Stability, Water Exchange, and Anion Binding Studies on Lanthanide(III) Complexes with a Macrocyclic Ligand Based on 1,7-Diaza-12-crown-4: Extremely Fast Water Exchange on the Gd<sup>3+</sup> Complex
作者:Zoltán Pálinkás、Adrián Roca-Sabio、Marta Mato-Iglesias、David Esteban-Gómez、Carlos Platas-Iglesias、Andrés de Blas、Teresa Rodríguez-Blas、Éva Tóth
DOI:10.1021/ic9011197
日期:2009.9.21
[Gd(bp12c4)(H2O)q]+ complex is present in hydration equilibrium between nine-coordinate, monohydrated, and ten-coordinate, bishydrated species. We attribute the fast exchange to the hydration equilibrium and to the flexible nature of the inner coordination sphere. The large negative value of the activation entropy (ΔS⧧ = −35 ± 8 J mol−1 K−1) points to an associative character for the water exchange and suggests
基于1,7-diaza-12-crown-4平台(bp12c4 2−)的吡啶甲酸衍生物配体形成稳定的Ln 3+配合物,其稳定性常数从早期镧系元素到中等镧系元素增加,其余部分则相对稳定。系列的对数(对于Ln = La,Gd和Yb分别为log K LnL = 16.81(0.06),18.82(0.01)和18.08(0.05))。络合物的形成速度很快,可以直接用电位滴定法评估稳定性常数。在Zn 2+存在下,[Gd(bp12c4)] +的解离经由质子和金属辅助途径进行,并且在这方面,该系统介于DTPA型和大环DOTA型螯合物之间,其解离分别由金属或质子辅助途径主导。Cu 2+交换显示出意想不到的pH依赖性,观察到的速率常数随质子浓度的增加而降低。通过17 O NMR评估,在[Gd(bp12c4)(H 2 O)q ] +络合物上的水交换速率极高(k ex 298 =(2.20±0.15)×10 8