Quantum Yield of DNA Strand Breaks under Photoexcitation of a Molecular Ruby

Photodynamic therapy (PDT) used for treating cancer relies on the generation of highly reactive oxygen species, e.g. singlet oxygen 1O2, by light-induced excitation of a photosensitizer (PS) in the presence of molecular oxygen, inducing DNA damage in close proximity of the PS. Although many precious metal complexes have been explored as PS for PDT and received clinical approval, only recently, the potential of photoactive complexes of bio-essential metals as PS was discovered. Using the DNA origami technology that can absolutely quantify DNA strand break cross sections, we assessed the potential of the luminescent transition metal complex [Cr(ddpd)2]3+ (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-ylpyridine-2,6-diamine) to damage DNA in an air-saturated aqueous environment upon low energy UV/Vis illumination. The quantum yield for strand breakage, i.e., the ratio of DNA strand breaks to the number of absorbed photons, was determined to 1 – 4%, indicating efficient transformation of photons into DNA strand breaks by [Cr(ddpd)2]3+.