Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs （abbreviated XBAYs） were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the 1H NMR chemical...Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs （abbreviated XBAYs） were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the 1H NMR chemical shifts （δH（CH=N）） and 13C NMR chemical shifts （δc（CH=N）） of the CH=N bridging group from di-substituted to multi-substituted XBAYs was made based on a total of 182 samples of XBAYs, together with the NMR data of other 129 samples of di-substituted XBAYs quoted from literatures. The results show thatthe substituent specific cross-interaction effect parameter （△（∑σ）2） plays an important role in quantifying the δc（CH=N） values of XBAYs, but it is negligible for quantifying the δH （CH=N） values; the other substituent parameters also present different influences on the δc （CH=N） and （δH （CH=N）. On the whole, the contributions of X and Y to the δc （CH=N） of XBAYs are balanced, but the δH（CH=N） values of XBAYs mainly rely on the contributions of X.展开更多
Accurate chemical shifts of hydrogen atoms in CH groups are difficult to obtain. To solve this problem, relative chemical shifts are introduced. Internal and external standard methods were used to measure the chemical...Accurate chemical shifts of hydrogen atoms in CH groups are difficult to obtain. To solve this problem, relative chemical shifts are introduced. Internal and external standard methods were used to measure the chemical shifts in a whole-concentration of N-methylacetamide- water system. Determination of the chemical shifts of hydrogen atoms, especially those of CH groups, according to the two methods yielded significant differences. Relative chemical shifts were proven to be independent of the reference and may be applied to other systems.展开更多
1H NMR chemical shifts of binary aqueous mixtures of acylamide, alcohol, dimethyl sulphoxide (DMSO), and acetone are correlated by statistical associating fluid theory (SAFT) association model. The comparison between ...1H NMR chemical shifts of binary aqueous mixtures of acylamide, alcohol, dimethyl sulphoxide (DMSO), and acetone are correlated by statistical associating fluid theory (SAFT) association model. The comparison between SAPT association model and Wilson equation shows that the former is better for dealing with aqueous solutions. Finally, the specialties of both models are discussed.展开更多
A quantitative structure-spectrum relationship (QSSR) model was developed to simulate 13C nuclear magnetic resonance (NMR) spectra of carbinol carbon atoms for 55 alcohols. The proposed model,using multiple linear reg...A quantitative structure-spectrum relationship (QSSR) model was developed to simulate 13C nuclear magnetic resonance (NMR) spectra of carbinol carbon atoms for 55 alcohols. The proposed model,using multiple linear regression,contained four descriptors solely extracted from the molecular structure of compounds. The statistical results of the final model show that R2= 0.982 4 and S=0.869 8 (where R is the correlation coefficient and S is the standard deviation). To test its predictive ability,the model was further used to predict the 13C NMR spectra of the carbinol carbon atoms of other nine compounds which were not included in the developed model. The average relative errors are 0.94% and 1.70%,respectively,for the training set and the predictive set. The model is statistically significant and shows good stability for data variation as tested by the leave-one-out (LOO) cross-validation. The comparison with other approaches also reveals good performance of this method.展开更多
After the geometry optimization at B3LYP/6-31＋G（d,p） level,the calculations of the NMR chemical shifts of a series of stilbene analogues were carried out by means of Gauge Including Atomic Orbitals（GIAO） method a...After the geometry optimization at B3LYP/6-31＋G（d,p） level,the calculations of the NMR chemical shifts of a series of stilbene analogues were carried out by means of Gauge Including Atomic Orbitals（GIAO） method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,respectively.The 13C NMR chemical shifts calculated at both HF/6-31＋G（d） and B3LYP/6-31＋G（d,p） levels are in agreement with the observed values.By virtue of a series of linear correction equations（δpred.=a＋bδcalcd.） of the 13C chemical shifts,accurate prediction of 13C chemical shifts was achieved for the new stilbene compounds.For the 13C NMR chemical shifts calculated at HF/6-31＋G（d） level,the linear correlation of δpred.with δexptl.is excellent,and the square of correlation coefficient,r2,is 0.9985.The maximum absolute difference between δpred.and δexptl.,Δδ,is 2.3,and the root-mean-square error between δpred.and δexptl.is 0.98.In the meantime,for those obtained at B3LYP/6-31＋G（d,p） level,the linear correlation of δpred.with δexptl.is also excellent,and the square of correlation coefficient,r2,is up to 0.9987.The maximum absolute difference between δpred.and δexptl.,Δδ,is 2.2,and the root-mean-square error between δpred.and δexptl.is only 0.88.展开更多
