共查询到20条相似文献,搜索用时 15 毫秒
1.
酰胺是肽的基本结构单元, 而且在蛋白质的二级结构中与酰胺联系的氢键对蛋白质的稳定起着十分重要的作用. 作为蛋白质模型化合物热力学性质研究的一部分, 报道了甲酰胺在乙二醇水溶液中的稀释焓. 相似文献
2.
Qiang Zhao Qing-Xiang Lu Min Liu De-Zhi Sun Lin-Wei Li 《Journal of solution chemistry》2009,38(2):231-240
The concentration effect on the dilution enthalpies (Δdil
H
m) of colchicine (COL) in aqueous NaCl solutions has been investigated by isothermal titration microcalorimetry at 298.15 K.
The corresponding homogeneous enthalpic interaction coefficients have been calculated according to the excess enthalpy concept.
The results show that the dilution enthalpies of COL in aqueous NaCl solutions at different mass fractions are positive. The
overall trend is that enthalpies of dilution become more positive with the increase of the salt mass fraction. The values
of enthalpic pair-wise interaction coefficients, h
2, have been obtained by fitting the data of the enthalpies of dilution with a viral expansion. The results can be interpreted
from the view of solute-solute and solute-solvent interactions involved in the solvent effects. 相似文献
3.
应用等温流动微量热法测定了298.15 K时互为旋光异构体的D-甘露醇与D-山梨醇在不同浓度的氯化钠水溶液中的稀释焓, 利用 McMillan-Mayer 理论计算了D-甘露醇与D-山梨醇在不同浓度的氯化钠水溶液中的焓对相互作用系数. 结果表明, D-甘露醇和D-山梨醇在氯化钠水溶液中的焓对相互作用系数h2均为正值, h2的值随着氯化钠浓度的增加皆逐渐增大, 但D-山梨醇的焓对相互作用系数h2增大的速率[dh2 /dm(NaCl)]比 D-甘露醇的要大. 根据两多元醇分子构象结构的差异, 溶质-溶质相互作用和溶质-溶剂相互作用对结果进行了解释. 相似文献
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丝氨酸在蔗糖水溶液中的稀释焓 总被引:2,自引:0,他引:2
利用LKB 2277生物活性检测仪分别测定了298.15 K时丝氨酸在不同组成的蔗糖水溶液中的稀释焓, 利用McMillan-Mayer理论,计算了丝氨酸在不同组成的蔗糖水溶液中的焓对相互作用系数,并与其在葡萄糖水溶液中的焓对相互作用系数h2进行了比较.结果表明,丝氨酸在蔗糖和葡萄糖水溶液中的焓对相互作用系数h2都是负值,并且随着糖浓度的增加,h2系数的绝对值逐渐减少.根据溶质-溶质相互作用和溶质-溶剂相互作用对结果进行了解释. 相似文献
6.
The dilution enthalpies of formamide in aqueous methanol and ethanol solutions have been determined using a CSC-4400 isothermal calorimeter at 298.15 K. The homogeneous solution enthalpic interaction coefficients have been calculated over a range of alcohol concentrations according to the excess enthalpy concept. The results show that the enthalpic pair interaction coefficients h
2 of formamide are negative in aqueous alcohol solutions and pass through a minimum in mixed solvents, whereas the h
2 coefficients of formamide in aqueous ethanol solutions are more negative than those in aqueous methanol solutions. The results are discussed in terms of solute-solute and solute-solvent interactions. 相似文献
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8.
The enthalpies of mixing of aqueous solutions have been determined for sucrose with six different amino acids (glycine, l-alanine, l-serine, l-valine, l-proline and l-threonine) at 298.15 K, by using a LKB-2277 flow microcalorimetric system. These results, along with the enthalpies of dilution of these solutes for the initial solutions, were used to determine the enthalpic interaction coefficients (h
xy, h
xyy, h
xxy) of the McMillan–Mayer Theory. The pair-wise cross interaction coefficients of amino acids and sucrose are discussed from the viewpoint of solute–solute interactions. 相似文献
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10.
Sue E. Gillespie Xuemin Chen John L. Oscarson Reed M. Izatt 《Journal of solution chemistry》1998,27(2):183-194
Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of KOH and CsOH at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and for aqueous solutions of NaOH, KOH, and CsOH at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of NaOH at 300°C and 9.3 MPa and at 325°C and 12.4 MPa were included when fitting the Pitzer parameters. The concentration range of the hydroxide solutions was 0.5–0.02 molal. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for alkali metal ion association with hydroxide ion were estimated from the heat data. For all systems, the enthalpy changes and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature. 相似文献
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12.
