Unusually sharp dependence of water exchange rate versus lanthanide ionic radii for a series of tetraamide complexes
Unusually sharp dependence of water exchange rate versus lanthanide ionic radii for a series of tetraamide complexes
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DOI：
10.1021/ja017133k
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发表时间：
2002-04-24
影响因子：
15
通讯作者：
Sherry, AD
中科院分区：
文献类型：
--
作者：
Zhang, SR;Wu, KC;Sherry, AD
四酰胺配体DOTA-四(甘氨酸乙酯)与溶液中存在的稀土(III)离子形成络合物，主要以方形反棱柱结构存在，与单个缓慢交换的内球水分子形成络合物。变温1H和17O核磁共振研究表明，这些络合物中的结合水寿命与Ln3+阳离子的离子半径密切相关。用一种新的稀土诱导位移技术从体水共振中揭示了SmL3+和YL3+络合物的束缚水17O共振。在EuL3+络合物中，结合水寿命(τM298)为∼800μS，但对于离子半径较大和较小的Ln3+阳离子，结合水寿命变短(几微秒)。这表明，在这个大环四胺体系中，水交换是微调的，各种Ln3+络合物满足有效MT试剂所需的交换要求Δω*τM≥1。
The tetraamide ligand, DOTA-tetra(glycine ethyl ester), forms complexes with the lanthanide(III) cations that exist in solution predominantly as the square antiprism structure with single, slowly exchanging inner-sphere water molecule. Variable-temperature1H and17O NMR studies revealed that the bound water lifetimes in these complexes were sharply dependent upon the ionic radius of Ln3+cation. A novel lanthanide-induced shift technique was used to unmask the bound water17O resonance of SmL3+and YL3+complexes from the bulk water resonance. The bound water lifetime (τM298) was ∼800 μs in the EuL3+complex but became much shorter (several microseconds) for Ln3+cations with larger and smaller ionic radii. This demonstrates that water exchange is exquisitely fine-tuned in this macrocyclic tetraamide system and that a variety of Ln3+complexes meet with the exchange requirement, Δω*τM≥ 1, necessary for an efficient MT agent.