The solubility of nonivamide in dimethyl sulfoxide, methanol, acetone, ethyl acetate, methyl tert-butyl ether, acetonitrile, n-hexane and water over the temperature range of 293.2 K to 323.2 K was measured. The result...The solubility of nonivamide in dimethyl sulfoxide, methanol, acetone, ethyl acetate, methyl tert-butyl ether, acetonitrile, n-hexane and water over the temperature range of 293.2 K to 323.2 K was measured. The results reveal that the solubility of nonivamide is greatly influenced by the hydrogen-bond basicity of solvent and increases with temperature. The experimental data were correlated with the modified Apelblat equation. The dissolution enthalpy and entropy of nonivamide in different solvents were obtained from the correlation of lnx with 1/T using the van't Hoff equation. The calculated nonivamide solubility is in good agreement with experimental data for most of the solvents.展开更多
The assessment of the real in-service-time(RIST)and the equivalent in-service-time(EIST)of double base rocket propellants(DBRPs)is of utmost importance for the safe storage and use of weapon systems as well as the eff...The assessment of the real in-service-time(RIST)and the equivalent in-service-time(EIST)of double base rocket propellants(DBRPs)is of utmost importance for the safe storage and use of weapon systems as well as the efficiency of the accelerated aging plans.In this work,four DBRPs with similar chemical composition and different natural aging have been artificially aged at T?338.65 K for 4 months with sampling every 30 days.The unaged and artificially aged samples have been investigated by vacuum stability test(VST)at five isothermal temperatures(T?333.15 K,343.15 K,353.15 K,363.15 K,and 373.15 K).The volume of the evolved gases in VST was found to decrease with natural/artificial aging.Furthermore,the VST data were treated and subjected to principal component analysis(PCA).The results showed excellent discrimination of the DBRP samples according to their stability thermal properties.Most of the variance was described by the first principal component(PC1)whose scores were linearly correlated with the natural aging durations when PCA is applied on VST data obtained at T?363.15 K.In light of the obtained results,a new experimental way for the estimation of the real/equivalent IST was proposed,which takes into account the impact of the natural aging of the sample.The approach predicts successfully the RIST of two similar DBRPs with a relative deviation of less than 2%.At the specific heating temperature T?338.65 K,the developed model provides more conceivable EIST values,with asymptotic behavior against artificial aging duration evolution,thus overcoming some shortcomings of the common generalized van’t Hoff formula(GvH).展开更多
With an adjusted model, we reconsider simple 1,2-dyotropic reactions with the introduction of a concept based on the intramolecular dynamics of a tetrahedron (van ’t Hoff modeling). In fact the dyotropic reactions ar...With an adjusted model, we reconsider simple 1,2-dyotropic reactions with the introduction of a concept based on the intramolecular dynamics of a tetrahedron (van ’t Hoff modeling). In fact the dyotropic reactions are strongly related to conversions originated from neighbouring group participation or anchimeric assistance, defined as the interaction of a center with a lone pair of electrons in an atom and the electrons present in aδor π bond. The researchful 1,2-dyotropic reactions, based on the 1,2-interchange of halogens, methyl and hydrogen taking place in a concerted fashion, are in competition with the two-step reaction in which the neighbouring group participation or anchimeric assistance comes to full expression by ionic dissociation of the other exchangeable (halogen) atom. As to be expected there is an essential difference between halogen or methyl exchange regarding the number of electrons participating in the transition state. This aspect becomes evident in the geometries of the corresponding transition state geometries. In this paper we refer to ab initio MO calculations and VB considerations. We consider the 1,2-halogen exchange as a combination of two SN2 reactions each containing four electrons. The van ’t Hoff dynamics appears a useful model in order to illustrate the computations in a straightforward manner.展开更多
Thermodynamic properties of complexes of Con ?go Red (CR) dye with amyloid ? (A?) peptides were studied by both absorption spectroscopy and isothermal titration calorimetry (ITC). Based on the absorption spectrum for ...Thermodynamic properties of complexes of Con ?go Red (CR) dye with amyloid ? (A?) peptides were studied by both absorption spectroscopy and isothermal titration calorimetry (ITC). Based on the absorption spectrum for the formation of CRAβ complexes in phosphate buffered saline solution (pH 7.4), van’t Hoff plots over a temperature range of 10oC to 70oC were created for CRAβ140, Aβ1228, and Aβ142. The plot for CR Aβ1228 complex showed a relatively linear feature within the given temperature range with ?H = –10.1 ?0.6 kJ/mol and ?S = + 0.128 ? 0.002 kJ/(mol K). However, the plot for CRAβ140 and CRAβ142 complexes exhibited two distinct linear regions with opposite slopes centered at a specific temperature, Ts, which was 54.7 ? 0.2℃ and 34.8 ? 0.2℃, respectively. The ITC experiments conducted at 25℃in water exhibited quite a different situation from the above mentioned spectroscopic approach. The ITC studies yielded a ?H of –85.3 ? 0.2 kJ/mol for the CRAβ1228 complex with negative entropy change –0.152 kJ/mol K). For CRAβ140, the ITC studies indicated the presence of two binding sites with ?H1 = –81.8 ? 0.3 kJ/mol and ?H2 = –119.5 ? 0.2 kJ/mol with K1 = 5.5 ? 0.7 ? 106 M1 and K2 = 6.9 ? 2.4 ? 108 M1, respectively. These binding constants are consistent with the model suggested by several studies. Both binding sites showed negative entropy changes suggesting that the formation of the complex is enthalpically driven. The disagreement in thermochemical values between two different methods confirmed that the enthalpy and entropy are heavily dependent on temperature and buffer/salt environment, and may involve inherently different reaction paths.展开更多
Reliable information on the solubility of hydrogen in aluminum and its alloys is critical to the effort of the aluminum industry to control and ameliorate the usually deleterious effects of hydrogen on the properties ...Reliable information on the solubility of hydrogen in aluminum and its alloys is critical to the effort of the aluminum industry to control and ameliorate the usually deleterious effects of hydrogen on the properties and performance of pure aluminum and aluminum alloy products. Unfortunately, there is a significant disparity between published values of hydrogen solubility in pure aluminum and aluminum alloys. This is because the measurement of the extremely low soluble hydrogen concentration in aluminum and its alloys is experimentally difficult. Also, the reproducibility, accuracy, and reliability of the hydrogen solubility values are very sensitive to the measurement techniques, test conditions, chemical composition, and state of the aluminum sample. Thus, no serious discussion of the reliability of reported values of hydrogen solubility in aluminum and its alloys can be undertaken without a critical assessment of the fundamental principles of the experimental techniques used in the determination of the reported values. In this article, a critical review of the fundamental principles of the experimental techniques used in the measurement of hydrogen solubility in liquid and solid pure aluminum and aluminum alloys is presented. In addition, the reliability and possible accuracy of reported values of hydrogen solubility in solid and liquid pure aluminum are critically assessed. Empirical equations for calculating hydrogen solubility in liquid and solid pure aluminum as a function of temperature and pressure, derived from the most reliable sets of data are recommended. At 101.3 kPa (1 atm.) hydrogen partial pressure, the most reliable values of hydrogen solubility at the melting point (833 K) of pure aluminum are 0.71 cm<sup>3</sup>/100g (i.e., 6.32 × 10<sup>-5</sup> wt.% H) and 0.043 cm<sup>3</sup>/100g (i.e., 3.81 × 10<sup>-6</sup> wt.% H), in the liquid and solid state, respectively. So, the partition coefficient of hydrogen in pure aluminum is 0.061.展开更多
基金Supported by the National Natural Science Foundation of China(20936005,21222601)the National High Technology Research and Development Program of China(2012AA040211)
文摘The solubility of nonivamide in dimethyl sulfoxide, methanol, acetone, ethyl acetate, methyl tert-butyl ether, acetonitrile, n-hexane and water over the temperature range of 293.2 K to 323.2 K was measured. The results reveal that the solubility of nonivamide is greatly influenced by the hydrogen-bond basicity of solvent and increases with temperature. The experimental data were correlated with the modified Apelblat equation. The dissolution enthalpy and entropy of nonivamide in different solvents were obtained from the correlation of lnx with 1/T using the van't Hoff equation. The calculated nonivamide solubility is in good agreement with experimental data for most of the solvents.
文摘The assessment of the real in-service-time(RIST)and the equivalent in-service-time(EIST)of double base rocket propellants(DBRPs)is of utmost importance for the safe storage and use of weapon systems as well as the efficiency of the accelerated aging plans.In this work,four DBRPs with similar chemical composition and different natural aging have been artificially aged at T?338.65 K for 4 months with sampling every 30 days.The unaged and artificially aged samples have been investigated by vacuum stability test(VST)at five isothermal temperatures(T?333.15 K,343.15 K,353.15 K,363.15 K,and 373.15 K).The volume of the evolved gases in VST was found to decrease with natural/artificial aging.Furthermore,the VST data were treated and subjected to principal component analysis(PCA).The results showed excellent discrimination of the DBRP samples according to their stability thermal properties.Most of the variance was described by the first principal component(PC1)whose scores were linearly correlated with the natural aging durations when PCA is applied on VST data obtained at T?363.15 K.In light of the obtained results,a new experimental way for the estimation of the real/equivalent IST was proposed,which takes into account the impact of the natural aging of the sample.The approach predicts successfully the RIST of two similar DBRPs with a relative deviation of less than 2%.At the specific heating temperature T?338.65 K,the developed model provides more conceivable EIST values,with asymptotic behavior against artificial aging duration evolution,thus overcoming some shortcomings of the common generalized van’t Hoff formula(GvH).