After the geometry optimization at B3LYP/6-31＋G（d,p） level,the NMR calcula-tions of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,re...After the geometry optimization at B3LYP/6-31＋G（d,p） level,the NMR calcula-tions of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,respectively.The 13C NMR chemical shifts calculated at HF/6-31＋G（d） level show better agreement with the observed values.By a series of linear correction equations （δpred=a ＋ bδcalc）,accurate prediction of 13C chemical shifts was achieved for the new fluorenone compound.The linear correlation of δpred with δexptl is excellent,and the square of correlation coefficient,r2,is up to 0.994.The maximum absolute difference between δpred and δexptl,Δδ,is 4.6 ppm,and the root-mean-square error between δpred and δexptl is only 2.6 ppm.展开更多
Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 （D6） and C24O have been performed using density functional theory （DFT） method. The geometric and electronic ...Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 （D6） and C24O have been performed using density functional theory （DFT） method. The geometric and electronic structures as well as the relative energies and thermal stabilities of various C24O2 isomers at the ground state have been calculated at the B3LYP/6-31G（d） level of theory. And the 1,4,2,5-C24O2 isomer was found to be the most stable geometry where two oxygen atoms were added to the longest carbon-carbon bonds in the same pentagon from a thermodynamic point of view. Based on the optimized neutral geometries, the vertical ionization potential and vertical electron affinity have been obtained. Meanwhile, the vibrational frequencies, IR spectrum, and 13C chemical shifts of various C24O2 isomers have been calculated and analyzed.展开更多
The interactions and structures of the urea-water system are studied by an all-atom molecular dynamics （MD） simulation. The hydrogen-bonding network and the radial distribution functions are adopted in MD simulation...The interactions and structures of the urea-water system are studied by an all-atom molecular dynamics （MD） simulation. The hydrogen-bonding network and the radial distribution functions are adopted in MD simulations. The structures of urea-water mixtures can be classified into different regions from the analysis of the hydrogen-bonding network. The urea molecule shows the certain tendency to the self-aggregate with the mole fraction of urea increasing. Moreover, the results of the MD simulations are also compare with the chemical shifts and viscosities of the urea aqueous solutions, and the statistical results of the average number hydrogen bonds in the MD simulations are in agreement with the experiment data such as chemical shifts of the hydrogen atom and viscosity.展开更多
The present paper covers the 199 Hg NMR chemical shifts of 24 substituted diphenylmercurials and phenyl(2-benzothiazolylthio)mercurials. There is a good linear relationship between the chemical shift and the Hammett c...The present paper covers the 199 Hg NMR chemical shifts of 24 substituted diphenylmercurials and phenyl(2-benzothiazolylthio)mercurials. There is a good linear relationship between the chemical shift and the Hammett constant of the substituents for both series of compounds, and electron donating substituents cause the chemical shift towards downfield.展开更多
Three ethylene-vinyl alcohol copolymers were studied by means of the substituent chemical shift (SCS) method. The SCS parameters of hydroxy (-OH) in two different solvents were obtained: in deuterium oxide/phenol (20/...Three ethylene-vinyl alcohol copolymers were studied by means of the substituent chemical shift (SCS) method. The SCS parameters of hydroxy (-OH) in two different solvents were obtained: in deuterium oxide/phenol (20/80 W/W ) the parameters are S_1 = 42.77±0.08ppm, S_2 = 7.15±0.06 ppm, S_3 (s)= -4.08±0.02ppm, S_3 (t) =-3.09±0.20ppm,S_4 = 0.48±0.03ppm, S_5 = 0.26±0.05ppm. In o-dichloro-benzen-d_4 S_1(s)=44.79±0.61ppm, S_2=7.40±0.00ppm, S_3(s)=-4.51±0.17ppm, S_3(t)=-3.13 ±0.00 ppm, S_4 =0.63±0.04ppm, S_5=0.36±0.00ppm.Simultaneously the ^(13)CNMR spectra of EVA copolymers were assigned by using the SCS parameters obtained.展开更多
