Yongmei Xia

Metal-Free Three-Component Oxyazidation of Alkenes with Trimethylsilyl Azide and N-Hydroxyphthalimide

A novel and facile oxyazidation of alkenes under metal-free and mild conditions has been reported. A remarkable feature of the developed procedure is consecutive construction of C-O and C-N bonds in one step. The process allows quick and selective assembly of alkyl azide from readily available starting materials, where N-hydroxyphthalimide was used as an oxygen-radical precursor and TMSN3 as the N3 source. A range of aromatic alkenes bearing synthetically useful functional groups was tolerated.

Nonthermal Effect of Microwave Irradiation in Nonaqueous Enzymatic Esterification

Microwave has nonthermal effects on enzymatic reactions, mainly caused by the polarities of the solvents and substrates. In this experiment, a model reaction with caprylic acid and butanol that was catalyzed by lipase from Mucor miehei in alkanes or arenes was employed to investigate the nonthermal effect in nonaqueous enzymatic esterification. With the comparison of the esterification carried by conventional heating and consecutive microwave irradiation, the positive nonthermal effect on the initial reaction rates was found substrate concentration-dependent and could be vanished ostensibly when the substrate concentration was over 2.0xa0molxa0L−1. The polar parameter log P well correlates the solvent polarity with the microwave effect, comparing to dielectric constant and assayed solvatochromic solvent polarity parameters. The log P rule presented in conventional heating-enzymatic esterification still fits in the microwaved enzymatic esterification. Alkanes or arenes with higher log P provided positive nonthermal effect in the range of 2u2009≤u2009log Pu2009≤u20094, but yielded a dramatic decrement after log Pu2009=u20094. Isomers of same log P with higher dielectric constant received stronger positive nonthermal effect. With lower substrate concentration, the total log P of the reaction mixture has no obvious functional relation with the microwave effect.

Short-chain aliphatic ester synthesis using Thermobifida fusca cutinase

Short-chain aliphatic esters are commonly used as fruit flavorings in the food industry. In this study, Thermobifida fusca (T. fusca) cutinase was used for the synthesis of aliphatic esters, and the maximum yield of ethyl caproate reached 99.2% at a cutinase concentration of 50U/ml, 40°C, and water content of 0.5%, representing the highest ester yield to date. The cutinase-catalyzed esterification displayed strong tolerance for water content (up to 8%) and acid concentration (up to 0.8M). At substrate concentrations ⩽0.8M, the ester yield remained above 80%. Moreover, ester yields of more than 98% and 95% were achieved for acids of C3-C8 and alcohols of C1-C6, respectively, indicating extensive chain length selectivity of the cutinase. These results demonstrate the superior ability of T. fusca cutinase to catalyze the synthesis of short-chain esters. This study provides the basis for industrial production of short-chain esters using T. fusca cutinase.

Production of a bioactive sweetener steviolbioside via specific hydrolyzing ester linkage of stevioside with a β-galactosidase.

A β-galactosidase from Kluyveromyces lactis was found to specifically catalyze hydrolysis of the glycosyl ester linkage of stevioside to yield steviolbioside, a rare sweetener that also exists in Stevia rebaudiana leaves. In a packed bed reactor, a reaction coupling separation was realized and a production yield of steviolbioside reached 90% in 6 h. The hydrolysis product steviolbioside presented higher cytoxicity on human normal cells (hepatocytes cell L02 and intestinal epithelial cell T84) than stevioside did. Comparing to the typical chemotherapy agent, 5-fluorouracil (5-FU), steviolbioside presents much lower cytotoxicity on all assayed human normal cells; it presented notable inhibition on human hepatocarcinoma cell Hep3B, human breast cancer cell MDA-MB-231 and human pancreatic cancer cell BxPC-3. The remarkable inhibition on MDA-MB-231 cells makes steviolbioside a potential remedy for human breast cancer, when steviolbioside is served as a natural sweetener.

A facile solvothermal approach for the synthesis of novel W-doped TiO2 nanoparticles/reduced graphene oxide composites with enhanced photodegradation performance under visible light irradiation

High performance W-doped TiO2 nanoparticles/reduced graphene oxide (W-TiO2/RGO) composites are successfully synthesized through a facile solvothermal method. During this process, TiO2 was doped with W6+ to generate W-TiO2 nanoparticles, and graphene oxide (GO) was reduced to reduced graphene oxide (RGO), which was uniformly covered with a large number of W-TiO2 nanoparticles. The prepared samples were characterized by various analytical and spectroscopic techniques, including transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), specific surface areas (BET) and photoluminescence (PL) spectroscopy. The photocatalytic properties of the prepared samples were evaluated by the photodegradation of methylene blue (MB) as a model pollutant under visible light irradiation. The results confirmed that TiO2 was doped with W6+ and showed the graphene nature of RGO in W-TiO2/RGO composites. Additionally, it was found that W6+ doping could improve the photoresponse of TiO2 nanoparticles under visible light irradiation and graphene could provide conductive electron channels for the separation of electrons and inhibit the recombination of electrons and holes, hence further improving the response of W-TiO2 nanoparticles under visible light irradiation. The W-TiO2/RGO composites exhibited a much higher photocatalytic activity than mono-modified or non-modified composites and the degradation rate of the W-TiO2/RGO composites toward MB could reach up to 99.8% in 90 min. No obvious inactivation has been observed in durability experiments. The mechanism of enhanced photocatalytic activity, which arose from the synergistic effect of W6+ doping and graphene incorporation, was also discussed.

