波谱学杂志

• 研究论文 • 上一篇    下一篇

铵水间质子交换的再研究: 不受扩散约束的化学交换

张永洪,  毛希安*   

  1. 中国科学院武汉物理与数学研究所波谱与原子分子物理国家重点实验室, 武汉 430071
  • 收稿日期:2002-02-26 修回日期:2002-04-23 出版日期:2002-09-05 发布日期:2002-09-05
  • 作者简介:张永洪(1970-),男,湖北天门人,博士研究生。*通讯联系人
  • 基金资助:

    国家自然科学基金资助项目(29725307).

REVISIT TO HYDROGEN EXCHANGE BETWEEN AMMONIUM AND WATER: Diffusion Independent Chemical Exchange

ZHANG Yong-hong,MAO Xi-an*   

  1. State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Wuhan Institute of Physics and Mathematics, The Chinese Academy of Sciences P.O. Box, 71010, Wuhan 430071, China
  • Received:2002-02-26 Revised:2002-04-23 Online:2002-09-05 Published:2002-09-05
  • Supported by:

    国家自然科学基金资助项目(29725307).

摘要:

对铵盐水溶液中铵离子与水分子间的质子交换进行了再研究. 以核磁共振(NMR) 波谱学方法测定了不同pH值, 不同温度和含不同共存盐浓度的氯化铵水溶液中质子交换速率, 组分自扩散系数及NMR自旋晶格弛豫时间. 结果显示铵水间的质子交换并不受交换主体分子或离子自扩散的约束. 交换机理包括化学键和氢键的交换. 在溶液中, 水分子以氢键为桥 梁连接铵和其因水解而产生的碱性部分——氨. 在氢交换的过程中, 氨从水分子接受一个氢 成为铵, 同时另外一端的铵提供一个氢给水分子而变成氨, 或者一个氢从水分子转移到氨而同 时另外一个氢从铵转移到水. 在铵水质子交换的过程中没有净的电荷转移. 在低pH条件下,  由水解产生的氨的浓度降低, 亦即铵-水-氨复合物减少, 结果氢交换的可能性降低. 这解释了生物氢交换体系中的一种常见的在低pH值条件下氢交换变慢的现象. 

关键词: 铵水溶液, 质子交换, 氢键, 化学键, 自扩散

Abstract:

Hydrogen exchange between ammonium and water is revisited. Exchange rate constants, diffusion coefficients and relaxation times for solutions with var ied pH, temperature and concentration of a coexisting salt are measured using NM Rspectroscopy. It is demonstrated that the hydrogen exchange in ammonium soluti ons is independent of apparent diffusion. The mechanism involves chemical-bond/ h ydrogen-bond exchange. In solutions, water molecules, with the help of hydrogen - bonding, serve as abridge to connect the ammonium with its base partner ammonia . During hydrogen exchange, the ammonia accepts a hydrogen from water while the a mmonium donates a hydrogen to water, or ahydrogen jumps from water to ammonium  and at the same time another hydrogen jumps back from ammonium to water. There is nonet hydrogen transfer between ammonium and water. At lower pH, the concentr ation of ammonia becomes lower and less ammonium-water-ammonia complex is form ed . As aresult, the probability of the hydrogen exchange is reduced. This explain s why at lower pH hydrogen exchange is slow, a common phenomenon observed in bio logical hydrogen exchange systems.

Key words: ammonium aqueous solution, hydrogen exchange, hydrogen bond, chemical bond, self-diffusion

中图分类号: