Reaction pathway and phase transitions in Al–Ti–Si system during differential thermal analysis

The present paper mainly studied the phase formation and reaction pathway of the Al–Ti–Si system in detail by thermal analysis combined with XRD and SEM observations. The phase formation sequence in Al–Ti–Si system from starting mixtures to final products with increasing temperature can be described as following: Al_(l) + Ti_(s) + Si_(s) → (Al–Si)_(l) + Ti_(s) + Si_(s) → Ti(Al,Si)_3(s) + Si_(s)Ti₅(Si,Al)₃ + Al_(l). More importantly, the solubility of Si in Ti(Al,Si)₃ decreased gradually while that of Al in Ti₅(Si,Al)₃ increased with temperature increasing, suggesting the transportation of Si atoms from intermediate aluminides Ti(Al,Si)₃ to final stable silicides Ti₅(Si,Al)₃ and hence further confirming the formation of Ti₅(Si,Al)₃ at the expense of Ti(Al,Si)₃.     

Three New Illudalane Sequiterpenoids from Pteris semipinnata

The chemical investigation of the aerial parts of Pteris semipinnata resulted in the isolation of three illudalane sesquiterpenoids, namely (2R)‐norpterosin B ( 1 ), (2R)‐12‐O‐β‐D ‐glucopyranosylnorpterosin B ( 2 ), and semipterosin A ( 3 ), along with three known compounds. The structures of 1 – 3 were established by spectroscopic methods, including extensive 2D‐NMR and CD analyses.     

An online method combining a Gasbench II with continuous flow isotope ratio mass spectrometry to determine the content and isotopic compositions of minor amounts of carbonate in silicate rocks

An online method using continuous flow isotope ratio mass spectrometry (CF‐IRMS) interfaced with a Gasbench II device was established to analyze carbon and oxygen isotopic compositions and to estimate the content of minor amounts of carbonate in silicate rocks. The mixtures of standard materials and high‐purity quartz are firstly used to calibrate different quantities of carbonate in silicates. The results suggest that the accuracy and precision of the online analysis are both better than those obtained using an offline method. There is a positive correlation between the carbonate weight and the Mass44 ion beam intensity (or peak area). When the weight of carbonate in the mixtures is greater than 70 µg (equal to ～1800 mV Mass44 ion beam intensity), the δ¹³C and δ¹⁸O values of samples usually have accuracy and precision of ±0.1‰ and ±0.2‰ (1σ), respectively. If the weight is less than 70 µg, some limitations (e.g., not perfectly linear) are encountered that significantly reduce the accuracy and precision. The measured δ¹⁸O values are systematically lower than the true values by ?0.3 to ?0.7‰; the lower the carbonate content, the lower the measured δ¹⁸O value. For samples with lower carbonate content, the required phosphoric acid doses are higher and more oxygen isotope exchanges with the water in the phosphoric acid. To guarantee accurate results with high precision, multiple analyses of in‐house standards and an artificial MERCK sample with δ¹³C values from ?35.58 to 1.61‰ and δ¹⁸O from 6.04 to 18.96‰ were analyzed simultaneously with the unknown sample. This enables correction of the measured raw data for the natural sample based on multiple‐point normalization. The results indicate that the method can be successfully applied to a range of natural rocks. Copyright © 2010 John Wiley & Sons, Ltd.     

Syntheses and characterizations of poly[2‐(dimethylamino)ethyl methacrylate]–poly(propylene oxide)–poly[2‐(dimethylamino)ethyl methacrylate] ABA triblock copolymers

A novel, near‐monodisperse, well‐defined ABA triblock copolymer, poly[2‐(dimethylamino)ethyl methacrylate]‐b‐poly(propylene oxide)‐b‐poly[2‐(dimethylamino)ethyl methacrylate], was synthesized via oxyanion‐initiated polymerization. The initiator was a telechelic‐type potassium alcoholate prepared from poly(propylene glycol) and KH in dry tetrahydrofuran. The copolymers produced were characterized by Fourier transform infrared, ¹H NMR, and gel permeation chromatography (GPC). GPC and ¹H NMR analyses showed that the products obtained were the desired copolymers, with narrow molecular weight distributions (ca. 1.09–1.11) very close to that of the original poly(propylene glycol). ¹H NMR, surface tension measurements, and dynamic light scattering all indicated that the triblock copolymer led to interesting aqueous solution behaviors, including temperature‐induced micellization and very high surface activity. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 624–631, 2002; DOI 10.1002/pola.10144     

Tirucallane‐Type Triterpenoids from Celastrus stylosus Wall.

