The crystal structure of [Co(NH3)5Br]Br2 has been determined ab initio from the conventional X-ray powder diffraction data. The approximate structure with all 7 indeyendent non-H atoms was solved by direct methods. Th...The crystal structure of [Co(NH3)5Br]Br2 has been determined ab initio from the conventional X-ray powder diffraction data. The approximate structure with all 7 indeyendent non-H atoms was solved by direct methods. The final orthorhombic unit-cell parameters after Rietveld refinement are: a=13.6927, b=10.7071, c=6.9400A, V=1017.47A3, F30=93(0.0075,43), M20=49, Z=4. Space group is Pnma. The structure agreement factors are: Rp=0.066,Rwp=0.090, RF=0.041, RB=0.042.展开更多
Two complexes,NdL_3·2C_2H_5OH and NdL_3·2H_2O where L=cyclohexane-carboxylate anion,were synthesized and the structure of the former was determined by the single-crystal X-ray diffration method. The crystal ...Two complexes,NdL_3·2C_2H_5OH and NdL_3·2H_2O where L=cyclohexane-carboxylate anion,were synthesized and the structure of the former was determined by the single-crystal X-ray diffration method. The crystal is triclinic,Pspace group with the cell parameters:a=1.2385(6),b=1.2385(6),c=0.9421(5) nm.α=91.69(4)°,β=98.49(4)°,γ=99.16(5)°,Z=2,V=1.436 nm^3.The structure was refined to R value of 0.0866.Each Nd atom is connected with other two Nd atoms by two bidentate and two tridentate carboxyl groups to form a linear polymer.The Nd atom is further coordinated by a chelating carboxyl and two ethanol molecules.So the central atom is nine-coordinated with a distorted monocapped square-antiprism geometry.The infrared spectra and the thermal analysis of the complexes were also studied.展开更多
A new Mutactimycin group antibiotic(XF-1)was isolated from the mycelium of Streptomyces sp.80-115 and its structure has been determined on the basis of its spectroscopical and chemical properties. XF-1 showed active a...A new Mutactimycin group antibiotic(XF-1)was isolated from the mycelium of Streptomyces sp.80-115 and its structure has been determined on the basis of its spectroscopical and chemical properties. XF-1 showed active against some Gram positive bacteria.展开更多
An alkaloid with a novel structure,named Hypodematine,was isolated from Hypodematium sinense Iwatsuki(belonging to Thelypterdaceae).Its structure was elucidated by means of the ~1H-~1H COSY' ~1H-^(13)C COSY and lo...An alkaloid with a novel structure,named Hypodematine,was isolated from Hypodematium sinense Iwatsuki(belonging to Thelypterdaceae).Its structure was elucidated by means of the ~1H-~1H COSY' ~1H-^(13)C COSY and long-range ~1H-^(13)C COSY spectroscopy to have the skeleton of benzo-aza-cyclooctatetraene with a phenyl substituent.Such basic structure has not been found in the na- tural product before.展开更多
A new highly oxygenated iridoid,lamiophlomiol C,was isolated from the roots of Lamiophlomis rotata and its structure was elucidated by spectrosoopic techniques and X-ray diffraction.
