Intercalation is not required for DNA light-switch behavior
Intercalation is not required for DNA light-switch behavior
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DOI：
10.1021/ja071001v
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发表时间：
2008-01-30
影响因子：
15
通讯作者：
Turro, Claudia
中科院分区：
文献类型：
--
作者：
Lutterman, Daniel A.;Chouai, Abdellatif;Turro, Claudia
DNA光开关配合物[Ru(bpy)(2)(tpph Z)](2)+ (1, bpy = 2,2′-联吡啶，tpphz =四吡啶[3,2-a:2′，3′-c:3′，2′-h:2′，3′-J]非那嗪]与DNA结合时发光，在有机溶剂中弱发射。迄今为止，过渡金属配合物的光开关行为通常被认为是DNA嵌入的确认。相反，本研究表明，非插层双金属配合物[(bpy)(2)Ru(tpphz)Ru(bpy)(2)](4+)(2)表现为DNA光开关。在水中观察到3 MLCT激发态2的弱发射λ em = 623 nm (Phi(em) = 1.4 x 10(-4))，在加入100 μ M小牛胸腺DNA （ct-DNA）后观察到红移（λ (em) = 702 nm）和强度增加40倍。加入浓度不断增加的2至1毫米鲱鱼精子DNA不会导致溶液粘度的增加，这表明该复合物不是插层剂。此外，还进行了实验，以确保发射增强不是由配合物的螺纹插入引起的。然而，原位生成的2以螺纹方式插入到ct-DNA的碱基对之间，在685边缘处显示出最大的发射，这与表面结合的2相比是蓝移的。DFT计算表明，2中的低洼轨道在贡献MLCT状态时预计会表现出非发射特征，这与观测到的2的发射强度相对于1的发射强度较低一致。据我们所知，目前的工作是非插层光开关金属配合物的第一个例子，从而表明光开关行为不能完全用作插层的确认。
The DNA light-switch complex [Ru(bpy)(2)(tpph Z)](2)+ (1, bpy = 2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'-c:3",2"-h:2"',3"'-J]phenazine) is luminescent when bound to DNA and in organic solvents and weakly emissive in water. To date, light-switch behavior by transition metal complexes has generally been regarded as confirmation of DNA intercalation. In contrast, the present work demonstrates that the nonintercalating bimetallic complex [(bpy)(2)Ru(tpphz)Ru(bpy)(2)](4+) (2) behaves as a DNA light-switch. Weak emission from the 3 MLCT excited state of 2 is observed in water lambda em = 623 nm (Phi(em) = 1.4 x 10(-4)), and a red shift (lambda(em) = 702 nm) and 40-fold increase in intensity are observed upon addition of 100 mu M calf thymus DNA (ct-DNA). Addition of increasing concentrations of 2 to 1 mM herring sperm DNA does not result in an increase in the viscosity of the solution, indicating that the complex is not an intercalator. Additionally, experiments were conducted to ensure that the emission enhancement did not arise from threading intercalation of the complex. The in situ generation of 2 intercalated between the base pairs of ct-DNA in a threading fashion, however, exhibits emission maximum at 685 rim, which is blue-shifted from that of surface-bound 2. DFT calculations show low-lying orbitals in 2 that are expected to exhibit nonemissive character when contributing to the MLCT state, in accord with the lower emission intensity observed for 2 relative to that for 1. To our knowledge, the present work is the first example of a nonintercalating light-switch metal complex, thus showing that light-switch behavior cannot be used exclusively as confirmation of intercalation.