Kinetics of the formation of [Ln(DOTAM)]3+ complexes
Kinetics of the formation of [Ln(DOTAM)]3+ complexes
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DOI：
10.1002/ejic.200700178
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发表时间：
2007-08-01
影响因子：
2.3
通讯作者：
Terreno, Enzo
中科院分区：
文献类型：
--
作者：
Baranyai, Zsolt;Banyai, Istvan;Terreno, Enzo
中性配体DOTA及其衍生物的镧系（III）配合物的形成动力学与含有负电荷垂坠基团的DOTA及其衍生物的形成动力学有很大不同。配合物[Ln(DOTAM)]（3+）在pH为4.7 ~ 5.8的范围内与Ln（3+）离子直接接触，形成完全去质子配体。没有检测到质子化中间体的形成，而质子化中间体是DOTA及其衍生物络合的特征。一般碱催化在[Ln(DOTAM)]（3+）的生成反应中不起作用，这也表明没有质子化中间体。用H-1 NMR研究了配体H(2)DOTAM（2+）和HDOTAM（+）的质子交换反应速率。质子交换被发现是一个一般的碱催化过程，因此它不能在这些配合物的形成中起重要作用。表征络合物[Ln(DOTAM)]（3+）形成的二阶速率常数k(L)比报道的开链多齿配体Ln（3+）络合物的类似速率常数低三到四个数量级。这些低kL值可以通过假设反应序列中的早期速率决定步骤（可能是第二或第三个Ln(3+)-酰胺键形成）来解释，从而导致(Ln(DOTAM)]（3+）复合物。(C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)。
The kinetics of the formation of lanthanide(III) complexes of the neutral ligand DOTAM differ considerably from those of DOTA and its derivatives, which contain negatively charged pendant groups. Formation of the complexes [Ln(DOTAM)](3+) occurs upon direct encounter of the Ln(3+) ions and the fully deprotonated ligand in the pH range 4.7-5.8. The formation of a protonated intermediate, which is characteristic of the complexation of DOTA and its derivatives, was not detected. General base catalysis is not valid in the formation reactions of [Ln(DOTAM) ](3+), which also indicates the absence of protonated intermediates. The rates of the proton-exchange reactions for the ligand species H(2)DOTAM(2+) and HDOTAM(+) have been studied by H-1 NMR spectroscopy. Proton ex change was found to be a general base-catalysed process, therefore it cannot play an important role in the formation of these complexes. The second-order rate constants, k(L), which characterize the formation of the complexes [Ln(DOTAM)](3+), are lower than the analogous rate constants reported for the Ln(3+) complexes of open-chain multidentate ligands by three to four orders of magnitude. These low kL values can be interpreted by assuming an early rate-determining step (probably the second or third Ln(3+)-amide bond formation) in the reaction sequence that leads to the (Ln(DOTAM)](3+) complex. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).