Two new coordination polymers,[Ni(Hpdc)(bib)(H_(2)O)]_(n)(1)and{[Ni(bib)_(3)](ClO_(4))_(2)}_(n)(2),were prepared by mixing Ni^(2+),3,5⁃pyrazoledicarboxylic acid(H3pdc)/p⁃nitrobenzoic acid and 1,4⁃bis(imidazol⁃1⁃ylmeth...Two new coordination polymers,[Ni(Hpdc)(bib)(H_(2)O)]_(n)(1)and{[Ni(bib)_(3)](ClO_(4))_(2)}_(n)(2),were prepared by mixing Ni^(2+),3,5⁃pyrazoledicarboxylic acid(H3pdc)/p⁃nitrobenzoic acid and 1,4⁃bis(imidazol⁃1⁃ylmethyl)butane(bib)by a hydrothermal method,respectively.X⁃ray crystallography reveals a 2D network constructed by six⁃coordinated Ni(Ⅱ)centers,bib,and Hpdc2-ligands in complex 1,while a 2D network is built by Ni(Ⅱ)and bib ligands in 2.Furthermore,the quantum⁃chemical calculations have been performed on‘molecular fragments’extracted from the crystal structure of 1 using the PBE0/LANL2DZ method in Gaussian 16 and the VASP program.CCDC:2343794,1;2343798,2.展开更多
The achievement of electrical spin control is highly desirable.One promising strategy involves electrically mod-ulating the Rashba spin orbital coupling effect in materials.A semiconductor with high sensitivity in its...The achievement of electrical spin control is highly desirable.One promising strategy involves electrically mod-ulating the Rashba spin orbital coupling effect in materials.A semiconductor with high sensitivity in its Rashba constant to external electric fields holds great potential for short channel lengths in spin field-effect transistors,which is crucial for preserving spin coherence and enhancing integration density.Hence,two-dimensional(2D)Rashba semiconductors with large Rashba constants and significant electric field responses are highly desirable.Herein,by employing first-principles calculations,we design a thermodynamically stable 2D Rashba semiconductor,YSbTe_(3),which possesses an indirect band gap of 1.04 eV,a large Rashba constant of 1.54 eV·Åand a strong electric field response of up to 4.80 e·Å^(2).In particular,the Rashba constant dependence on the electric field shows an unusual nonlinear relationship.At the same time,YSbTe_(3)has been identified as a 2D ferroelectric material with a moderate polarization switching energy barrier(~0.33 eV per formula).By changing the electric polarization direction,the Rashba spin texture of YSbTe_(3)can be reversed.These out-standing properties make the ferroelectric Rashba semiconductor YSbTe_(3)quite promising for spintronic applications.展开更多
Declining cognitive abilities can be a concomitant of advanced age.As language is closely associated with cognitive abilities,changes in language abilities can be an important marker of changes in cognitive abilities....Declining cognitive abilities can be a concomitant of advanced age.As language is closely associated with cognitive abilities,changes in language abilities can be an important marker of changes in cognitive abilities.The current study is to review cognitive studies of language and aging by first identifying and exploring the major clusters and pivotal articles and then detecting emerging trends.Data of 3,266 articles on language and aging from 2013 to 2022 were collected from the Web of Science Core Collection database.Adopting Document Co-citation Analysis,Freeman’s betweenness centrality metric(Freeman,2002)and Kleinberg’s burst detection algorithm(Kleinberg,2002),we explored major clusters,pivotal articles and emerging trends in this field.Cognition appears to be the most remarkable cluster.Bilingualism,speech production,listening effort,and reading comprehension are other major active clusters in a certain period.The most recent active cluster concerns the studies of Alzheimer’s disease.Articles serving as pivotal points concentrate on cognitive studies of the Framework for Understanding Effortful Listening(FUEL),the new Ease of Language Understanding model(EUL)and a hierarchical multi-representational generative framework of language comprehension.The progress in statistical methods,the relationship between language and cognitive impairment and the relationship between language abilities and cognition are the emerging trends.These emerging trends will provide some insights into how cognitive abilities influence language abilities in aging.展开更多