Structural determination plays a pivotal role in chemical research by providing detailed insights into molecular architecture and functionality.Single-crystal X-ray diffraction(SCXRD)is widely regarded as the premier ...Structural determination plays a pivotal role in chemical research by providing detailed insights into molecular architecture and functionality.Single-crystal X-ray diffraction(SCXRD)is widely regarded as the premier technique for achieving precise three-dimensional structural elucidation[1].The persistent challenge of determining atomic-level structures for non-crystalline or conformationally flexible molecules has driven transformative innovations in crystallographic methodologies[2-5].展开更多
Structure determination plays the most crucial role in the discovery of novel functional materials,because only by knowing the intrinsic structures can we accurately and completely understand their properties and appl...Structure determination plays the most crucial role in the discovery of novel functional materials,because only by knowing the intrinsic structures can we accurately and completely understand their properties and applications.However,most new materials are obtained in polycrystalline form or even as mixtures with multiple phases when first synthesized,presenting significant challenges in their structure determination and phase elucidation.Fortunately,the developed three-dimensional electron diffraction(3DED/MicroED)has provided a promising solution to overcome these challenges.In this study,we have constructed a state-of-the-art 3DED/MicroED data acquisition equipment by integrating a hybrid-pixel detector with a script developed for Serial EM,and thus successfully developed an automated 3DED/MicroED method for the high-throughput structure determination.To demonstrate its effectiveness,a multiphase sample with complex porous structures is employed,showcasing that individual phases and their structures can be identified and determined,respectively.One remarkable finding is the identification of an impurity metal-organic framework(MOF)that is completely invisible to traditional powder X-ray diffraction in a supposedly“pure”commercial MOF sample.Additionally,our method also enables the atomic-resolution structure determination of flexible covalent organic framework materials,which are highly sensitive to electron beams.Moreover,a new microporous aluminoborate is discovered using this rapid structure determination method.These experimental results highlight the enormous potential of our 3DED/MicroED method in the field of new materials discovery,offering a powerful tool for the structure determination of polycrystalline functional materials.展开更多
The exploratory synthesis and structural characterization of twodimensional(2D)honeycomb structured Ru-based compounds are key focuses in inorganic materials research,due to the various exotic electronic states arisin...The exploratory synthesis and structural characterization of twodimensional(2D)honeycomb structured Ru-based compounds are key focuses in inorganic materials research,due to the various exotic electronic states arising from the interplay of electron correlations and spinorbit coupling.Among these compounds,α-RuCl_(3) and RuBr_(3) are considered as the most promising candidates for quantum spin liquid(QSL)materials[1–3].As a homolog,α-RuI3 has attracted significant interest,but it still remains relatively unexplored.Recently,it was synthesized by high-temperature and high-pressure solid-state reaction,but reported to be different crystal structures by independent groups.Ni et al.and Nawa et al.considerα-RuI3 to be R-3(3R)and P-31c(2H)space group,respectively[4,5].Both structures have typical 2D characteristics,in which the edge-sharing RuI6 octahedra form honeycomb layers stacked along the c-axis.The primary difference lies in that the honeycomb layers stack in ABCABC mode in the 3R phase,while in ABAB mode in the 2H phase(Fig.S1).Yang et al.discussed the stability of 3R and 2H polymorphs in terms of the total energies and dynamics,finding both structures are stable.However,the total energy of the 2H phase is slightly higher,2.58 meV than that of the 3R analog[6].When it comes to the conductivity behaviour,α-RuCl3 andα-RuBr_(3) are semiconductors as normally observed in QSL materials.In contrast,α-RuI_(3) exhibits metallic response.In 2D materials,the band structure may be drastically modified by altering the stacking order[7].Hence,determining the crystal structure ofα-RuI_(3) is urgently required,which is a key step in comprehensive and in-depth analysis of its physical properties.展开更多
