# Ionic Liquids for Development of Heterogeneous Catalysts Based on Nanomaterials for Biocatalysis
## 3 Supported Ionic Liquid Phases in Biocatalysis  
The first reports concerning the supported ionic liquid phase (SILP) biocatalysts were reported in 2002. CALB was dissolved in 1-ethyl-3-methylimidazolium triflimide ([EMIM][NTT2]) or 1-butyl-3-methylimidazolium triflimide ([BMIM][NTT2]), then immobilized on the solid adsorbent (Celite) and used in a continuous butyl butyrate synthesis and the kinetic resolution of 1-phenylethanol in supercritical carbon dioxide (scCO\({}_{2}\)). The scheme of the kinetic resolution of 1-phenylethanol racemate is presented in Figure 3. For both the transesterification reactions, the enzyme showed good catalytic activity, selectivity, and, in the case of the kinetic resolution reaction, high enantioselectivity (>99.9%) and stability (16 cycles) in the anhydrous conditions [24]. In the next year, the same SILP system was tested for the kinetic resolution of 1-phenylethanol at a higher temperature (120 \({}^{\circ}\)C) and a lower scCO\({}_{2}\) pressure (10 MPa). The loss of activity was not observed, even after 10 cycles [25]. In both cases, the use of ionic liquids increased the stability and activity of the enzyme in a high-temperature and scCO\({}_{2}\) environment [24; 25]. Next, the studies of this group focused on the influence of the alkyl chain in the ionic liquid's cation on the enzyme  
Figure 2: Structures of ionic liquids used for enzyme stabilization. stabilization, and pointed out the importance of mass transport phenomena between ionic liquid and scCO\({}_{2}\), in the case of the heterogeneous catalyst. The SILP biocatalyst was tested in the continuous kinetic resolution of 1-phenylethanol in scCO\({}_{2}\). Immobilized on silica gel, CALB showed a 2000 times longer half-life time in the most hydrophobic IL (hexyl-trimethylammonium bis(trifluoromethylsulfonyl)imide), than in hexane [56]. The SILP-type biocatalyst, in the presence of scCO\({}_{2}\), was also studied in glycidyl butyrate synthesis. Firstly, the lipases from _Candida antarctica_ A (CALA), _Mucor nielei_ (MML), and CALB, were mixed with various ionic liquids and then their activity was tested. The CALB in [EMIM][NTf\({}_{2}\)] presented the best R/S ratio. Accordingly, a selected enzyme-IL mixture was immobilized on the solid particles and tested in a continuous process under scCO\({}_{2}\) conditions, resulting in high enantioselectivity and a little bit lower activity [57]. The other approach of performing biocatalysis under scCO\({}_{2}\) conditions is supported by the ionic liquid-like phase (SILLP). The enzyme-SILLP biocatalysts were described for the first time in 2007. In most cases, the enzymes were immobilized on polystyrene-divinylbenzene (PS-DVB) monolith, modified with imidazolium-based ionic liquids [27]. PS-DVB monolith is a very attractive support, due to the possibility of preparing proper morphologies, shapes, and properties, by cross-linking method synthesis. Modification of the polymeric surface can decrease the hydrophobicity of the support, when it is too high, which, in turn, can protect an enzyme from deactivation [58]. The first-studied SILLP biocatalyst was CALB immobilized onto PS-DVB, modified with imidazolium ionic liquid that was tested in the continuous flow citronethyl propionate synthesis in scCO\({}_{2}\). A high yield (93%) and stable activity (seven cycles) were reported for that catalytic system, at 80 \({}^{\circ}\)C [27]. The same SILLP biocatalyst was used in the combination with zeolites, in the continuous kinetic resolution of 1-phenylethanol in supercritical carbon dioxide. Previous reports of this group resulted in the high technological parameters (\(ee=97.4\%\), yield =74%) when immobilized CALB and zeolites were coated with ionic liquid in that process. To avoid the deactivation of the enzyme, the biocatalyst and acidic catalyst were packed under three different layers [59].