The ability of several ab initio models to predict experimental 29Si-NMR chemical shift is examined. The shielding values of trimethylsilyl chloride (A), t-butyldimethylsilyl chloride (B) and allyltrimethylsilane (C) ...The ability of several ab initio models to predict experimental 29Si-NMR chemical shift is examined. The shielding values of trimethylsilyl chloride (A), t-butyldimethylsilyl chloride (B) and allyltrimethylsilane (C) are calculated by GIAO , CSGT and IGAIM methods, using HF/6-31G*, B3LYP/6-31G*, HF/6-311+G **, B3LYP/6-311+G ** and MPW1PW91/6-311+G ** models respectively. The 29Si chemical shifts calculated by GIAO method using HF/6-311+G ** model are highly in agreement with those obtained experimentally. All of the models above reproduce the trends of chemical shifts in all cases studied, suggesting that the models are of practical value.展开更多
After the geometry optimizations at the B3LYP/6-31＋G（d,p） level, the NMR calculations of a series of 9,10-dihydrophenanthrene analogues have been carried out by GIAO method at the HF/6-31＋G（d） level. The calcula...After the geometry optimizations at the B3LYP/6-31＋G（d,p） level, the NMR calculations of a series of 9,10-dihydrophenanthrene analogues have been carried out by GIAO method at the HF/6-31＋G（d） level. The calculated ^13C NMR chemical shifts are in agreement with the observed values. By a series of linear correlation equations （δpred = a ＋ bδcal.c） of the ^13C chemical shifts, accurate prediction of ^13C chemical shifts was achieved for the new 9,10- dihydrophenanthrene compound, for which the predicted ^13C NMR chemical shifts are in quite good agreement with the experimental values. The linear correlation between δpred and δexptl is excellent, and the square of correlation coefficient, r^2, is up to 0.9973. The maximum absolute difference between δpred and δexptl, △δ, is 4.5 ppm, and the rms error between δpred and δexpt is 2.55 ppm. In the meantime, according to the theoretical predicted result, we could confirm that the new 9,10-dihydrophenanthrene analogue is erianthridin （2,7-dihydroxy-3,4-dimethoxy-9,10-dihydro- phenanthrene）.展开更多
On two dimensional maps of <sup>1</sup>H-<sup>13</sup>C correlation spectroscopy (H-C COSY) analysis for the mannan of <i>Candida tropicalis</i>, nine cross peaks of anomeric proton...On two dimensional maps of <sup>1</sup>H-<sup>13</sup>C correlation spectroscopy (H-C COSY) analysis for the mannan of <i>Candida tropicalis</i>, nine cross peaks of anomeric proton and carbon were useful for the purpose of obtaining information on the chemical structure of this molecule. Namely, the mannans was comb-like structure constructed with the linear <i>α</i>-1,6-linked polymannnosyl backbone and several oligomannnosyl side chains composed of <i>α</i>-1,2-, <i>α</i>-1,3-, and <i>β</i>-1,2-linkages. Therefore, in the structural investigation of comb-like mannan, two-dimensional H-C COSY analysis is as useful as two-dimensional nuclear Hartmann-Hahn (HOHAHA) analysis.展开更多
Although anisotropic NMR spectroscopy has emerged as a powerful method for determining the relative configuration of complex natural products,major challenges persist with structurally flexible molecules.In this study...Although anisotropic NMR spectroscopy has emerged as a powerful method for determining the relative configuration of complex natural products,major challenges persist with structurally flexible molecules.In this study,we conducted a system-atic comparative analysis of stereochemical elucidation,combining anisotropic NMR spectroscopy and density functional theory(DFT)calculations on spiroepicoccin B(1)and epicoccin V(2),which were characterized as thiodiketopiperazine marine natural products isolated from the deep-sea-derived fungus Epicoccum nigrum SD-388.For the flexible compound 2,we compared various conformational sampling approaches,including an assessment of the quality of relative energies within the obtained ensembles.We demonstrated the critical role of dispersion correction within DFT computations to precisely account for weak non-bonded intramolecular interactions.By integrating anisotropic NMR analysis,chemical shifts,elec-tronic circular dichroism,and DFT computations,we determined the absolute configurations and conformational ensembles for 1 and 2,respectively,highlighting the significance of the intramolecular methyl-πinteraction in stabilizing one of the conformers.Our study introduces new strategies to address conformational flexibility in the stereochemical elucidation of challenging organic molecules.展开更多
