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In the present study, pear polyphenol oxidase (PPO) was purified, immobilized and applied for the synthesis of theaflavin-3,3′-digallate (TF3). Firstly, PPO of pear ( Pyrus bretschneideri Rehd cv. Huangguan) was purified 24.36-fold in specific activity with a recovery of 6.77% by sequential use of precipitation with 70% saturated ammonium sulfate and chromatography of DEAE-Sepharose Fast Flow column. The purified pear PPO, found to be a dimer of identical subunits of molecular mass 35 kDa, was then successfully immobilized onto Fe 3 O 4 /chitosan nanoparticles via glutaraldehyde coupling reaction. Finally, TF3 was effectively synthesized by applying the immobilized PPO as biocatalyst with epicatechin gallate (ECG) and epigallocatechin-3- O -gallate (EGCG) as substrates, and the maximum yield of TF3 was 42.23% based on the amount of ECG added. In addition, the immobilized enzyme still remained 85% of its initial ability after successive usage of 8 cycles and could be stored for 30 days with less loss of activity. All the results suggest that the developed procedure is quite useful and has great potential for synthesis of TF3 and other theaflavins.
Various 3-dimensional C/CeO 2 hollow nanostructure frameworks (3D C/CeO 2 HNFs) were synthesized by using a polymer blowing process that is accelerated by adding a certain amount of cerium nitrate. Polyvinylpyrrolidone was used as the polymer. The resulting HNFs were characterized by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. The HNFs possess a large specific surface area, and the CeO 2 nanocrystals consist of a single phase. The HNFs display intrinsic peroxidase-like activity and can catalyze the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine in the presence of H 2 O 2 to produce a blue product. The method was applied to the quantification of H 2 O 2 with a 5.2 nM detection limit. The analytical range is from 10 nM to 1 μM. Schematic of the preparation of a 3-dimensional C/CeO 2 hollow nanostructure framework by a polyvinylpyrrolidone-blowing process accelerated by Ce(NO 3 ) 3 . They were applied to H 2 O 2 detection by catalyzing the oxidation of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to the oxidized 3,3′,5,5′-tetramethylbenzidine (oxTMB) to produce blue-color reaction.
Herein, we demonstrate the fabrication of cross-linked membranes based on sulfonated poly(arylene ether ketone sulfone) containing pendant amino groups (AM-SPAEKS) and triazole-grafted 3-Glycidyloxypropyltrimethoxysilane (GT) cross-linkers by a sol-gel process, then the obtained cross-linked membranes are named as AMSP/GT membranes. The GT cross-linkers are synthesized by the ring-opening reaction of the epoxy group and 3-amino-1,2,4-triazole. The AMSP/GT cross-linked membranes exhibit excellent thermal, oxidation and dimensional stability. Furthermore, the AMSP/GT membranes possess a low methanol permeability coefficient (9.95 × 10 −7 cm 2 s −1 at 60 °C) due to the formation of cross-linked network structures. In addition, the proton conductivity and relative selectivity of the AMSP/GT membranes are higher, at elevated temperatures (>80 °C), than AM-SPAEKS membranes. The highest proton conductivity of 0.135 S cm −1 is demonstrated, for the AMSP/GT-30 membrane, at 100 °C. The relative selectivity of AMSP/GT-30 can reach 7.54 × 10 4 S scm −3 which is three times higher than that of the AM-SPAEKS, at 60 °C. These results indicate that the AMSP/GT membranes can be promising candidates for practical applications such as proton exchange fuel cells etc.
