Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Inorg Chem. 2010 Sep 6;49(17):8025-33. doi: 10.1021/ic101054u.
The mechanism of the reaction of CuFL1 (FL1 = 2-{2-chloro-6-hydroxy-5-[(2-methylquinolin-8-ylamino)methyl]-3-oxo-3H-xanthen-9-yl}benzoic acid) with nitric oxide (NO) to form the N-nitrosated product FL1-NO in buffered aqueous solutions was investigated. The reaction is first-order in [CuFL1], [NO], and [OH(-)]. The observed rate saturation at high base concentrations is consistent with a mechanism in which the protonation state of the secondary amine of the ligand is important for reactivity. This information provides a rationale for designing faster-reacting probes by lowering the pK(a) of the secondary amine. Activation parameters for the reaction of CuFL1 with NO indicate an associative mechanism (DeltaS(double dagger) = -120 +/- 10 J/mol.K) with a modest thermal barrier (DeltaH(double dagger) = 41 +/- 2 kJ/mol; E(a) = 43 +/- 2 kJ/mol). Variable-pH electron paramagnetic resonance experiments reveal that, as the secondary amine of CuFL1 is deprotonated, electron density shifts to yield a new spin-active species having electron density localized on the deprotonated amine nitrogen atom. This result suggests that FL1-NO formation occurs when NO attacks the deprotonated secondary amine of the coordinated ligand, followed by inner-sphere electron transfer to Cu(II) to form Cu(I) and release of FL1-NO from the metal.
在缓冲水溶液中研究了 CuFL1（FL1=2-{2-氯-6-羟基-5-[(2-甲基喹啉-8-基氨基)甲基]-3-氧代-3H-呫吨-9-基}苯甲酸）与一氧化氮（NO）反应形成 N-亚硝化产物 FL1-NO 的反应机制。该反应对[CuFL1]、[NO]和[OH(-)]呈一级反应。在高碱浓度下观察到的速率饱和与配体仲胺的质子化状态对反应性很重要的机制一致。这些信息为通过降低仲胺的 pK(a)来设计更快反应的探针提供了依据。CuFL1 与 NO 反应的活化参数表明反应遵循缔合机制（DeltaS(double dagger) = -120 +/- 10 J/mol.K），热障适中（DeltaH(double dagger) = 41 +/- 2 kJ/mol；E(a) = 43 +/- 2 kJ/mol）。可变 pH 值电子顺磁共振实验表明，随着 CuFL1 仲胺的去质子化，电子密度转移导致产生新的自旋活性物种，其电子密度定域在去质子化的胺氮原子上。这一结果表明，当 NO 攻击配位配体的去质子化仲胺时，形成 FL1-NO，随后发生内球电子转移到 Cu(II)以形成 Cu(I)并从金属释放 FL1-NO。