文摘With an adjusted model, we reconsider simple 1,2-dyotropic reactions with the introduction of a concept based on the intramolecular dynamics of a tetrahedron (van ’t Hoff modeling). In fact the dyotropic reactions are strongly related to conversions originated from neighbouring group participation or anchimeric assistance, defined as the interaction of a center with a lone pair of electrons in an atom and the electrons present in aδor π bond. The researchful 1,2-dyotropic reactions, based on the 1,2-interchange of halogens, methyl and hydrogen taking place in a concerted fashion, are in competition with the two-step reaction in which the neighbouring group participation or anchimeric assistance comes to full expression by ionic dissociation of the other exchangeable (halogen) atom. As to be expected there is an essential difference between halogen or methyl exchange regarding the number of electrons participating in the transition state. This aspect becomes evident in the geometries of the corresponding transition state geometries. In this paper we refer to ab initio MO calculations and VB considerations. We consider the 1,2-halogen exchange as a combination of two SN2 reactions each containing four electrons. The van ’t Hoff dynamics appears a useful model in order to illustrate the computations in a straightforward manner.
文摘Thermodynamic properties of complexes of Con ?go Red (CR) dye with amyloid ? (A?) peptides were studied by both absorption spectroscopy and isothermal titration calorimetry (ITC). Based on the absorption spectrum for the formation of CRAβ complexes in phosphate buffered saline solution (pH 7.4), van’t Hoff plots over a temperature range of 10oC to 70oC were created for CRAβ140, Aβ1228, and Aβ142. The plot for CR Aβ1228 complex showed a relatively linear feature within the given temperature range with ?H = –10.1 ?0.6 kJ/mol and ?S = + 0.128 ? 0.002 kJ/(mol K). However, the plot for CRAβ140 and CRAβ142 complexes exhibited two distinct linear regions with opposite slopes centered at a specific temperature, Ts, which was 54.7 ? 0.2℃ and 34.8 ? 0.2℃, respectively. The ITC experiments conducted at 25℃in water exhibited quite a different situation from the above mentioned spectroscopic approach. The ITC studies yielded a ?H of –85.3 ? 0.2 kJ/mol for the CRAβ1228 complex with negative entropy change –0.152 kJ/mol K). For CRAβ140, the ITC studies indicated the presence of two binding sites with ?H1 = –81.8 ? 0.3 kJ/mol and ?H2 = –119.5 ? 0.2 kJ/mol with K1 = 5.5 ? 0.7 ? 106 M1 and K2 = 6.9 ? 2.4 ? 108 M1, respectively. These binding constants are consistent with the model suggested by several studies. Both binding sites showed negative entropy changes suggesting that the formation of the complex is enthalpically driven. The disagreement in thermochemical values between two different methods confirmed that the enthalpy and entropy are heavily dependent on temperature and buffer/salt environment, and may involve inherently different reaction paths.
文摘Reliable information on the solubility of hydrogen in aluminum and its alloys is critical to the effort of the aluminum industry to control and ameliorate the usually deleterious effects of hydrogen on the properties and performance of pure aluminum and aluminum alloy products. Unfortunately, there is a significant disparity between published values of hydrogen solubility in pure aluminum and aluminum alloys. This is because the measurement of the extremely low soluble hydrogen concentration in aluminum and its alloys is experimentally difficult. Also, the reproducibility, accuracy, and reliability of the hydrogen solubility values are very sensitive to the measurement techniques, test conditions, chemical composition, and state of the aluminum sample. Thus, no serious discussion of the reliability of reported values of hydrogen solubility in aluminum and its alloys can be undertaken without a critical assessment of the fundamental principles of the experimental techniques used in the determination of the reported values. In this article, a critical review of the fundamental principles of the experimental techniques used in the measurement of hydrogen solubility in liquid and solid pure aluminum and aluminum alloys is presented. In addition, the reliability and possible accuracy of reported values of hydrogen solubility in solid and liquid pure aluminum are critically assessed. Empirical equations for calculating hydrogen solubility in liquid and solid pure aluminum as a function of temperature and pressure, derived from the most reliable sets of data are recommended. At 101.3 kPa (1 atm.) hydrogen partial pressure, the most reliable values of hydrogen solubility at the melting point (833 K) of pure aluminum are 0.71 cm<sup>3</sup>/100g (i.e., 6.32 × 10<sup>-5</sup> wt.% H) and 0.043 cm<sup>3</sup>/100g (i.e., 3.81 × 10<sup>-6</sup> wt.% H), in the liquid and solid state, respectively. So, the partition coefficient of hydrogen in pure aluminum is 0.061.
基金National Natural Science Foundation of China(No.20573098)Science and Technology Foundation of the National Defence Key Laboratory of Propellant and Explosive Combustion of China(9140C3501050701)
