Two symmetric ligands harbouring two TEMPO radicals and two functionalized acetamide arms (R = OMe (L₁), CF₃ (L₂)) were prepared and chelated to lanthanide ions (Eu^III, Yb^III for both L₁ and L₂, Dy^III for L₁). Luminescence measurements on the europium complexes support the coordination of a single water molecule. The TEMPO arms are magnetically interacting in L₁ (and its complexes) but not in L₂. The TEMPO moieties can be reversibly oxidized into an oxoammonium (0.33–0.36 V vs. Fc⁺/Fc) or reduced into a hydroxylamine (ill-defined redox wave, reduction by ascorbate), which are both diamagnetic. The europium complexes [Eu(L₁)]³⁺ and [Eu(L₂)]³⁺ in their hydroxylamine form exhibit a temperature dependent CEST effect, which is maximal at 25 °C (30%) and 37 °C (12%), respectively. The CEST activity is dramatically reduced in the corresponding nitroxide forms due to the paramagnetism of the ligand. The europium complexes show no cytotoxicity against M21 cell lines over long incubation times (72 h) at high concentration (40 μM).

中文翻译：

---

用于氧化还原监测的对称 CEST 活性镧系配合物

制备了两个含有两个 TEMPO 自由基和两个功能化乙酰胺臂的对称配体（R = OMe ( L ₁ )、CF ₃ ( L ₂ )）并螯合到镧系离子（L ₁和L ₂^{的 Eu III}、Yb ^III、Dy ^III对于L ₁ )。对铕配合物的发光测量支持单个水分子的协调。TEMPO 臂在L ₁（及其复合物）中有磁性相互作用，但在L _2中没有. TEMPO 部分可以可逆地氧化成氧铵（0.33–0.36 V vs. Fc ⁺ /Fc）或还原成羟胺（不明确的氧化还原波，被抗坏血酸还原），它们都是抗磁性的。羟胺形式的铕配合物[Eu(L ₁ )] ³⁺和[Eu(L ₂ )] ³⁺表现出温度依赖性 CEST 效应，在 25 °C (30%) 和 37 °C (12 ％）， 分别。由于配体的顺磁性，CEST 活性在相应的氮氧化合物形式中显着降低。在高浓度 (40 μM) 下长时间孵育 (72 小时) 后，铕复合物对 M21 细胞系没有细胞毒性。