In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the re...In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.展开更多
To study the chemical constituents of Hedysarum gmelinii. Methods Theconstituents were separated and purified by different methods of chromatography, and theirstructures were elucidated by DR, MS and NMR. Results Eigh...To study the chemical constituents of Hedysarum gmelinii. Methods Theconstituents were separated and purified by different methods of chromatography, and theirstructures were elucidated by DR, MS and NMR. Results Eight compounds were isolated from Hedysarumgmelinii, including three triteipenoids, two flavonoids and two other compounds. Their structureswere identified as squasapogenol (1), soyasapogenol (2), lupeol (3), 3, 9-dihydroxy coumestan (4),3-hydroxy-9-me-thoxy pterocarpan (5), β-sitosterol (6), palmatic acid (7), and hexadecanoic acid 2,3-dihydroxypropyl ester (8). Conclusion All the compounds have been isolated from this plant forthe first time. Compounds 1 — 4 and 8 were obtained from this genus for the first time. The NMRdata of 1 are reported for the first time.展开更多
Two novel flavone glycosides, 3′_hydroxy_5,4′_dimethoxy_6,7_methylenedioxyflavone_3_O_[β_D_xylopyranosyl(1→6)]_β_D_glucopyranoside (1) and 5,4′_dimethoxy_3′_isopropenylacetyl_6,7_methylenedioxyflavone_3_O_[β_D...Two novel flavone glycosides, 3′_hydroxy_5,4′_dimethoxy_6,7_methylenedioxyflavone_3_O_[β_D_xylopyranosyl(1→6)]_β_D_glucopyranoside (1) and 5,4′_dimethoxy_3′_isopropenylacetyl_6,7_methylenedioxyflavone_3_O_[β_D_xylopyranoxyl(1→6)]_β_D_glucopyranoside (2), were isolated from Polygonum sphaerostachyum Meisn., and their structures were deduced by spectral and chemical methods. This is the first report on the isolation of flavone glycosides from P. sphaerostachyum.展开更多
Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of ...Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of formation and development of a sliding ground fissure by the circular sliding slice method.Moreover, we established a prediction model of a sliding fissure based on a mechanical mechanism,and verified its reliability on face 52,304, an engineering example, situated at Daliuta coal mine of Shendong mining area in western China. The results show that the stress state of a mining slope is changed by its gravity and additional stress from the shallow-buried coal seam and gully terrain. The mining slope is found to be most unstable when the ratio of the down-sliding to anti-sliding force is the maximum, causing local fractures and sliding fissures. The predicted angles for the sliding fissure of face 52,304 on both sides of the slope are found to be 64.2° and 82.4°, which are in agreement with the experimental data.展开更多
An elliptical wind field model of typhoons is put forward based on the characteristics of the typhoon wind fields occurring in the Yellow Sea and Bohai Sea. By contrasting it with the circular typhoon wind field model...An elliptical wind field model of typhoons is put forward based on the characteristics of the typhoon wind fields occurring in the Yellow Sea and Bohai Sea. By contrasting it with the circular typhoon wind field model, it is found that the elliptical model can adequately represent the real wind field and trace the process of a typhoon storm surge. The numerically simulated results of storm surges by using the elliptical model are in good agreement with the observations and markedly better than those by using the circular model.展开更多
文摘In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.
基金National Natural Science Foundation of China (20432030)
文摘To study the chemical constituents of Hedysarum gmelinii. Methods Theconstituents were separated and purified by different methods of chromatography, and theirstructures were elucidated by DR, MS and NMR. Results Eight compounds were isolated from Hedysarumgmelinii, including three triteipenoids, two flavonoids and two other compounds. Their structureswere identified as squasapogenol (1), soyasapogenol (2), lupeol (3), 3, 9-dihydroxy coumestan (4),3-hydroxy-9-me-thoxy pterocarpan (5), β-sitosterol (6), palmatic acid (7), and hexadecanoic acid 2,3-dihydroxypropyl ester (8). Conclusion All the compounds have been isolated from this plant forthe first time. Compounds 1 — 4 and 8 were obtained from this genus for the first time. The NMRdata of 1 are reported for the first time.
基金The National Natural Science Foundation of China(29572064)
文摘Two novel flavone glycosides, 3′_hydroxy_5,4′_dimethoxy_6,7_methylenedioxyflavone_3_O_[β_D_xylopyranosyl(1→6)]_β_D_glucopyranoside (1) and 5,4′_dimethoxy_3′_isopropenylacetyl_6,7_methylenedioxyflavone_3_O_[β_D_xylopyranoxyl(1→6)]_β_D_glucopyranoside (2), were isolated from Polygonum sphaerostachyum Meisn., and their structures were deduced by spectral and chemical methods. This is the first report on the isolation of flavone glycosides from P. sphaerostachyum.
基金Projects funded by the National Key Basic Research Development Program(No.2013CB227904)the National Natural Science Foundation of China(No.41272389)+1 种基金China Postdoctoral Science Foundation(No.2014M561931)the Natural Science Foundation of Hebei Province(No.D2014402007)
文摘Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of formation and development of a sliding ground fissure by the circular sliding slice method.Moreover, we established a prediction model of a sliding fissure based on a mechanical mechanism,and verified its reliability on face 52,304, an engineering example, situated at Daliuta coal mine of Shendong mining area in western China. The results show that the stress state of a mining slope is changed by its gravity and additional stress from the shallow-buried coal seam and gully terrain. The mining slope is found to be most unstable when the ratio of the down-sliding to anti-sliding force is the maximum, causing local fractures and sliding fissures. The predicted angles for the sliding fissure of face 52,304 on both sides of the slope are found to be 64.2° and 82.4°, which are in agreement with the experimental data.
基金supported by the Nationa1 High Technology Research and Development Program of China(863 Program)(Grant No.2002AA639370)the Natural Science Foundation of Shandong Province(Grant No.Q99E02)the Special Fund of Excellent Ph.D Dissertation(200021).
文摘An elliptical wind field model of typhoons is put forward based on the characteristics of the typhoon wind fields occurring in the Yellow Sea and Bohai Sea. By contrasting it with the circular typhoon wind field model, it is found that the elliptical model can adequately represent the real wind field and trace the process of a typhoon storm surge. The numerically simulated results of storm surges by using the elliptical model are in good agreement with the observations and markedly better than those by using the circular model.
