Ionic liquid buffered

The heme enzyme chloroperoxidase (CPO), produced by the marine fungus Caldariomycesfumago, is a versatile enzyme which exhibits a broad spectrum of chemical reactivities and it is recognized as a most promising biocatalyst for synthetic applications. Recently, pure (R)-phenyl methylsulfoxide (ee > 99 %) was prepared by chemo- and stereo-selective oxidation of phenyl methylsulfide with CPO in citrate buffer-ionic liquid mixtures. ... 

Fig. 4.4 Cyclic voltammogram at tungsten of a neutral buffered, ionic liquid protonated to a partial pressure of 6.1 Torr HCl.

The electrodeposition of alkaline and alkaline earth metals has been investigated in the neutral (buffered) ionic liquids for the purpose of applying the ionic liquids to electrolytes of rechargeable batteries using these metals as anodes. However, the... 

The anodic dissolution of magnesium. Mg, has been reported as possible in the basic or buffered ionic liquids that consist of EMI+ and DMPI [20]. However, the deposition of Mg is impossible due to the instability of metallic Mg against these organic cations, whereas the formation of Al-Mg alloys containing Mg up to 2.2 at% has been observed in the acidic EMICI-AICI3 ionic liquid [21]. Calcium and strontium dichlorides, CaCla and SrCla, are soluble in an acidic EMICI-AICI3 ionic liquid and the co-deposition of calcium and strontium with bismuth and copper has been examined in the acidic ionic liquid [22]. 

The electrodeposition of cadmium, Cd, is possible in the basic and neutral EMICI-AICI3 ionic liquids [56, 58]. In the basic ionic liquid, cadmium dichloride, CdCl2, dissolves and forms a divalent cadmium chlorocomplex anion, CdCl [69], which is reducible to metallic Cd at around — 1.2 V. In the case of a neutral buffered ionic liquid, the electrodeposition of Cd is observed at around —1.0 V, which is slightly positive than in the basic ionic liquid probably caused by the formation of more reducible species, CdCl3. ... 

A buffered ionic liquid is one in which the neutrality is maintained by reaction of excess alkali metal chloride when acid AICI3 is added. The latent acidity of this neutral system becomes observable when a weak base (B) such as A/,A/-dimethylaniline, pyrrole, or acetylferrocene is added.Reaction between the added base and the AICI3 results in adduct formation with precipitation of the alkali chloride MCI (Eq 2.29). 

For this specific task, ionic liquids containing allcylaluminiums proved unsuitable, due to their strong isomerization activity [102]. Since, mechanistically, only the linkage of two 1-butene molecules can give rise to the formation of linear octenes, isomerization activity in the solvent inhibits the formation of the desired product. Therefore, slightly acidic chloroaluminate melts that would enable selective nickel catalysis without the addition of alkylaluminiums were developed [104]. It was found that an acidic chloroaluminate ionic liquid buffered with small amounts of weak organic bases provided a solvent that allowed a selective, biphasic reaction with [(H-COD)Ni(hfacac)]. 

A similar catalytic dimerization system has been investigated [40] in a continuous flow loop reactor in order to study the stability of the ionic liquid solution. The catalyst used is the organometallic nickel(II) complex (Hcod)Ni(hfacac) (Hcod = cyclooct-4-ene-l-yl and hfacac = l,l,l,5,5,5-hexafluoro-2,4-pentanedionato-0,0 ), and the ionic liquid is an acidic chloroaluminate based on the acidic mixture of 1-butyl-4-methylpyridinium chloride and aluminium chloride. No alkylaluminium is added, but an organic Lewis base is added to buffer the acidity of the medium. The ionic catalyst solution is introduced into the reactor loop at the beginning of the reaction and the loop is filled with the reactants (total volume 160 mL). The feed enters continuously into the loop and the products are continuously separated in a settler. The overall activity is 18,000 (TON). The selectivity to dimers is in the 98 % range and the selectivity to linear octenes is 52 %. 

In some cases, impurities in the ionic liquids resulted in dramatic pH shifts, causing enzyme inactivation. This could sometimes be overcome simply by titration or higher buffer concentrations. In other cases, purification of the ionic liquid or an improved synthesis might be necessary. 

Enzymatic reactions are often performed in aqueous buffer solution addition of increasing amounts of ionic liquids sometimes caused precipitates of unknown composition. 

In order to broaden the field of biocatalysis in ionic liquids, other enzyme classes have also been screened. Of special interest are oxidoreductases for the enan-tioselective reduction of prochiral ketones [40]. Formate dehydrogenase from Candida boidinii was found to be stable and active in mixtures of [MMIM][MeS04] with buffer (Entry 12) [41]. So far, however, we have not been able to find an alcohol dehydrogenase that is active in the presence of ionic liquids in order to make use of another advantage of ionic liquids that they increase the solubility of hydrophobic compounds in aqueous systems. On addition of 40 % v/v of [MMIM][MeS04] to water, for example, the solubility of acetophenone is increased from 20 mmol to 200 mmol L ... 