D-甘露醇与D-山梨醇在纯水和卤化钠水溶液中的稀释焓 总被引:1,自引:0,他引:1
应用等温流动微量热技术测定了298.15 K下D-甘露醇和D-山梨醇在纯水和卤化钠水溶液中的稀释焓,利用M cM illan理论计算了D-甘露醇和D-山梨醇在纯水和卤化钠水溶液中焓相互作用系数.结果表明,D-甘露醇和D-山梨醇在纯水和卤化钠水溶液中的二阶焓相互作用系数均为正值,并随着卤离子半径的变化而相应变化;且同种溶剂中,D-甘露醇的二阶焓相互作用系数要大于D-山梨醇的.结合两分子结构的差异,通过溶质-溶质相互作用和溶剂-溶质相互作用对这一结果进行了讨论. 相似文献
13.
J. M. Arsuaga F. Fernández-Martín J. Núñez 《Journal of Thermal Analysis and Calorimetry》1998,52(3):991-996
The enthalpies of dilution of aqueous solutions of [Co(en)3]Cl3 and [Co(tn)3Cl3 (where en=1,2-diaminoethane, and tn=1,3-diaminopropane) were measured at 278.15 K up to 1 mol kg-1, using a large isoperibolic calorimeter, with the 'long-jump' method. Relative apparent molar enthalpies, LΦ>, were extracted via an empirical equation relating LΦ> and molality. These new values were compared with previous results at 298.15 K on the same aqueous systems. Theoretical
predictions were satisfied, but an unexpectedly broad divergence was found for such close temperatures. A tentative explanation
is put forward.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Protocatechuic acid, a major metabolite of antioxidant polyphenols found in green tea, has been shown to prevent carcinogenesis or antitumor growth in vitro and in vivo studies. The dilution enthalpies ΔdilHm, dissociation enthalpies ΔdisHm and thermodynamic dissociation constants Ka for protocatechuic acid in aqueous NaCl or KCl solutions were simultaneously determined by mixing-flow microcalorimetry at T = 298.15 K. In order to verify the reliability of the fitted dissociation parameters, the values of dissociation enthalpies and thermodynamic dissociation constants were also determined by isothermal titration calorimetry and electrical conductivity methods. The Ka values obtained through the proposed method agree well with those reported in literatures and obtained by other techniques. Enthalpic interaction coefficients (h2, h3 and h4) were computed according to the McMillan–Mayer model. The trends of h2 and ΔdisHm for protocatechuic acid with increasing salt molality in both the salt solutions were obtained. The different influence of KCl and NaCl on the values of h2 and ΔdisHm were discussed in terms of (solute + solute) and (solute + solvent) interactions. The results showed that it is possible to perform in a single calorimetric experiment the simultaneous determination of dilution enthalpies, dissociation enthalpies and constants in a given solvent. 相似文献
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17.
Sue E. Gillespie Xuemin Chen John L. Oscarson Reed M. Izatt 《Journal of solution chemistry》1997,26(1):47-61
Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of LiCl, KCl, and CsCl
at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and 350°C and 17.6 MPa. The concentration range of the chloride solutions was 0.5
to 0.02m. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data.
Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for ion association of the chloride salts
were estimated from the heat data. For all systems, the enthalpy and entropy changes were positive and had accelerating increases
with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature. 相似文献
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19.
丝氨酸在醇-水溶液中的溶解焓 总被引:1,自引:0,他引:1
用RD-496III双热流精密微热量计测量了L-丝氨酸在纯水以及异丙醇、1,2-丙二醇和丙三醇水溶液中的溶解焓, 并计算了从水到醇-水溶液中的迁移焓. 实验发现, L-丝氨酸在水及醇-水溶液中的溶解焓都是正值, 它从水到醇-水溶液中的迁移焓也都是正值, 并且基本上随着醇浓度的增加而增加, 说明在溶解过程中, 溶质与混合溶剂分子的部分去水化吸热过程占主要地位. 另外, 实验还发现L-丝氨酸从水到异丙醇水溶液中的迁移焓大于在1,2-丙二醇水溶液中的, 更大于在丙三醇水溶液中的, 这是由于羟基的减少导致了疏水-亲水作用的增加和亲水-亲水作用的减弱. 相似文献
20.
水溶液中氨基酸与甲脲的焓相互作用 总被引:6,自引:0,他引:6
用LKB-2277精密微热量计测定了298.15 K时甘氨酸、L-丙氨酸、L-丝氨酸、L-缬 氨酸、L-苏氨酸和L-脯氨酸六种α-氨基酸分别与甲脲分子在水溶液中的混合过程焓变及 这些溶质分子在水溶液中的稀释焓.实验数据根据McMillan-Mayer理论进行回归分析,得到 各级交叉焓相互作用系数.讨论了不同氨基酸与甲脲分子的相互作用机制.结果表明,氨基酸 的两性离子部分、α-碳上的非极性脂肪侧基、极性的羟基侧基和五元吡咯环结构对交叉焓 对作用系数hxy具有不同贡献.与尿素相比,甲脲分子中-CH3基团的引入明显增强了分子的 疏水性. 相似文献