The crystalline sponge method is a pragmatic and promising strategy for molecular structure determination.However,the dominant metal-organic framework crystal sponge platforms always face poor chemical stability,espec...The crystalline sponge method is a pragmatic and promising strategy for molecular structure determination.However,the dominant metal-organic framework crystal sponge platforms always face poor chemical stability,especially solvent instability,hampering their application in a vaster domain.Herein,we report an ultrastable π-π stacked porous organic molecular framework which exhibits permanent porosity,high thermal stability,and good chemical resistance.It can efficiently implement an approach to molecular structure determination via a single-crystal-to-single-crystal transformation.This is the first example utilizing π-π stacked porous organic molecular framework as“crystalline sponge”to determine a wide variety of vips,ranging from hydrophilic to hydrophobic,and from aliphatic to aromatic,which complements the crystalline sponges based on the famous metal-organic frameworks.More importantly,it can achieve rapid structure determination of small molecules within 3 h.展开更多
The cryo-electron microscopy(cryo-EM)is one of the most powerful technologies available today for structural biology.The RELION(Regularized Likelihood Optimization)implements a Bayesian algorithm for cryo-EM structure...The cryo-electron microscopy(cryo-EM)is one of the most powerful technologies available today for structural biology.The RELION(Regularized Likelihood Optimization)implements a Bayesian algorithm for cryo-EM structure determination,which is one of the most widely used software in this field.Many researchers have devoted effort to improve the performance of RELION to satisfy the analysis for the ever-increasing volume of datasets.In this paper,we focus on performance analysis of the most time-consuming computation steps in RELION and identify their performance bottlenecks for specific optimizations.We propose several performance optimization strategies to improve the overall performance of RELION,including optimization of expectation step,parallelization of maximization step,accelerating the computation of symmetries,and memory affinity optimization.The experiment results show that our proposed optimizations achieve significant speedups of RELION across representative datasets.In addition,we perform roofline model analysis to understand the effectiveness of our optimizations.展开更多
Kanglemeisu A (C50H63O19N·CH3OH) is the product of an actinomyces species from a soil sample gathered in China. Kanglemeisu A belongs to the triclinic system, space group P1,unit cell:a=12.760（3）, b=10.287（2）...Kanglemeisu A (C50H63O19N·CH3OH) is the product of an actinomyces species from a soil sample gathered in China. Kanglemeisu A belongs to the triclinic system, space group P1,unit cell:a=12.760（3）, b=10.287（2）, c=9.926（2） , α=88.39（2）,β=78.64（2）, γ=89.14（2）. RANTAN direct method is used to solve the structure.The final discrepancy factor is R=0.0689, after atom coordinates and temperature factors have been refined with full matrix least squares.The structure skeleton consists of four parts, the naphthalene nucleus connected to the 5-membered ring, a 17-membered ring connected to C2, a dimethyl butane diacid extended out from C20, β-D-3,4-OO’ methylenedigitoxose passing through an oxygen bridge O6 and linked to C27 of ansa ring.展开更多
Metal–organic frameworks(MOFs) are crystalline porous materials with tunable properties, exhibiting great potential in gas adsorption, separation and catalysis.[1,2]It is challenging to visualize MOFs with transmissi...Metal–organic frameworks(MOFs) are crystalline porous materials with tunable properties, exhibiting great potential in gas adsorption, separation and catalysis.[1,2]It is challenging to visualize MOFs with transmission electron microscopy(TEM) due to their inherent instability under electron beam irradiation. Here, we employ cryo-electron microscopy(cryoEM) to capture images of MOF ZIF-8, revealing inverted-space structural information at a resolution of up to about 1.7A and enhancing its critical electron dose to around 20 e^(-)/A^(2). In addition, it is confirmed by electron-beam irradiation experiments that the high voltage could effectively mitigate the radiolysis, and the structure of ZIF-8 is more stable along the [100] direction under electron beam irradiation. Meanwhile, since the high-resolution electron microscope images are modulated by contrast transfer function(CTF) and it is difficult to determine the positions corresponding to the atomic columns directly from the images. We employ image deconvolution to eliminate the impact of CTF and obtain the structural images of ZIF-8. As a result, the heavy atom Zn and the organic imidazole ring within the organic framework can be distinguished from structural images.展开更多