The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate.To understand the impact of entropy,we performed ab initio static and molecular dynamics free energy simulati...The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate.To understand the impact of entropy,we performed ab initio static and molecular dynamics free energy simulations of ethane dehydrogenation over Co@BEA zeolite at different temperatures.AIMD simulations showed that a sharp decrease in free energy barrier as temperature increased.Our analysis of the temperature dependence of activation free energies uncovered an unusual entropic effect accompanying the reaction.The unique spatial structures around the Co active site at different temperatures influenced both the extent of charge transfer in the transition state and the arrangement of 3d orbital energy levels.We provided explanations consistent with the principles of thermodynamics and statistical physics.The insights gained at the atomic level have offered a fresh interpretation of the intricate long-range interplay between local chemical reactions and extensive chemical environments.展开更多
Stoichiometry has long been addressed in the studies of ecosystem ecology, but it was almost ignored for a long time. Until recently, ecologists have become aware that stoichiometry could provide a new tool to study e...Stoichiometry has long been addressed in the studies of ecosystem ecology, but it was almost ignored for a long time. Until recently, ecologists have become aware that stoichiometry could provide a new tool to study ecology from genes to the biosphere. Among this trend, N:P stoichiometry is used actively in ecological interactions since nitrogen (N) and phosphorus (P) are the two most important elements in most ecosystems. This article reviews the application of N:P stoichiometry to the studies of ecological problems at different levels, including ecosystem, community and species. Meanwhile, we also provide the cellular basis of N:P stoichiometry, identify the shortages in the use of N:P stoichiometry theory, and put forward some perspectives for future research to be conducted.展开更多
Nineβ‐cyclodextrin derivatives containing an amino group were synthesized via nucleophilic sub‐stitution from mono（6‐O‐p‐tolylsulfonyl）‐β‐cyclodextrin and used in asymmetric biomimetic Mi‐chael addition re...Nineβ‐cyclodextrin derivatives containing an amino group were synthesized via nucleophilic sub‐stitution from mono（6‐O‐p‐tolylsulfonyl）‐β‐cyclodextrin and used in asymmetric biomimetic Mi‐chael addition reactions in water at room temperature. The mechanism responsible for the moder‐ate activity and enantioselectivity of the β‐cyclodextrin derivatives was explored using nuclear magnetic resonance spectroscopy, namely 2D 1H rotating‐frame overhauser effect spectroscopy （ROESY）, ultraviolet absorption spectroscopy, and quantum chemical calculations, which provide a useful technique for investigating the formation of inclusion complexes. The effects of the pH of the reaction medium, theβ‐cyclodextrin derivative dosage, the structure of the modifying amino group, and various substrates on the yield and enantioselectivity were investigated. The results indicated that these factors had an important effect on the enantiomeric excess （ee） in the reaction system. Experiments using a competitor for inclusion complex formation showed that a hydrophobic cavity is necessary for enantioselective Michael addition. A comparison of the reactions using 4‐nitro‐β‐nitrostyrene and 2‐nitro‐β‐nitrostyrene showed that steric hindrance improved the enan‐tioselectivity. This was verified by the optimized geometries obtained from quantum chemical cal‐culations. An ee of 71%was obtained in the asymmetric Michael addition of cyclohexanone and 2‐nitro‐β‐nitrostyrene, using （S）‐2‐aminomethylpyrrolidine‐modified β‐CD as the catalyst, in an aqueous buffer solution, i.e., CH3COONa‐HCl （pH 7.5）.展开更多
[Objective] The aim was to indentify diseased leaves of broad bean by vibra- tional spectroscopy. [Method] In this paper, broad bean rust, fusarium rhizome rot, broad bean zonate spot, yellow leaf curl virus and norma...[Objective] The aim was to indentify diseased leaves of broad bean by vibra- tional spectroscopy. [Method] In this paper, broad bean rust, fusarium rhizome rot, broad bean zonate spot, yellow leaf curl virus and normal leaves were studied using Fourier transform infrared spectroscopy combined with chemometrics. [Result] The spectra of the samples were similar, only with minor differences in absorption inten- sity of several peaks. Second derivative analyses show that the significant difference of all samples was in the range of 1 200-700 cm2. The data in the range of 1 200- 700 cm＇ were selected to evaluate correlation coefficients, hierarchical cluster analy- sis （HCA） and principal component analysis （PCA）. Results showed that the correla- tion coefficients are larger than 0.928 not only between the healthy leaves, but also between the same diseased leaves. The values between healthy and diseased leaves, and among diseased leaves, are all declined. HCA and PCA yielded about 73.3% and 82.2% accuracy, respectively. [Conclusion] This study demonstrated that FTIR techniques might be used to detect crop diseases.展开更多
