Feruloyl esterase (FAE; EC 3.1.1.73) catalyzes the hydrolysis of the 4-hydroxy-3-methoxycinnamoyl group in an esterified sugar to assist in waste biomass degradation or to release ferulic acid (FA). An FAE-producing strain was isolated from humus soil samples and identified as Bacillus pumilus SK52.001. The BpFAE gene from B. pumilus SK52.001 was speculated and heterogeneously expressed in Bacillus subtilis WB800 for the first time. The enzyme exists as a monomer with 303 amino acids and a molecular mass of 33.6 kDa. Its specific activity was 377.9 ± 10.3 U/ (mg protein), using methyl ferulate as a substrate. It displays an optimal alkaline pH of 9.0, an optimal temperature of 50 °C, and half-lives of 1434, 327, 235, and 68 min at 50, 55, 60, and 65 °C, respectively. Moreover, the purified BpFAE released 4.98% FA of the alkali-acidic extractable FA from de-starched wheat bran (DSWB). When the DSWB was enzymatically degraded by the synergistic effect of the BpFAE and commercial xylanase, the FA amount reached 49.47%. It suggested that the alkaline BpFAE from B. pumilus SK52.001, which was heterologously expressed in B. subtilis WB800, possesses great potential for biomass degradation and achieving high-added value FA production from food by-products.
Zwitterionic structure is necessary for Ni complexes to catalyze carbonylative polymerization (COP) of cyclic ethers. The cationic charge at the Ni center imparts sufficient electrophilicity to the Ni-acyl bond for it to react with cyclic ethers to give an acyl-cyclic ether oxonium intermediate, while the ligand-centered anionic charge ensures that the resultant oxonium cation is ion-paired with the Ni nucleophile. The current catalysts give non-alternating copolymers of carbon monoxide and cyclic ethers and are the most effective when both ethylene oxide and tetrahydrofuran are present as the cyclic ether monomers.
Iron oxide-hydroxide (FeOOH), a naturally abundant iron-based material, has been widely applied in electrode materials, adsorption of harmful ions, and degradation of organic pollutants. However, it has rarely been used as a heterogeneous catalyst in organic reactions. Herein, we attempt to extend its application to the catalytic synthesis of imines by preparing a Ce-doped α-FeOOH catalyst. The as-prepared Fe 0.9 Ce 0.1 OOH exhibited excellent catalytic performance in the atom-economic synthesis of imines by one-pot oxidative coupling from alcohols and amines. Mechanistic experiments and corresponding characterizations demonstrate that FeOOH acts as an intermediate facilitating the [O] cycling of Ce 4+ /Ce 3+ , enhancing the oxygen-activating capacity of the catalyst to accelerate the rate-controlling step of benzyl alcohol oxidation. Moreover, the FeOOH surface is rich in acid sites, which greatly promote the condensation of aldehyde and amine. The present work may provide new insights into the design of novel active and eco-friendly catalysts for organic oxidation reactions.
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