Repurposing of carbon dioxide to valuable chemicals and fuels with the assistance of renewable energy is essential for balanced carbon cycle.Here,a new CO_(2)conversion strategy was demonstrated that utilized concentr...Repurposing of carbon dioxide to valuable chemicals and fuels with the assistance of renewable energy is essential for balanced carbon cycle.Here,a new CO_(2)conversion strategy was demonstrated that utilized concentrated solar energy to directly drive chemical looping reverse water gas shift process,which simultaneously coupled the photothermal and photochemical effects to achieve enhanced CO_(2)reduction reactivity and 100%CO selectivity.The solar-driven chemical looping CO_(2)reduction on Ni-Fe_(2)O_(3/)La_(0.8)Sr_(0.2)FeO_(3)exhibited great activity,with an average CO production rate of up to 0.28 mmol/g_(oc)/min at 283℃The product yield of the solar-driven reaction was almost 600%higher than that of the thermal reaction at the same temperature.The CO production overcame the thermodynamic equilibrium limitation under the combined impact of thermal and non-thermal effects of direct-light illumination.Light irradiation reinforced reactive gas adsorption and dissociation of carbonate intermediates,and stimulated oxygen ion migration and lattice oxygen transformation,thus promoting the reactivity.The concept of concentrated solar energy to drive chemical looping reverse water gas shift opens a new avenue for effective CO_(2)resource utilization and solar fuel production.展开更多
An unusual negative 1H NMR chemical shift of methyl group was discovered in condensation product of isoco-palane diterpenoid with p-toluenesulfonyl hydrazide.2D NMR,computational studies and single-crystal X-ray dif-f...An unusual negative 1H NMR chemical shift of methyl group was discovered in condensation product of isoco-palane diterpenoid with p-toluenesulfonyl hydrazide.2D NMR,computational studies and single-crystal X-ray dif-fraction analysis showed that the C-20 methyl group was shielded.展开更多
13C NMR chemical shifts have been calculated for structures of some substituted 3-anilino-2-nitrobenzo- [b]thiophenes （2o） and 2-anilino-3-nitrobenzo[b]thiophenes （3o） derivatives containing OH, NH2, OMe, Me, Et, ...13C NMR chemical shifts have been calculated for structures of some substituted 3-anilino-2-nitrobenzo- [b]thiophenes （2o） and 2-anilino-3-nitrobenzo[b]thiophenes （3o） derivatives containing OH, NH2, OMe, Me, Et, H, F, Cl and Br. The molecular structures were fully optimized using B3LYP/6-31G（d,p）. The calculation of the 13C shielding tensors employed the GAUSSIAN 03 implementation of the gauge-including atomic orbital （GIAO） and continuous set of gauge transformations （CSGT） by using 6-311 ＋＋G（d,p） basis set at density functional levels of theories （DFT）. The isotropic and the anisotropy parameters of chemical shielding for all compounds are calculated. The predicted 13C chemical shifts are derived from equation δ=σ0＋σ where δ is the chemical shift, σ is the absolute shielding, and σ0 is the absolute shielding of the standard TMS. Excellent linear relationships have been observed between experimental and calculated 13C NMR chemical shifts for all derivatives.展开更多
Density functional theory(DFT)calculations were carried out on some cyclohexane derivatives to investigate the deviation atoms on the 1-and 4-positions of chair plane.The deviations of chair plane of two position in t...Density functional theory(DFT)calculations were carried out on some cyclohexane derivatives to investigate the deviation atoms on the 1-and 4-positions of chair plane.The deviations of chair plane of two position in the cyclohexane derivatives were calculated at the B3LYP/6–31++G(d,p)level.Furthermore,we investigated the correlation between deviations of two positions from chair plane on the chemical shift hydrogen atoms on the 4-position.展开更多
