The enamines, iminium ions, and oxazolidinones are thought to be the key intermediates in the proline-catalyzed reactions of aldehydes or ketones, but there is an extensive contro- versy about their roles. Here, the c...The enamines, iminium ions, and oxazolidinones are thought to be the key intermediates in the proline-catalyzed reactions of aldehydes or ketones, but there is an extensive contro- versy about their roles. Here, the corresponding transition states connecting any two of the three kinds of species are located at the wB97XD/6-311＋＋G＊＊ level of theory. The calcula- tions demonstrate that the oxazolidinones are the predominant species in both the gas phase and solvents; there exists tautomeric equilibrium among these species and the equilibriums are controlled by the employed solvents and temperature in the reaction. These results demonstrate that the concentration and role of the mentioned species are controlled by the employed solvent and temperature. A new reaction pathway is presented herein for the trans- formation between iminium ions and oxazolidinones through iminium ion-water complex and oxazolidinone-water complex. The calculations demonstrate that the rate-limiting step in proline-catalyzed Mannich reaction between acetaldehyde/keteones and N-Boc imines is the formation of the C-C bond rather than the intermediates tautomerization. These calculations rationalize the available experimental observations and can be valuable in optimizing the experimental conditions of asymmetric organic-catalyzed reactions of aldehydes or ketones.展开更多
The molecular structures of indazole and 3-halogeno-indazole tautomers were calculated by the B3LYP method at the 6-311G^＊＊ level, both in the gaseous and aqueous phases, with full geometry optimization. The geometr...The molecular structures of indazole and 3-halogeno-indazole tautomers were calculated by the B3LYP method at the 6-311G^＊＊ level, both in the gaseous and aqueous phases, with full geometry optimization. The geometry and electronic structure of the tautomers of indazole, 3-halogeno-indazole and their transition states were obtained. The Onsager solvate theory model was employed for the aqueous solution calculations. The results of the calculation indicated that the N1-H form of the studied molecule is more stable than that of the N2-H form. The influences of the different 3-halogeno and solvent effects on the geometry, energy, charge and activation energy were discussed. The reaction mechanism of the tautomerization of indazole and 3-halogeno-indazole was also studied and a three-membered cyclic transition state of the tautomer reaction has been obtained.展开更多
The IR spectroscopic data indicate the tautomeric transformations of typical aprotonic organic fluids such as methane halides with gross formulas CHX3 （X = Cl, Br）, CH2X2 （X = CI, Br, I） and CCl4 at normal conditi...The IR spectroscopic data indicate the tautomeric transformations of typical aprotonic organic fluids such as methane halides with gross formulas CHX3 （X = Cl, Br）, CH2X2 （X = CI, Br, I） and CCl4 at normal conditions. These transformations lead to the appearance in molecules of activated hydrogen atoms similar in the spectral behaviour to the bounded proton. The classical analysis of IR bands in 5000-600 cm^-1 region, for studied samples and their deuterated derivatives, proves the existence in the presented organic fluids of hydrogen and dihydrogen bonds. This bonding promotes the formation of supramolecular structure in methane halides. The mechanism of unusual binding in liquid phase in terms of common knowledge for the basic chemical properties of the examined compounds is discussed.展开更多
The pyrolysis mechanisms of quinoline and isoquinoline were investigated using the density functional theory of quantum chemistry,including eight reaction paths and a common tautomeric intermediate 1-indene imine.It i...The pyrolysis mechanisms of quinoline and isoquinoline were investigated using the density functional theory of quantum chemistry,including eight reaction paths and a common tautomeric intermediate 1-indene imine.It is concluded that the conformational tautomerism of the intermediate decides the pyrolysis products(C6H6,HC≡C—C≡N,C6H5C≡N and HC≡CH)to be the same,and also decides the total disappearance rates of the reactants to be the same,for both original reactants quinoline and isoquinoline during the pyrolysis reaction.The results indicate that the intramolecular hydrogen migration is an important reaction step,which often appears in the paths of the pyrolysis mechanism.The activation energies of the rate determining steps are obtained.The calculated results are in good agreement with the experimental results.展开更多
Herein reported is an example of one-dimensional coordination polymer [Co11(3,5-DBsq)2(dpg)]·(3,5-H2DBcat)2 (1) (3,5-DBsq = 3,5-di-tert-butylsemiquinonate, 3,5-H2DBcat = 3,5-di-tert-butyl-benzene-1,2-diol, dpg = ...Herein reported is an example of one-dimensional coordination polymer [Co11(3,5-DBsq)2(dpg)]·(3,5-H2DBcat)2 (1) (3,5-DBsq = 3,5-di-tert-butylsemiquinonate, 3,5-H2DBcat = 3,5-di-tert-butyl-benzene-1,2-diol, dpg = meso-alpha,beta-di(4-pyridyl)glycol) capable of undergoing thermal and photoinduced valence tautomeric transitions.展开更多
