Synchrotron radiation based combined technique can provide multiple structural information simultaneously,which is an important development direction of structural detection.In this study,a novel small-angle X-ray sca...Synchrotron radiation based combined technique can provide multiple structural information simultaneously,which is an important development direction of structural detection.In this study,a novel small-angle X-ray scattering/X-ray diffraction/X-ray absorption fine structure(SAXS/XRD/XAFS)combined setup was constructed,where an area detector,a curved detector,and a point detector are,respectively,used for the measurements of SAXS,XRD,and XAFS signals.A detailed description about the combined setup was given.A minitype diamond detector coupled to a SAXS beamstop was used to record the transmitted X-ray intensity,making the scattering(SAXS and XRD)signal measurement compatible with the absorption(XAFS)signal measurement,avoiding mechanical switching.The two-way sampling strategy was used to acquire XAFS signals,shortening the non-counting time.The two-way and one-way sampling strategies were discussed.High-frequency sampling scheme was used to collect experimental signals,improving the measurement efficiency and signal-to-noise ratio.A detailed description and discussion about the high-frequency scheme were also given in this paper.Except the rotation of monochromator,there is no mechanical movement in measurements,time resolution may reach the level of seconds.Using this SAXS/XRD/XAFS combined setup,SAXS,XRD,and XAFS signals can be acquired simultaneously.With some in-situ sample environment system,the newlydeveloped combined technique can be used to track the structure evolution in complex fluids.During the formation processes of(BiO)2CO3 and ZnAPO-34 particles,the changes of in-situ experimental data with reaction time demonstrate that SAXS/XRD/XAFS combined technique is feasible to track the dynamic process.展开更多
Diels-Alder reaction is one of the most important reactions in organic synthesis and has witnessed great achievements in total syntheses of complex natural products.In this review,we will focus on the [4+2] cycloaddit...Diels-Alder reaction is one of the most important reactions in organic synthesis and has witnessed great achievements in total syntheses of complex natural products.In this review,we will focus on the [4+2] cycloaddition that utilizes 2-pyrone as the diene component.Major advances of its applications in the total syntheses of natural products in the past fifty years will be discussed here.展开更多
Chiral heteroatom-containing bicyclic scaffolds are important pharmacophores and prevalent in bioactive natural products and drug molecules.Herein,we report a unified approach for the divergent synthesis of chiral het...Chiral heteroatom-containing bicyclic scaffolds are important pharmacophores and prevalent in bioactive natural products and drug molecules.Herein,we report a unified approach for the divergent synthesis of chiral heteroatom-containing bicyclic derivatives by lanthanide(lil)-catalyzed asymmetric inverse-electron-demand Diels-Alder reactions of 2-pyrones.These reactions occur with vari-ous readily available dihydropyrroles and dihydrofurans as dienophiles,providing a step-economical synthetic platform for densely functionalized ciss-hydroindoles and cis-hydrobenzofurans with excellent yields and enantioselectivities.The synthetic utility of this approach is demonstrated by the concise synthesis of(-)-α-lycorane and(-)-lycorine alkaloids.展开更多
Introduction Nanofiber orientation in suspensions determines the performance of nanoparticle suspensions which have potential applications in intelligent control.Material and method Na2Ti3O7 nanofibers were prepared w...Introduction Nanofiber orientation in suspensions determines the performance of nanoparticle suspensions which have potential applications in intelligent control.Material and method Na2Ti3O7 nanofibers were prepared with a hydrothermal method.The orientation degree of Na2Ti3O7 nanofibers in silicone oil has been studied by in situ small-angle X-ray scattering technique.Thünemann–Ruland method was used to extract the distribution widths of Na2Ti3O7 nanofibers in the suspensions.Conclution An empirical formula has been proposed to describe the dependence of nanofiber orientation degree on the external electric-field strength(E)and the nanofiber concentration(C).The results demonstrate that the response of nanofiber orientation to the electric field can be divided into exponential and linear stages before and after the inflection point of electric-field strength(Ec0.09 kV/mm).Low concentration of suspension is more sensitive to the external electric field.The increase in nanofiber concentration will decrease the response sensitivity of nanofiber orientation degree to the change of E.The critical concentration of Na2Ti3O7 nanofibers in the suspension is about 5 wt%.This study is expected to give new clue for the structurally responsive mechanism of anisotropic nanoparticles in suspensions to electric-field strength and particle concentration.展开更多
A Mythen detector has been equipped at the beamline 4B9A of Beijing Synchrotron Radiation Facility （BSRF）, which is expected to enable BSRF to perform time-resolved measurement of X-ray diffraction （XRD） full-prof...A Mythen detector has been equipped at the beamline 4B9A of Beijing Synchrotron Radiation Facility （BSRF）, which is expected to enable BSRF to perform time-resolved measurement of X-ray diffraction （XRD） full-profiles. In this paper, the thermal expansion behavior of metal indium has been studied by using the in-situ XRD technique with the Mythen detector. The indium was heated from 303 to 433 K with a heating rate of 2 K/rain. The in-situ XRD full-profiles were collected with a rate of one profile per 10 seconds. Rietveld refinement was used to extract the structural parameters. The results demonstrate that these collected quasi-real-time XRD profiles can be well used for structural analysis. The metal indium was found to have a nonlinear thermal expansion behavior from room temperature to the melting point （429.65 K）. The a-axis of the tetragonal unit cell expands with a biquadratic dependency on temperature, while the c-axis contracts with a cubic dependency on temperature. By the time-resolved XRD measurements, it was observed that the [200] preferred orientation can maintain to about 403.15 K. While （110） is the last and detectable crystal plane just before melting of the polycrystalline indium foil. This study is not only beneficial to the application of metal indium, but also exhibits the capacity of in-situ time-resolved XRD measurements at the X-ray diffraction station of BSRF.展开更多
基金This work was supported by the National Key Research and Development Program of China(Nos.2017YFA0403000 and 2017YFA0403100).