Steviol, a natural product inhibits proliferation of the gastrointestinal cancer cells intensively

New anticancer agents with lower toxicity have been always urged because of drug resistance associated with overused chemotherapy agents. In this study, steviol, a colonic metabolite of natural sweetener and also a component in leaves of stevia rebaudiana bertoni, was found to possess intensive anticancer activity on the human gastrointestinal cancer cells. Steviol inhibited six human gastrointestinal cancer cells intensively as 5-fluorouracil did at 100 μg/mL. The inhibition mechanism follows mitochondrial apoptotic pathway that was evidenced by increase of Bax/Bcl-2 ratio, activation of p21 and p53; and caspase 3-independent mechanism was also involved. These results are consistent with the miRNA expression analysis. The most regulated miRNAs in the steviol treated gastrointestinal cancer cells were miR-203a-3p (log2 =1.32) and miR-6088 (log2 =-2.54) in HCT-116, miR-1268b (log2 =19.85) and miR-23c (log2 =-2.05) in MKN-45. In view of the metabolic characteristics of steviol and its cytotoxicity on the cancer cells, steviol could be a chemotherapy agent potentially for cancer treatment.

Soymeal-catalyzed facile and economic bioproduction of soybean oil hydroperoxide

Abstract The catalytic performance of defatted soymeal in the hydroperoxidation of soybean oil, which exploits the simultaneous release of enzyme and lipoxygenation, was evaluated using ethanol as a co-solvent. The influences of various parameters on hydroperoxide yield, including co-solvent, pH, temperature and dosage of soymeal and soybean oil, were investigated. The reaction catalyzed by crude lipoxygenase was carried out to compare its catalytic performance with that of soymeal. As a result, a facile, cheap and practical biotransformation for the synthesis of lipid hydroperoxide with satisfactory yield catalyzed by soymeal has been demonstrated.

Zirconium tripolyphosphate as an efficient catalyst for the hydrogenation of ethyl levulinate to γ-valerolactone with isopropanol as hydrogen donor

Hydrogenation of levulinic acid and its esters to produce γ-valerolactone (GVL) is an important reaction in the process of biomass valorization. Herein, a series of novel and porous acid–base bifunctional Zirconium tripolyphosphate were successfully synthesized and utilized to catalyze the hydrogenation of ethyl levulinate (EL) to GVL. It was found that Zr-TPPA-3 with a large number of Lewis acid–base sites and a high specific area displayed the highest catalytic activity, a satisfied GVL yield of 93.1% with 99.5% EL conversion was obtained under the optimal reaction conditions. In addition, poisoning experiments revealed that the acid–base sites play a synergistic effect in the hydrogenation of EL to GVL, and finally proposed a plausible reaction mechanism.

A facile approach for the synthesis of Z-scheme photocatalyst ZIF-8/g-C3N4 with highly enhanced photocatalytic activity under simulated sunlight

In this study, ZIF-8-modified g-C3N4 (ZIF-8/g-C3N4) composites were successfully synthesized by hydrothermal reaction. The properties of the ZIF-8/g-C3N4 composites were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence (PL) spectroscopy. The results indicated that the ZIF-8 grew on the surface of the g-C3N4, forming closely contacted interfaces between the ZIF-8 and the g-C3N4 component. The photocatalytic performance of the ZIF-8/g-C3N4 composites was evaluated through the photodegradation of Rhodamine B (RhB). The results showed that 99.8% of RhB was degraded by the ZIF-8/g-C3N4 composite with 3 wt% of ZIF-8 in 60 min under simulated sunlight, which was much higher than that of pure g-C3N4 and ZIF-8. This highly enhanced photocatalytic activity of the ZIF-8/g-C3N4 composites can be mainly attributed to strong interfacial interaction promoting the photo-generated electron–hole separation and migration. The results of radical scavenger experiments showed that ˙O2− and h+ were the dominant reactive species in the photocatalytic reaction. In addition, the ZIF-8/g-C3N4 composites showed excellent stability over several reaction cycles. Finally, a possible Z-scheme photocatalytic mechanism was proposed based on the experimental results.

Influence of substrates on the in vitro kinetics of steviol glucuronidation and interaction between steviol glycosides metabolites and UGT2B7

Abstract Steviol glycosides, a natural sweetener, may perform bioactivities via steviol, their main metabolite in human digestion. The metabolising kinetics, i.e. glucuronidation kinetics and interaction between steviol glycosides or their metabolites and metabolising enzyme, are important for understanding the bioactivity and cytotoxicity. The present study investigated kinetics of steviol glucuronidation in human liver microsome and a recombinant human UDP-glucuronosyltransferases isomer, UGT2B7, along with molecular docking to analyse interaction between UGT2B7 and steviol or glucose. The active pocket of UGT2B7 is consisted of Arg352, Leu347, Lys343, Phe339, Tyr354, Lys355 and Leu353. The influence of stevioside, rebaudioside A, glucose and some chemotherapy reagents on the glucuronidation was also studied. The predicted hepatic clearence suggested that steviol could be classified as high-clearence drug. The steviol glycosides did not affect the glucuronidation of steviol notably.