The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods. The geometries and frequencies of the reactants, transition states and products have been performed at...The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods. The geometries and frequencies of the reactants, transition states and products have been performed at B3LYP/6-311＋＋G（d,p） level, and single-point energy calculations for all the stationary points were carried out at DFT calculations of the optimized structures with the G3B3 level. The ionization energies of toluene and the ap- pearance energies for major fragment ions, C7H7＋, C6H5＋, C5H6＋, C5H5＋, are determined to be 8.90, 11.15 or 11.03, 12.72, 13.69, 16.28 eV, respectively, which are all in good agree- ment with published experimental data. With the help of available published experimental data and theoretical results, four dissociative photoionization channels have been proposed： CTHT＋＋H, C6Hs＋＋CH3, C5H6＋WC2H2, CsHs＋＋C2H2＋H. Transition structures and intermediates for those isomerization processes are determined in this work. Especially, the structures of C5H6＋ and C5H5＋ produced by dissociative photoionization of toluene have been defined as chain structure in this work with theoretical calculations.展开更多
Quantum mechanics and molecular dynamics are used to simulate guanidinium ionic liquids. Results show that the stronger interaction exists between guanidine cation and chlorine anion with interaction energy about 109....Quantum mechanics and molecular dynamics are used to simulate guanidinium ionic liquids. Results show that the stronger interaction exists between guanidine cation and chlorine anion with interaction energy about 109.216 kcal/mol. There are two types of spatial distribution for the title system： middle and top. Middle mode is a more stable conformation according to energy and geometric distribution. It is also verified by radial distribution function. The continuous increase of carbon dioxide （CO2） does not affect the structure of ionic liquids, but CO2 molecules are always captured by the cavity of ionic liquids.展开更多
[Objective]The aim was to carry out stoichiometry on the early-spring herbs functional group in subtropical artificial wetland.[Method]UV-Vis spectrophotometer was used for the determination of nitrate-nitrogen,ammoni...[Objective]The aim was to carry out stoichiometry on the early-spring herbs functional group in subtropical artificial wetland.[Method]UV-Vis spectrophotometer was used for the determination of nitrate-nitrogen,ammonium nitrogen and phosphorus concentrations.Potassium persulfate absorptiometry was used for the measurement of total N content,while the flame photometer was used to detect the potassium and sodium concentration in plants.All the nutrient determination of plant samples were repeated for four times.[Result]The four nutrient concentrations in almost all samples were in the normal range of natural plant nutrition concentrations;in early-spring herbs functional groups,different species showed diversity on the nutrient concentrations;plant height had no significant effect on the nutrient concentrations in plants;the nutrient concentrations of non-grass group plants were higher than that of grass group plants;the nutrient concentrations of the annual herb were higher than that of perennial herbs.[Conclusion]The study had provided basis for the understanding of the effects of changes in nutritional conditions on species diversity,community structure and succession of the system.展开更多
文摘Two new coordination polymers,[Ni(Hpdc)(bib)(H_(2)O)]_(n)(1)and{[Ni(bib)_(3)](ClO_(4))_(2)}_(n)(2),were prepared by mixing Ni^(2+),3,5⁃pyrazoledicarboxylic acid(H3pdc)/p⁃nitrobenzoic acid and 1,4⁃bis(imidazol⁃1⁃ylmethyl)butane(bib)by a hydrothermal method,respectively.X⁃ray crystallography reveals a 2D network constructed by six⁃coordinated Ni(Ⅱ)centers,bib,and Hpdc2-ligands in complex 1,while a 2D network is built by Ni(Ⅱ)and bib ligands in 2.Furthermore,the quantum⁃chemical calculations have been performed on‘molecular fragments’extracted from the crystal structure of 1 using the PBE0/LANL2DZ method in Gaussian 16 and the VASP program.CCDC:2343794,1;2343798,2.
基金supported by the National Natural Science Foundation of China(22322304,22273092,22373095)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB0450101)+2 种基金the Innovation Program for Quantum Science and Technology(2021ZD0303306)the USTC Tang ScholarThe authors wish to acknowledge the Supercomputing Center of the USTC for providing computational resources.
