The motivation of this work was to probe whether coordination of esculetin to cobalt(III) could lead to a complex with the required properties to function as a redox‐activated drug delivery platform, selective for hypoxic environments. The complex [Co(esc)(py₂en)]ClO₄·(CH₃OH)₂ (1) was obtained and fully characterized by CHN elemental analysis, single‐crystal X‐ray diffractometry, UV/Vis and fluorescence spectroscopy, and ESI mass spectrometry. The redox behavior of 1 was evaluated by cyclic and square wave voltammetry analyses in MeCN and PBS buffer, which revealed distinct potentials for the Co³⁺/Co²⁺ processes in aqueous and organic solutions. In PBS, the potential is within the accepted ideal range (–0.2 to –0.4 V vs. SHE) for reduction in biological systems. Thus, a selective release of the coumarin ligand in a hypoxic environment upon reduction was simulated by investigating reactions of 1 with sodium dithionite in argon‐, air‐, and O₂‐saturated atmospheres. An [O₂]‐dependent dissociation of esculetin was monitored over a 72 h period at 25 °C by UV/Vis spectroscopy and confirmed by fluorescence spectroscopy and ESI‐MS data. These results provide strong evidence of a hypoxia‐selective, redox‐activated mechanism for the release of esculetin from this cobalt(III) complex.

中文翻译：

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具有低氧选择性的氧化还原激活药物递送平台的Esculetin-Cobalt（III）原型

这项工作的目的是探讨七叶皂素与钴（III）的配位是否会导致具有所需特性的复合物，以用作氧化还原激活的药物输送平台，对缺氧环境具有选择性。获得了复合物[Co（esc）（py ₂ en）] ClO ₄ ·（CH ₃ OH）₂（1），并通过CHN元素分析，单晶X射线衍射，UV / Vis和荧光光谱对其进行了全面表征，和ESI质谱。在MeCN和PBS缓冲液中通过循环和方波伏安法分析了1的氧化还原行为，发现了Co ³⁺ / Co ^2+的不同电势水溶液和有机溶液中的过程。在PBS中，减少生物系统的电势在公认的理想范围内（相对于SHE为–0.2至–0.4 V）。因此，通过研究1与连二亚硫酸钠在氩气，空气和O ₂饱和气氛中的反应，模拟了还原后低氧环境中香豆素配体的选择性释放。在25°C下通过紫外/可见光谱在72 h内监测七叶草素的[O ₂ ]依赖性解离，并通过荧光光谱和ESI-MS数据进行确认。这些结果提供了从这种钴（III）复合物中释放七叶皂素的低氧选择性，氧化还原激活机制的有力证据。