Graphical A convenient, rapid and electrochemical one-pot protocol is designed for the synthesis of pyrazolo[3,4- b ]quinolines derivatives. The reaction is carried out in an undivided cell equipped with an iron cathode and a graphite anode in the presence of sodium bromide as a supporting electrolyte. Fourteen pyrazolo[3,4- b ]quinoline derivatives are obtained under a constant current of 30 mA after 0.14 F/mol of electricity passed. A convenient, rapid and electrochemical one-pot protocol was developed successfully for the preparation of pyrazolo[3,4- b ]-quinoline derivatives. The reaction is carried out in a 25 mL three neck flask equipped with graphite electrode as anode and iron electrode as cathode (electrode area of 1 cm 2 ) with sodium bromide as supporting electrolyte at room temperature in ethanol. Fourteen pyrazolo-[3,4- b ]-quinoline derivatives were synthesized by use of various aldehyde (including aryl aldehydes and aliphatic aldehydes), dimedone and 5-amino-3-methyl-1-phenylpyrazole as substrates in good yields (76–86 %) with a constant current of 30 mA after 0.14 F/mol of electricity passed. All aimed products were characterized by IR, 1 H NMR and HRMS. Notably, the presented method features ecologically sound, simple experimental procedure and good yields.
The selective oxidation of alkylbenzenes contributes greatly to the production of high-value chemicals. However, developing novel and efficient catalysts remains a great challenge. To explore new and efficient catalysts, a series of POMs of H(4+n)SiMo(12−n)VnO40 (SiMoVn, n = 1, 2 and 3) were reacted with rht-MOF-1 ([Cu6O(TZI)3(H2O)6]4·nH2O) by a one-pot self-assembly solvothermal method. As a result, three SiMoVn@rht-MOF-1 (1, n = 1; 2, n = 2 and 3, n = 3) were isolated. Single crystal analysis revealed that SiMoVn were successfully introduced in the cages of rht-MOF-1. When complex 3 was employed as a catalyst, it effectively catalyzed the selective oxidation of alkylbenzene with a conversion of 99% and selectivity of 99% under optimized reaction conditions. Recycling experiments proved that complex 3 is stable and recyclable after six cycles. In comparison with analogous catalysts, complex 3 exhibits outstanding catalytic performance. Furthermore, the kinetics and reaction mechanism were investigated and verified by EPR and XPS analysis. This approach paves a facile route to prepare POMs@MOFs for the selective oxidation of various alkylbenzenes.
Seven magnetic covalent organic framework molecularly imprinted polymers with magnetic responsiveness, large specific surface area, and molecular recognition ability were successfully synthesized, suitable for the separation of cyanidin-3-O-glucoside from complex samples. Using a room-temperature synthesis strategy, covalent organic frameworks accompanied by imprinted sites were formed in one step on the functionalized magnetic nanoparticles with 1,6-hexanediamine. The composite materials were easy to prepare and showed high adsorption capacity (127 mg g–1) together with favorable adsorption selectivity for cyanidin-3-O-glucoside over other flavonoids and phenolic acids. Magnetic covalent organic framework molecularly imprinted polymers exhibited good stability in 10 adsorption–desorption cycles. This work established a new method of extracting and separating high-purity anthocyanins and even unstable natural compounds.
Development of new birefringent crystals with enhanced properties remains an ongoing research priority. Through the exploration of guanidinium-containing oxalates with the structural modulation of Pb 2+ and Cl - , a new birefringent crystal, [C(NH 2 ) 3 ]Pb(C 2 O 4 )Cl·H 2 O (GPCCH), was successfully obtained. GPCCH was characterized by two types of π-conjugated building units, which contributes to the coexistence of a wide bandgap of 3.98 eV and a large birefringence of 0.24@546 nm. These findings highlight the synergistic role of π-conjugated building units and partially-chlorinated lead-containing units played in generating fascinating UV birefringent crystals.
Accumulating evidence indicates that consumption of berries may exert beneficial effects against oxidative stress mediated diseases. Pelargonidin -3-O- glucoside (Pg3G), a bioactive ingredient in strawberry, has been reported to possess a potent antioxidant capacity. This study was therefore designed to develop an effective method to prepare pure Pg3G from strawberry and investigate its protective effect against H 2 O 2 -induced oxidative stress. According to our results, Pg3G occupied 85.55% of total anthocyanin content in strawberry. 240 mg of Pg3G with the purity of 97.26% was finally isolated from 320 g of strawberry lyophilized powder (SLP) by combination of AB-8 macroporous resin and high-speed counter-current chromatography (HSCCC) technologies. Further study unveiled that Pg3G significantly inhibited H 2 O 2 -induced ROS generation, GSH depletion and mitochondrial dysfunction, thereby ameliorating H 2 O 2 -induced oxidative stress. Overall, this study suggests that pelargonidin -3-O- glucoside can be used as a natural bioactive agent to prevent cellular oxidative stress.
