DNA-interacting lanthanide complexes with a DOTA-derived dipyrido[3,2-a;2',3'-c]phenazine ligand for near-infrared luminescence.

Dipyrido[3,2-a:2',3'-c]phenazine (dppz) is well known for its ability to interact with DNA and is ideally suited for sensitizing near-infrared (NIR)-emitting lanthanide ions such as Nd3+, Er3+ and Yb3+. The combination of these properties gives perspective for the utilization of lanthanide complexes incorporating a dppz moiety for biomedical applications. Here, we present the synthesis of novel lanthanide complexes with an embedded dppz moiety [Ln(DO3A-dppz)] (Ln = all lanthanides except Pm; DO3A = 1,4,7,10-tetraazadodecane-1,4,7-triacetic acid) derived from clinically used [Ln(DOTA)] complexes (DOTA = 1,4,7,10-tetraazadodecane-1,4,7,10-tetraacetic acid). Structural analyses of all the complexes reveal interesting behavior, showing a share of isomers in the structures linked to lanthanide contraction and ionic radii. Photoluminescence studies provide excitation and emission spectra of the complexes with compatible central ions Nd3+, Er3+, Yb3+ and Eu3+, along with decay times of the complexes with Yb3+ and Eu3+. All complexes are weakly soluble in water with good stability in Tris-HCl buffer, and their affinity towards model calf-thymus DNA was tested using a SYBR Green I displacement assay. Overall, the obtained results are promising for the development of [Ln(DO3A-dppz)] complexes towards future applications in biomedical imaging.