文摘Synchrotron radiation based combined technique can provide multiple structural information simultaneously,which is an important development direction of structural detection.In this study,a novel small-angle X-ray scattering/X-ray diffraction/X-ray absorption fine structure(SAXS/XRD/XAFS)combined setup was constructed,where an area detector,a curved detector,and a point detector are,respectively,used for the measurements of SAXS,XRD,and XAFS signals.A detailed description about the combined setup was given.A minitype diamond detector coupled to a SAXS beamstop was used to record the transmitted X-ray intensity,making the scattering(SAXS and XRD)signal measurement compatible with the absorption(XAFS)signal measurement,avoiding mechanical switching.The two-way sampling strategy was used to acquire XAFS signals,shortening the non-counting time.The two-way and one-way sampling strategies were discussed.High-frequency sampling scheme was used to collect experimental signals,improving the measurement efficiency and signal-to-noise ratio.A detailed description and discussion about the high-frequency scheme were also given in this paper.Except the rotation of monochromator,there is no mechanical movement in measurements,time resolution may reach the level of seconds.Using this SAXS/XRD/XAFS combined setup,SAXS,XRD,and XAFS signals can be acquired simultaneously.With some in-situ sample environment system,the newlydeveloped combined technique can be used to track the structure evolution in complex fluids.During the formation processes of(BiO)2CO3 and ZnAPO-34 particles,the changes of in-situ experimental data with reaction time demonstrate that SAXS/XRD/XAFS combined technique is feasible to track the dynamic process.
基金The National Natural Science Foundation of China (Grant No. 21801043), the "Z1000-Youth Talents Plan", and Fudan University (start-up gra nt) are ack no wledged for fi nan cial support.
文摘Diels-Alder reaction is one of the most important reactions in organic synthesis and has witnessed great achievements in total syntheses of complex natural products.In this review,we will focus on the [4+2] cycloaddition that utilizes 2-pyrone as the diene component.Major advances of its applications in the total syntheses of natural products in the past fifty years will be discussed here.
基金the National Natural Science Foundation of China(Grant No.22071030)Fudan University for financial support。
文摘Chiral heteroatom-containing bicyclic scaffolds are important pharmacophores and prevalent in bioactive natural products and drug molecules.Herein,we report a unified approach for the divergent synthesis of chiral heteroatom-containing bicyclic derivatives by lanthanide(lil)-catalyzed asymmetric inverse-electron-demand Diels-Alder reactions of 2-pyrones.These reactions occur with vari-ous readily available dihydropyrroles and dihydrofurans as dienophiles,providing a step-economical synthetic platform for densely functionalized ciss-hydroindoles and cis-hydrobenzofurans with excellent yields and enantioselectivities.The synthetic utility of this approach is demonstrated by the concise synthesis of(-)-α-lycorane and(-)-lycorine alkaloids.
基金the Ministry of Science and Technology of China(Grant No.2017YFA0403000)the National Natural Science Foundation of China(Grant No.11405199).
文摘Introduction Nanofiber orientation in suspensions determines the performance of nanoparticle suspensions which have potential applications in intelligent control.Material and method Na2Ti3O7 nanofibers were prepared with a hydrothermal method.The orientation degree of Na2Ti3O7 nanofibers in silicone oil has been studied by in situ small-angle X-ray scattering technique.Thünemann–Ruland method was used to extract the distribution widths of Na2Ti3O7 nanofibers in the suspensions.Conclution An empirical formula has been proposed to describe the dependence of nanofiber orientation degree on the external electric-field strength(E)and the nanofiber concentration(C).The results demonstrate that the response of nanofiber orientation to the electric field can be divided into exponential and linear stages before and after the inflection point of electric-field strength(Ec0.09 kV/mm).Low concentration of suspension is more sensitive to the external electric field.The increase in nanofiber concentration will decrease the response sensitivity of nanofiber orientation degree to the change of E.The critical concentration of Na2Ti3O7 nanofibers in the suspension is about 5 wt%.This study is expected to give new clue for the structurally responsive mechanism of anisotropic nanoparticles in suspensions to electric-field strength and particle concentration.
基金supported by the National Natural Science Foundationof China(Grant Nos.U1232203,U1432104,11405199,11305198 and U1332107)the special fund on repairing infrastructure and purchasing fixed assets of Ministry of Finance of China
文摘A Mythen detector has been equipped at the beamline 4B9A of Beijing Synchrotron Radiation Facility （BSRF）, which is expected to enable BSRF to perform time-resolved measurement of X-ray diffraction （XRD） full-profiles. In this paper, the thermal expansion behavior of metal indium has been studied by using the in-situ XRD technique with the Mythen detector. The indium was heated from 303 to 433 K with a heating rate of 2 K/rain. The in-situ XRD full-profiles were collected with a rate of one profile per 10 seconds. Rietveld refinement was used to extract the structural parameters. The results demonstrate that these collected quasi-real-time XRD profiles can be well used for structural analysis. The metal indium was found to have a nonlinear thermal expansion behavior from room temperature to the melting point （429.65 K）. The a-axis of the tetragonal unit cell expands with a biquadratic dependency on temperature, while the c-axis contracts with a cubic dependency on temperature. By the time-resolved XRD measurements, it was observed that the [200] preferred orientation can maintain to about 403.15 K. While （110） is the last and detectable crystal plane just before melting of the polycrystalline indium foil. This study is not only beneficial to the application of metal indium, but also exhibits the capacity of in-situ time-resolved XRD measurements at the X-ray diffraction station of BSRF.