Two new tirucallane‐type triterpenoids, (24Z)‐tirucalla‐7,24‐diene‐3β,11β,26‐triol ( 1 ) and (3S,24R)‐tirucall‐7‐ene‐3,24,25‐triol ( 2 ), along with the known compound celastrol ( 3 ), were isolated from the root barks of Celastrus stylosus Wall . The structures of 1 – 3 were established by spectroscopic methods, including extensive 2D NMR and MS analyses. It is the first report on tirucallane‐type triterpenoids from the genus Celastrus and may be of vital chemotaxonomic significance.     

How polydispersity of network polymers influences strain-induced crystal nucleation in a rubber

Network polymers in a rubber or a gel often contain non-uniform chain lengths. By means of dynamic Monte Carlo simulations of polymer mixtures with various compositions of two chain lengths, we investigated how the factor of polydispersity influences their strain-induced crystal nucleation. Under a high temperature and a high strain rate, the stretching of both polymers revealed that crystal nucleation is mainly accelerated by the presence of short-chain polymers; nevertheless, both polymers join together in the nucleation process. Further analysis proved that crystal nucleation is initiated from those highly stretched short segments, which are rich on the short-chain polymers.     

Purification and Characterization of a Urethanase from Penicillium variabile

Urethanase produced by Penicillium variabile was purified through ultrasonication, concentration by polyethylene glycol 20,000, and Superdex G-200 gel filtration chromatography. The molecular weight of urethanase was determined to be around 96 kDa by gel filtration. The purified enzyme showed a single band in SDS-PAGE with the molecular weight of ~13.7 kDa, which suggests that the enzyme has a multimeric structure composed of the same subunits. Peptide map fingerprinting analysis was then carried out by MALDI/TOF-TOF MS. Within the known sequences in NCBI, glucosamine-6-phosphate deaminase and 6-phosphogluconate dehydrogenase get high score as compared with urethanase. Sequence analysis informs that N-terminal sequence of urethanase is GTNTADNDAA. The Minchaelis constant (K _m) and maximum reaction rate (V _m) of urethanase are 27.2 mmol/L and 156.25 μmol/L min, respectively.     

Highly Diastereo‐ and Enantioselective Michael Addition of Nitroalkanes to 2‐Enoyl‐Pyridine N‐Oxides Catalyzed by Scandium(III)/Copper(II) Complexes

A C₂‐symmetric Schiff‐base ligand, derived from tridentate‐Schiff‐base, was developed and successfully applied to the asymmetric Michael addition of nitroalkanes to 2‐enoyl‐pyridine N‐oxides. With this newly catalytic system, an unprecedented diastereoselectivity was obtained in the asymmetric Michael addition of nitroalkanes to 2‐enoyl‐pyridine N‐oxides. In addition, a switch in enantioselectivity was achieved by using this newly catalytic system and our previous catalyst. After a facile reduction, the optically active adduct was converted to a biologically active dihydro‐2H‐pyrrol 4 a . Furthermore, a connection of two tridentate‐Schiff‐base subunits proved to be an effective strategy in ligand design.     

有机化学实验线上课程之扬长避短教学设计与实践篇

当前疫情线上教学重心正逐渐转移为如何优化线上课程。针对化学实验线上课程短于实验过程控制环节,而线下课程在时空、科教融合和课堂互动等存在一定的局限性的两难现状,我们以有机化学实验线上课程为例,介绍如何通过重建教案和重整课件、视频、虚拟仿真实验和MOOC等资源,对实验预习、直播课堂、实验过程控制和实验拓展等重要教学环节进行再设计,提高学生主动学习成效和促进科教融合的协同培养。     

Anti-inflammatory bibenzyls from the stems of Dendrobium huoshanense via bioassay guided isolation

Abstract

The stems of Dendrobium huoshanense have long been used to prevent various diseases, including inflammatory diseases. This study was aimed to explain the anti-inflammatory effect of D. huoshanense stems in LPS-induced RAW 264.7 macrophages and to discover potential anti-inflammatory compounds. Results exhibited that D. huoshanense stems ethanol extract could significantly inhibit LPS-induced production of NO, TNF-α and IL-1β. Based on bioassay guided strategy, four bibenzyls (1–4) were isolated from D. huoshanense stems for the first time. Anti-inflammatory assay showed 1–4 could remarkably inhibit the production of NO in LPS-induced macrophages. Moreover, quantitative RT-PCR analysis displayed that the mRNA levels of iNOs, TNF-α and IL-1β could also be significantly reduced by 1–4. These results suggested that D. huoshanense stems ethanol extract and bibenzyls 1–4 might be well developed as therapeutic agent to prevent inflammatory diseases.