Boosting the alkaline hydrogen evolution and oxidation reaction(HER/HOR)kinetics is vital to practicing the renewable hydrogen cycle in alkaline media.Recently,intensive research has demonstrated that interface engine...Boosting the alkaline hydrogen evolution and oxidation reaction(HER/HOR)kinetics is vital to practicing the renewable hydrogen cycle in alkaline media.Recently,intensive research has demonstrated that interface engineering is of critical significance for improving the performance of heterostructured electrocatalysts particularly toward the electrochemical reactions involving multiple reaction intermediates like alkaline hydrogen electrocatalysis,and the research advances also bring substantial non-trivial fundamental insights accordingly.Herein,we review the current status of interface engineering with respect to developing efficient heterostructured electrocatalysts for alkaline HER and HOR.Two major subjects—how interface engineering promotes the reaction kinetics and what fundamental insights interface engineering has brought into alkaline HER and HOR—are discussed.Specifically,heterostructured electrocatalysts with abundant interfaces have shown substantially accelerated alkaline hydrogen electrocatalysis kinetics owing to the synergistic effect from different components,which could balance the adsorption/desorption behaviors of the intermediates at the interfaces.Meanwhile,interface engineering can effectively tune the electronic structures of the active sites via electronic interaction,interfacial bonding,and lattice strain,which would appropriately optimize the binding energy of targeted intermediates like hydrogen.Furthermore,the confinement effect is critical for delivering high durability by sustaining high density of active sites.At last,our own perspectives on the challenges and opportunities toward developing efficient heterostructured electrocatalysts for alkaline hydrogen electrocatalysis are provided.展开更多
When a population structure is modelled as a square lattice,the cooperation may be improved for an evolutionary prisoner dilemma game or be inhibited for an evolutionary snowdrift game.In this work,we investigate coop...When a population structure is modelled as a square lattice,the cooperation may be improved for an evolutionary prisoner dilemma game or be inhibited for an evolutionary snowdrift game.In this work,we investigate cooperation in a population on a square lattice where the interaction among players contains both prisoner dilemma game and snowdrift game.The heterogeneity in interaction is introduced to the population in two different ways:the heterogenous character of interaction assigned to every player(HCP) or the heterogenous character of interaction assigned to every link between any two players(HCL).The resonant enhancement of cooperation in the case of HCP is observed while the resonant inhibition of cooperation in the case of HCL is prominent.The explanations on the enhancement or inhibition of cooperation are presented for these two cases.展开更多
Rationally designed heterostructures provide attractive prospects for energy storage electrodes by combining different active materials with distinct electrochemical properties.Herein,through a phase separation strate...Rationally designed heterostructures provide attractive prospects for energy storage electrodes by combining different active materials with distinct electrochemical properties.Herein,through a phase separation strategy,a heterostructure of SnO_(2) encapsulated by amorphous Nb_(2)O_(5) is spontaneously synthesized.Insertion-type anode Nb_(2)O_(5) outer shell,playing as reaction containers and fast ionic pathways,physically inhibits the Sn atoms’migration and enhances the reaction kinetics.Moreover,strong chemical interactions are found at the SnO_(2)/Nb_(2)O_(5) interfaces,which ensure the solid encapsulation of the SnO_(2) cores even after 500 cycles.When used for lithium-ion batteries,this heterostructured anode exhibits high cycling stability with a capacity of 626 mAhg^(-1) after 1000 cycles at 2Ag^(-1)(85% capacity retention)and good rate performance with the capacity of 340 mAhg^(-1) at 8Ag^(-1).展开更多
Various studies have demonstrated that the foundation species genetic diversity can have direct effects that extend beyond the individual or population level, affecting the dependent communities. Additionally, these e...Various studies have demonstrated that the foundation species genetic diversity can have direct effects that extend beyond the individual or population level, affecting the dependent communities. Additionally, these effects may be indirectly extended to higher trophic levels throughout the entire community. Quercus castanea is an oak species with characteristics of foundation species beyond pre- senting a wide geographical distribution and being a dominant element of Mexican temperate forests. In this study, we analyzed the influence of population （He） and individual （HL） genetic diversity of Q. castanea on its canopy endophagous insect community and associated parasitoids. Specifically, we studied the composition, richness （S） and density of leaf-mining moths （Lepidoptera： Tischeridae, Citheraniidae）, gall-forming wasps （Hymenoptera： Cynipidae）, and canopy parasitoids of Q. castanea. We sampled 120 trees belonging to six populations （20/site） through the previously recognized gradi- ent of genetic diversity. In total, 22 endophagous insect species belonging to three orders （Hymenoptera, Lepidoptera, and Diptera） and 20 parasitoid species belonging to 13 families were identified. In general, we observed that the individual genetic diversity of the host plant （HL） has a significant positive effect on the S and density of the canopy endophagous insect communities. In contrast, He has a significant negative effect on the S of endophagous insects. Additionally, indirect effects of HL were observed, affecting the S and density of parasitoid insects. Our results suggest that genetic variation in foundation species can be one of the most important factors governing the dynamics of tritrophic interactions that involve oaks, herbivores, and parasitoids.展开更多
