Dimethoxynitrophenyl-EDTA (DMNP) is a popular calcium cage that is frequently used to investigate the role of Ca²⁺ in signaling processes in vivo. Lanthanides have been used in Ca²⁺ biomimetics due to similarities in coordination properties of Ln³⁺ and Ca²⁺ that may enable fluorescence and NMR studies of functional and structural properties of Ca²⁺ binding proteins. In this study, we show that Tb³⁺, Eu³⁺, and Nd³⁺ bind strongly to DMNP in a 1:1 ratio. Isothermal titration calorimetric measurements of Ca²⁺ displacement by Ln³⁺ in DMNP provide the equilibrium binding constants for Ln³⁺DMNP complexation with association constants, K₁₁ = (1.2 ± 0.7) × 10¹² M^–1 for Eu³⁺, (2.5 ± 1.7) × 10¹² M^–1 for Nd³⁺, and (2.8 ± 0.8) × 10¹² M^–1 for Tb³⁺. The kinetics and thermodynamics of Ca²⁺, Mg²⁺, and Tb³⁺ release from DMNP were characterized using photothermal beam deflection (PBD). Ligand release from the DMNP cage was rapid and occurred within 10 μs upon cage photofragmentation and was associated with similar reaction volume and enthalpy changes that can be attributed to the photoreleased ion solvation. In the case of Ca²⁺DMNP photodissociation at subsaturating Ca²⁺ concentrations, we observed a slower phase with a lifetime of 300 μs that we attribute to Ca²⁺ rebinding to unphotolyzed DMNP. These results demonstrate that DMNP can serve as an effective photolabile cage for oxophilic Ln³⁺ that has similar coordination properties to Ca²⁺ and Mg²⁺.

中文翻译：

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DMNP 作为 Ln3+ 的有效笼：光谱和热力学研究


二甲氧基硝基苯基-EDTA (DMNP) 是一种流行的钙笼，经常用于研究 Ca ²⁺ 在体内信号传导过程中的作用。由于 Ln ³⁺ 和 Ca ²⁺ 配位特性的相似性，镧系元素已被用于 Ca ²⁺ 仿生材料，这可以实现功能和结构特性的荧光和核磁共振研究Ca ²⁺ 结合蛋白。在本研究中，我们表明 Tb ³⁺ 、 Eu ³⁺ 和 Nd ³⁺ 以 1:1 的比例与 DMNP 牢固结合。 DMNP 中 Ln ³⁺ 对 Ca ²⁺ 置换的等温滴定量热测量提供了 Ln ³⁺ DMNP 络合的平衡结合常数和缔合常数 K ₁₁ M ^–1 对于 Eu ³⁺ , (2.5 ± 1.7) × 10 ¹² Nd ³⁺ 为 M ^–1 ，Tb ³⁺ 为 (2.8 ± 0.8) × 10 ¹² M ^–1 。使用光热束偏转 (PBD) 表征了 DMNP 中 Ca ²⁺ 、Mg ²⁺ 和 Tb ³⁺ 释放的动力学和热力学。配体从 DMNP 笼中快速释放，并在笼光断裂后 10 μs 内发生，并与类似的反应体积和可归因于光释放离子溶剂化的焓变化相关。对于亚饱和 Ca ²⁺ 浓度下的 Ca ²⁺ DMNP 光解离，我们观察到寿命为 300 μs 的较慢相，我们将其归因于 Ca ²⁺ 重新结合为未光解的 DMNP。这些结果表明，DMNP 可以作为亲氧性 Ln ³⁺ 的有效光不稳定笼，其与 Ca ²⁺ 和 Mg ²⁺ 具有相似的配位特性。