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Studies on 2-Formylphenylboronic Acid-Based Ser/Thr ligation and Cys/Pen ligation

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Chinese Journal of Chemistry 2021年第10期39卷 2795-2800页

作者： Zhenquan Sun xuechen li Department of Chemistry State Key Laboratory of Synthetic ChemistryThe University of Hong KongHong KongSAR999077 China

Main observation and conclusion Developing an effective chemoselective ligation strategy for assembling unprotected peptide segments is important to peptide/protein *** ligation efficiency and selectivity depend on the chemistry between the C-terminal active ester of the peptide(e.g.,the thioester in Native Chemical ligation or the salicylaldehyde ester in Ser/Thr ligation and Cys/Pen ligation)and N-terminal functional groups of the second peptide(Cys or Ser/Thr).Increasing the reactivity of the ligation and decreasing the hydrolysis of the active ester are more like the opposite sites in *** investigated the potential application of the peptide acyl ester of 2-formylphenylboronic acid(2-FPBA)in the Ser/Thr ligation and Cys/Pen *** the assistance of boronic acid group,the peptidyl FPBA ester showed remarkable stability in aqueous buffer and its reactivity towards Ser/Thr and Cys/Pen also ***,the strong coordination of the amine at the N-terminus and boronic acid suppressed the acyl transfer process when the peptide acyl group was *** effects should be made to enhance the ligation chemistry.

关键词： Peptides Ser/Thr ligation Cys/Pen ligation Boron Conjugation

Strategies for network security

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Science China(Information Sciences) 2015年第1期58卷 120-133页

作者： li AngSheng li xuechen PAN YiCheng ZHANG Wei State Key Laboratory of Computer Science Institute of Software Chinese Academy of Sciences Beijing No.4 High School University of Chinese Academy of Sciences

Security of networks has become an increasingly important issue in the highly connected *** depends on attacks. Typical attacks include both cascading failure of virus spreading and of information propagation and physical attacks of removal of nodes or edges. Numerous experiments have shown that none of the existing models construct secure networks, and that the universal properties of power law and small world phenomenon of networks seem unavoidable obstacles for security of networks against attacks. Here, we propose a new strategy of attacks, the attack of rules of evolution of networks. By using the strategy, we proposed a new model of networks which generates provably secure networks. It was shown both analytically and numerically that the best strategy is to attack on the rules of the evolution of networks, that the second best strategy is the attack by cascading failure models, that the third best strategy is the physical attack of removal of nodes or edges, and that the least desirable strategy is the physical attack of deleting structures of the networks. The results characterize and classify the strategies for network security, providing a foundation for a security theory of networks. Equally important, our results demonstrate that security can be achieved provably by structures of networks, that there is a tradeoff between the roles of structures and of thresholds in security engineering,and that power law and small world property are never obstacles of security of networks. Our model explores a number of new principles of networks, including some topological principles, probabilistic principles, and combinatorial principles. The new principles build the foundation for new strategies for enhancing security of networks, and for new protocols of communications and security of the Internet and computer networks etc. We anticipate that our theory can be used in analyzing security of real systems in economy, society and technology.

关键词： complex networks security of networks strategy for network security cascading failure model of networks

Professor Henry N.C. Wong, extraordinary synthetic chemist and great mentor

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Chinese Chemical Letters 2019年第8期30卷 1461-1462页

作者： Zhen Yang xuechen li School of Chemical Biology&Biotechnology Peking UniversityShenzhen 518055China State Key Laboratory of Synthetic Chemistry Department of ChemistryThe University of Hong KongHong KongChina

Professor Henry *** obtained his *** with First Class Honours from The Chinese University of Hong Kong(CUHK)in 1973 and his *** from University College London(with Professor Franz Sondheimer)in *** working at Harvard University as a Postdoctoral Associate with Professor Robert ***,he returned to University College London to begin his independent research undertaking as Ramsay Memorial *** 1980 to 1982,Professor Wong did research at Shanghai Inst让ute of Organic Chemistry,The Chinese Academy of *** 1982,he went back to Hong Kong,and started his career at CUHK his alma *** retired in 2018,and is now Emeritus Professor of Chemistry and Research Profess or.

关键词： doctor Woodward N.

Establishing the structure-activity relationship of teixobactin

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Chinese Chemical Letters 2019年第8期30卷 1468-1480页

作者： Eilidh Matheson Kang Jin xuechen li Department of Chemistry State Key Laboratory of Synthetic ChemistryThe University of Hong KongHong KongChina Laboratory of Marine Drugs and Bioprodcuts Qingdao National Laboratory for Marine Science and TechnologyQingdao 266237China School of Chemistry University of EdinburghEdinburghUK

In 2015,a new antimicrobial peptide agent was discovered,termed *** the past few years,the structure-activity relationship of teixobactin has been extensively ***,the updated studies have been summarized to provide structure-activity relationship established to *** can be seen that position 1,2,5 and 6 of teixobactin are not tolerant of diversion from the native amino *** positions 7 and 11,native amino acids give the highest activity but there is tolerance for other amino *** 3,4,9 and 10 are very tolerant of substitution while maintaining good potency and a broad activity *** does not depend on absolute stereochemistry,but on the relative stereochemistry and positions 1,4,5,and 8 must contain D-amino *** ring and tail structure are necessary for activity,macrolactone and lactam rings are both *** teixobactin analogues show greater activity than native *** conducted animal studies show positive results with no animal deaths.

