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

Ionic liquids (ILs) are new solvents widely used in many technologies due to their unique and advantageous physicochemical properties. In biotechnological applications, ILs can be used along with microorganisms such as Saccharomyces cerevisiae. Due to the enormous number of ILs that can be synthesized through the combination of different anions and cations, it is necessary to have an easy and quick tool for the preliminary screening of their biocompatibility for being used in biotechnological applications. In this work, the agar well diffusion test was successfully applied as a rapid method to identify toxic/nontoxic ILs toward S. cerevisiae. Sixty-three ILs containing a diverse set of cations and anions were used. Through this methodology, nine fully biocompatible ILs toward S. cerevisiae were identified, including: [Bmim+] [NO3−], [HOPmim+] [NO3−], [Bmim+] [NTf2−], [N8,8,8,1+] [NTf2−], [S2,2,2+] [NTf2−], [EMPyr+] [NTf2−], [BMPi+] [NTf2−], [Moxa+] [MeSO4−] and [Chol+] [H2PO4−]. The analysis of the results also provides preliminary rules to enable the design of biocompatible ILs with S. cerevisiae. In this context, the toxicity was mainly determined by the cation nature although some anions can also display a strong influence on the IL biocompatibility as the bistriflimide anion. Besides, it was observed that an increase in the alkyl chain length of cations, such as imidazolium or pyridinium, involves an increase in the IL toxicity.