Organic Synthesis

Methods for stabilizing and activating enzymes in ionic liquids—a review

“…55 Lou et al 56 4 ]. They explained that the decreasing stability was, in general, consistent with the increasing order of nucleophilicity (PF 6 − < BF 4 − < Tf 2 N − < dca − ), where the more nucleophilic anions tend to interact with the positively charged sites in enzymes and to modify the enzyme's conformation. On the other hand, they also realized that the enzyme stability was in agreement with the hydrophobicity of ILs: both enzymes were more stable in hydrophobic ILs than in hydrophilic ones (see more discussion in a later section).…”

“…This suggests higher anion nucleophilicity correlating with higher enzymatic activity. In a second acylation reaction of 2-phenyl-1-propylamine with 4-pentenoic acid, however, Irimescu and Kato 61 observed that PF 6 − based ILs afforded fastest reaction rates, followed by OTf − and BF 4 − based ILs. The rather confusing results may be because the enzymatic reaction is affected by multiple factors of ILs such as nucleophilicity, hydrophobicity, viscosity and impurity.…”

“…They explained that OTf − and BF 4 − are more nucleophilic than PF 6 − . The second factor could be IL hydrophobicity (see more discussion in a later section) because lipases seemed more active in hydrophobic ILs than in hydrophilic ones.…”

“…However, it is not quite clear if such an effect exists in pure ILs or ILs with trace amounts of water, and how the IL hydrophobicity may influence the kosmotropicity. For example, PF 6 − is a chaotropic anion, 70 and denatures enzymes when dissolved in aqueous solutions as Na + or K + salt (more denaturing than BF 4 − and MeSO 4 − for mushroom tyrosinase 76 ). However, PF 6 − based ILs (such as [BMIM][PF 6 ]) are hydrophobic, and thus the solubility and degree of ion dissociation of ILs in water are limited.…”

Development of a Supported Ionic Liquid Phase (SILP) Catalyst for Slurry‐Phase Friedel–Crafts Alkylations of Cumene

“…[13] Numerous applications of these acidic chloroaluminate ionic liquids have been already reported. [14] Examples include various alkylation reactions of benzene and toluene with alkyl halides and alkenes as the alkylation agent, [15][16][17] linear alkylbenzene production for surfactant synthesis [18] and isobutene alkylation with 2-butene. [19] In the last five years the immobilization of catalytic ionic liquids on porous supports has become known as the so-called "supported ionic liquid phase (SILP)" concept.…”