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
Keto-enol tautomers of curcumin were confirmed by reversed-phase liquid chromatography（RPLC）/ hybrid quadrupole ion trap/time-of-flight mass spectrometry（QIT/TOFMS）.Tautomers gave different MS/MS spectra in negati...Keto-enol tautomers of curcumin were confirmed by reversed-phase liquid chromatography（RPLC）/ hybrid quadrupole ion trap/time-of-flight mass spectrometry（QIT/TOFMS）.Tautomers gave different MS/MS spectra in negative mode.Different mass spectra were also obtained by hydrogen/deuterium exchange LC/MS/MS in positive mode.Our results suggest that enol form is the major form in the solution（water/acetonitrile）.展开更多
Base pair mismatch has been regarded as the main source of DNA point mutations, where minor shortlived tautomers were usually involved. However, the detection and characterization of these unnatural species pose chall...Base pair mismatch has been regarded as the main source of DNA point mutations, where minor shortlived tautomers were usually involved. However, the detection and characterization of these unnatural species pose challenges to existing techniques. Here, by using systematic structural and ultrafast resonance Raman(RR) spectral analysis for the four possible conformers of guanine-cytosine base pairs, the prominent marker Raman bands were identified. We found that the hydrogen bonding vibrational region from 2300 cm^(-1) to 3700 cm^(-1) is ideal for the identification of these short live species. The marker bands provide direct evidence for the existence of the tautomer species, thus offering an effective strategy to detect the short-lived minor species. Ultrafast resonance Raman spectroscopy would be a powerful tool to provide direct evidence of critical dynamical details of complex systems involving protonation or tautomerization.展开更多
Density Functional Theory method is applied to investigate the enol-keto tautomerism of both acyclic and cyclic α-fluorine-β-diketones. It is shown that, for acyclic cases, α-fluorine could improve the relative sta...Density Functional Theory method is applied to investigate the enol-keto tautomerism of both acyclic and cyclic α-fluorine-β-diketones. It is shown that, for acyclic cases, α-fluorine could improve the relative stability of keto tautomer by lessening intramolecular hydrogen bond of enol form, whereas the relative stability of cyclic enol could be attributed to two factors： destabilization of keto and stabilization of enol. Furthermore, the relative stabilities of all enol tautomers are improved in THF to different extents.展开更多
A theoretical study of the reactivity of quinoline-4-one derivatives is undertaken in order to understand the involved mechanisms. The calculations were carried out in gas phase and in N, N-Dimethylformamide (DMF) sol...A theoretical study of the reactivity of quinoline-4-one derivatives is undertaken in order to understand the involved mechanisms. The calculations were carried out in gas phase and in N, N-Dimethylformamide (DMF) solution. The Density Functional Theory (DFT) with B3LYP functional associated to 6-311G (d) and 6-311+G (d) bases is used to perform these calculations. The results of the thermodynamic parameters showed that there is an equilibrium relation between the different tautomers. This equilibrium can be used to explain the failure to obtain tetrahydroquinoline from 5,8-dimethoxy-quinolin-4-one. Reactivity analysis from Frontier Molecular Orbitals theory and Fukui function calculations revealed that ketone forms are less reactive than enol ones. The methoxyl substituent decreases the acidity of the nitrogen and oxygen atoms of quinolin-4-one while the bromine increases the acidity of the same sites. These results foresee that nitrogen deprotonation in the case of the brominated compound is easier than in the case of methoxylated ones.展开更多
The potential energy surface of H（13） proton in base cytosine of the DNA molecules is calculated at the Caussian 98 MP2/6-311C（d,p） level. Two potential wells are found. One corresponds to the normal cytosine, whi...The potential energy surface of H（13） proton in base cytosine of the DNA molecules is calculated at the Caussian 98 MP2/6-311C（d,p） level. Two potential wells are found. One corresponds to the normal cytosine, while the other corresponds to its trans-imino tautomer. The estimated tunneling probability of the H（13） proton from one well to another well shows that the life time of the proton staying in one of these wells is about 600 yrs. It is too long to let tautomers of cytosine be in thermodynamical equilibrium in a room temperature gas phase experiment.展开更多