The linear dispersion relation of a trapezoidally corrugated slow wave structure （TCSWS） is analyzed and presented. The size parameters of the TCSWS are chosen in such a way that they operate in the x-band frequency...The linear dispersion relation of a trapezoidally corrugated slow wave structure （TCSWS） is analyzed and presented. The size parameters of the TCSWS are chosen in such a way that they operate in the x-band frequency range. The dispersion relation is solved by utilizing the Rayleigh-Fourier method by expressing the radial function in terms of the Fourier series. A highly accurate synthetic technique is also applied to determine the complete dispersion characteristics from experimentally measured resonances （cold test）. Periodic structures resonate at specific frequencies when the terminals are shorted numerical calculation, synthetic technique and cold appropriately. The dispersion characteristics obtained from test are compared, and an excellent agreement is achieved.展开更多
The polysaccharides from Sepia esculenta ink are potential candidates for biomedical applications due to their functional properties.In our study,a heteropolysaccharide,SE-1,isolated from Sepia esculenta ink,had a mol...The polysaccharides from Sepia esculenta ink are potential candidates for biomedical applications due to their functional properties.In our study,a heteropolysaccharide,SE-1,isolated from Sepia esculenta ink,had a molecular weight of 13.1 kDa and a monosaccharide composition of Man:GlcN:GlcUA:GalN:Xyl:Fuc=1.00:1.38:0.65:2.89:0.76:1.99.Through partial acid hydrolysis,me-thylation and one-and two-dimensional nuclear magnetic resonance(1D and 2D NMR)spectroscopic analyses,it is indicated that the structure of SE-1 consists of→4)-α-D-GlcpNAc-(1→,→4)-α-L-Fucp-(1→,→3)-α-D-GalpNAc-(1→,→2,6)-α-D-Manp-(1→and→3)-β-D-GlcpUA-(1→as the main chain and single terminalβ-D-Xylp-(1→,which links to O-2 of(1→2,6)-α-Manp,as the side chain.A new aminosugar-abundant heteropolysaccharide was isolated from S.esculenta ink for the first time.展开更多
The solid solutions of CdYFeWO7,which are cubic pyrochlores of the type A2B2O7,have been prepared and their structures were determined using Ab initio method.Rietveld refinement of the powder XRD data showed that CdYF...The solid solutions of CdYFeWO7,which are cubic pyrochlores of the type A2B2O7,have been prepared and their structures were determined using Ab initio method.Rietveld refinement of the powder XRD data showed that CdYFeWO7 adopted cubic(Fd-3m) structure,while oxides crystallized in a defect-pyrochlore structure where both O(48f) and O (8b) sites were partially occupied,and the frustrated cations sublattice precluded long range ordering of Fe/W in the pyrochlore structure.Charge distribution analysis also sug...展开更多
The multiple oligopeptides have been regarded as promising alignment media due to their structural diverseness and tendency for self-assembly in solution.Herein,an assembled amphiphilic peptide alignment medium,i.e.,C...The multiple oligopeptides have been regarded as promising alignment media due to their structural diverseness and tendency for self-assembly in solution.Herein,an assembled amphiphilic peptide alignment medium,i.e.,C15eCONH-Phg-Phg-IIIKK-CONH2 with un-natural amino acids for the determination of anisotropic parameters of NMR is introduced.The amphiphilic peptide can be self-assembled at low concentrations in DMSO and is stable and highly homogeneous.The NMR spectrum collected with the addition of the medium had fewer background signals.The utility of the acquired RDC data is demon-strated to determine relative configuration of three natural products,Helminthosporic acid,Estrone,and a-Santonin.展开更多
The compound of dimethyl trans-3-（2-bromophenyl）-2-methylisoxazolidine-4,5-dicarboxylate has been synthesized and characterized by IR, 1H-NMR, 13C-NMR, 2D-NMR （COSY, NOESY, HMQC, HMBC） and UV-vis. spectroscopy tec...The compound of dimethyl trans-3-（2-bromophenyl）-2-methylisoxazolidine-4,5-dicarboxylate has been synthesized and characterized by IR, 1H-NMR, 13C-NMR, 2D-NMR （COSY, NOESY, HMQC, HMBC） and UV-vis. spectroscopy techniques and single-crystal X-ray diffraction （XRD）. The biological activities of the title compound have been investigated in detail. The new compound crystallizes in monoclinic, space group C2/c with a = 26.9263（10）, b = 7.0970（2）, c = 19.8554（7） ？, and β = 126.630（2）. In addition to the single crystal structure, the molecular geometry, vibrational frequencies, chemical shifts, molecular electrostatic potential and frontier molecular orbital analysis of the title compound in the ground state have been calculated by Density Functional Theory （DFT） method.展开更多
