University of Coimbra, Coimbra Chemistry Centre (CQC), Department of Chemistry, 3004-535 Coimbra, Portugal.
Centre de Biophysique Moléculaire, CNRS, UPR 4301, Université d'Orléans, Rue Charles Sadron, 45071 Orléans Cedex 2, France.
Photochem Photobiol Sci. 2020 Nov 11;19(11):1522-1537. doi: 10.1039/d0pp00214c.
The photophysical properties of Eu3+ and Tb3+ complexes of DOTAGA and DO3A-monoamide conjugates of the Pittsburgh compound B (PiB) chromophore, prepared using linkers of different lengths and flexibilities, and which form stable negatively charged (LnL1), and uncharged (LnL2) complexes, respectively, were studied as potential probes for optical detection of amyloid aggregates. The phenylbenzothiazole (PiB) moiety absorbs light at wavelengths longer than 330 nm with a high molar absorption coefficient in both probes, and acts as an antenna in these systems. The presence of the luminescent Ln3+ ion quenches the excited states of PiB through an energy transfer process from the triplet state of PiB to the metal centre, and structured emission is seen from Eu3+ and Tb3+. The luminescence study indicates the presence of a 5D4 → T1 back transfer process in the Tb3+ complexes. It also provides insights on structural properties of the Eu3+ complexes, such as the high symmetry environment of the Eu3+ ion in a single macrocyclic conformation and the presence of one water molecule in its inner coordination sphere. The overall quantum yield of luminescence of EuL1 is higher than for EuL2. However, their low values reflect the low overall sensitization efficiency of the energy transfer process, which is a consequence of the large distances between the metal center and the antenna, especially in the EuL2 complex. DFT calculations confirmed that the most stable conformation of the Eu3+ complexes involves a combination of a square antiprismatic (SAP) geometry of the chelate and an extended conformation of the linker. The large calculated average distances between the metal center and the antenna point to the predominance of the Förster energy transfer mechanism, especially for EuL2. This study provides insights into the behavior of amyloid-targeted Ln3+ complexes as optical probes, and contributes towards their rational design.
Eu3+ 和 Tb3+ 配合物的光物理性质，DOTAGA 和 DO3A-单酰胺缀合物的匹兹堡化合物 B (PiB) 发色团，使用不同长度和灵活性的接头制备，分别形成稳定的带负电荷 (LnL1) 和不带电荷 (LnL2) 配合物，作为光学检测淀粉样蛋白聚集的潜在探针进行了研究。苯并噻唑 (PiB) 部分在两个探针中在长于 330nm 的波长处吸收光，具有高摩尔吸光系数，并且在这些系统中作为天线起作用。发光 Ln3+ 离子的存在通过从 PiB 的三重态到金属中心的能量转移过程猝灭 PiB 的激发态，并且从 Eu3+ 和 Tb3+ 看到结构发射。发光研究表明在 Tb3+ 配合物中存在 5D4→T1 反向转移过程。它还提供了有关 Eu3+ 配合物结构性质的见解，例如在单个大环构象中 Eu3+ 离子的高对称性环境以及在其内部配位球中存在一个水分子。EuL1 的发光量子产率高于 EuL2。然而，它们的低值反映了能量转移过程整体敏化效率低，这是金属中心与天线之间距离大的结果，尤其是在 EuL2 配合物中。DFT 计算证实，Eu3+ 配合物的最稳定构象涉及螯合物的四方反棱柱 (SAP) 几何形状和接头的扩展构象的组合。金属中心和天线之间的计算平均距离大，表明 Förster 能量转移机制占主导地位，尤其是对于 EuL2。这项研究提供了对作为光学探针的淀粉样蛋白靶向 Ln3+ 配合物行为的深入了解，并为其合理设计做出了贡献。