Achieving simultaneous polarization and spin switching at room temperature is essential for advanced multi-state storage and control applications,particularly in magnetoelectrics and electron spintronics,yet such mate...Achieving simultaneous polarization and spin switching at room temperature is essential for advanced multi-state storage and control applications,particularly in magnetoelectrics and electron spintronics,yet such materials are exceedingly rare.Based on polar molecular valence tautomerism of Co^(Ⅲ)(3,5-DBcat)(3,5-DBsq)(trans-4-stypy)_(2)(1),room-temperature spin and polarization switching was achieved via electron transfer.Notably,the ferroelectric polarization and spin switching in 1 are modulated by both temperature and light.The successful implementation of room-temperature polarization and spin switching in 1 signifies an important advancement toward practical applications.展开更多
The influence of binding of cisplatin adducts on tautomeric equilibrium of guanine was investigated using quantum chemical method. The monoaqua adduct [Pt（NH3）2Cl（H2O）]^＋ and the diaqua adduct [Pt（NHa）2（H2O）2...The influence of binding of cisplatin adducts on tautomeric equilibrium of guanine was investigated using quantum chemical method. The monoaqua adduct [Pt（NH3）2Cl（H2O）]^＋ and the diaqua adduct [Pt（NHa）2（H2O）2]^2＋ were chosen for coordination to the N（7） site of guanine tautomers. The results demonstrate that the platinum adducts influence moderately on tautomeric equilibrium, but do not change the relative stability of tautomers whether in gas phase or in aqueous solution. The keto form having H atom at N（1） and N（9） was always the predominant structure when cisplatin adducts were bound to guanine. However, other forms could coexist in water. Meanwhile, our calculations suggest that the tautomeric equilibrium should be via the same intermediate.展开更多
<正> Four enol-form binuclear copper complexes with different exogenous bridges, [Cu2(L)(μ-Cl)] (1), [Cu(L)(μ-N3)]· DMF (2), [Cu2(L)(μ-OCH3)] (3) and [Cu2(L)(μ-C3H3N2)]· 1/2C2H5OH (4), where L is t...<正> Four enol-form binuclear copper complexes with different exogenous bridges, [Cu2(L)(μ-Cl)] (1), [Cu(L)(μ-N3)]· DMF (2), [Cu2(L)(μ-OCH3)] (3) and [Cu2(L)(μ-C3H3N2)]· 1/2C2H5OH (4), where L is the trivalence anion of binucleating ligand 2,6-diformyl-4-methylphenol di(tenzoylhydrazone), have been synthesized and characterized. Crystal data for complex (3) are as follows: space group P1- , a=0.8294(1), 6=0.9333(3), c= 1.473 6(6) nm, α=79.51(3)°, β=80.93(2)°,γ=81.32(2)°, Z=1. The magnetic measurements indicated that the effect of exogenous bridging ligands on magnetic interaction is corresponding to that in spectrochemical series. The effect of enol- and keto-form tautomer on magnetic interaction was explained from the point of view of structural factors and electron effects by using molecular mechanks and quantum chemistry calculations.展开更多
Ab initio MP2 and DFT studies on the tautomers of cytosine and the related hydrated tautomers have been carried out. The ground-state structures of four tautomers of cytosine and related transition states were fully o...Ab initio MP2 and DFT studies on the tautomers of cytosine and the related hydrated tautomers have been carried out. The ground-state structures of four tautomers of cytosine and related transition states were fully optimized. The vibrational frequency analysis was performed on all the optimized structures. Detailed intrinsic reaction coordinate （IRC） calculations were carded out to guarantee the optimized transition-state structures being connected to the related tautomers. We obtained the relative stability order for the tautomers of cytosine and the related hydrated tautomers. In the isolated and hydrated condition, the bond types of C（2）--O（7） and C（4）--N（8） greatly affect the stability of the cytosine tautomers. Moreover, we have explored the influence of the water molecules on the intramolecular proton transfer between the keto and enol forms of the cytosine tautomers. The first water molecule obviously decreases the isomerization activation energy for the monohydrated cytosine tautomers. It is shown that the isomerization energy barrier changes only a little when the second and third water molecules are added in the reaction loop. The solvent effects have an obvious influence on the proton-transfer barrier of the isolated cytosine. However, the solvent effects seem to be insignificant for the isomerization energy barriers of the monohydrated, dihydrated and trihydrated cytosine. The water molecule in these complexes can be looked on as the explicit water. Therefore, the explicit water model may be more credible to explore the intramolecular proton transfer, in comparison with the PCM which is the implicit water model.展开更多
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.