An approach for distinguishing two types of positional isomers of dimeric shikonin and its analogs was explored with ^(4)JC,H long-range correlation by prolonging the acquisition time at ^(2,3)JC,H values of 2.0 and 8...An approach for distinguishing two types of positional isomers of dimeric shikonin and its analogs was explored with ^(4)JC,H long-range correlation by prolonging the acquisition time at ^(2,3)JC,H values of 2.0 and 8.0Hz.Furthermore,the ^(1)H(proton)nuclear magnetic resonance(NMR)pattern of phenolic hydroxyl protons was developed as a“diagnosis signal”to ascertain the relative location of each side chain in DMSO-d_(6) at sample concentrations of 0.022-0.034 mol/L.The chemical shift differences of 0.6ppm between OH-5' and OH-1 and between OH-8'and OH-4 are assigned to Type A and Type B,respectively.All reported ambiguous structures were corrected by this pattern.Additionally,the steric structures of isolated compounds were elucidated by quantum chemical calculations of electronic circular dichroism(ECD)spectra.展开更多
基金supported by the National Natural Science Foundation of China(No.21672058 and No.21272063)
文摘Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs （abbreviated XBAYs） were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the 1H NMR chemical shifts （δH（CH=N）） and 13C NMR chemical shifts （δc（CH=N）） of the CH=N bridging group from di-substituted to multi-substituted XBAYs was made based on a total of 182 samples of XBAYs, together with the NMR data of other 129 samples of di-substituted XBAYs quoted from literatures. The results show thatthe substituent specific cross-interaction effect parameter （△（∑σ）2） plays an important role in quantifying the δc（CH=N） values of XBAYs, but it is negligible for quantifying the δH （CH=N） values; the other substituent parameters also present different influences on the δc （CH=N） and （δH （CH=N）. On the whole, the contributions of X and Y to the δc （CH=N） of XBAYs are balanced, but the δH（CH=N） values of XBAYs mainly rely on the contributions of X.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.20903026）, the Talents Introduction Foundation for Universities of Guangdong Province （No.2011）, Scientific Research Foundation of the Natural Science Foundation of Guangdong Province, China （No.S2011010002483）, and Science and Technology Planning Project of Guangzhou （No.2013J4100071）.
文摘Accurate chemical shifts of hydrogen atoms in CH groups are difficult to obtain. To solve this problem, relative chemical shifts are introduced. Internal and external standard methods were used to measure the chemical shifts in a whole-concentration of N-methylacetamide- water system. Determination of the chemical shifts of hydrogen atoms, especially those of CH groups, according to the two methods yielded significant differences. Relative chemical shifts were proven to be independent of the reference and may be applied to other systems.
基金Supported by the National Natural Science Foundation of China (No. 29976035)the Natural Science Foundation of Zhejiang Provincial (No. RC01051).
文摘1H NMR chemical shifts of binary aqueous mixtures of acylamide, alcohol, dimethyl sulphoxide (DMSO), and acetone are correlated by statistical associating fluid theory (SAFT) association model. The comparison between SAPT association model and Wilson equation shows that the former is better for dealing with aqueous solutions. Finally, the specialties of both models are discussed.
基金Projects(20775010, 21075011) supported by the National Natural Science Foundation of ChinaProject(2008AA05Z405) supported by the National High-tech Research and Development Program of China+2 种基金Project(09JJ3016) supported by the Natural Science Foundation of Hunan Province, ChinaProject(09C066) supported by the Scientific Research Fund of Hunan Provincial Education Department, ChinaProject(2010CL01) supported by the Foundation of Hunan Provincial Key Laboratory of Materials Protection for Electric Power and Transportation, China
文摘A quantitative structure-spectrum relationship (QSSR) model was developed to simulate 13C nuclear magnetic resonance (NMR) spectra of carbinol carbon atoms for 55 alcohols. The proposed model,using multiple linear regression,contained four descriptors solely extracted from the molecular structure of compounds. The statistical results of the final model show that R2= 0.982 4 and S=0.869 8 (where R is the correlation coefficient and S is the standard deviation). To test its predictive ability,the model was further used to predict the 13C NMR spectra of the carbinol carbon atoms of other nine compounds which were not included in the developed model. The average relative errors are 0.94% and 1.70%,respectively,for the training set and the predictive set. The model is statistically significant and shows good stability for data variation as tested by the leave-one-out (LOO) cross-validation. The comparison with other approaches also reveals good performance of this method.
