Departamento de Ciencias Biomédicas, Universidad CEU-Cardenal Herrera, CEU Universities, C/Ramón y Cajal, s/n, 46115 Alfara del Patriarca, Valencia, Spain.
Departamento de Quı́mica Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Edificio de Institutos de Paterna, Apdo 22085, 46071 Valencia, Spain.
Inorg Chem. 2020 May 18;59(10):7306-7317. doi: 10.1021/acs.inorgchem.0c00690. Epub 2020 May 7.
We report the synthesis and characterization of the macrocyclic ligand 2,2'-((2-(3,9-bis(carboxymethyl)-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-6-yl)ethyl)azanediyl)diacetic acid (HL) and several of its complexes with lanthanide ions. The structure of the free ligand was determined using X-ray diffraction measurements. Two N atoms of the pyclen moiety in the position are protonated in the solid state, together with the exocyclic N atom and one of the carboxylate groups of the ligand. The relaxivity of the Gd complex was found to increase from 6.7 mM s at pH 8.6 to 8.5 mM s below pH ≈ 6.0. Luminescence lifetime measurements recorded from HO and DO solutions of the Eu complex evidence the presence of a single complex species in solution at low pH (∼5.0) that contains two inner-sphere water molecules. DFT calculations suggest that the coordination environment of the Ln ion is fulfilled by the four N atoms of the pyclen unit, two oxygen atoms of the macrocyclic acetate groups, and an oxygen atom of an exocyclic carboxylate group. The two inner-sphere water molecules complete coordination number nine around the metal ion. At high pH (∼9.3), the lifetime of the excited D level of Eu displays a biexponential behavior that can be attributed to the presence of two species in solution with hydration numbers of = 0 and = 1. The H NMR and DOSY spectra recorded from solutions of the Eu and Y complexes reveal a structural change triggered by pH and the formation of small aggregates at high pH values.
我们报告了大环配体 2,2'-((2-(3,9-双（羧甲基）-3,6,9-三氮杂-1(2,6)-吡啶并环十二烷-6-基)乙基)亚氨基)二乙酸（HL）及其与镧系元素离子的几种配合物的合成与表征。通过 X 射线衍射测量确定了游离配体的结构。在固态中，pyclen 部分的两个 N 原子在位置上被质子化，与环外 N 原子和配体的一个羧酸盐基团一起。发现 Gd 配合物的弛豫率从 pH 8.6 时的 6.7 mM s 增加到 pH ≈ 6.0 以下时的 8.5 mM s。从 Eu 配合物的 HO 和 DO 溶液中记录的荧光寿命测量证明，在低 pH（约 5.0）下，溶液中存在一种包含两个内球水分子的单一配合物物种。DFT 计算表明，Ln 离子的配位环境由 pyclen 单元的四个 N 原子、大环乙酸酯基团的两个氧原子和一个环外羧酸盐基团的氧原子满足。两个内球水分子完成了金属离子周围的九配位。在高 pH（约 9.3）下，Eu 的激发 D 能级的寿命显示出双指数行为，这可以归因于溶液中存在两种具有水合数 = 0 和 = 1 的物种。Eu 和 Y 配合物溶液中记录的 1 H NMR 和 DOSY 谱揭示了由 pH 触发的结构变化以及在高 pH 值下形成的小聚集体。
