水/乙醇混合溶剂中氨基酸离解的取代基效应

Substituent Effect on Dissociation of Amino Acids in Water/Ethanol Mixtures

用LKB-2277 BioActivity Monitor测定了298.15K时甘氨酸,丙氨酸和丝氨酸在水/乙醇混合溶剂中的离解焓,计算了相应的离解熵.根据三个氨基酸分别与某一参考酸之间的质子交换反应,重点讨论了溶剂结构变化对取代基效应焓,熵变化的影响.实验结果表明在水/乙醇混合溶剂的最大结构化区域,取代基效应最为显著.认为在混合溶剂的富水区大块的似冰山结构的水分子簇的寿命大大延长.

In this paper, the dissociation enthalpies of three amino acids in ethanol/water mixtures at 298.15K have been determined by LKB - 2277 BioActivity Monitor. Combined with the values of free energies, the dissociation entropies have been calculated. Several proton exchange reactions between the given amino acids and the reference acids selected in ethanol/water mixtures have been examined in detail Solute - solvent interactions and the structural effect of the ethanol/water mixtures have been discussed. Trie results show that substituent effect is most effective in the region with the strongest structural enhancement of the mixed solvents. It is considered that the life of the bulky iceberg - like water clusters is lengthened greatly in the region rich in water.