基金Supported by the Scientific Research Foundation of Department of Education of Yunnan Province,China(No.09Y0181)
文摘After the geometry optimization at B3LYP/6-31＋G（d,p） level,the calculations of the NMR chemical shifts of a series of stilbene analogues were carried out by means of Gauge Including Atomic Orbitals（GIAO） method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,respectively.The 13C NMR chemical shifts calculated at both HF/6-31＋G（d） and B3LYP/6-31＋G（d,p） levels are in agreement with the observed values.By virtue of a series of linear correction equations（δpred.=a＋bδcalcd.） of the 13C chemical shifts,accurate prediction of 13C chemical shifts was achieved for the new stilbene compounds.For the 13C NMR chemical shifts calculated at HF/6-31＋G（d） level,the linear correlation of δpred.with δexptl.is excellent,and the square of correlation coefficient,r2,is 0.9985.The maximum absolute difference between δpred.and δexptl.,Δδ,is 2.3,and the root-mean-square error between δpred.and δexptl.is 0.98.In the meantime,for those obtained at B3LYP/6-31＋G（d,p） level,the linear correlation of δpred.with δexptl.is also excellent,and the square of correlation coefficient,r2,is up to 0.9987.The maximum absolute difference between δpred.and δexptl.,Δδ,is 2.2,and the root-mean-square error between δpred.and δexptl.is only 0.88.
文摘After the geometry optimization at B3LYP/6-31＋G（d,p） level,the NMR calcula-tions of a series of fluorenone analogues have been carried out by GIAO method at HF/6-31＋G（d） level and B3LYP/6-311G＋（2d,p） level,respectively.The 13C NMR chemical shifts calculated at HF/6-31＋G（d） level show better agreement with the observed values.By a series of linear correction equations （δpred=a ＋ bδcalc）,accurate prediction of 13C chemical shifts was achieved for the new fluorenone compound.The linear correlation of δpred with δexptl is excellent,and the square of correlation coefficient,r2,is up to 0.994.The maximum absolute difference between δpred and δexptl,Δδ,is 4.6 ppm,and the root-mean-square error between δpred and δexptl is only 2.6 ppm.
文摘Quantum chemical calculations on some possible equilibrium geometries of C24O2 isomers derived from C24 （D6） and C24O have been performed using density functional theory （DFT） method. The geometric and electronic structures as well as the relative energies and thermal stabilities of various C24O2 isomers at the ground state have been calculated at the B3LYP/6-31G（d） level of theory. And the 1,4,2,5-C24O2 isomer was found to be the most stable geometry where two oxygen atoms were added to the longest carbon-carbon bonds in the same pentagon from a thermodynamic point of view. Based on the optimized neutral geometries, the vertical ionization potential and vertical electron affinity have been obtained. Meanwhile, the vibrational frequencies, IR spectrum, and 13C chemical shifts of various C24O2 isomers have been calculated and analyzed.
基金This work was supported by the National Natural Science Foundation of China （No.20903026）, the Doctoral Scientific Research Foundation of the Natural Science Foundation of Guangdong Province （No.7301567）, and the Research Foundation of Guangdong Pharmaceutical University （No.2006YKX05）.
文摘The interactions and structures of the urea-water system are studied by an all-atom molecular dynamics （MD） simulation. The hydrogen-bonding network and the radial distribution functions are adopted in MD simulations. The structures of urea-water mixtures can be classified into different regions from the analysis of the hydrogen-bonding network. The urea molecule shows the certain tendency to the self-aggregate with the mole fraction of urea increasing. Moreover, the results of the MD simulations are also compare with the chemical shifts and viscosities of the urea aqueous solutions, and the statistical results of the average number hydrogen bonds in the MD simulations are in agreement with the experiment data such as chemical shifts of the hydrogen atom and viscosity.
文摘The present paper covers the 199 Hg NMR chemical shifts of 24 substituted diphenylmercurials and phenyl(2-benzothiazolylthio)mercurials. There is a good linear relationship between the chemical shift and the Hammett constant of the substituents for both series of compounds, and electron donating substituents cause the chemical shift towards downfield.
文摘Three ethylene-vinyl alcohol copolymers were studied by means of the substituent chemical shift (SCS) method. The SCS parameters of hydroxy (-OH) in two different solvents were obtained: in deuterium oxide/phenol (20/80 W/W ) the parameters are S_1 = 42.77±0.08ppm, S_2 = 7.15±0.06 ppm, S_3 (s)= -4.08±0.02ppm, S_3 (t) =-3.09±0.20ppm,S_4 = 0.48±0.03ppm, S_5 = 0.26±0.05ppm. In o-dichloro-benzen-d_4 S_1(s)=44.79±0.61ppm, S_2=7.40±0.00ppm, S_3(s)=-4.51±0.17ppm, S_3(t)=-3.13 ±0.00 ppm, S_4 =0.63±0.04ppm, S_5=0.36±0.00ppm.Simultaneously the ^(13)CNMR spectra of EVA copolymers were assigned by using the SCS parameters obtained.
文摘The ability of several ab initio models to predict experimental 29Si-NMR chemical shift is examined. The shielding values of trimethylsilyl chloride (A), t-butyldimethylsilyl chloride (B) and allyltrimethylsilane (C) are calculated by GIAO , CSGT and IGAIM methods, using HF/6-31G*, B3LYP/6-31G*, HF/6-311+G **, B3LYP/6-311+G ** and MPW1PW91/6-311+G ** models respectively. The 29Si chemical shifts calculated by GIAO method using HF/6-311+G ** model are highly in agreement with those obtained experimentally. All of the models above reproduce the trends of chemical shifts in all cases studied, suggesting that the models are of practical value.
基金supported by the Scientific Research Foundation of Department of Education of Yunnan Province (No. 2010Z035)
文摘After the geometry optimizations at the B3LYP/6-31＋G（d,p） level, the NMR calculations of a series of 9,10-dihydrophenanthrene analogues have been carried out by GIAO method at the HF/6-31＋G（d） level. The calculated ^13C NMR chemical shifts are in agreement with the observed values. By a series of linear correlation equations （δpred = a ＋ bδcal.c） of the ^13C chemical shifts, accurate prediction of ^13C chemical shifts was achieved for the new 9,10- dihydrophenanthrene compound, for which the predicted ^13C NMR chemical shifts are in quite good agreement with the experimental values. The linear correlation between δpred and δexptl is excellent, and the square of correlation coefficient, r^2, is up to 0.9973. The maximum absolute difference between δpred and δexptl, △δ, is 4.5 ppm, and the rms error between δpred and δexpt is 2.55 ppm. In the meantime, according to the theoretical predicted result, we could confirm that the new 9,10-dihydrophenanthrene analogue is erianthridin （2,7-dihydroxy-3,4-dimethoxy-9,10-dihydro- phenanthrene）.
文摘On two dimensional maps of <sup>1</sup>H-<sup>13</sup>C correlation spectroscopy (H-C COSY) analysis for the mannan of <i>Candida tropicalis</i>, nine cross peaks of anomeric proton and carbon were useful for the purpose of obtaining information on the chemical structure of this molecule. Namely, the mannans was comb-like structure constructed with the linear <i>α</i>-1,6-linked polymannnosyl backbone and several oligomannnosyl side chains composed of <i>α</i>-1,2-, <i>α</i>-1,3-, and <i>β</i>-1,2-linkages. Therefore, in the structural investigation of comb-like mannan, two-dimensional H-C COSY analysis is as useful as two-dimensional nuclear Hartmann-Hahn (HOHAHA) analysis.
基金supported by the Leibniz-Forschungsinstitut für Molekulare Pharmakologie(FMP)and the Deutsche Forschungsgemeinschaft(DFG,German Research Foun-dation)under RTG 2473 Bioactive Peptides(392923329)A.F.K.and H.S.under Germany’s Excellence Strategy-EXC 2008/1(UniSysCat,390540038)to C.J.S.and H.S.+2 种基金the National Natural Science Foundation of China(U2006203)to B.-G.W.X.-L.Lsupport from the Taishan Scholars Program(tsqn202306366,China).A.N.-Vthanks National Council for Scien-tific and Technological Development(CNPq)for a research fellowship(309873/2023-1).
文摘Although anisotropic NMR spectroscopy has emerged as a powerful method for determining the relative configuration of complex natural products,major challenges persist with structurally flexible molecules.In this study,we conducted a system-atic comparative analysis of stereochemical elucidation,combining anisotropic NMR spectroscopy and density functional theory(DFT)calculations on spiroepicoccin B(1)and epicoccin V(2),which were characterized as thiodiketopiperazine marine natural products isolated from the deep-sea-derived fungus Epicoccum nigrum SD-388.For the flexible compound 2,we compared various conformational sampling approaches,including an assessment of the quality of relative energies within the obtained ensembles.We demonstrated the critical role of dispersion correction within DFT computations to precisely account for weak non-bonded intramolecular interactions.By integrating anisotropic NMR analysis,chemical shifts,elec-tronic circular dichroism,and DFT computations,we determined the absolute configurations and conformational ensembles for 1 and 2,respectively,highlighting the significance of the intramolecular methyl-πinteraction in stabilizing one of the conformers.Our study introduces new strategies to address conformational flexibility in the stereochemical elucidation of challenging organic molecules.
