F. Tomás-Alonso

Over-activity and stability of laccase using ionic liquids: screening and application in dye decolorization

The use of a wide range of water miscible and immiscible ionic liquids (ILs) as reaction media for ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) oxidation by Trametes versicolor laccase was studied. Thirteen ILs were shown to be suitable media for the laccase oxidation reaction, increasing the activity with respect to conventional media. Among them, the water-miscible IL choline dihydrogen phosphate [Chol][H2PO4] allowed over-laccase activity with an enhancement rate of 451% at 25 °C and pH 7.0. This ionic liquid improved the stability of the enzyme in the face of high temperature and high pH, while storage at room temperature in aqueous medium was increased up to 4.5 times. Moreover, it was found that in the reaction medium for decolourizing dyes (antraquinonic and azoic) using laccase increased the decolourization rate by up to 216% and 137% for the azoic dyes Acid Black 1 and Remazol Brilliant Blue R, respectively. A high decolorization rate was also obtained for a mixture of dyes (80% within 8 h). To understand the effect of [Chol][H2PO4] on the secondary protein structure of the laccase, several spectroscopic techniques were used such as Circular Dichroism (CD), Fourier transform infrared (FT-IR) and Fluorescence, all of which demonstrated that the β sheet structure was affected. A shift to an α-helix structure [Chol][H2PO4] could be responsible for the enhancement of the enzyme activity observed at 300 mM.

Chapter 9 – Ion-Selective Electrodes Based on Ionic Liquids

This chapter seeks to provide an overview of a special type of ion-selective electrode based on ionic liquids and their role in modern potentiometry. The particularities of ionic liquids, which are well known and explained in other fields, are used to develop a number of potentiometric sensors in which these liquids act as plasticizers, ion exchangers, or both. The electrodes are based on polymer inclusion membranes made with ionic liquids, with and without added plasticizers and ionophores. The reported electrodes include conventional configurations with an inner solution and solid contact ion-selective electrodes. We have tried to systematize the extensive information available in the literature concerning the composition and performance of ion-selective electrodes based on ionic liquids and the main ionophores used in them. Finally, a brief review of their principal applications in the analysis of real samples is provided.