Unprecedented regioselective acylation of flavonoid aglycones was achieved using Candida antarctica lipase B (CALB). The rapid screening of product formation was performed by the use of the high resolution phenol-type OH (1)H NMR spectral region recorded after the addition of picric acid.
In this work, neoteric and biodegradable ionic liquids (ILs) based on various hydroxyl ammonium cations and formic acid anion have been used as media for biocatalytic oxidoreductions catalyzed by different metalloproteins. The effect of these ILs on the biocatalytic behavior and structure of solubilized enzymes was investigated using cytochrome c (cyt c) as a model protein. The use of ILs-based media enhances the tolerance of cyt c against the denaturing effect of H 2 O 2 and increases (up to 20 fold) its catalytic efficiency compared to that observed in buffer. This beneficial effect strongly correlates with the concentration of ILs used, as well as the chaotropicity of their cations. UV-vis, circular dichroism and Fourier transform infrared (FT-IR) spectroscopic studies indicated that, the effect of ILs on the catalytic behavior of cyt c could be correlated with slight structural changes on the protein molecule and/or perturbations of the heme microenvironment. The use of hydroxyl ammonium-based ILs as reaction media increased (up to 4-fold) the decolorization activity of cyt c. All ILs used were recycled and successfully reused three times indicating the potential application of these novel ILs as environmentally friendly media for biocatalytic processes of industrial interest. Ionic liquids (ILs), also called molten salts, are 2 mixtures of cations and anions that melt below 100 o C and 3 have received considerable attention over the last decade as an 4 environmentally friendly alternative to organic solvents. Due to 5 their interesting physical and chemical properties, such as 6 negligible vapour pressure, ability to dissolve various 7 hydrophobic/hydrophilic compounds and excellent chemical 8 and thermal stability, they have been widely used as "green" 9 media for biocatalytic processes. 1-3 The first studies of enzyme-10 catalyzed reactions in ILs were reported in so called second 11 generation ILs, which are mainly based on cations of 12 heterogeneous cyclic amines, such as substituted imidazoliums 13 and alkyl pyridiniums, as well as poor nucleophilic anions, 15 In the last years, numerous studies of second 16 generation ILs, in the context of biocatalysis, revealed that 17 many enzymes exhibit excellent selectivity and activity and 18 maintain very high thermal and operational stability in these 19 solvents. 6-12 However, their use in large scale applications is 20 limited due to their difficult preparation and high cost. 1 21 Moreover, concerns have arisen regarding the environmental 42 combination of a Brønsted acid with a Brønsted base. 22,28 43 Furthermore, both cation and anion exhibit a considerably low
Biocatalytic lipophilization of hydroxycinnamic acids was performed in several BF(4)(-) and PF(6)(-) imidazolium ionic liquids using immobilized lipases. The influence of various reaction parameters on the performance of the biocatalytic process was pointed out, using as model reaction the esterification of ferulic acid. The biocatalytic lipophilization strongly depended on the ion composition of ionic liquids used. Conversions and initial reaction rates were significantly higher in PF(6)(-) as compared with BF(4)(-) ionic liquids and commonly used organic solvents. The high enzyme stability and the relative solubility of substrate versus product in PF(6)(-) ionic liquids can account for the improved synthesis of lipophilic ferulates. These lipophilic derivatives, when used at a concentration of up to 400-fold lower than the parental compound, efficiently inhibited the oxidation of isolated LDL, HDL and total serum in vitro. Moreover, it has been shown for the first time that the lipophilic ferulates improve the antioxidant efficiency of the HDL(3c) towards LDL in vitro oxidation.
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