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991.
992.
本文报导了在十种手性铵盐催化下芳醛和氯仿的不对称诱导反应。同时还对影响产物旋光纯度的因素及其诱导机理进行了讨论。 相似文献
993.
希夫碱钴配合物的吸氧热力学及其自氧化作用 总被引:2,自引:0,他引:2
本文合成了一个新的双Schiff碱钴配合物,并研究了该配合物在吡啶溶液中的吸氧过程热力学。在4—24℃范围内,吸氧摩尔比为1:1,吸氧过程热力学参数为:△H=-26.8(±0.5)kJ/mol,△S=-89.2(±1.8)J/mol·K。在30—45℃范围内,吸氧摩尔比为2:1,吸氧过程的热力学参数为:△H=-172.6(±9.14)kJ/mol,△S=-517.3(±29.4)J/mol·K。温度超过45℃,自氧化作用变得明显,配合物中苄羟基被氧化为醛基。提出了可能的氧化反应机理。 相似文献
994.
Yukun Ma Xiaoxia You Dr. Jinbo Zhang Dr. Xiaowu Wang Dr. Xinhui Kou Prof. Dr. Shaofeng Liu Prof. Dr. Ronglin Zhong Prof. Dr. Zhibo Li 《Angewandte Chemie (International ed. in English)》2023,62(25):e202303315
Chemoselective terpolymerization can produce polymer materials with diverse compositions and sequential structures, and thus have attracted considerable attention in the field of polymer synthesis. However, the intrinsic complexity of three-component system also brings great chanllenge, in regard to the reactivity and selectivity of different monomers. Herein, we report the terpolymerization of CO2/epoxide/anhydride by a binary organocatalytic C3N3-Py-P3/TEB (triethylborane) system. Both the activity and chemoselectivity were highly dependent upon the molar ratio of C3N3-Py-P3 to TEB, and sequence-controlled poly(ester-carbonate) copolymers were readily synthesized through one-pot/one-step methodology by tuning the stoichiometric ratio of phosphazene/TEB. In particular, C3N3-Py-P3/TEB with a molar ratio of 1/0.5 exhibited an unprecedentedly high chemoselectivity for ring-opening alternating copolymerization (ROAC) of cyclohexene oxide (CHO) and phthalic anhydride (PA) first and then ROAC of CO2/CHO. Thus, well-defined triblock polycarbonate-b-polyester-b-polycarbonate copolymers can be produced from the mixture of CO2, CHO and PA using a bifunctional initiator. With C3N3-Py-P3/TEB=1/1, tapered copolymers were obtained, while random copolymers with high content of polycarbonate (PC) were synthesized with further increasing the amount of TEB. The mechanism of the unexpected chemoselectivity was further investigated by DFT calculations. 相似文献
995.
Bin Wu Tianxiao Sun Ya You Haibing Meng Dulce M. Morales Mailis Lounasvuori Abbas Beheshti Askari Li Jiang Feng Zeng Baoshan Hu Xiangzhi Zhang Renzhong Tai Zhichuan J. Xu Tristan Petit Liqiang Mai 《Angewandte Chemie (International ed. in English)》2023,62(27):e202219188
Metal/nitrogen-doped carbons (M−N−C) are promising candidates as oxygen electrocatalysts due to their low cost, tunable catalytic activity and selectivity, and well-dispersed morphologies. To improve the electrocatalytic performance of such systems, it is critical to gain a detailed understanding of their structure and properties through advanced characterization. In situ X-ray absorption spectroscopy (XAS) serves as a powerful tool to probe both the active sites and structural evolution of catalytic materials under reaction conditions. In this review, we firstly provide an overview of the fundamental concepts of XAS and then comprehensively review the setup and application of in situ XAS, introducing electrochemical XAS cells, experimental methods, as well as primary functions on catalytic applications. The active sites and the structural evolution of M−N−C catalysts caused by the interplay with electric fields, electrolytes and reactants/intermediates during the oxygen evolution reaction and the oxygen reduction reaction are subsequently discussed in detail. Finally, major challenges and future opportunities in this exciting field are highlighted. 相似文献
996.
Jingxi Deng Ruixue Bai Dr. Jun Zhao Guoquan Liu Dr. Zhaoming Zhang Dr. Wei You Prof. Wei Yu Prof. Xuzhou Yan 《Angewandte Chemie (International ed. in English)》2023,62(37):e202309058
Simultaneously introducing covalent and supramolecular cross-links into one system to construct dually cross-linked networks, has been proved an effective approach to prepare high-performance materials. However, so far, features and advantages of dually cross-linked networks compared with those possessing individual covalent or supramolecular cross-linking points are rarely investigated. Herein, on the basis of comparison between supramolecular polymer network (SPN), covalent polymer network (CPN) and dually cross-linked polymer network (DPN), we reveal that the dual cross-linking strategy can endow the DPN with integrated advantages of CPN and SPN. Benefiting from the energy dissipative ability along with the dissociation of host–guest complexes, the DPN shows excellent toughness and ductility similar to the SPN. Meanwhile, the elasticity of covalent cross-links in the DPN could rise the structural stability to a level comparable to the CPN, exhibiting quick deformation recovery capacity. Moreover, the DPN has the strongest breaking stress and puncture resistance among the three, proving the unique property advantages of dual cross-linking method. These findings gained from our study further deepen the understanding of dynamic polymeric networks and facilitate the preparation of high-performance elastomeric materials. 相似文献
997.