文摘The enamines, iminium ions, and oxazolidinones are thought to be the key intermediates in the proline-catalyzed reactions of aldehydes or ketones, but there is an extensive contro- versy about their roles. Here, the corresponding transition states connecting any two of the three kinds of species are located at the wB97XD/6-311＋＋G＊＊ level of theory. The calcula- tions demonstrate that the oxazolidinones are the predominant species in both the gas phase and solvents; there exists tautomeric equilibrium among these species and the equilibriums are controlled by the employed solvents and temperature in the reaction. These results demonstrate that the concentration and role of the mentioned species are controlled by the employed solvent and temperature. A new reaction pathway is presented herein for the trans- formation between iminium ions and oxazolidinones through iminium ion-water complex and oxazolidinone-water complex. The calculations demonstrate that the rate-limiting step in proline-catalyzed Mannich reaction between acetaldehyde/keteones and N-Boc imines is the formation of the C-C bond rather than the intermediates tautomerization. These calculations rationalize the available experimental observations and can be valuable in optimizing the experimental conditions of asymmetric organic-catalyzed reactions of aldehydes or ketones.
文摘The molecular structures of indazole and 3-halogeno-indazole tautomers were calculated by the B3LYP method at the 6-311G^＊＊ level, both in the gaseous and aqueous phases, with full geometry optimization. The geometry and electronic structure of the tautomers of indazole, 3-halogeno-indazole and their transition states were obtained. The Onsager solvate theory model was employed for the aqueous solution calculations. The results of the calculation indicated that the N1-H form of the studied molecule is more stable than that of the N2-H form. The influences of the different 3-halogeno and solvent effects on the geometry, energy, charge and activation energy were discussed. The reaction mechanism of the tautomerization of indazole and 3-halogeno-indazole was also studied and a three-membered cyclic transition state of the tautomer reaction has been obtained.
文摘The IR spectroscopic data indicate the tautomeric transformations of typical aprotonic organic fluids such as methane halides with gross formulas CHX3 （X = Cl, Br）, CH2X2 （X = CI, Br, I） and CCl4 at normal conditions. These transformations lead to the appearance in molecules of activated hydrogen atoms similar in the spectral behaviour to the bounded proton. The classical analysis of IR bands in 5000-600 cm^-1 region, for studied samples and their deuterated derivatives, proves the existence in the presented organic fluids of hydrogen and dihydrogen bonds. This bonding promotes the formation of supramolecular structure in methane halides. The mechanism of unusual binding in liquid phase in terms of common knowledge for the basic chemical properties of the examined compounds is discussed.
基金Supported by the National Basic Research Program of China （2005CB221203）, the National Natural Science Foundation of China （20576087, 20776093） and the Foundation of Shanxi Province （2006011022, 2009021015）.
文摘The pyrolysis mechanisms of quinoline and isoquinoline were investigated using the density functional theory of quantum chemistry,including eight reaction paths and a common tautomeric intermediate 1-indene imine.It is concluded that the conformational tautomerism of the intermediate decides the pyrolysis products(C6H6,HC≡C—C≡N,C6H5C≡N and HC≡CH)to be the same,and also decides the total disappearance rates of the reactants to be the same,for both original reactants quinoline and isoquinoline during the pyrolysis reaction.The results indicate that the intramolecular hydrogen migration is an important reaction step,which often appears in the paths of the pyrolysis mechanism.The activation energies of the rate determining steps are obtained.The calculated results are in good agreement with the experimental results.
基金financial support from the National Natural Science Foundation of China (90922012, 20971106 & 21021061)the Natural Science Foundation of Fujian Province for Distinguished Young Scientists (2009J06006)
文摘Herein reported is an example of one-dimensional coordination polymer [Co11(3,5-DBsq)2(dpg)]·(3,5-H2DBcat)2 (1) (3,5-DBsq = 3,5-di-tert-butylsemiquinonate, 3,5-H2DBcat = 3,5-di-tert-butyl-benzene-1,2-diol, dpg = meso-alpha,beta-di(4-pyridyl)glycol) capable of undergoing thermal and photoinduced valence tautomeric transitions.