Quartz (Si02) and other silicates are generally stable in acidic solutions but will dissolve in highly alkaline waste solutions, decreasing the pH of the waste. The process by which this reaction occurs is complicated because it creates complex mixtures of nonionic and ionic species of silica. Scrivner and colleagues39 discuss these reactions in some detail. They observe that the silicates in solution buffer the liquid. Also, laboratory experiments in which alkaline wastes have been mixed... 

As reported by Griengl and coworkers, benzaldehyde, decanal, undecanal, and dodecanal were reacted with HCN in a two-phase solvent system aqueous buffer and ionic liquids 1 -ethyl-3-methylimidazolium tetrafluoroborate, 1 -methyl-3-propylimidazolium tetrafluoroborate, and l-butyl-3-methyl-imidazolium tetrafluoroborate in the presence of the HNLs from Prunus amygdalus and Hevea brasiliensis. When compared with the use of organic solvents as the nonaqueous phase, the reaction rate was significantly increased and the enantioselectivity remained good [51]. 

M. Vaher, M. Koel and M. Kaljurand, Non-aqueous capillary electrophoresis in acetonitrile using ionic-liquid buffer electrolytes. Chromatographia Supplement, 53 (2001) 302-306. 

The primary source of error is ground loop currents. This is caused by galvanic errors introduced by small potentials resulting from the ionic liquids and dissimilar metals that the electrode is in contact with in a bioreactor. Additional sources of error are interactions with other electrodes. We have frequently found that a pH electrode not connected to an isolation amplifier that floats the reference can show errors of 1-2 pH units. A simple test is to measure the pH of a buffered solution on-line and off-line to check the accuracy of a measurement. 

Thioanisole (6.2 mg, 50 /imol) and CPO (67.4 U) were magnetically stirred at room temperature in a 10 mL test tube for 5 min in 2 mL of a mixture of ionic liquid-sodium citrate buffer solution (0.1 m, pH 5). A 1 1 mixture was used in the case of [Nni20H][Citr] and [mmimHCHsSOJ, whereas a 0.6 1.4 mixture was employed in the case of [Nni20H][OAc]. Hydrogen peroxide solution (7 wt%) was added in two portions initially 50 pmo and then an additional 25 /imol after 2 h. After 4 h the reaction was quenched by the addition of excess Na2S203. 

Table 11.1 Oxidation ofthioanisole with hydrogen peroxide and CPO at room temperature in a 1 1 ionic liquid/citrate buffer...

Ionic liquid Amount (v/v) of IL in citrate buffer (%) Conversion (%) Products ... 

An excellent demonstration of the tunability of ionic liquids for catalysis is provided by an investigation of the dimerization of 1-butene (235). A Ni(cod)(hfacac) catalyst (Scheme 23) was evaluated for the selective dimerization of 1-butene after it was dissolved in various chloroaluminate ionic liquids. Earlier work on this reaction with the same catalyst in toluene led to the observations of low activity and difficult catalyst separation. In ionic liquids of varying acidity, little catalytic activity was found. However, a remarkable activity was achieved by adding a weak buffer base to an acidic ionic liquid. The reaction took place in a biphasic reaction mode with facile catalyst separation and catalyst recycling. A high selectivity to the dimer product was obtained because of a fast extraction of the Cg product from the ionic liquid phase, with the minimization of consecutive reaction to give trimers. Among a number of weak base buffers, a chinoline was chosen. The catalyst performance was compared with that in toluene. The catalyitc TOF at 90°C in toluene was... 

FIGURE 17.1 (iJ)-Af,Af,Af-trimethyl-2-aminobutanol-bis(trifluoromethane-sulfon)imidate as tbe cbiral additive. (A) CE BGE Na-pbospbate buffer pH 6.0 and lOmM ionic liquid, analyte propranolol. (B) HPLC, mobile phase H2O acetonitrile (AcN) (6 4) with 10 mM ionic liquid, analyte 2,2 -diamino-l,l -binafthalene. (C) GC capillary column coated with the chiral ionic liquid, analyte citronella. (Reprinted with permission from Anal. Lett., 39, 1447, 2006. Copyright 2006, Taylor Francis.)... 

Scheme 5.2-21 Ni-catalyzed, diphasic, linear dimerization in a slightly acidic, buffered chloroaluminate ionic liquid.

Clay/ionic liquid modified electrodes Sun investigated the use of Hb/clay/IL composite MEs for the electrocatalytic detection of HjOj, TCA, and nitrite [43]. The IL [C4CiIm][PFg] (2 mL) was stirred with bentonite clay (1 mg) for 1 h after which 1 mg of Hb was dispersed into the mixture. A volume of this dispersion was then cast onto a freshly polished basal plane pyrolytic graphite (BPPG) electrode. UV-Vis studies revealed the position of the Hb Soret band to be 410 and 412 nm for dry and buffer-immersed films, respectively. This is consistent with a near-native environment surrounding the heme within Hb in the Hb/clay/... 

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