Abstract
It is widely believed that lipases in ionic liquids (ILs) possess higher enzyme activity, stability and selectivity; however, reaction equilibrium is always limited by product inhibition, and the product is difficult to separate from non-volatile ILs using distillation. To solve this problem, using trialkylphosphine oxide (TOPO) as a complexing agent, a novel biphase of reactive solvent and IL was firstly reported for caffeic acid phenethyl ester (CAPE) production from methyl caffeate (MC) and 2-phenylethanol (PE) catalyzed by lipase via transesterification. The effects of the reaction parameters and their action mechanism were investigated, and the inhibition of CAPE against bacterial wilt pathogen Ralstonia solanacearum was firstly measured. The MC conversion of 98.83% ± 0.76% and CAPE yield of 96.29% ± 0.07% were obtained by response surface methodology in the 25 g/L TOPO-cyclohexane/[Bmim][Tf2N] (1:1, v/v); the complex stoichiometry calculation and FTIR spectrum confirmed that the reversible hydrogen-bond complexation between TOPO and caffeates significantly enhances the cooperative effect of two phases on the lipase-catalyzed reaction. The temperature was reduced by 14 °C; the MC concentration increased by 3.33-fold; the ratio of catalyst to donor decreased by 4.5-fold; and Km decreased 1.08-fold. The EC50 of CAPE against R. solanacearum was 0.17–0.75 mg/mL, suggesting that CAPE is a potential in vitro inhibitor of plant pathogenic bacteria.
Highlights
Biphase catalysis is an important protocol in a number of synthesis processes and has been identified as an active technique in many chemical reactions [1,2,3]
Our preliminary study proposed two schemes: one is to add 2% (v/v) DMSO as a co-solvent in the ionic liquids (ILs) to improve the solubility of caffeic acid (CA) from 4.5 g/L–9 g/L, obtaining a caffeic acid phenethyl ester (CAPE) yield of 79.53% via esterification from CA and PE [19]; the other is to use a continuous-flow packed-bed microreactor to replace a batch reactor, using methyl caffeate (MC) to replace CA, and a CAPE yield of 93.21% was achieved via transesterification from MC and PE [9]
Since the lipase-catalyzed synthesis of CAPE via transesterification using MC as a simple and accessible feedstock has been proven a feasible procedure [20,21], [Bmim][Tf2 N] is suitable for the dissolution of substrate MC due to its polarity being lower than that of [Emim][Tf2 N] [22], so we proposed a novel biphase of reactive solvent/[Bmim][Tf2 N] based on the idea of improving substrate solubility and the principle of biphase catalysis
Summary
Biphase catalysis is an important protocol in a number of synthesis processes and has been identified as an active technique in many chemical reactions [1,2,3]. It is highly desirable to develop a novel biphase system containing ILs and solvents with high efficiency for the lipase-catalyzed reaction. The anti-pathogen activity to control bacterial wilt, and the conventionally chemical control methods, such as 2% methanol of our lipase-catalyzed CAPE was studied in this work. The growth inhibition kinetic models for the lipase-catalyzed synthesis of CAPE using different media were proposed and activity of CAPE against bacterial wilt pathogen strain R. solanacearum was measured. Results and Discussion bacterial wilt pathogen strain R. solanacearum was measured
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