Said Gmouh

Criteria to Design Green Enzymatic Processes in Ionic Liquid/Supercritical Carbon Dioxide Systems

Five different ionic liquids (ILs) based on quaternary ammonium cations, with functional side chains ((3‐hydroxypropyl)‐trimethyl‐, (3‐cyanopropyl)‐trimethyl‐, butyl‐trimethyl‐, (5‐cyanopentyl)‐trimethyl‐ and hexyl‐trimethyl‐) associated with the same anion (bis(trifluoromethane)sulfonyl amide)), were synthesized, and their suitability for Candida antarctica lipase B (CALB)‐catalyzed ester synthesis in IL/supercritical carbon dioxide (scCO2) biphasic systems was assayed. Catalytic efficiency of the system has been analyzed as a function of both enzyme properties and mass‐transfer phenomena criteria. First, the suitability of these ILs as enzymic reaction media was tested for the kinetic resolution of rac‐phenylethanol. All ILs were found to be suitable media for enzyme catalysis, the best catalytic parameter (5.3 U/mg specific activity, 94.9% selectivity) being obtained for the (5‐cyanopentyl)‐trimethylammonium. Second, enzyme stability in all of the ILs was studied at 50 °C over a period of 50 days, and data were analyzed by a two‐step kinetic deactivation model. All of the ILs were shown to act as stabilizing agents with respect to hexane, producing an increase in the free energy of deactivation (to 25 kJ/mol protein) and an improvement in the half‐life time of the enzyme (2000‐fold), which agrees with the observed increased hydrophobicity of the cation alkyl side chain (measured by Hansenapos;s solubility parameter, δ). By using two different CALB‐IL systems with different hydrophobicity in the cation, continuous processes to synthesize six different short chain alkyl esters (butyl acetate, butyl propionate, butyl butyrate, hexyl propionate, hexyl butyrate, and octyl propionate) in scCO2 at 10 MPa and 50 °C were carried out. Both rate‐limiting parameters (synthetic activity and scCO2–ILs mass‐transfer phenomena) were related with the δ‐parameter of the ILs‐alkyl chain and reagents.

Dynamic structure–function relationships in enzyme stabilization by ionic liquids

The stability of α-chymotrypsin and Candida antarctica lipase B (CALB) in two ionic liquids (i.e. 1-ethyl-3-methyl-imidazolium, bis[(trifluoromethyl)sulfonyl]imide [emim] [NTf2], and butyl-trimethylamonium bis[(trifluoromethyl)sulfonyl]imide [btma] [NTf2]) has been studied. Both enzymes were strongly stabilized by the ionic liquids, the respective half-life times increasing 96 and 1660 times, with respect to those obtained in classical organic solvents such as 1-propanol and hexane, respectively. The stabilization of both enzymes by ionic liquids may be related to the associated structural changes of proteins that they can be observed by both fluorescence and circular dichroism spectroscopic studies.

Electrocatalytic dimerisation of PhBr and PhCH2Br in [BMIM]+NTf2− ionic liquid

Abstract The preparative electrocatalytic homocouplings of PhBr and PhCH 2 Br, yielding in biphenyl and 1,2-diphenylethane, respectively, were performed using NiCl 2 (bipy) complex in new reusable media for electrosynthesis, [BMIM]NTf 2 .

Superoxide-stable ionic liquids: new and efficient media for electrosynthesis of functional siloxanes

The electrogeneration of diorganylsilanones from difunctional precursors Y(CH(2))(3)(Me)SiX(2) and Ph(2)SiX(2)(Y = NH(2), CF(3), CN; X = Cl, OEt, OMe), performed in the presence of hexamethyldisiloxane or hexamethylcyclotrisiloxane (D(3)) in the ionic liquids [C(5)H(5)NC(8)F(18)].NTf(2), [C(5)H(5)NC(18)H(38)].NTf(2) and Me(3)BuN.NTf(2), which reveal high solubility of oxygen and are inert toward superoxide anion, allows functionalized siloxanes to be produced selectively in good isolated yields.