyzed were based on the cations imidazolium, pyridinium, pyrrolidinium, piperidinium, morpholinium, oxazolinium, phosphonium, ammonium, and sulfonium, in combination with different anions. The toxicities of this wide group of ILs on Shewanella sp. were determined using two methods: 1) the agar disk-diffusion test and 2) the growth inhibition test in liquid media. The relationship between toxicity and IL chemical structure was elucidated. A decrease in the hydrophobicity of the alkyl chain length was found to be a key factor to reduce IL toxicity. On the other hand, phosphonium-based ILs containing long alkyl chains were shown to be largely incompatible with Shewanella sp.

Discovering Low Toxicity Ionic Liquids for Saccharomyces cerevisiae by Using the Agar Well Diffusion Test

“…It is also important to remark the high toxicity observed for [Bmim+ ] [BF 4 − ] compared to [BDImim + ] [BF 4 − ].The inclusion of the methyl substituent in the R2 position of the imidazolium ring could reduce the acidic proton in 2, so lowering the toxicity of the IL. This effect was also recently observed for Shewanella[89].…”

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“…microorganism was largely incompatible with ILs with long alkyl chains that contained phosphonium-based cations. 78 Although it was previously assumed that the cation was the primary cause of toxicity, however, the importance of the anion should not be overlooked. Cho et al (2008) reported the toxicity of [Bmim]-based cation with different anions such as Br − , Cl − , [BF 4 ] − , [PF 6 ] − , [CF 3 SO 3 ] − , [C 8 H 17 SO 4 ] − and [SbF 6 ] − on Selenastrum capricornutum .…”

“…microorganism was largely incompatible with ILs with long alkyl chains that contained phosphonium-based cations. 78 Although it was previously assumed that the cation was the primary cause of toxicity, however, the importance of the anion should not be overlooked. ] − , which could be due to their ability to undergo hydrolysis in water.…”

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“…To that end, past studies showed that reducing hydrophobicity of alkyl chains was key to lowering IL toxicity. [33][34][35][36][37] In exploring this structure-activity relationship, Coleman and Gathergood proposed that adding polar functional groups, especially protic moieties, to alkyl side chains significantly decreases the likelihood of IL toxicity. 34 Despite the cation's primary role in narcosis, Cho et al and Santos et al showed that some anions, such as fluorinated ones, drive toxicity in imidazolium and cholinium-based ILs, which are generally regarded as safe.…”