文摘The achievement of electrical spin control is highly desirable.One promising strategy involves electrically mod-ulating the Rashba spin orbital coupling effect in materials.A semiconductor with high sensitivity in its Rashba constant to external electric fields holds great potential for short channel lengths in spin field-effect transistors,which is crucial for preserving spin coherence and enhancing integration density.Hence,two-dimensional(2D)Rashba semiconductors with large Rashba constants and significant electric field responses are highly desirable.Herein,by employing first-principles calculations,we design a thermodynamically stable 2D Rashba semiconductor,YSbTe_(3),which possesses an indirect band gap of 1.04 eV,a large Rashba constant of 1.54 eV·Åand a strong electric field response of up to 4.80 e·Å^(2).In particular,the Rashba constant dependence on the electric field shows an unusual nonlinear relationship.At the same time,YSbTe_(3)has been identified as a 2D ferroelectric material with a moderate polarization switching energy barrier(~0.33 eV per formula).By changing the electric polarization direction,the Rashba spin texture of YSbTe_(3)can be reversed.These out-standing properties make the ferroelectric Rashba semiconductor YSbTe_(3)quite promising for spintronic applications.
文摘Declining cognitive abilities can be a concomitant of advanced age.As language is closely associated with cognitive abilities,changes in language abilities can be an important marker of changes in cognitive abilities.The current study is to review cognitive studies of language and aging by first identifying and exploring the major clusters and pivotal articles and then detecting emerging trends.Data of 3,266 articles on language and aging from 2013 to 2022 were collected from the Web of Science Core Collection database.Adopting Document Co-citation Analysis,Freeman’s betweenness centrality metric(Freeman,2002)and Kleinberg’s burst detection algorithm(Kleinberg,2002),we explored major clusters,pivotal articles and emerging trends in this field.Cognition appears to be the most remarkable cluster.Bilingualism,speech production,listening effort,and reading comprehension are other major active clusters in a certain period.The most recent active cluster concerns the studies of Alzheimer’s disease.Articles serving as pivotal points concentrate on cognitive studies of the Framework for Understanding Effortful Listening(FUEL),the new Ease of Language Understanding model(EUL)and a hierarchical multi-representational generative framework of language comprehension.The progress in statistical methods,the relationship between language and cognitive impairment and the relationship between language abilities and cognition are the emerging trends.These emerging trends will provide some insights into how cognitive abilities influence language abilities in aging.
文摘The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate.To understand the impact of entropy,we performed ab initio static and molecular dynamics free energy simulations of ethane dehydrogenation over Co@BEA zeolite at different temperatures.AIMD simulations showed that a sharp decrease in free energy barrier as temperature increased.Our analysis of the temperature dependence of activation free energies uncovered an unusual entropic effect accompanying the reaction.The unique spatial structures around the Co active site at different temperatures influenced both the extent of charge transfer in the transition state and the arrangement of 3d orbital energy levels.We provided explanations consistent with the principles of thermodynamics and statistical physics.The insights gained at the atomic level have offered a fresh interpretation of the intricate long-range interplay between local chemical reactions and extensive chemical environments.
文摘Stoichiometry has long been addressed in the studies of ecosystem ecology, but it was almost ignored for a long time. Until recently, ecologists have become aware that stoichiometry could provide a new tool to study ecology from genes to the biosphere. Among this trend, N:P stoichiometry is used actively in ecological interactions since nitrogen (N) and phosphorus (P) are the two most important elements in most ecosystems. This article reviews the application of N:P stoichiometry to the studies of ecological problems at different levels, including ecosystem, community and species. Meanwhile, we also provide the cellular basis of N:P stoichiometry, identify the shortages in the use of N:P stoichiometry theory, and put forward some perspectives for future research to be conducted.
基金supported by the National Natural Science Foundation of China (21425627,21376279)~~
文摘Nineβ‐cyclodextrin derivatives containing an amino group were synthesized via nucleophilic sub‐stitution from mono（6‐O‐p‐tolylsulfonyl）‐β‐cyclodextrin and used in asymmetric biomimetic Mi‐chael addition reactions in water at room temperature. The mechanism responsible for the moder‐ate activity and enantioselectivity of the β‐cyclodextrin derivatives was explored using nuclear magnetic resonance spectroscopy, namely 2D 1H rotating‐frame overhauser effect spectroscopy （ROESY）, ultraviolet absorption spectroscopy, and quantum chemical calculations, which provide a useful technique for investigating the formation of inclusion complexes. The effects of the pH of the reaction medium, theβ‐cyclodextrin derivative dosage, the structure of the modifying amino group, and various substrates on the yield and enantioselectivity were investigated. The results indicated that these factors had an important effect on the enantiomeric excess （ee） in the reaction system. Experiments using a competitor for inclusion complex formation showed that a hydrophobic cavity is necessary for enantioselective Michael addition. A comparison of the reactions using 4‐nitro‐β‐nitrostyrene and 2‐nitro‐β‐nitrostyrene showed that steric hindrance improved the enan‐tioselectivity. This was verified by the optimized geometries obtained from quantum chemical cal‐culations. An ee of 71%was obtained in the asymmetric Michael addition of cyclohexanone and 2‐nitro‐β‐nitrostyrene, using （S）‐2‐aminomethylpyrrolidine‐modified β‐CD as the catalyst, in an aqueous buffer solution, i.e., CH3COONa‐HCl （pH 7.5）.