The paper investigates the determinants of capital structure in Nigerian listed insurance firms using data obtained from annual report of the sampled firms for the period of 2001-2010. It used five explanatory variabl...The paper investigates the determinants of capital structure in Nigerian listed insurance firms using data obtained from annual report of the sampled firms for the period of 2001-2010. It used five explanatory variables to measure their effects on debt ratio. Multiple regression is employed as a tool of analysis. The result reveals that all the explanatory variables have statistically and significantly influenced the explained variable. The results approve the prediction of pecking order theory in the case of profitability and trade-off theory in case of tangibility variables. The growth variable supports the agency theory hypothesis whereas size variable confirms to the asymmetry of information theory. It is therefore recommended that the management of listed insurance firms in Nigeria should always consider their positions using these capital structure determinants as important inputs before embarking on debt financing decision.展开更多
This paper attempts to analyze the important determinants of capital structure in the medicine manufacturing industry of China. Two measures including the ratio of long-term debt to asset and the ratio of total debt t...This paper attempts to analyze the important determinants of capital structure in the medicine manufacturing industry of China. Two measures including the ratio of long-term debt to asset and the ratio of total debt to asset are used as the proxies of leverage, while dependent variables used are asset structure, growth, firm size, profitability and risk. The evidences presented here indicate that asset structure and size significantly influence the capital structure choice.展开更多
Reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine derived from 4-phenylphenol cyanate ester and phenyl glycidyl ether were analyzed. In addition to an isocyanurate compound and an oxazolidone compound w...Reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine derived from 4-phenylphenol cyanate ester and phenyl glycidyl ether were analyzed. In addition to an isocyanurate compound and an oxazolidone compound which were well known as reaction products of cyanate esters and epoxy resins, compounds with hybrid ring structure of cyanurate/isocyanurate were determined. Gibbs free energies of the compound having hybrid ring structure of cyanurate/isocyanurate with two isocyanurate moiety were found to be lower than that of the compound with cyanurate ring structure through calculations. Calculation data supported the existence of hybrid ring structure of cy-anurate/isocyanurate. It was revealed that isomerization from cyanurate to isocyanurate occurs via hybrid ring structure of cyanurate/isocyanurate in the reaction of aryl cyanurate and epoxy.展开更多
文摘The crystal structure of [Co(NH3)5Br]Br2 has been determined ab initio from the conventional X-ray powder diffraction data. The approximate structure with all 7 indeyendent non-H atoms was solved by direct methods. The final orthorhombic unit-cell parameters after Rietveld refinement are: a=13.6927, b=10.7071, c=6.9400A, V=1017.47A3, F30=93(0.0075,43), M20=49, Z=4. Space group is Pnma. The structure agreement factors are: Rp=0.066,Rwp=0.090, RF=0.041, RB=0.042.
文摘Two complexes,NdL_3·2C_2H_5OH and NdL_3·2H_2O where L=cyclohexane-carboxylate anion,were synthesized and the structure of the former was determined by the single-crystal X-ray diffration method. The crystal is triclinic,Pspace group with the cell parameters:a=1.2385(6),b=1.2385(6),c=0.9421(5) nm.α=91.69(4)°,β=98.49(4)°,γ=99.16(5)°,Z=2,V=1.436 nm^3.The structure was refined to R value of 0.0866.Each Nd atom is connected with other two Nd atoms by two bidentate and two tridentate carboxyl groups to form a linear polymer.The Nd atom is further coordinated by a chelating carboxyl and two ethanol molecules.So the central atom is nine-coordinated with a distorted monocapped square-antiprism geometry.The infrared spectra and the thermal analysis of the complexes were also studied.
文摘A new Mutactimycin group antibiotic(XF-1)was isolated from the mycelium of Streptomyces sp.80-115 and its structure has been determined on the basis of its spectroscopical and chemical properties. XF-1 showed active against some Gram positive bacteria.
文摘An alkaloid with a novel structure,named Hypodematine,was isolated from Hypodematium sinense Iwatsuki(belonging to Thelypterdaceae).Its structure was elucidated by means of the ~1H-~1H COSY' ~1H-^(13)C COSY and long-range ~1H-^(13)C COSY spectroscopy to have the skeleton of benzo-aza-cyclooctatetraene with a phenyl substituent.Such basic structure has not been found in the na- tural product before.
文摘A new highly oxygenated iridoid,lamiophlomiol C,was isolated from the roots of Lamiophlomis rotata and its structure was elucidated by spectrosoopic techniques and X-ray diffraction.
文摘Structural determination plays a pivotal role in chemical research by providing detailed insights into molecular architecture and functionality.Single-crystal X-ray diffraction(SCXRD)is widely regarded as the premier technique for achieving precise three-dimensional structural elucidation[1].The persistent challenge of determining atomic-level structures for non-crystalline or conformationally flexible molecules has driven transformative innovations in crystallographic methodologies[2-5].