It has been found it more difficult in completely degrading A-ring of tetracycline (TC) than completely degrading B-D rings of tetracycline. Thus, it is very necessary to find an effective route to completely degrading A-ring of tetracycline. In this work, a Z-scheme heterojuncted core-shell La(OH) 3 @BaTiO 3 composite (LB) was designed and fabricated through hydrothermal method . Many characterization techniques were employed to investigate the microstructure, phases, composition, energy band structure , and the lifetime of photogenerated carriers. In the mean time, the photocatalytic properties, including the degradation of A-ring and B-D rings of TC, as well as active species during photo-degradation were investigated. It is found that the as-prepared LB has an improved lifetime of photo-produced carriers, as well as high photocatalytic properties, being attributed to the core-shell structured heterojunction La(OH) 3 @BaTiO 3 . In addition, it is also found that ·O 2 − is more effective on degrading A-ring of TC than other active species, likely owed to the PKa3 value (3.3) of A-ring in TC. This work has supplied a route to completely degrading the A-ring of TC: rationally design and prepare a Z-scheme heterojuncted composites which supply very negative conduction band bottom potential.
Compared with jagged and rod-like raw products, the spherulitic 3-nitro-1,2,4-triazol-5-one (NTO) crystalline powder is generally superior in the formulation. However, the growth mechanism and corresponding influential factors for NTO spherulites remain to be deeply explored. Herein, the morphological evolutions of NTO crystals in alcohol solvents under a range of maximum supersaturation (Smax) are systematically investigated. It was found that differences in solvent-crystal interface interactions determine the primary morphology of the growing crystals while the magnitude of Smax determines the subsequent polycrystalline evolution. The cooling rate, initial concentration and stirring rate all could affect the crystal morphology by changing the Smax. It is demonstrated that there exists a critical Smax range (1.75–1.88) above which the formation of spherulites is kinetically favorable. Face indexing tests suggest that the (0 0 1) plane of NTO is mostly prone to twinning at low supersaturation, which is because that the molecular layers on the (0 0 1) surface are prone to twisting and the energy difference before and after is only 8.77 kJ mol−1. Then, the interfacial growth theory is employed to explain how a growing crystal plane develops from smooth to rough with non-crystallographic sub-individuals as the crystallization driving force increases. The change of morphology has a positive consequence in improving the safety performance of NTO crystalline powder under drop-weight impact. These findings would forward the understanding of the spherulitic crystallization process for energetic crystals.
Skeletal fluorosis is a chronic metabolic bone disease caused by long-term excessive fluoride intake. Abnormal differentiation of osteoblasts plays an important role in disease progression. Research on the mechanism of fluoride-mediated bone differentiation is necessary for the prevention and treatment of skeletal fluorosis. In the present study, a rat model of fluorosis was established by exposing it to drinking water containing 50 mg/L F − . We found that fluoride promoted Runt-related transcription factor 2 (RUNX2) as well as superoxide dismutase 2 (SOD2) and sirtuin 3 (SIRT3) expression in osteoblasts of rat bone tissue. In vitro, we also found that 4 mg/L sodium fluoride promoted osteogenesis-related indicators as well as SOD2 and SIRT3 expression in MG-63 and Saos-2 cells. In addition, we unexpectedly discovered that fluoride suppressed the levels of reactive oxygen species (ROS) and mitochondrial reactive oxygen species (mtROS) in osteoblasts. When SOD2 or SIRT3 was inhibited in MG-63 cells, fluoride-decreased ROS and mtROS were alleviated, which in turn inhibited fluoride-promoted osteogenic differentiation. In conclusion, our results suggest that SIRT3/SOD2 mediates fluoride-promoted osteoblastic differentiation by down-regulating reactive oxygen species.
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