基金Supported by National Natural Science Foundation of China(30960179)Natural Science Foundation of Yunnan Province(2007A048M)~~
文摘[Objective] The aim was to indentify diseased leaves of broad bean by vibra- tional spectroscopy. [Method] In this paper, broad bean rust, fusarium rhizome rot, broad bean zonate spot, yellow leaf curl virus and normal leaves were studied using Fourier transform infrared spectroscopy combined with chemometrics. [Result] The spectra of the samples were similar, only with minor differences in absorption inten- sity of several peaks. Second derivative analyses show that the significant difference of all samples was in the range of 1 200-700 cm2. The data in the range of 1 200- 700 cm＇ were selected to evaluate correlation coefficients, hierarchical cluster analy- sis （HCA） and principal component analysis （PCA）. Results showed that the correla- tion coefficients are larger than 0.928 not only between the healthy leaves, but also between the same diseased leaves. The values between healthy and diseased leaves, and among diseased leaves, are all declined. HCA and PCA yielded about 73.3% and 82.2% accuracy, respectively. [Conclusion] This study demonstrated that FTIR techniques might be used to detect crop diseases.
文摘The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods. The geometries and frequencies of the reactants, transition states and products have been performed at B3LYP/6-311＋＋G（d,p） level, and single-point energy calculations for all the stationary points were carried out at DFT calculations of the optimized structures with the G3B3 level. The ionization energies of toluene and the ap- pearance energies for major fragment ions, C7H7＋, C6H5＋, C5H6＋, C5H5＋, are determined to be 8.90, 11.15 or 11.03, 12.72, 13.69, 16.28 eV, respectively, which are all in good agree- ment with published experimental data. With the help of available published experimental data and theoretical results, four dissociative photoionization channels have been proposed： CTHT＋＋H, C6Hs＋＋CH3, C5H6＋WC2H2, CsHs＋＋C2H2＋H. Transition structures and intermediates for those isomerization processes are determined in this work. Especially, the structures of C5H6＋ and C5H5＋ produced by dissociative photoionization of toluene have been defined as chain structure in this work with theoretical calculations.
基金ACKNOWLEDGMENTS This work was supported by the Open Project Program of Key Laboratory of Theoretical Chemistry and Molecular Simulation of Ministry of Education, Hunan University of Science and Technology, China （No.E21104）, the National Natural Science Foundation of China （No.21201062 and No.21172066）, and the International Cooperation Project （No.2013DFG60060）.
文摘Quantum mechanics and molecular dynamics are used to simulate guanidinium ionic liquids. Results show that the stronger interaction exists between guanidine cation and chlorine anion with interaction energy about 109.216 kcal/mol. There are two types of spatial distribution for the title system： middle and top. Middle mode is a more stable conformation according to energy and geometric distribution. It is also verified by radial distribution function. The continuous increase of carbon dioxide （CO2） does not affect the structure of ionic liquids, but CO2 molecules are always captured by the cavity of ionic liquids.
基金Supported by National Natural Science Foundation of China(30370146)~~
文摘[Objective]The aim was to carry out stoichiometry on the early-spring herbs functional group in subtropical artificial wetland.[Method]UV-Vis spectrophotometer was used for the determination of nitrate-nitrogen,ammonium nitrogen and phosphorus concentrations.Potassium persulfate absorptiometry was used for the measurement of total N content,while the flame photometer was used to detect the potassium and sodium concentration in plants.All the nutrient determination of plant samples were repeated for four times.[Result]The four nutrient concentrations in almost all samples were in the normal range of natural plant nutrition concentrations;in early-spring herbs functional groups,different species showed diversity on the nutrient concentrations;plant height had no significant effect on the nutrient concentrations in plants;the nutrient concentrations of non-grass group plants were higher than that of grass group plants;the nutrient concentrations of the annual herb were higher than that of perennial herbs.[Conclusion]The study had provided basis for the understanding of the effects of changes in nutritional conditions on species diversity,community structure and succession of the system.
