Tuning of hydrophilic ionic liquids concentration: A way to prevent enzyme instability

Ionic liquids (Us) are considered as green alternatives to organic solvents in various enzymatic biotechnological processes. A wide variety of hydrophilic and hydrophobic ionic liquids have been synthesized in order to investigate their effects on both enzyme activity and stability. In most cases, hydrophobic ILs such as those containing PF6(-) anion have shown better performances in enzymatic reactions. In the present work, the effect of alkyl chain length of [CnMIM][Br] (n = 2,4, 6,12) on hydrolytic activity of Thermoanaerobacter thermohydrosulfuricus lipase (TTL), as a model enzyme, was evaluated and compared with [C4MIM][PF6] as a hydrophobic ionic liquid. Moreover, effect of hydrophilic ILs on the activity and thermal stability of TTL in different concentrations of ionic liquids was studied. The results showed that TTL had the highest lipase activity in the presence of 0.3 M [C2MIM][Br], 1 M [C4MIM][Br] and 0.3 M [C6MIM][Br]. However, no significant effect was revealed in the presence of [C12MIM][Br]. A comparison between the effects of [C4MIM][PF6] and [C4MIM][Br] on the TL thermostability at 85 degrees C and 90 degrees C revealed that the hydrophobic anion PF6(-) provided a good stabilizing effect for TTL; although the influence of hydrophilic functions is also promising. According to the findings, it could be concluded that the TL and probably similar enzymes can be used for several biotransformation reactions by tuning the hydrophilic ionic liquids concentrations as solvents. (C) 2015 Elsevier B.V. All rights reserved.