基金supported by the National Natural Science Foundation of China(22371121)the Natural Science Foundation of Jiangsu Province(BK20230772)the Fundamental Research Funds for Central Universities of China(020514380306)。
文摘Structure determination plays the most crucial role in the discovery of novel functional materials,because only by knowing the intrinsic structures can we accurately and completely understand their properties and applications.However,most new materials are obtained in polycrystalline form or even as mixtures with multiple phases when first synthesized,presenting significant challenges in their structure determination and phase elucidation.Fortunately,the developed three-dimensional electron diffraction(3DED/MicroED)has provided a promising solution to overcome these challenges.In this study,we have constructed a state-of-the-art 3DED/MicroED data acquisition equipment by integrating a hybrid-pixel detector with a script developed for Serial EM,and thus successfully developed an automated 3DED/MicroED method for the high-throughput structure determination.To demonstrate its effectiveness,a multiphase sample with complex porous structures is employed,showcasing that individual phases and their structures can be identified and determined,respectively.One remarkable finding is the identification of an impurity metal-organic framework(MOF)that is completely invisible to traditional powder X-ray diffraction in a supposedly“pure”commercial MOF sample.Additionally,our method also enables the atomic-resolution structure determination of flexible covalent organic framework materials,which are highly sensitive to electron beams.Moreover,a new microporous aluminoborate is discovered using this rapid structure determination method.These experimental results highlight the enormous potential of our 3DED/MicroED method in the field of new materials discovery,offering a powerful tool for the structure determination of polycrystalline functional materials.
基金supported by the National Natural Science Foundation of China(No.22090041)the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(No.2017ZT07C069)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(No.2022B1515120014)the Natural Science Foundation of Zhejiang Province(No.LQ21A040010).
文摘The exploratory synthesis and structural characterization of twodimensional(2D)honeycomb structured Ru-based compounds are key focuses in inorganic materials research,due to the various exotic electronic states arising from the interplay of electron correlations and spinorbit coupling.Among these compounds,α-RuCl_(3) and RuBr_(3) are considered as the most promising candidates for quantum spin liquid(QSL)materials[1–3].As a homolog,α-RuI3 has attracted significant interest,but it still remains relatively unexplored.Recently,it was synthesized by high-temperature and high-pressure solid-state reaction,but reported to be different crystal structures by independent groups.Ni et al.and Nawa et al.considerα-RuI3 to be R-3(3R)and P-31c(2H)space group,respectively[4,5].Both structures have typical 2D characteristics,in which the edge-sharing RuI6 octahedra form honeycomb layers stacked along the c-axis.The primary difference lies in that the honeycomb layers stack in ABCABC mode in the 3R phase,while in ABAB mode in the 2H phase(Fig.S1).Yang et al.discussed the stability of 3R and 2H polymorphs in terms of the total energies and dynamics,finding both structures are stable.However,the total energy of the 2H phase is slightly higher,2.58 meV than that of the 3R analog[6].When it comes to the conductivity behaviour,α-RuCl3 andα-RuBr_(3) are semiconductors as normally observed in QSL materials.In contrast,α-RuI_(3) exhibits metallic response.In 2D materials,the band structure may be drastically modified by altering the stacking order[7].Hence,determining the crystal structure ofα-RuI_(3) is urgently required,which is a key step in comprehensive and in-depth analysis of its physical properties.
基金supported by the National Nature Science Foundation of China(grant nos.21871266,21731006,and 21403241)the Strategic Priority Research Program of the Chinese Academy of Sciences(grant no.XDB20000000)+1 种基金Key Research Program of Frontier Science CAS(grant no.QYZDY-SSW-SLH025)Youth Innovation Promotion Association CAS.
文摘The crystalline sponge method is a pragmatic and promising strategy for molecular structure determination.However,the dominant metal-organic framework crystal sponge platforms always face poor chemical stability,especially solvent instability,hampering their application in a vaster domain.Herein,we report an ultrastable π-π stacked porous organic molecular framework which exhibits permanent porosity,high thermal stability,and good chemical resistance.It can efficiently implement an approach to molecular structure determination via a single-crystal-to-single-crystal transformation.This is the first example utilizing π-π stacked porous organic molecular framework as“crystalline sponge”to determine a wide variety of vips,ranging from hydrophilic to hydrophobic,and from aliphatic to aromatic,which complements the crystalline sponges based on the famous metal-organic frameworks.More importantly,it can achieve rapid structure determination of small molecules within 3 h.
基金the National Key R&D Program of China(2020YFB1506703)the National Natural Science Foundation of China(Grant No.62072018)the Open Project Program of the State Key Laboratory of Mathematical Engineering and Advanced Computing(2019A12).
