Université de Bretagne Occidentale, UMR-CNRS 6521, UFR des Sciences et Techniques, 6 avenue Victor le Gorgeu, C.S. 93837, 29238 Brest Cedex 3, France.
Inorg Chem. 2012 Jun 18;51(12):6916-27. doi: 10.1021/ic300784v. Epub 2012 May 31.
The syntheses of a new 1,4,7,10-tetraazacyclododecane (cyclen) derivative bearing a picolinate pendant arm (HL1), and its 1,4,8,11-tetraazacyclotetradecane (cyclam) analogue HL2, were achieved by using two different selective-protection methods involving the preparation of cyclen-bisaminal or phosphoryl cyclam derivatives. The acid-base properties of both compounds were investigated as well as their coordination chemistry, especially with Cu(2+), in aqueous solution and in solid state. The copper(II) complexes were synthesized, and the single crystal X-ray diffraction structures of compounds of formula Cu(HL)(2)·H(2)O (L = L1 or L2), CuL1 and [CuL2]Cl·2H(2)O, were determined. These studies revealed that protonation of the complexes occurs on the carboxylate group of the picolinate moiety. Stability constants of the complexes were determined at 25.0 °C and ionic strength 0.10 M in KNO(3) using potentiometric titrations. Both ligands form complexes with Cu(2+) that are thermodynamically very stable. Additionally, both HL1 and HL2 exhibit an important selectivity for Cu(2+) over Zn(2+). The kinetic inertness in acidic medium of both complexes of Cu(2+) was evaluated by spectrophotometry revealing that CuL2 is much more inert than CuL1. The determined half-life values also demonstrate the very high kinetic inertness of CuL2 when compared to a list of copper(II) complexes of other macrocyclic ligands. The coordination geometry of the copper center in the complexes was established in aqueous solution from UV-visible and electron paramagnetic resonance (EPR) spectroscopy, showing that the solution structures of both complexes are in excellent agreement with those of crystallographic data. Cyclic voltammetry experiments point to a good stability of the complexes with respect to metal ion dissociation upon reduction of the metal ion to Cu(+) at about neutral pH. Our results revealed that the cyclam-based ligand HL2 is a very attractive receptor for copper(II), presenting a fast complexation process, a high kinetic inertness, and important thermodynamic and electrochemical stability.
新的 1,4,7,10-四氮杂环十二烷（环十二烷）衍生物，带有一个吡啶甲酸侧臂（HL1），以及其 1,4,8,11-四氮杂环十四烷（环十四烷）类似物 HL2 的合成，是通过使用两种不同的选择性保护方法实现的，包括环十二烷双亚胺或磷酸环十二烷衍生物的制备。研究了两种化合物的酸碱性质以及它们的配位化学性质，特别是与 Cu(2+)在水溶液和固态中的配位化学性质。合成了铜（II）配合物，并确定了配合物的单晶 X 射线衍射结构，式为Cu(HL)(2)·H(2)O（L = L1 或 L2）、CuL1和[CuL2]Cl·2H(2)O。这些研究表明，配合物的质子化发生在吡啶甲酸部分的羧酸盐基团上。在 25.0°C 和 0.10M 的 KNO(3)中，使用电位滴定法测定了配合物的稳定常数。两种配体都与 Cu(2+)形成热力学非常稳定的配合物。此外，HL1 和 HL2 对 Cu(2+)具有重要的选择性，而对 Zn(2+)则没有选择性。通过分光光度法评估了两种 Cu(2+)配合物在酸性介质中的动力学惰性，结果表明CuL2比CuL1更惰性。确定的半衰期值也表明，与其他大环配体的铜（II）配合物相比，CuL2具有非常高的动力学惰性。配合物中铜中心的配位几何结构在水溶液中通过紫外-可见和电子顺磁共振（EPR）光谱确定，表明两种配合物的溶液结构与晶体学数据非常吻合。循环伏安实验表明，在中性 pH 值下，金属离子还原为 Cu(+)时，配合物对金属离子离解具有良好的稳定性。我们的研究结果表明，基于环十四烷的配体 HL2 是铜（II）的一种非常有吸引力的受体，具有快速的络合过程、高动力学惰性以及重要的热力学和电化学稳定性。