In Gyu Kim Won Ho Jung Gayeon You Hyukjin Lee Yoo Jin Shin Sun Woo Lim Byung Ha Chung Hyejung Mok 《Macromolecular bioscience》2023,23(4):2200423
In this study, a novel polyhistidine-incorporated lipid nanoparticle (pHis/LNP) is developed for the delivery of therapeutic globotriaosylceramide (Gb3) synthase siRNAs using a microfluidic device with pHis as a biocompatible method of endosome escape. To inhibit the expression of Gb3 synthase, six siRNAs against Gb3 synthase are designed and an optimal siRNA sequence is selected. Selected Gb3 synthase siRNA is incorporated into pHis/LNP to prepare a spherical siRNA pHis/LNP with a size of 62.5 ± 1.9 nm and surface charge of −13.3 ± 4.2 mV. The pHis/LNP successfully protects siRNAs from degradation in 50% serum condition for 72 h. Prepared pHis/LNP exhibits superior stability for 20 days and excellent biocompatibility for A549 cells. After treatment with fluorescence-labeled LNPs, dotted fluorescent signals are co-localized with Lysotracker in cells with LNPs, whereas strong and diffused fluorescence intensity is observed in cells with pHis/LNPs probably due to successful endosomal escape. The extent of Gb3 synthase gene silencing by siRNA pHis/LNP is greatly improved (6.0-fold) compared to that by siRNA/LNP. Taken together, considering that the fabricated siRNA pHis/LNP exhibits excellent biocompatibility and superior gene silencing activity over conventional LNP, these particles can be utilized for the delivery of a wide range of therapeutic siRNAs. 相似文献
998.
Prof. Yanyong Wang Dr. Yanjing Wang Dr. Minglei Song Dr. Siping Chen Dr. Jianrong Wei Dr. Jie You Dr. Bo Zhou Prof. Shuangyin Wang 《Angewandte Chemie (International ed. in English)》2023,62(21):e202217601
Nano-reduced iron (NRI) is a promising uranium adsorbent due to its strong reducibility and good selectivity, but it still faces the challenges of slow kinetics, limited and non-renewable active sites. In this work, we realized high efficiency uranium extraction under ultra-low cell voltage (−0.1 V) in seawater with 20 ppm UO2(NO3)2 solution by coupling electrochemical mediated FeII/FeIII redox and uranium extraction. The adsorption capacity and extraction efficiency of NRI after electrochemical uranium extraction (EUE) could reach 452 mg/g and 99.1 %, respectively. Combined with quasi-operando/operando characterization technologies, we clarified the mechanism of EUE and revealed that continuously regenerating FeII active sites by electroreduction could significantly enhance the property of EUE. This work here provides a new electrochemical mediated and low energy consumption uranium extraction strategy which also provides a reference for other metal resource recovery. 相似文献
999.
Yongsuk Jung Seok Yeol Yoo Yonghoon Jin Jaehyun You Seungcheol Han Jeongwoo Yu Prof. Dr. Yoonsu Park Prof. Dr. Seung Hwan Cho 《Angewandte Chemie (International ed. in English)》2023,62(13):e202218794
Here, we report a highly chemo-, diastereo-, and enantioselective allyl-allyl coupling between branched allyl alcohols and α-silyl-substituted allylboronate esters, catalyzed by a chiral iridium complex. The α-silyl-substituted allylboronate esters can be chemoselectively coupled with allyl electrophiles, affording a diverse set of enantioenriched (E)-1-boryl-substituted 1,5-dienes in good yields, with excellent stereoselectivity. By permuting the chiral iridium catalysts and the substrates, we efficiently and selectively obtained all four stereoisomers bearing two consecutive chiral centers. Mechanistic studies via density functional theory calculations revealed the origins of the diastereo- and chemoselectivities, indicating the pivotal roles of the steric interaction, the β-silicon effect, and a rapid desilylation process. Additional synthetic modifications for preparing a variety of enantioenriched compounds containing contiguous chiral centers are also included. 相似文献
1000.
Dimension-Controllable and Photo-Responsive Supramolecular Organic Framworks through Cucurbit[8]uril-based Self-Assembly 下载免费PDF全文
Jie Wang You Li Zi-juan Hai Yang-yang Yan Zan Hua Zhong-kai Wang Guang Yang 《化学物理学报(中文版)》2022,35(5):774-782
Dimension-controllable supramolecular organic frameworks (SOFs) with aggregation-enhanced fluorescence are hierarchically fabricated through the host-guest interactions of cucurbit[8]uril (CB[8]) and coumarin-modified tetraphenylethylene derivatives (TPEC). The three-dimensional layered SOFs could be constructed from the further stacking of two-dimensional mono-layered structures via simply regulating the self-assembly conditions including the culturing time and concentration. Upon light irradiation under the wavelength of 365 nm, the photodimerization of coumarin moieties occurred, which resulted in the transformation of the resultant TPEC\begin{document}$ _n $\end{document} /CB[8]\begin{document}$ _{4n} $\end{document} two-dimensional SOFs into robust covalently-connected 2D polymers with molecular thickness. Interestingly, the supramolecular system of TPEC\begin{document}$ _n $\end{document} /CB[8]\begin{document}$ _{4n} $\end{document} exhibited intriguing multicolor fluorescence emission from yellow to blue in the time range of 0\begin{document}$ - $\end{document} 24 h at 365 nm irradiation, possessing potential applicability for photochromic fluorescence ink. 相似文献