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121.
Guifa Zhai Wenyan Wang Dr. Wei Xu Guo Sun Chaoqun Hu Xiangming Wu Zisong Cong Liang Deng Yanrong Shi Prof. Dr. Peter F. Leadlay Prof. Dr. Heng Song Prof. Dr. Kui Hong Prof. Dr. Zixin Deng Prof. Dr. Yuhui Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(50):22926-22930
The colinearity of canonical modular polyketide synthases, which creates a direct link between multienzyme structure and the chemical structure of the biosynthetic end-product, has become a cornerstone of knowledge-based genome mining. Herein, we report genetic and enzymatic evidence for the remarkable role of an enoylreductase in the polyketide synthase for azalomycin F biosynthesis. This internal enoylreductase domain, previously identified as acting only in the second of two chain extension cycles on an initial iterative module, is shown to also catalyze enoylreduction in trans within the next module. The mechanism for this rare deviation from colinearity appears to involve direct cross-modular interaction of the reductase with the longer acyl chain, rather than back transfer of the substrate into the iterative module, suggesting an additional and surprising plasticity in natural PKS assembly-line catalysis. 相似文献
122.
Yuhong Li Xin-Ping Wu Cong Liu Meng Wang Benteng Song Guiyun Yu Gang Yang Wenhua Hou Xue-Qing Gong Luming Peng 《物理化学学报》2020,36(4):1905021-0
Partially reduced TiO2 nanomaterials have attracted significant interest because of their visible-light activity for catalysis and photodegradation. Herein, we prepared a partially reduced anatase TiO2 (Re-A-TiO2) nanoparticle material using a fast combustion method, demonstrating good activity toward decomposing methyl orange under visible light irradiation. The surface structure of the prepared material, after being surface-selectively 17O-labeled with H217O (17O-enriched water), was studied via 17O and 1H solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, and the obtained results were compared to those of non-reduced anatase TiO2 (A-TiO2). The EPR results showed that the concentrations of paramagnetic species (i.e., oxygen vacancies (OV) and Ti3+) in Re-A-TiO2 were much higher than that in A-TiO2, while the former was associated with a higher OV/Ti3+ ratio. The intensities of the EPR signals were significantly affected by the adsorbed water, and this phenomenon was explored in combination with 1H NMR spectroscopy. The 1H species on Re-A-TiO2 appeared at larger chemical shifts, denoting the increased acidity of the sample, and these 1H species on Re-A-TiO2 were more difficult to remove than those on A-TiO2. On the other hand, different features were observed for the signals arising from the two-coordinated oxygen atoms (μ2-O) in 17O NMR, suggesting a typical anatase TiO2(101) surface on A-TiO2, but a more complex surface environment for Re-A-TiO2. Furthermore, a larger amount of hydroxyl groups (OH) were observed on Re-A-TiO2 compared to that on A-TiO2, indicating a larger proportion of exposed (001) facets on Re-A-TiO2. However, the μ2-O signals broadened and became similar when the drying temperature was increased to 100 ℃, indicating a non-faceted anatase TiO2 surface in such conditions. Based on the EPR and NMR results, a significant fraction of the OH species is believed to be formed from the reaction of the paramagnetic centers and adsorbed water molecules. The 1H→17O cross polarization (CP) MAS and two-dimensional heteronuclear correlation (2D HETCOR) NMR spectra were used to verify the spatial proximity of the hydrogen and oxygen species, confirming the spectral assignments of a strongly adsorbed water and one type of surface OH species. In particular, the 1H NMR signals at approximately 11 ppm were ascribed to the hydrogen species in the intramolecular hydrogen bond. In summary, this study investigated the paramagnetic species and surface structure of anatase TiO2 materials by combining EPR along with 1H and 17O solid-state NMR spectroscopy. The differences in the surface structures of Re-A-TiO2 and A-TiO2 should be closely related to their different properties toward the photodegradation of methyl orange. 相似文献
123.
ABSTRACTTwo series of novel side-chain liquid crystal (LC) polysiloxanes grafted with chiral liquid crystalline dimers containing cholesteryl mesogens were synthesised. The chemical structure and LC properties of comonomers and polymers were characterised by FTIR, 1H-NMR, DSC, TGA, POM and XRD. M1 and M2 were chiral nematic (N*) dimers, and M3 was an achiral LC monomer displaying nematic mesophase in a narrow mesomorphic temperature range, while the copolymers exhibited N* mesophase whose mesomorphic temperature ranges were much wider than those of the comonomers. Moreover, the glass transition temperatures and isotropization temperatures of the polymers all decreased with decreasing the dimer components. Reflection spectra showed that Pa series tend to attain wide-band selective reflection at long wavelengths, while Pb series were more potential at short wavelengths with narrow bandwidths. Decreasing the dimer components led the wavelength of the selective reflection to blue shift, which was an abnormal phenomenon in chiral mixture system. 相似文献
124.
Wang Cong Wu Yancong Qu Yao Zhao Kun Xu Jianhua Xia Xinzhao Wu Huilu 《Transition Metal Chemistry》2020,45(8):523-529
Three new metal complexes, namely: [Mn(AIDB)Cl2]·DMF (1), [Zn(AIDB)Br2]·CH3OH (2) and [Co(AIDB)Cl2]·CH3OH (3) having a ligand bis(benzimidazol-2-ylmethyl)allylamine (AIDB), have been synthesized in high yields and characterized by elemental analyses, molar conductivities, IR, UV–Vis spectra and single-crystal X-ray diffraction. The structural analysis revealed that all the three complexes 1–3 have five-coordinated trigonal bipyramid geometry where the degree of distorting is 1>3>2. In vitro antioxidant activity assay demonstrates that the complexes 1 and 3 display high scavenging activity against hydroxyl (OH·) and superoxide (O2−·) radicals.
