The Structural Effect of Methyl Substitution on the Binding of Polypyridyl Ru–dppz Complexes to DNA

Polypyridyl ruthenium complexes have been intensively studied and possess photophysical properties that are both interesting and useful. They can act as probes for DNA, with a substantial enhancement in emission when bound, and can induce DNA damage upon photoirradiation. Therefore, the synthesis and characterization of DNA binding of new complexes is an area of intense research activity. While knowledge of how the binding of derivatives compares to that of the parent compound is highly desirable, this information can be difficult to obtain. Here we report the synthesis of three new methylated complexes, [Ru­(TAP)2(dppz-10-Me)]­Cl2, [Ru­(TAP)2(dppz-10,12-Me2)]­Cl2, and [Ru­(TAP)2(dppz-11-Me)]­Cl2 (TAP = 1,4,5,8-tetraazaphenanthrene; dppz = dipyrido­[3,2-a:2′,3′-c]­phenazine), and examine the consequences for DNA binding through the use of atomic-resolution X-ray crystallography. We find that the methyl groups are located in discrete positions with a complete directional preference. This may help to explain the quenching behavior found in solution for analogous [Ru­(phen)2(dppz)]2+ derivatives.

多吡啶钌配合物已得到广泛且深入的研究，其光物理性质兼具理论研究价值与实际应用潜力。该类配合物可用作DNA分子探针，与DNA结合后荧光发射强度会显著增强，且在光辐照条件下可诱导DNA损伤。因此，新型配合物的合成及其与DNA结合特性的表征，是当前研究热点之一。尽管学界亟需明确衍生物与母体化合物的DNA结合行为差异，但此类相关信息往往难以获取。本文报道了三种新型甲基化配合物：[Ru(TAP)₂(dppz-10-Me)]Cl₂、[Ru(TAP)₂(dppz-10,12-Me₂)]Cl₂以及[Ru(TAP)₂(dppz-11-Me)]Cl₂（其中TAP为1,4,5,8-四氮杂菲（1,4,5,8-tetraazaphenanthrene），dppz为二吡啶并[3,2-a:2′,3′-c]吩嗪（dipyrido[3,2-a:2′,3′-c]phenazine）），并借助原子分辨率X射线晶体学技术，研究其与DNA结合的行为特征。研究结果表明，甲基基团以离散的空间位置排布，且呈现完全的方向性偏好。这一发现有助于解释溶液中类似[Ru(phen)₂(dppz)]²+衍生物所表现出的荧光淬灭行为。