MP2 and DFT/B3LYP calculations with Aug-cc-pvTz and Aug-cc-pvQz basis set levels are used to investigate the equilibrium structures and isomerization of H2SO isomers. All of the transition states have been...MP2 and DFT/B3LYP calculations with Aug-cc-pvTz and Aug-cc-pvQz basis set levels are used to investigate the equilibrium structures and isomerization of H2SO isomers. All of the transition states have been calculated and confirmed by the intrinsic reaction coordinate (IRC). The calculated results show that H2SO isomers have three equilibrium structures and the linear structure is the most stable while the branched H2OS is the most unstable (the relative energies are 0.0, 82.1 and 155.3 kJ/mol for HSOH, H2SO and H2OS, respectively with the zero point vibrational energy correction at B3LYP/Aug-cc-pvQz level). It is difficult for the linear HSOH to convert to the branched H2SO and H2OS isomers due to the high activation energies (higher than ca. 200 and 160 kJ/mol, respectively). The predicted thermodynamic results also suggest that the linear structure is the most stable and may be the only species that can be found experimentally. The kinetic results demonstrate that the isomerization is a unimolecular one, and the reaction rate is slow.展开更多
Theoretical investigations have been carried out on the mechanism and kinetics for the reaction of CF 3 CHO + Cl using duallevel direct dynamics method. The potential energy surface information was obtained at the MCQ...Theoretical investigations have been carried out on the mechanism and kinetics for the reaction of CF 3 CHO + Cl using duallevel direct dynamics method. The potential energy surface information was obtained at the MCQCISD/3//MP2/cc-pVDZ level and the kinetic calculations were done using variational transition state theory with interpolated single-point energy (VTST-ISPE) approach. The calculated results show that the reaction proceeds primarily via the H-abstraction channel, while the Cl-addition channel is unfavorable due to the higher barriers. The improved canonical variational transition-state theory (ICVT) with the small-curvature tunneling correction (SCT) was used to calculate the rate constants. The theoretical rate constants at room temperature are in general agreement with the experimental values. A three-parameter rate constant expression was fitted over a wide temperature range of 200-2000 K.展开更多
The reaction CHClBr＋NO2 was investigated via quantum chemical methods and kinetic calculations. The reaction mechanism on the singlet potential energy surface（PES） was considered by B3LYP method, and the energies w...The reaction CHClBr＋NO2 was investigated via quantum chemical methods and kinetic calculations. The reaction mechanism on the singlet potential energy surface（PES） was considered by B3LYP method, and the energies were calculated at the CCSD（T） and CASPT2 levels of theory. The rate constants and the ratios of products were obtained by utilizing VTST and RRKM methods over wide temperature and pressure ranges. Our results indicate that carbon-to-nitrogen approach via a barrierless process is preferred in the initial association of CHClBr and NO2. The dominant product is BrNO＋CHCIO（PI）, which agrees well with the experimental observation. P2（ClNO＋CHBrO） and P3（HNO＋CBrClO） may also have minor contributions to the reaction. The calculated overall rate constants are independent of pressure and consistent with the experimental data, which can be fitted with the following equation over the temperature range of 200--1500 K： k（T）=2.31 × 10^-15T^0.99exp（771/T）. Compared with reaction CH2Br＋NO2, reaction CHCIBr＋NO2 has decreased the overall rate constants.展开更多
The mechanism and dynamical properties for the reaction of NCS and OH radicals have been investigated theoretically. The minimum energy paths (MEP) of the reaction were calculated using the density functional theory (...The mechanism and dynamical properties for the reaction of NCS and OH radicals have been investigated theoretically. The minimum energy paths (MEP) of the reaction were calculated using the density functional theory (DFT) at the B3LYP/6-311+G** level, and the energies along the MEP were further refined at the QCISD(T)/6-311+G** level. As a result, the reaction mechanism of the title reaction involves three channels, producing HCS+NO and HNC+SO products, respectively. Path I and path II are competitive, with some advantages for path I in kinet-ics. As for path III, it looks difficult to react for its high energy barrier. Moreover, the rate constant have been cal-culated over the temperature range of 8002500 K using canonical variational transition-state theory (CVT). It was found that the rate constants for both path I and path II are negatively dependent on temperature, which is similar with the experimental results for reactions of NCS with NO and NO2, and the variational effect for the rate constant calculation plays an important role in whole temperature range.展开更多
The folding dynamics of small single-domain proteins is a current focus ofsimulations and experiments. Many of these proteins are ‘two-state folders’, i.e. pro-teins that fold rather directly from the denatured stat...The folding dynamics of small single-domain proteins is a current focus ofsimulations and experiments. Many of these proteins are ‘two-state folders’, i.e. pro-teins that fold rather directly from the denatured state to the native state, without pop-ulating metastable intermediate states. A central question is how to characterize theinstable, partially folded conformations of two-state proteins, in particular the rate-limiting transition-state conformations between the denatured and the native state.These partially folded conformations are short-lived and cannot be observed directlyin experiments. However, experimental data from detailed mutational analyses of thefolding dynamics provide indirect access to transition states. The interpretation ofthese data, in particular the reconstruction of transition-state conformations, requiressimulation and modeling. The traditional interpretation of the mutational data aimsto reconstruct the degree of structure formation of individual residues in the transitionstate, while a novel interpretation aims at degrees of structure formation of cooperativesubstructures such as α-helices and β-hairpins. By splitting up mutation-induced freeenergies into secondary and tertiary structural components, the novel interpretationresolves some of the inconsistencies of the traditional interpretation.展开更多
基金The project was supported by Fujian Provincial Department of Education (JA03020) and the Provincial Administration of Science and Technology of Fujian (2002J018)
文摘MP2 and DFT/B3LYP calculations with Aug-cc-pvTz and Aug-cc-pvQz basis set levels are used to investigate the equilibrium structures and isomerization of H2SO isomers. All of the transition states have been calculated and confirmed by the intrinsic reaction coordinate (IRC). The calculated results show that H2SO isomers have three equilibrium structures and the linear structure is the most stable while the branched H2OS is the most unstable (the relative energies are 0.0, 82.1 and 155.3 kJ/mol for HSOH, H2SO and H2OS, respectively with the zero point vibrational energy correction at B3LYP/Aug-cc-pvQz level). It is difficult for the linear HSOH to convert to the branched H2SO and H2OS isomers due to the high activation energies (higher than ca. 200 and 160 kJ/mol, respectively). The predicted thermodynamic results also suggest that the linear structure is the most stable and may be the only species that can be found experimentally. The kinetic results demonstrate that the isomerization is a unimolecular one, and the reaction rate is slow.
基金supported by the National Natural Science Foundation of China (20973077, 20303007)the Program for New Century Excellent Talents in University (NCET)
文摘Theoretical investigations have been carried out on the mechanism and kinetics for the reaction of CF 3 CHO + Cl using duallevel direct dynamics method. The potential energy surface information was obtained at the MCQCISD/3//MP2/cc-pVDZ level and the kinetic calculations were done using variational transition state theory with interpolated single-point energy (VTST-ISPE) approach. The calculated results show that the reaction proceeds primarily via the H-abstraction channel, while the Cl-addition channel is unfavorable due to the higher barriers. The improved canonical variational transition-state theory (ICVT) with the small-curvature tunneling correction (SCT) was used to calculate the rate constants. The theoretical rate constants at room temperature are in general agreement with the experimental values. A three-parameter rate constant expression was fitted over a wide temperature range of 200-2000 K.
基金Supported by the National Natural Science Foundation of China（Nos.20973077, 21373098, 21503114, U 1301243, 21274064, 21373114, 51273092）.
文摘The reaction CHClBr＋NO2 was investigated via quantum chemical methods and kinetic calculations. The reaction mechanism on the singlet potential energy surface（PES） was considered by B3LYP method, and the energies were calculated at the CCSD（T） and CASPT2 levels of theory. The rate constants and the ratios of products were obtained by utilizing VTST and RRKM methods over wide temperature and pressure ranges. Our results indicate that carbon-to-nitrogen approach via a barrierless process is preferred in the initial association of CHClBr and NO2. The dominant product is BrNO＋CHCIO（PI）, which agrees well with the experimental observation. P2（ClNO＋CHBrO） and P3（HNO＋CBrClO） may also have minor contributions to the reaction. The calculated overall rate constants are independent of pressure and consistent with the experimental data, which can be fitted with the following equation over the temperature range of 200--1500 K： k（T）=2.31 × 10^-15T^0.99exp（771/T）. Compared with reaction CH2Br＋NO2, reaction CHCIBr＋NO2 has decreased the overall rate constants.
基金Project supported by the Natural Science Foundation of Jilin Province (No. 20010344) the Foundation of Education Bureau of Hainan Province (No. hjkj200312) and the Science Foundation for Excellent Youth of Northeast Normal University (No. 111382).
文摘The mechanism and dynamical properties for the reaction of NCS and OH radicals have been investigated theoretically. The minimum energy paths (MEP) of the reaction were calculated using the density functional theory (DFT) at the B3LYP/6-311+G** level, and the energies along the MEP were further refined at the QCISD(T)/6-311+G** level. As a result, the reaction mechanism of the title reaction involves three channels, producing HCS+NO and HNC+SO products, respectively. Path I and path II are competitive, with some advantages for path I in kinet-ics. As for path III, it looks difficult to react for its high energy barrier. Moreover, the rate constant have been cal-culated over the temperature range of 8002500 K using canonical variational transition-state theory (CVT). It was found that the rate constants for both path I and path II are negatively dependent on temperature, which is similar with the experimental results for reactions of NCS with NO and NO2, and the variational effect for the rate constant calculation plays an important role in whole temperature range.
文摘The folding dynamics of small single-domain proteins is a current focus ofsimulations and experiments. Many of these proteins are ‘two-state folders’, i.e. pro-teins that fold rather directly from the denatured state to the native state, without pop-ulating metastable intermediate states. A central question is how to characterize theinstable, partially folded conformations of two-state proteins, in particular the rate-limiting transition-state conformations between the denatured and the native state.These partially folded conformations are short-lived and cannot be observed directlyin experiments. However, experimental data from detailed mutational analyses of thefolding dynamics provide indirect access to transition states. The interpretation ofthese data, in particular the reconstruction of transition-state conformations, requiressimulation and modeling. The traditional interpretation of the mutational data aimsto reconstruct the degree of structure formation of individual residues in the transitionstate, while a novel interpretation aims at degrees of structure formation of cooperativesubstructures such as α-helices and β-hairpins. By splitting up mutation-induced freeenergies into secondary and tertiary structural components, the novel interpretationresolves some of the inconsistencies of the traditional interpretation.
