L-胱氨酸在盐酸、氢氧化钠、氢氧化钾水溶液中的稀释过程热力学

Thermodynamics of Dilution of L-Cystine in Aqueous Solution of Sodium Hydroxide, Potassium Hydroxide or Hydrochloric Acid

应用流动式等温精密微量热技术测定了298.15,303.15,308.15,313.15和318.15K5个不同温度下L-胱氨酸在一种强酸性和两种强碱性溶剂中的稀释焓.根据改进的McMillan-Mayer理论对所测数据进行关联,得到了表观摩尔稀释焓对浓度变化的经验方程和各级焓相互作用系数(h2)和二阶熵相互作用系数(s2),根据溶质-溶质,溶质-溶剂等弱相互作用对二阶焓、熵相互作用系数进行了讨论.结果表明对在水相中胱氨酸的二阶相互作用而言,二价阳离子比二价阴离子具有较强的介质效应;不同温度下的二阶焓相互作用系数与温度成线性关系,因而二阶熵相互作用系数在实验温度范围内为一常量.

The enthalpies of dilution of L-cystine in solutions of two strong alkalis and one strong acid have been determined by isothermal flow-mixed microcalorimetry at the temperatures of 298.15, 303.15, 308.15, 313.15 and 318.15 K. Empirical equations of apparent enthalpies of dilution varying with the concentration of the amino acid have been obtained from the experimental data in terms of the improved McMillan-Mayer theory. Enthalpic interaction coefficients, h(2), h(3), and h(4), and pairwise entropic interaction coefficient s(2) have been gotten. The values of pairwise enthalpic interaction coefficient, h(2), have been discussed in the light of solute-solute and solute-solvent interactions. The results indicate that medium effect on the bivalent cation of L-cystine is stronger than on the bivalent anion. The values of h(2) show quite well straight-line dependence on temperature and pairwise entropic interaction coefficient, s(2), is a constant in the experimental range of temperature.