基金funding support from “Hundred Talents Program” of Zhejiang University, Chinapartially supported by the Australian Research Council (ARC) Discovery Project (DP200100365)
文摘Boosting the alkaline hydrogen evolution and oxidation reaction(HER/HOR)kinetics is vital to practicing the renewable hydrogen cycle in alkaline media.Recently,intensive research has demonstrated that interface engineering is of critical significance for improving the performance of heterostructured electrocatalysts particularly toward the electrochemical reactions involving multiple reaction intermediates like alkaline hydrogen electrocatalysis,and the research advances also bring substantial non-trivial fundamental insights accordingly.Herein,we review the current status of interface engineering with respect to developing efficient heterostructured electrocatalysts for alkaline HER and HOR.Two major subjects—how interface engineering promotes the reaction kinetics and what fundamental insights interface engineering has brought into alkaline HER and HOR—are discussed.Specifically,heterostructured electrocatalysts with abundant interfaces have shown substantially accelerated alkaline hydrogen electrocatalysis kinetics owing to the synergistic effect from different components,which could balance the adsorption/desorption behaviors of the intermediates at the interfaces.Meanwhile,interface engineering can effectively tune the electronic structures of the active sites via electronic interaction,interfacial bonding,and lattice strain,which would appropriately optimize the binding energy of targeted intermediates like hydrogen.Furthermore,the confinement effect is critical for delivering high durability by sustaining high density of active sites.At last,our own perspectives on the challenges and opportunities toward developing efficient heterostructured electrocatalysts for alkaline hydrogen electrocatalysis are provided.
基金Supported by Natural Science Foundation of China under Grant No. 11147112
文摘When a population structure is modelled as a square lattice,the cooperation may be improved for an evolutionary prisoner dilemma game or be inhibited for an evolutionary snowdrift game.In this work,we investigate cooperation in a population on a square lattice where the interaction among players contains both prisoner dilemma game and snowdrift game.The heterogeneity in interaction is introduced to the population in two different ways:the heterogenous character of interaction assigned to every player(HCP) or the heterogenous character of interaction assigned to every link between any two players(HCL).The resonant enhancement of cooperation in the case of HCP is observed while the resonant inhibition of cooperation in the case of HCL is prominent.The explanations on the enhancement or inhibition of cooperation are presented for these two cases.
基金supported by China Postdoctoral Science Foundation(2020M671242 and 2021T140688)the Special Research Assistant program of CASthe Super Postdoctoral Fellow Program of Shanghai。
文摘Rationally designed heterostructures provide attractive prospects for energy storage electrodes by combining different active materials with distinct electrochemical properties.Herein,through a phase separation strategy,a heterostructure of SnO_(2) encapsulated by amorphous Nb_(2)O_(5) is spontaneously synthesized.Insertion-type anode Nb_(2)O_(5) outer shell,playing as reaction containers and fast ionic pathways,physically inhibits the Sn atoms’migration and enhances the reaction kinetics.Moreover,strong chemical interactions are found at the SnO_(2)/Nb_(2)O_(5) interfaces,which ensure the solid encapsulation of the SnO_(2) cores even after 500 cycles.When used for lithium-ion batteries,this heterostructured anode exhibits high cycling stability with a capacity of 626 mAhg^(-1) after 1000 cycles at 2Ag^(-1)(85% capacity retention)and good rate performance with the capacity of 340 mAhg^(-1) at 8Ag^(-1).
文摘Various studies have demonstrated that the foundation species genetic diversity can have direct effects that extend beyond the individual or population level, affecting the dependent communities. Additionally, these effects may be indirectly extended to higher trophic levels throughout the entire community. Quercus castanea is an oak species with characteristics of foundation species beyond pre- senting a wide geographical distribution and being a dominant element of Mexican temperate forests. In this study, we analyzed the influence of population （He） and individual （HL） genetic diversity of Q. castanea on its canopy endophagous insect community and associated parasitoids. Specifically, we studied the composition, richness （S） and density of leaf-mining moths （Lepidoptera： Tischeridae, Citheraniidae）, gall-forming wasps （Hymenoptera： Cynipidae）, and canopy parasitoids of Q. castanea. We sampled 120 trees belonging to six populations （20/site） through the previously recognized gradi- ent of genetic diversity. In total, 22 endophagous insect species belonging to three orders （Hymenoptera, Lepidoptera, and Diptera） and 20 parasitoid species belonging to 13 families were identified. In general, we observed that the individual genetic diversity of the host plant （HL） has a significant positive effect on the S and density of the canopy endophagous insect communities. In contrast, He has a significant negative effect on the S of endophagous insects. Additionally, indirect effects of HL were observed, affecting the S and density of parasitoid insects. Our results suggest that genetic variation in foundation species can be one of the most important factors governing the dynamics of tritrophic interactions that involve oaks, herbivores, and parasitoids.