文摘The cryo-electron microscopy(cryo-EM)is one of the most powerful technologies available today for structural biology.The RELION(Regularized Likelihood Optimization)implements a Bayesian algorithm for cryo-EM structure determination,which is one of the most widely used software in this field.Many researchers have devoted effort to improve the performance of RELION to satisfy the analysis for the ever-increasing volume of datasets.In this paper,we focus on performance analysis of the most time-consuming computation steps in RELION and identify their performance bottlenecks for specific optimizations.We propose several performance optimization strategies to improve the overall performance of RELION,including optimization of expectation step,parallelization of maximization step,accelerating the computation of symmetries,and memory affinity optimization.The experiment results show that our proposed optimizations achieve significant speedups of RELION across representative datasets.In addition,we perform roofline model analysis to understand the effectiveness of our optimizations.
文摘Kanglemeisu A (C50H63O19N·CH3OH) is the product of an actinomyces species from a soil sample gathered in China. Kanglemeisu A belongs to the triclinic system, space group P1,unit cell:a=12.760（3）, b=10.287（2）, c=9.926（2） , α=88.39（2）,β=78.64（2）, γ=89.14（2）. RANTAN direct method is used to solve the structure.The final discrepancy factor is R=0.0689, after atom coordinates and temperature factors have been refined with full matrix least squares.The structure skeleton consists of four parts, the naphthalene nucleus connected to the 5-membered ring, a 17-membered ring connected to C2, a dimethyl butane diacid extended out from C20, β-D-3,4-OO’ methylenedigitoxose passing through an oxygen bridge O6 and linked to C27 of ansa ring.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074409 and 12374021)。
文摘Metal–organic frameworks(MOFs) are crystalline porous materials with tunable properties, exhibiting great potential in gas adsorption, separation and catalysis.[1,2]It is challenging to visualize MOFs with transmission electron microscopy(TEM) due to their inherent instability under electron beam irradiation. Here, we employ cryo-electron microscopy(cryoEM) to capture images of MOF ZIF-8, revealing inverted-space structural information at a resolution of up to about 1.7A and enhancing its critical electron dose to around 20 e^(-)/A^(2). In addition, it is confirmed by electron-beam irradiation experiments that the high voltage could effectively mitigate the radiolysis, and the structure of ZIF-8 is more stable along the [100] direction under electron beam irradiation. Meanwhile, since the high-resolution electron microscope images are modulated by contrast transfer function(CTF) and it is difficult to determine the positions corresponding to the atomic columns directly from the images. We employ image deconvolution to eliminate the impact of CTF and obtain the structural images of ZIF-8. As a result, the heavy atom Zn and the organic imidazole ring within the organic framework can be distinguished from structural images.
文摘The linear dispersion relation of a trapezoidally corrugated slow wave structure （TCSWS） is analyzed and presented. The size parameters of the TCSWS are chosen in such a way that they operate in the x-band frequency range. The dispersion relation is solved by utilizing the Rayleigh-Fourier method by expressing the radial function in terms of the Fourier series. A highly accurate synthetic technique is also applied to determine the complete dispersion characteristics from experimentally measured resonances （cold test）. Periodic structures resonate at specific frequencies when the terminals are shorted numerical calculation, synthetic technique and cold appropriately. The dispersion characteristics obtained from test are compared, and an excellent agreement is achieved.
基金funded by the Natural Science Founda-tion of Zhejiang Province,China(No.LTGS23D060001)the Scientific Research Foundation for the Introduc-tion of Talent of Zhejiang Ocean University(No.JX6311130823).
文摘The polysaccharides from Sepia esculenta ink are potential candidates for biomedical applications due to their functional properties.In our study,a heteropolysaccharide,SE-1,isolated from Sepia esculenta ink,had a molecular weight of 13.1 kDa and a monosaccharide composition of Man:GlcN:GlcUA:GalN:Xyl:Fuc=1.00:1.38:0.65:2.89:0.76:1.99.Through partial acid hydrolysis,me-thylation and one-and two-dimensional nuclear magnetic resonance(1D and 2D NMR)spectroscopic analyses,it is indicated that the structure of SE-1 consists of→4)-α-D-GlcpNAc-(1→,→4)-α-L-Fucp-(1→,→3)-α-D-GalpNAc-(1→,→2,6)-α-D-Manp-(1→and→3)-β-D-GlcpUA-(1→as the main chain and single terminalβ-D-Xylp-(1→,which links to O-2 of(1→2,6)-α-Manp,as the side chain.A new aminosugar-abundant heteropolysaccharide was isolated from S.esculenta ink for the first time.
