Low energy light induced DNA photocleavage with a bis-ruthenated porphyrin

• A new porphyrin and its ruthenium analog have been synthesized.
• The compounds have been characterized by spectroscopic and electrochemical techniques.
• The ruthenated porphyrin shows the ability to photo-nick plasmid DNA when irradiated with low energy light.

When the new porphyrin 5,15-(4-pyridyl)-10,20-(4-trifluoromehtylphenyl)porphyrin is reacted with two equivalents of Ru(bipy)2Cl2 (where bipy = 2,2′-bipyridine) formation of the target ruthenated porphyrin is achieved with 57% yield. Strong electronic transitions are observed in the visible region of the spectrum associated with the porphyrins Soret and four Q-bands. A shoulder at slightly higher energy than the Soret band is attributed to the Ru(dπ) to bipy(π∗) metal to ligand charge transfer (MLCT) band. The bipyridyl π to π∗ transition occurs at 295 nm. Cyclic voltammetry experiments of the porphyrin indicate porphyrin centered reductions in the cathodic direction with no noticeable oxidation process within the window scanned. The ruthenated porphyrin shows the characteristic quasireversible redox couple in the anodic region indicative of oxidation of Ru(II) to Ru(III). A single redox couple for Ru(III/II) indicates no electronic interaction between the ruthenium moieties. DNA titrations using calf thymus (CT) DNA and the ruthenium porphyrin give an unusually large binding constant Kb = (1.1 ± 0.7) × 106 M−1 indicating a strong interaction between complex and DNA. When aqueous solutions of supercoiled DNA and ruthenium porphyrin are irradiated with visible light (energy lower than 550 nm) complete nicking of the DNA is observed.

Aqueous solutions of a new bis-ruthenated porphyrin give an unusually high binding constant associated with a strong interaction toward calf-thymus DNA. When aqueous solutions of this complex and plasmid DNA are irradiated with low energy light complete photo-nicking of the DNA plasmid is observed.Figure optionsDownload as PowerPoint slide