The development of catalytic asymmetric methods that enable access to value-added functionalities or structures,exemplified by allylic alcohols,is a highly interesting yet challenging topic from both academic and indu...The development of catalytic asymmetric methods that enable access to value-added functionalities or structures,exemplified by allylic alcohols,is a highly interesting yet challenging topic from both academic and industrial perspectives.However,before recent advances in chemical catalysis,there were scarce protocols toward constructing enantioenriched tertiary allylic alcohol scaffolds.In this context,peptide-mimic phosphonium salts were found to be highly efficient in catalytic asymmetricα-hydroxylation ofα,β-unsaturated and/orβ,Y-unsaturated compounds with satisfactory regio-and stereochemical outcomes(up to 97%yield and 95%ee).This methodology tolerates a broad array of substrates and thus provides an expeditious and unified platform for the assembly of enantioenriched tertiary allylic alcohols by avoiding the use of additional reductants and expensive metal catalysts.Furthermore,the power of this protocol is enlarged by simple conditions and the use of air as a source of hydroxyl functionality.展开更多
Passive vibration isolation systems have been widely applied due to their low power consumption and high reliability.Nevertheless,the design of vibration isolators is usually limited by the narrow space of installatio...Passive vibration isolation systems have been widely applied due to their low power consumption and high reliability.Nevertheless,the design of vibration isolators is usually limited by the narrow space of installation,and the requirement of heavy loads needs the high supporting stiffness that leads to the narrow isolation frequency band.To improve the vibration isolation performance of passive isolation systems for dynamic loaded equipment,a novel modular quasi-zero stiffness vibration isolator(MQZS-VI)with high linearity and integrated fluid damping is proposed.The MQZS-VI can achieve high-performance vibration isolation under a constraint mounted space,which is realized by highly integrating a novel combined magnetic negative stiffness mechanism into a damping structure:The stator magnets are integrated into the cylinder block,and the moving magnets providing negative-stiffness force also function as the piston supplying damping force simultaneously.An analytical model of the novel MQZS-VI is established and verified first.The effects of geometric parameters on the characteristics of negative stiffness and damping are then elucidated in detail based on the analytical model,and the design procedure is proposed to provide guidelines for the performance optimization of the MQZS-VI.Finally,static and dynamic experiments are conducted on the prototype.The experimental results demonstrate the proposed analytical model can be effectively utilized in the optimal design of the MQZS-VI,and the optimized MQZS-VI broadened greatly the isolation frequency band and suppressed the resonance peak simultaneously,which presented a substantial potential for application in vibration isolation for dynamic loaded equipment.展开更多
基金Financial support was provided by the National Natural Science Foundation of China(22222109,21921002,22101189 and 22371190)the National Key R&DProgramof China(2018YFA0903500)+3 种基金Beijing National Laboratory for Molecular Sciences(BNLMs202101)Sichuan Science Foundation for Distinguished Young Scholars(2023NSFSC1921)Sichuan Provincial Natural Science Foundation(2022NSFSC1181,24NSFSC6590)Fundamental Research Funds from Sichuan University(2020SCUNL108)and Fundamental Research Funds for the Central Universities.
文摘The development of catalytic asymmetric methods that enable access to value-added functionalities or structures,exemplified by allylic alcohols,is a highly interesting yet challenging topic from both academic and industrial perspectives.However,before recent advances in chemical catalysis,there were scarce protocols toward constructing enantioenriched tertiary allylic alcohol scaffolds.In this context,peptide-mimic phosphonium salts were found to be highly efficient in catalytic asymmetricα-hydroxylation ofα,β-unsaturated and/orβ,Y-unsaturated compounds with satisfactory regio-and stereochemical outcomes(up to 97%yield and 95%ee).This methodology tolerates a broad array of substrates and thus provides an expeditious and unified platform for the assembly of enantioenriched tertiary allylic alcohols by avoiding the use of additional reductants and expensive metal catalysts.Furthermore,the power of this protocol is enlarged by simple conditions and the use of air as a source of hydroxyl functionality.
基金supported by the National Key R&D Program of China(Grant Nos.2020YFB2007300 and 2020YFB2007601)the National Natural Science Foundation of China(Grant Nos.52075193,52305107,and 52275112)+1 种基金the National Science and Technology Major Project of China(Grant No.2017ZX02101007-002)the Postdoctoral Science Foundation of China(Grant No.2022M711250).
文摘Passive vibration isolation systems have been widely applied due to their low power consumption and high reliability.Nevertheless,the design of vibration isolators is usually limited by the narrow space of installation,and the requirement of heavy loads needs the high supporting stiffness that leads to the narrow isolation frequency band.To improve the vibration isolation performance of passive isolation systems for dynamic loaded equipment,a novel modular quasi-zero stiffness vibration isolator(MQZS-VI)with high linearity and integrated fluid damping is proposed.The MQZS-VI can achieve high-performance vibration isolation under a constraint mounted space,which is realized by highly integrating a novel combined magnetic negative stiffness mechanism into a damping structure:The stator magnets are integrated into the cylinder block,and the moving magnets providing negative-stiffness force also function as the piston supplying damping force simultaneously.An analytical model of the novel MQZS-VI is established and verified first.The effects of geometric parameters on the characteristics of negative stiffness and damping are then elucidated in detail based on the analytical model,and the design procedure is proposed to provide guidelines for the performance optimization of the MQZS-VI.Finally,static and dynamic experiments are conducted on the prototype.The experimental results demonstrate the proposed analytical model can be effectively utilized in the optimal design of the MQZS-VI,and the optimized MQZS-VI broadened greatly the isolation frequency band and suppressed the resonance peak simultaneously,which presented a substantial potential for application in vibration isolation for dynamic loaded equipment.