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991.
Fan Yang Wenhui Hu Chongqing Yang Margaret Patrick Andrew L. Cooksy Jian Zhang Jeffery A. Aguiar Chengcheng Fang Yinghua Zhou Ying Shirley Meng Jier Huang Jing Gu 《Angewandte Chemie (International ed. in English)》2020,59(11):4572-4580
A gas‐phase approach to form Zn coordination sites on metal–organic frameworks (MOFs) by vapor‐phase infiltration (VPI) was developed. Compared to Zn sites synthesized by the solution‐phase method, VPI samples revealed approximately 2.8 % internal strain. Faradaic efficiency towards conversion of CO2 to CO was enhanced by up to a factor of four, and the initial potential was positively shifted by 200–300 mV. Using element‐specific X‐ray absorption spectroscopy, the local coordination environment of the Zn center was determined to have square‐pyramidal geometry with four Zn?N bonds in the equatorial plane and one Zn‐OH2 bond in the axial plane. The fine‐tuned internal strain was further supported by monitoring changes in XRD and UV/Visible absorption spectra across a range of infiltration cycles. The ability to use internal strain to increase catalytic activity of MOFs suggests that applying this strategy will enhance intrinsic catalytic capabilities of a variety of porous materials. 相似文献
992.
Wing Ying Chow Brendan P. Norman Norman B. Roberts Lakshminarayan R. Ranganath Christian Teutloff Robert Bittl Melinda J. Duer James A. Gallagher Hartmut Oschkinat 《Angewandte Chemie (International ed. in English)》2020,59(29):11937-11942
Alkaptonuria (AKU) is a rare disease characterized by high levels of homogentisic acid (HGA); patients suffer from tissue ochronosis: dark brown pigmentation, especially of joint cartilage, leading to severe early osteoarthropathy. No molecular mechanism links elevated HGA to ochronosis; the pigment's chemical identity is still not known, nor how it induces joint cartilage degradation. Here we give key insight on HGA‐derived pigment composition and collagen disruption in AKU cartilage. Synthetic pigment and pigmented human cartilage tissue both showed hydroquinone‐resembling NMR signals. EPR spectroscopy showed that the synthetic pigment contains radicals. Moreover, we observed intrastrand disruption of collagen triple helix in pigmented AKU human cartilage, and in cartilage from patients with osteoarthritis. We propose that collagen degradation can occur via transient glycyl radicals, the formation of which is enhanced in AKU due to the redox environment generated by pigmentation. 相似文献
993.
Pan Li Shijun Xu Chunyang Yu Zi‐Ying Li Jianping Xu Zi‐Mu Li Lingyi Zou Xuebing Leng Shan Gao Zhiqiang Liu Xiaoyun Liu Shaodong Zhang 《Angewandte Chemie (International ed. in English)》2020,59(18):7113-7121
Considerable efforts have been made to increase the topological complexity of mechanically interlocked molecules over the years. Three‐dimensional catenated structures composed of two or several (usually symmetrical) cages are one representative example. However, owing to the lack of an efficient universal synthetic strategy, interlocked structures made up of dissymmetric cages are relatively rare. Since the space volume of the inner cavity of an interlocked structure is smaller than that outside it, we developed a novel synthetic approach with the voluminous reductant NaBH(OAc)3 that discriminates this space difference, and therefore selectively reduces the outer surface of a catenated dimer composed of two symmetric cages, thus yielding the corresponding catenane with dissymmetric cages. Insight into the template effect that facilitates the catenation of cages was provided by computational and experimental techniques. 相似文献
994.
Pengpeng Shao Ruxin Yao Ge Li Mengxi Zhang Shuai Yuan Xiaoqi Wang Yuhao Zhu Xianming Zhang Lin Zhang Xiao Feng Bo Wang 《Angewandte Chemie (International ed. in English)》2020,59(11):4401-4405
Commercial ultrafiltration membranes have proliferated globally for water treatment. However, their pore sizes are too large to sieve gases. Conjugated microporous polymers (CMPs) feature well‐developed microporosity yet are difficult to be fabricated into membranes. Herein, we report a strategy to prepare molecular‐sieving membranes by partitioning the mesoscopic channels in water ultrafiltration membrane (PSU) into ultra‐micropores by space‐confined polymerization of multi‐functionalized rigid building units. Nine CMP@PSU membranes were obtained, and their separation performance for H2/CO2, H2/N2, and H2/CH4 pairs surpass the Robeson upper bound and rival against the best of those reported membranes. Furthermore, highly crosslinked skeletons inside the channels result in the structural robustness and transfer into the excellent aging resistance of the CMP@PSU. This strategy may shed light on the design and fabrication of high‐performance polymeric gas separation membranes. 相似文献
995.
Yongjie Zhang Xiaopei Li Wenqin Zhu Mingshuai Fan Shuwei Wang Minjie Qu Yi Zhang Shuai Wang 《先进技术聚合物》2020,31(7):1602-1611
Polysiloxane/polyolefin copolymers have drawn much attention recently and emerged as a new group of functional polyolefin since they possess distinctive properties and find great potential applications in many areas (eg, compatibilizer, processing aid and surface modifier). However, traditional routes to synthesize polysiloxane/polyolefin copolymers generally require multi‐step labor‐consuming procedures. Herein, we report a novel one‐step synthesis of polydimethylsiloxane graft polyethylene (PDMS‐g‐PE) mimics. It was found that PDMS‐g‐PE mimics, namely vinylmethylsiloxane‐dimethylsiloxane‐(C30‐45 alkyl)methylsiloxane copolymers (short for VD‐AMS), could be formed via a one‐step synthetic procedure based on the siloxane equilibrium process between silanol‐terminated vinylmethylsiloxane‐methylsiloxane copolymer and (C30‐45 alkyl)methylsilicone. The chemical structures of VD‐AMS were characterized unambiguously using Fourier transform infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry. The correlation between reaction conditions and the structural parameters of VD‐AMS was established. Based on our experimental results, a plausible mechanism for the synthesis of VD‐AMS was proposed. Scanning electron microscopy micrographs showed that VD‐AMS could function as an efficient compatibilizer for immiscible PE/silicone blend. Given that the precursors of VD‐AMS are commercially available with low prices and that VD‐AMS can be easily synthesized under mild conditions, we believe VD‐AMS can represent as a competitive potential compatibilizer due to its relatively low cost. 相似文献
996.
建立电感耦合等离子体质谱法同时测定金银花中铅、镉、铬、镍、铜、砷6种有毒元素含量。采用微波消解法进行前处理,以钪、铟、铋3种元素作为内标物,用电感耦合等离子体质谱法对50批金银花样品中铅、镉、铬、镍、铜、砷6种有毒元素含量进行测定,以内标法定量,并应用SPSS软件对测定值进行统计学分析。6种有毒元素的质量浓度在0~300μg/L范围内线性良好,相关系数均不小于0.9997。6种有毒元素的检出限为0.003~0.020 mg/kg,样品加标回收率为80.0%~111.0%,相对标准偏差为0.71%~3.82%(n=6)。50批金银花样品中共计有14批样品有毒元素含量超出2015年版《中华人民共和国药典》规定,超标率为28%。聚类分析将50批样品分为3大类。该方法操作简单,灵敏度高,专属性好,可准确快速地同时测定金银花中多种有毒元素含量,可作为中药材品质及安全性监管的技术手段。 相似文献
997.
Shuo Tao Xiaolei Li Xiaoge Wang Ying Wei Yunling Jia Jing Ju Yuanhui Cheng Huaisheng Wang Shuwen Gong Xingjun Yao Haixu Gao Cunyin Zhang Qiqi Zang Zhijian Tian 《Angewandte Chemie (International ed. in English)》2020,59(9):3455-3459
The synthesis of hierarchical nanosized zeolite materials without growth modifiers and mesoporogens remains a substantial challenge. Herein, we report a general synthetic approach to produce hierarchical nanosized single‐crystal aluminophosphate molecular sieves by preparing highly homogeneous and concentrated precursors and heating at elevated temperatures. Accordingly, aluminophosphate zeotypes of LTA (8‐rings), AEL (10‐rings), AFI (12‐rings), and ‐CLO (20‐rings) topologies, ranging from small to extra‐large pores, were synthesized. These materials show exceptional properties, including small crystallites (30–150 nm), good monodispersity, abundant mesopores, and excellent thermal stability. A time‐dependent study revealed a non‐classical crystallization pathway by particle attachment. This work opens a new avenue for the development of hierarchical nanosized zeolite materials and understanding their crystallization mechanism. 相似文献
998.