基金supported by the National Natural Science Foundation of China (20771100, 20831004)CIAC, CAS (CX07QZJC30)
文摘The solid solutions of CdYFeWO7,which are cubic pyrochlores of the type A2B2O7,have been prepared and their structures were determined using Ab initio method.Rietveld refinement of the powder XRD data showed that CdYFeWO7 adopted cubic(Fd-3m) structure,while oxides crystallized in a defect-pyrochlore structure where both O(48f) and O (8b) sites were partially occupied,and the frustrated cations sublattice precluded long range ordering of Fe/W in the pyrochlore structure.Charge distribution analysis also sug...
基金supported by the National Natural Science Foundation of China(21874158)the Science and Technology Major Program of Gansu Province of China(22ZD6FA006 and 23ZDFA015)+1 种基金We are also grateful for the financial support from the Science and Technology Program of Henan Province(232102311180)the foundation for the University Young Key Teacher of Henan Province(2024GGJS116).
文摘The multiple oligopeptides have been regarded as promising alignment media due to their structural diverseness and tendency for self-assembly in solution.Herein,an assembled amphiphilic peptide alignment medium,i.e.,C15eCONH-Phg-Phg-IIIKK-CONH2 with un-natural amino acids for the determination of anisotropic parameters of NMR is introduced.The amphiphilic peptide can be self-assembled at low concentrations in DMSO and is stable and highly homogeneous.The NMR spectrum collected with the addition of the medium had fewer background signals.The utility of the acquired RDC data is demon-strated to determine relative configuration of three natural products,Helminthosporic acid,Estrone,and a-Santonin.
基金the Faculty of Arts and Sciences, Ondokuz Mayis University, Turkey, for the use of the STOE IPDS-II diffractometer (purchased under grant F.279 of the University Research Fund)
文摘The compound of dimethyl trans-3-（2-bromophenyl）-2-methylisoxazolidine-4,5-dicarboxylate has been synthesized and characterized by IR, 1H-NMR, 13C-NMR, 2D-NMR （COSY, NOESY, HMQC, HMBC） and UV-vis. spectroscopy techniques and single-crystal X-ray diffraction （XRD）. The biological activities of the title compound have been investigated in detail. The new compound crystallizes in monoclinic, space group C2/c with a = 26.9263（10）, b = 7.0970（2）, c = 19.8554（7） ？, and β = 126.630（2）. In addition to the single crystal structure, the molecular geometry, vibrational frequencies, chemical shifts, molecular electrostatic potential and frontier molecular orbital analysis of the title compound in the ground state have been calculated by Density Functional Theory （DFT） method.
文摘The paper investigates the determinants of capital structure in Nigerian listed insurance firms using data obtained from annual report of the sampled firms for the period of 2001-2010. It used five explanatory variables to measure their effects on debt ratio. Multiple regression is employed as a tool of analysis. The result reveals that all the explanatory variables have statistically and significantly influenced the explained variable. The results approve the prediction of pecking order theory in the case of profitability and trade-off theory in case of tangibility variables. The growth variable supports the agency theory hypothesis whereas size variable confirms to the asymmetry of information theory. It is therefore recommended that the management of listed insurance firms in Nigeria should always consider their positions using these capital structure determinants as important inputs before embarking on debt financing decision.
文摘This paper attempts to analyze the important determinants of capital structure in the medicine manufacturing industry of China. Two measures including the ratio of long-term debt to asset and the ratio of total debt to asset are used as the proxies of leverage, while dependent variables used are asset structure, growth, firm size, profitability and risk. The evidences presented here indicate that asset structure and size significantly influence the capital structure choice.
文摘Reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine derived from 4-phenylphenol cyanate ester and phenyl glycidyl ether were analyzed. In addition to an isocyanurate compound and an oxazolidone compound which were well known as reaction products of cyanate esters and epoxy resins, compounds with hybrid ring structure of cyanurate/isocyanurate were determined. Gibbs free energies of the compound having hybrid ring structure of cyanurate/isocyanurate with two isocyanurate moiety were found to be lower than that of the compound with cyanurate ring structure through calculations. Calculation data supported the existence of hybrid ring structure of cy-anurate/isocyanurate. It was revealed that isomerization from cyanurate to isocyanurate occurs via hybrid ring structure of cyanurate/isocyanurate in the reaction of aryl cyanurate and epoxy.
