Solution properties of the LnIII complexes of a novel octadentate chelator with rigidified iminodiacetate arms
作者:Lorenzo Tei、Zsolt Baranyai、Claudio Cassino、Marianna Fekete、Ferenc K. Kálmán、Mauro Botta
DOI:10.1039/c2dt31684f
日期:——
A novel octadentate ligand derived from the core structure of EGTA (ethyleneglycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) with two piperidine-cis-dicarboxylic acid moieties spaced by a triethylenedioxy chain (L1) has been synthesised with the aim to assess the effect of the structural rigidity on the thermodynamic and kinetic stabilities of its LnIII complexes. The stability constants of [Ln(L1)]− complexes show a weaker binding affinity for Ln3+ ions of L1 than EGTA. On the other hand, the selectivity of L1 for Ca2+ over Mg2+ is one of the highest ever reported. The kinetic inertness has been also investigated and faster rates of both acid catalysed and metal assisted decomplexation have been measured for [Gd(L1)]− as compared to [Gd(EGTA)]−. The 1H- and 13C NMR spectra of the diamagnetic La3+, Y3+ and Lu3+ complexes in aqueous media show pronounced stereochemical rigidity and the occurrence of a structural change across the lanthanide series. Finally, a complete 1H and 17O NMR relaxometric study indicates that [Gd(L1)]− possesses a nine-coordinate ground state with one inner coordination sphere water molecule characterized by a fast rate of exchange (298kex = 59 × 106 s−1).
我们合成了一种新型八齿配体,该配体来自 EGTA(乙二醇-双(2-氨基乙基醚)-N,N,N′,N′-四乙酸)的核心结构,其中有两个哌啶-顺式二羧酸分子,中间间隔着一条三亚乙二氧基链(L1),目的是评估结构刚性对其 LnIII 复合物热力学和动力学稳定性的影响。Ln(L1)]- 复合物的稳定性常数表明,与 EGTA 相比,L1 与 Ln3+ 离子的结合亲和力较弱。另一方面,L1 对 Ca2+ 而非 Mg2+ 的选择性是有报道以来最高的。此外,还对动力学惰性进行了研究,与[Gd(EGTA)]- 相比,[Gd(L1)]- 在酸催化和金属辅助下的解络合速率更快。二磁性 La3+、Y3+ 和 Lu3+ 复合物在水介质中的 1H 和 13C NMR 光谱显示出明显的立体化学刚性,以及整个镧系元素系列的结构变化。最后,一项完整的 1H 和 17O NMR 驰豫度研究表明,[Gd(L1)]- 具有九配位基态,其中一个内配位层水分子具有快速交换速率(298kex = 59 × 106 s-1)的特点。