基金support by National Natural Science Foundation of China(NSFC)under Grant No.52488201(Basic Science Center Program),Grant No.52241601and 52176026。
文摘Repurposing of carbon dioxide to valuable chemicals and fuels with the assistance of renewable energy is essential for balanced carbon cycle.Here,a new CO_(2)conversion strategy was demonstrated that utilized concentrated solar energy to directly drive chemical looping reverse water gas shift process,which simultaneously coupled the photothermal and photochemical effects to achieve enhanced CO_(2)reduction reactivity and 100%CO selectivity.The solar-driven chemical looping CO_(2)reduction on Ni-Fe_(2)O_(3/)La_(0.8)Sr_(0.2)FeO_(3)exhibited great activity,with an average CO production rate of up to 0.28 mmol/g_(oc)/min at 283℃The product yield of the solar-driven reaction was almost 600%higher than that of the thermal reaction at the same temperature.The CO production overcame the thermodynamic equilibrium limitation under the combined impact of thermal and non-thermal effects of direct-light illumination.Light irradiation reinforced reactive gas adsorption and dissociation of carbonate intermediates,and stimulated oxygen ion migration and lattice oxygen transformation,thus promoting the reactivity.The concept of concentrated solar energy to drive chemical looping reverse water gas shift opens a new avenue for effective CO_(2)resource utilization and solar fuel production.
基金supported by National Natural Science Foundation of China(No.21302053)Science and Technology Commission of Shanghai Mu-nicipality(No.14DZ1900102)the Fundamental Research Funds for the Central University(No.WY1113007)。
文摘An unusual negative 1H NMR chemical shift of methyl group was discovered in condensation product of isoco-palane diterpenoid with p-toluenesulfonyl hydrazide.2D NMR,computational studies and single-crystal X-ray dif-fraction analysis showed that the C-20 methyl group was shielded.
文摘13C NMR chemical shifts have been calculated for structures of some substituted 3-anilino-2-nitrobenzo- [b]thiophenes （2o） and 2-anilino-3-nitrobenzo[b]thiophenes （3o） derivatives containing OH, NH2, OMe, Me, Et, H, F, Cl and Br. The molecular structures were fully optimized using B3LYP/6-31G（d,p）. The calculation of the 13C shielding tensors employed the GAUSSIAN 03 implementation of the gauge-including atomic orbital （GIAO） and continuous set of gauge transformations （CSGT） by using 6-311 ＋＋G（d,p） basis set at density functional levels of theories （DFT）. The isotropic and the anisotropy parameters of chemical shielding for all compounds are calculated. The predicted 13C chemical shifts are derived from equation δ=σ0＋σ where δ is the chemical shift, σ is the absolute shielding, and σ0 is the absolute shielding of the standard TMS. Excellent linear relationships have been observed between experimental and calculated 13C NMR chemical shifts for all derivatives.
文摘Density functional theory(DFT)calculations were carried out on some cyclohexane derivatives to investigate the deviation atoms on the 1-and 4-positions of chair plane.The deviations of chair plane of two position in the cyclohexane derivatives were calculated at the B3LYP/6–31++G(d,p)level.Furthermore,we investigated the correlation between deviations of two positions from chair plane on the chemical shift hydrogen atoms on the 4-position.
基金funded by the CAMS Innovation Fund for Medical Sciences(CIFMS,No.2021-I2M-1-028).
文摘An approach for distinguishing two types of positional isomers of dimeric shikonin and its analogs was explored with ^(4)JC,H long-range correlation by prolonging the acquisition time at ^(2,3)JC,H values of 2.0 and 8.0Hz.Furthermore,the ^(1)H(proton)nuclear magnetic resonance(NMR)pattern of phenolic hydroxyl protons was developed as a“diagnosis signal”to ascertain the relative location of each side chain in DMSO-d_(6) at sample concentrations of 0.022-0.034 mol/L.The chemical shift differences of 0.6ppm between OH-5' and OH-1 and between OH-8'and OH-4 are assigned to Type A and Type B,respectively.All reported ambiguous structures were corrected by this pattern.Additionally,the steric structures of isolated compounds were elucidated by quantum chemical calculations of electronic circular dichroism(ECD)spectra.
