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铵水间质子交换的再研究 :不受扩散约束的化学交换(英文)

REVISIT TO HYDROGEN EXCHANGE BETWEEN AMMONIUM AND WATER:Diffusion Independent Chemical Exchange
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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 . Hydrogen exchange between ammonium and water is revisited. Exchange rate constants, diffusion coefficients and relaxation times for solutions with varied pH, temperature and concentration of a coexisting salt are measured using NMR spectroscopy. It is demonstrated that the hydrogen exchange in ammonium solutions is independent of apparent diffusion. The mechanism involves chemical bond/hydrogen bond exchange. In solutions, water molecules, with the help of hydrogen bonding, serve as a bridge to connect the ammonium with its base partner ammonia. During hydrogen exchange, the ammonia accepts a hydrogen from water while the ammonium donates a hydrogen to water, or a hydrogen jumps from water to ammonium and at the same time another hydrogen jumps back from ammonium to water. There is no net hydrogen transfer between ammonium and water. At lower pH, the concentration of ammonia becomes lower and less ammonium water ammonia complex is formed. As a result, the probability of the hydrogen exchange is reduced. This explains why at lower pH hydrogen exchange is slow, a common phenomenon observed in biological hydrogen exchange systems.
出处 《波谱学杂志》 CAS CSCD 北大核心 2002年第3期235-245,共11页 Chinese Journal of Magnetic Resonance
基金 国家自然科学基金资助项目 ( 2 972 530 7)
关键词 化学交换 铵水溶液 质子交换 氢键 化学键 自扩散 核磁共振波谱分析 ammonium aqueous solution hydrogen exchange hydrogen bond chemical bond self diffusion
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