Chunhua Zhao Shan Yan Qin Li Hucheng Zhu Zhiyu Zhong Ying Ye Zixin Deng Yonghui Zhang 《Angewandte Chemie (International ed. in English)》2020,59(24):9478-9484
While halogenated nucleosides are used as common anticancer and antiviral drugs, naturally occurring halogenated nucleosides are rare. Adechlorin (ade) is a 2′‐chloro nucleoside natural product first identified from Actinomadura sp. ATCC 39365. However, the installation of chlorine in the ade biosynthetic pathway remains elusive. Reported herein is a Fe2+‐α‐ketoglutarate halogenase AdeV that can install a chlorine atom at the C2′ position of 2′‐deoxyadenosine monophosphate to afford 2′‐chloro‐2′‐deoxyadenosine monophosphate. Furthermore, 2′,3′‐dideoxyadenosine‐5′‐monophosphate and 2′‐deoxyinosine‐5′‐monophosphate can also be converted, albeit 20‐fold and 2‐fold, respectively, less efficiently relative to the conversion of 2′‐deoxyadenosine monophosphate. AdeV represents the first example of a Fe2+‐α‐ketoglutarate‐dependent halogenase that converts nucleotides into chlorinated analogues. 相似文献
999.
Shuai Liu Xiaomeng Liu Sangen Zhao Youchao Liu Lina Li Qingran Ding Yanqiang Li Zheshuai Lin Junhua Luo Maochun Hong 《Angewandte Chemie (International ed. in English)》2020,59(24):9414-9417
Birefringent materials, which can modulate the polarization of light, are almost exclusively limited to oxides. Peroxides have long been overlooked as birefringent materials, because they are usually not stable in air. Now, the first peroxide birefringent material Rb2VO(O2)2F is reported, the single crystals of which keep transparency after being exposed in the air for two weeks. Interestingly, Rb2VO(O2)2F does not feature an optimal anisotropic structure, but its birefringence (Δn=0.189 at 546 nm) exceeds those of the majority of oxides. According to the first‐principles calculations, this exceptional birefringence should be attributed to the strong electronic interactions between localized π orbital of O22? anions and V5+ 3d orbitals, which may be also favorable to the stability in the air for Rb2VO(O2)2F. These findings distinguish peroxides as a brand‐new class of birefringent materials that may possess birefringence superior to the traditional oxides. 相似文献
1000.
Jinhu Wei Liangliang Wu Hai‐Xu Wang Xiting Zhang Chun‐Wai Tse Cong‐Ying Zhou Jie‐Sheng Huang Chi‐Ming Che 《Angewandte Chemie (International ed. in English)》2020,59(38):16561-16571
Reliable methods for enantioselective cis‐dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis‐α‐[FeII(2‐Me2‐BQPN)(OTf)2], which bears a tetradentate N4 ligand (Me2‐BQPN=(R,R)‐N,N′‐dimethyl‐N,N′‐bis(2‐methylquinolin‐8‐yl)‐1,2‐diphenylethane‐1,2‐diamine), was prepared and characterized. With this complex as the catalyst, a broad range of trisubstituted electron‐deficient alkenes were efficiently oxidized to chiral cis‐diols in yields of up to 98 % and up to 99.9 % ee when using hydrogen peroxide (H2O2) as oxidant under mild conditions. Experimental studies (including 18O‐labeling, ESI‐MS, NMR, EPR, and UV/Vis analyses) and DFT calculations were performed to gain mechanistic insight, which suggested possible involvement of a chiral cis‐FeV(O)2 reaction intermediate as an active oxidant. This cis‐[FeII(chiral N4 ligand)]2+/H2O2 method could be a viable green alternative/complement to the existing OsO4‐based methods for asymmetric alkene dihydroxylation reactions. 相似文献