基金supported by the Research Fund for the Doctoral Program of Higher Education(No.20110002110052)
文摘Keto-enol tautomers of curcumin were confirmed by reversed-phase liquid chromatography（RPLC）/ hybrid quadrupole ion trap/time-of-flight mass spectrometry（QIT/TOFMS）.Tautomers gave different MS/MS spectra in negative mode.Different mass spectra were also obtained by hydrogen/deuterium exchange LC/MS/MS in positive mode.Our results suggest that enol form is the major form in the solution（water/acetonitrile）.
基金the financial support from the National Key Research and Development Program of China(No.2019YFA0708703)the National Natural Science Foundation of China(NSFC,No.21773309)+3 种基金the High-level Science Foundation of Qingdao Agricultural University(No.663/1114351)the Hefei National Laboratory for Physical Sciences at the Microscale(No.KF2020004)Xiangyang Science and Technology Research and Development(No.2020YL09)Hubei University of Arts and Science(Nos.HLOM222003,2020kypytd002)。
文摘Base pair mismatch has been regarded as the main source of DNA point mutations, where minor shortlived tautomers were usually involved. However, the detection and characterization of these unnatural species pose challenges to existing techniques. Here, by using systematic structural and ultrafast resonance Raman(RR) spectral analysis for the four possible conformers of guanine-cytosine base pairs, the prominent marker Raman bands were identified. We found that the hydrogen bonding vibrational region from 2300 cm^(-1) to 3700 cm^(-1) is ideal for the identification of these short live species. The marker bands provide direct evidence for the existence of the tautomer species, thus offering an effective strategy to detect the short-lived minor species. Ultrafast resonance Raman spectroscopy would be a powerful tool to provide direct evidence of critical dynamical details of complex systems involving protonation or tautomerization.
基金This project was supported by the Natural Science Foundation of China (No. 20502022) and the Ph.D. Fund of Ningbo (No. 2004A610010)
文摘Density Functional Theory method is applied to investigate the enol-keto tautomerism of both acyclic and cyclic α-fluorine-β-diketones. It is shown that, for acyclic cases, α-fluorine could improve the relative stability of keto tautomer by lessening intramolecular hydrogen bond of enol form, whereas the relative stability of cyclic enol could be attributed to two factors： destabilization of keto and stabilization of enol. Furthermore, the relative stabilities of all enol tautomers are improved in THF to different extents.
文摘A theoretical study of the reactivity of quinoline-4-one derivatives is undertaken in order to understand the involved mechanisms. The calculations were carried out in gas phase and in N, N-Dimethylformamide (DMF) solution. The Density Functional Theory (DFT) with B3LYP functional associated to 6-311G (d) and 6-311+G (d) bases is used to perform these calculations. The results of the thermodynamic parameters showed that there is an equilibrium relation between the different tautomers. This equilibrium can be used to explain the failure to obtain tetrahydroquinoline from 5,8-dimethoxy-quinolin-4-one. Reactivity analysis from Frontier Molecular Orbitals theory and Fukui function calculations revealed that ketone forms are less reactive than enol ones. The methoxyl substituent decreases the acidity of the nitrogen and oxygen atoms of quinolin-4-one while the bromine increases the acidity of the same sites. These results foresee that nitrogen deprotonation in the case of the brominated compound is easier than in the case of methoxylated ones.
基金The project supported by National Natural Science Foundation of China under Grant Nos. 10305001 and 10475002 with the calculations supported by the High Performance Computing Center of China （Beijing）
文摘The potential energy surface of H（13） proton in base cytosine of the DNA molecules is calculated at the Caussian 98 MP2/6-311C（d,p） level. Two potential wells are found. One corresponds to the normal cytosine, while the other corresponds to its trans-imino tautomer. The estimated tunneling probability of the H（13） proton from one well to another well shows that the life time of the proton staying in one of these wells is about 600 yrs. It is too long to let tautomers of cytosine be in thermodynamical equilibrium in a room temperature gas phase experiment.
基金supported by the National Natural Science Foundation of China (2371235,92061107,92161203)。
文摘Achieving simultaneous polarization and spin switching at room temperature is essential for advanced multi-state storage and control applications,particularly in magnetoelectrics and electron spintronics,yet such materials are exceedingly rare.Based on polar molecular valence tautomerism of Co^(Ⅲ)(3,5-DBcat)(3,5-DBsq)(trans-4-stypy)_(2)(1),room-temperature spin and polarization switching was achieved via electron transfer.Notably,the ferroelectric polarization and spin switching in 1 are modulated by both temperature and light.The successful implementation of room-temperature polarization and spin switching in 1 signifies an important advancement toward practical applications.
基金Project supported by the Science Foundation of Jinan University （No. 639）.
文摘The influence of binding of cisplatin adducts on tautomeric equilibrium of guanine was investigated using quantum chemical method. The monoaqua adduct [Pt（NH3）2Cl（H2O）]^＋ and the diaqua adduct [Pt（NHa）2（H2O）2]^2＋ were chosen for coordination to the N（7） site of guanine tautomers. The results demonstrate that the platinum adducts influence moderately on tautomeric equilibrium, but do not change the relative stability of tautomers whether in gas phase or in aqueous solution. The keto form having H atom at N（1） and N（9） was always the predominant structure when cisplatin adducts were bound to guanine. However, other forms could coexist in water. Meanwhile, our calculations suggest that the tautomeric equilibrium should be via the same intermediate.
基金Project supported by the National Natural Science Foundation of China
文摘<正> Four enol-form binuclear copper complexes with different exogenous bridges, [Cu2(L)(μ-Cl)] (1), [Cu(L)(μ-N3)]· DMF (2), [Cu2(L)(μ-OCH3)] (3) and [Cu2(L)(μ-C3H3N2)]· 1/2C2H5OH (4), where L is the trivalence anion of binucleating ligand 2,6-diformyl-4-methylphenol di(tenzoylhydrazone), have been synthesized and characterized. Crystal data for complex (3) are as follows: space group P1- , a=0.8294(1), 6=0.9333(3), c= 1.473 6(6) nm, α=79.51(3)°, β=80.93(2)°,γ=81.32(2)°, Z=1. The magnetic measurements indicated that the effect of exogenous bridging ligands on magnetic interaction is corresponding to that in spectrochemical series. The effect of enol- and keto-form tautomer on magnetic interaction was explained from the point of view of structural factors and electron effects by using molecular mechanks and quantum chemistry calculations.
基金Project supported by the National Natural Science Foundation of China （Nos. 21133005, 20873055, 21073080, 21011120087） and Education Bureau of Liaoning Province （No. 2009T057）.
文摘Ab initio MP2 and DFT studies on the tautomers of cytosine and the related hydrated tautomers have been carried out. The ground-state structures of four tautomers of cytosine and related transition states were fully optimized. The vibrational frequency analysis was performed on all the optimized structures. Detailed intrinsic reaction coordinate （IRC） calculations were carded out to guarantee the optimized transition-state structures being connected to the related tautomers. We obtained the relative stability order for the tautomers of cytosine and the related hydrated tautomers. In the isolated and hydrated condition, the bond types of C（2）--O（7） and C（4）--N（8） greatly affect the stability of the cytosine tautomers. Moreover, we have explored the influence of the water molecules on the intramolecular proton transfer between the keto and enol forms of the cytosine tautomers. The first water molecule obviously decreases the isomerization activation energy for the monohydrated cytosine tautomers. It is shown that the isomerization energy barrier changes only a little when the second and third water molecules are added in the reaction loop. The solvent effects have an obvious influence on the proton-transfer barrier of the isolated cytosine. However, the solvent effects seem to be insignificant for the isomerization energy barriers of the monohydrated, dihydrated and trihydrated cytosine. The water molecule in these complexes can be looked on as the explicit water. Therefore, the explicit water model may be more credible to explore the intramolecular proton transfer, in comparison with the PCM which is the implicit water model.