相似文献125.
碳氢键选择氧化是合成化学领域的重要课题,其中烷烃选择性羟化反应更是面临着化学选择性、区域选择性和立体选择性等多重挑战.细胞色素P450酶广泛分布于动植物和微生物体内,是公认的多功能生物氧化催化剂.P450酶对惰性C-H键的选择性氧化具有独特优势,在催化烷烃选择性羟化反应方面拥有巨大潜力.本综述简述了P450单加氧酶及其催化烷烃选择性羟化的反应机理,梳理了来自CYP153家族、CYP52家族和其他家族的天然P450酶催化各类烷烃底物的氧化反应和选择性,讨论了理性设计和定向进化策略在开发烷烃羟化P450突变酶过程中的经典案例,介绍了底物工程、诱饵分子、双功能小分子协同催化等几种化学活化P450酶的策略及其在烷烃羟化上的应用,探讨了P450酶在烷烃选择性羟化方面所面临的挑战和解决途径,并展望了其应用前景. 相似文献
126.
建立了化妆品中西咪替丁及雷尼替丁的高效液相色谱-四极杆/飞行时间高分辨质谱检测方法,并对其质谱裂解规律进行研究。待测样品经甲醇超声提取,过滤膜后经Zorbax SB-Aq色谱柱(3.0 mm×100 mm,1.8μm)分离,用乙腈-含0.1%甲酸的水溶液梯度洗脱后,在双喷雾电喷雾离子源正离子模式下检测,数据采集使用一级母离子全扫描和目标二级离子扫描。在不同的化妆品基质中,西咪替丁和雷尼替丁分别在5.65~113 ng/mL和4.95~99.0 ng/mL范围内线性关系良好(r0.999),检出限分别为1.1、0.99 ng/mL,定量下限分别为5.6、5.0 ng/mL;2种待测物在低、中、高3个加标水平下的回收率为86.7%~110%,相对标准偏差(RSD)为0.90%~6.0%,方法重复性良好(RSD10%)。该方法前处理简单,灵敏度较好,线性、回收率及重复性均满足方法学要求,可用于化妆品中西咪替丁和雷尼替丁的筛查测定。 相似文献
127.
Hollow multishelled structures(HoMSs)Co3O4 with specially appointed shell number(double-,triple-and quadruple-)were accurately prepared by a sequential templating approach.Due to the superiorities of inimitable porous multishelled structure,triple-HoMSs Co3O4 achieved the best performance among all the samples with a specific capacitance of 1028.9 F/g at 10 mV/s and 688.2 F/g at 0.5 A/g,respectively.Furthermore,the electrode delivered a high rate performance(89.8%retention at 10 A/g)and excellent cycle stability(6.8%loss over 2000 cycles),showing a great promise for practical application in the future. 相似文献
128.
Huan Ge Dongya Wang Yue Pan Yuanyuan Guo Hongyu Li Fan Zhang Xinyuan Zhu Yuehua Li Chuan Zhang Ling Huang 《Angewandte Chemie (International ed. in English)》2020,59(21):8133-8137
DNA‐modified lanthanide‐doped upconversion nanoparticles (DNA‐UCNPs) that combine the functions of DNA and the optical features of UCNPs have shown great promise in a wide range of fields. However, challenges remain in precisely tethering and orienting the DNA strands on the UCNP surface. Herein, we systematically investigate the sequence dependence of DNAs in their interactions with UCNPs, and reveal that poly‐cytosine (poly‐C) has high affinity for the UCNP surface. A general approach to synthesize monodispersed DNA‐UCNP conjugates is developed using poly‐C‐containing diblock DNA strands. The poly‐C segment of the DNA strand binds to the surfaces of UCNPs and the second segment is oriented perpendicularly on the UCNP surface, making the DNA‐UCNPs highly stable and monodispersed in aqueous solution. The dense layer of DNA on the UCNP surface enables the programmable assembly of UCNPs with other DNA‐functionalized nanoparticles or DNA origamis through hybridization, resulting in the formation of well‐organized complex structures. 相似文献
129.
Joji Tanaka Satu Hkkinen Parker T. Boeck Yidan Cong Sbastien Perrier Sergei S. Sheiko Wei You 《Angewandte Chemie (International ed. in English)》2020,59(18):7203-7208
An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification. 相似文献
130.
建立高效液相色谱-串联质谱法同时测定土壤中戊唑醇、腈菌唑、腈苯唑、氟硅唑、三唑酮、丙环唑、烯唑醇、苯醚甲环唑8种杀菌剂残留量的方法。采用QuEChERS样品前处理方法对土壤样品进行提取、净化和富集,用电喷雾离子源、正负离子扫描,以多反应监测(MRM)模式进行定性和定量分析。在优化的实验条件下,8种杀菌剂的质量浓度在0.01~0.50 mg/L范围内与色谱峰面积均成良好的线性关系,相关系数均大于0.995,方法检出限为0.005~0.010 mg/kg。样品平均加标回收率为85.6%~102.2%,测定结果的相对标准偏差为4.6%~13.2%(n=5)。该方法操作简便,灵敏度和准确度高,满足土壤中戊唑醇等8种杀菌剂残留量的测定要求。 相似文献