Synthesis, DNA binding mode, singlet oxygen photogeneration and DNA photocleavage activity of ruthenium compounds with porphyrin–imidazo[4,5‐ f ]phenanthroline conjugated ligand

Using 1,10‐phenanothroline‐5,6‐dione and 10,20‐bis(4‐methylphenyl)porphyrin copper as starting materials, a conjugated porphyrin–imidazo[4,5‐ f ]‐1,10‐phenanothroline ligand (Por 1 ) was prepared. Subsequently, the copper complex of Por 1 was reacted with Ru(1,10‐phenanothroline) 2 Cl 2 to yield ruthenium compound Por 2 . After removal of copper metal under acid condition, the free base porphyrin of Por 2 (Por 3 ) was prepared. The structure of these compounds was confirmed using UV–visible, 1 H NMR, mass and infrared spectroscopies and elemental analysis. Through UV–visible, fluorescence and circular dichroism analyses, the interaction modes between Por 1 – 3 and calf thymus DNA were investigated. Por 1 interacted with DNA via outside groove face, but Por 2 and Por 3 showed intercalative interaction with DNA. Binding constants between Por 1 – 3 and DNA were 7.79 × 10 5 , 1.29 × 10 6 and 1.32 × 10 6  M −1 , respectively. With 5,10,15,20‐tetraphenylporphyrin (H 2 TPP) as a control, the singlet oxygen ( 1 O 2 ) generation of Por 1 – 3 was measured using the 1,3‐diphenylisobenzofuran method. The 1 O 2 generation rate of Por 1 – 3 followed the order: Por 3 >Por 1 >H 2 TPPP >Por 2 . Por 1 and Por 3 showed better 1 O 2 quantum yields than Por 2 , which were almost threefold higher than that of H 2 TPP. The DNA cleavage ability of Por 1 – 3 was analyzed using gel electrophoresis. Por 3 showed higher DNA photocleavage activity, with more than 50% photocleavage rate at 20 μM. These results suggest that amphipathic (hydrophilic/lipophilic) Por 3 with conjugated Por 1 ligand is a potential photosensitizer in cancer therapy.