关键词： Teixobactin Antibacterial Peptide synthesis Structure-activity relationship Cyclic peptides

15^(th) Chinese International Peptide Symposium

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Chinese Chemical Letters 2018年第7期29卷 999-1000页

作者： xuechen li Lei liu Yanmei li Department of Chemistry The University of Hong Kong Department of Chemistry Tsinghua University

As one of the most important and influential peptide conferences in the world,Chinese International Peptide Symposium(CPS)was founded in 1990 and has been held every two years for14 consecutive *** July 4thto 6th,2018,the 15th CPS will be held in Shenzhen and hosted by Tsinghua *** conference will focus on the topics of"Peptide:Technological Innovation and a Better life",covering the synthesis,structure and function of peptides and proteins,peptide-based drug discovery,

关键词： 15th Chinese International Peptide Symposium this special issue

Development of aspartic acid ligation for peptide cyclization derived from serine/threonine ligation

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Chinese Chemical Letters 2018年第7期29卷 1119-1122页

作者： Ci Xu Jianchao Xu Han liu xuechen li Department of Chemistry State Key Laboratory of Synthetic ChemistryThe University of Hong Kong

Based on a mechanism analogous to the serine/threonine ligation, the aspartic acid ligation, which is facilitated by the γ-amino alcohol based ligation and oxidation, is developed and applied to the synthesis of cyclic peptides. The γ-hydroxyl group triggers the ring-chain tautomerization via a 6-endo-trig process,while the δ-hydroxyl group facilitates the oxidative cleavage of the vicinal diol to give carboxylic acid.

关键词： Aspartic acid ligation Peptide cyclization Serine/threonine ligation Ring-chain tautomerization Acyl transfer Selective oxidation

Global core,and galaxy structure of networks

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Science China(Information Sciences) 2014年第7期57卷 5-24页

作者： ZHANG Wei PAN YiCheng PENG Pan li JianKou li xuechen li AngSheng State Key Laboratory of Computer Science Institute of SoftwareChinese Academy of Sciences Beijing No.4 High School

We propose a novel approach,namely local reduction of networks,to extract the global core(GC,for short)from a complex *** algorithm is built based on the small community phenomenon of *** global cores found by our local reduction from some classical graphs and benchmarks convince us that the global core of a network is intuitively the supporting graph of the network,which is"similar to"the original graph,that the global core is small and essential to the global properties of the network,and that the global core,together with the small communities gives rise to a clear picture of the structure of the network,that is,the galaxy structure of *** implement the local reduction to extract the global cores for a series of real networks,and execute a number of experiments to analyze the roles of the global cores for various real *** each of the real networks,our experiments show that the found global core is small,that the global core is similar to the original network in the sense that it follows the power law degree distribution with power exponent close to that of the original network,that the global core is sensitive to errors for both cascading failure and physical attack models,in the sense that a small number of random errors in the global core may cause a major failure of the whole network,and that the global core is a good approximate solution to the r-radius center problem,leading to a galaxy structure of the network.

关键词： complex networks local reduction global core small community phenomenon social network

Acoustic emissions evaluation of the dynamic splitting tensile properties of steel fiber reinforced concrete under freeze-thaw cycling

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Frontiers of Structural and Civil Engineering 2023年第9期17卷 1341-1356页

作者： Hua ZHANG Xinyue liU lingyu BAI Shanshan JI Luoyu PAN xuechen li College of Civil and Transportation Engineering Hohai UniversityNanjing 210098China

This study empirically investigated the influence of freeze-thaw cycling on the dynamic splitting tensile properties of steel fiber reinforced concrete(SFRC).Brazilian disc splitting tests were conducted using four loading rates(0.002,0.02,0.2,and 2 mm/s)on specimens with four steel fiber contents(0%,0.6%,1.2%,and 1.8%)subjected to 0 and 50 freeze-thaw *** dynamic splitting tensile damage characteristics were evaluated using acoustic emission(AE)parameter analysis and Fourier transform spectral *** results quantified using the freeze-thaw damage factor defined in this paper indicate that the degree of damage to SFRC caused by freeze-thaw cycling was aggravated with increasing loading rate but mitigated by increasing fiber *** percentage of low-frequency AE signals produced by the SFRC specimens during loading decreased with increasing loading rate,whereas that of high-frequency AE signals ***-thaw action had little effect on the crack types observed during the early and middle stages of the loading process;however,the primary crack type observed during the later stage of loading changed from shear to tensile after the SFRC specimens were subjected to freeze-thaw ***,the results of this study indicate that the freeze-thaw damage to SFRC reduces AE signal activity at low frequencies.

关键词： steel fiber reinforced concrete freeze-thaw cycling Brazilian disc splitting test acoustic emission technique dynamic splitting tensile acoustic emission properties

Experimental test of robustness of composite pulses to non-static classic noise in NMR

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Science China(Physics,Mechanics & Astronomy) 2017年第2期60卷 80-81页

作者： li xuechen ZHANG PanPan CHU JingDi li JiYuan JIA PengYing Key Lab of Photo-Electronics Information Materials of Hebei Provinc

High fidelity and robust quantum control is the requirement for Quantum Information Processing （QIP） and quantum cornputing applications. Many negative factors, like pulse length error, system-bath coupling and the fluctuation of electronic instruments, deviate the quantum system evolution from the ideal path. To suppress these errors, many quantum manipulation techniques have been proposed. Composite pulses are designed to suppress off resonance error, pulse length error or the combination of them.

关键词：噪声鲁棒性脉冲核磁共振复合量子信息处理实验静态长度误差