Binding interactions with biological targets and DNA photocleavage activity of Pr(III) and Nd(III) complexes of dipyridoquinoxaline

•[Ln(dpq)(DMF)2(NO3)3] complexes of dipyridoquinoxaline were structurally studied.•Dpq act as DNA binder and antenna on photoexcitation via energy transfer to Ln(III).•Efficient binding interaction with DNA and BSA with the complexes observed.•The complexes show remarkable photo-induced DNA damage via formation of ROS.

Two new lanthanide(III) complexes [Ln(dpq)(DMF)2(NO3)3], where Ln = Pr (1), Nd (2), dpq = dipyrido[3,2-d:2′,3′-f]quinoxaline, DMF = N,N-dimethylformamide were synthesized, characterized by various spectroscopic methods and single crystal X-ray crystallography. They were studied for their DNA and protein binding and photo-induced DNA cleavage activity. The complexes displays ten-coordinate [LnN2O8] bicapped dodecahedron coordination geometry from a bidentate N,N  -donor dpq ligand, two DMF and three bidentate NO3- anions. The complexes 1 and 2 showed intense ligand centered absorption bands ∼300–350 nm originated from n/π → π∗ transition from dipyridoquinoxaline (dpq). The binding interaction of complexes studied with UV–vis spectroscopy, competitive displacement of ethidium bromide and isothermal titration calorimetry (ITC) shows that the complexes display efficient binding affinity to calf thymus DNA with binding constant (Kb) of ∼104 M−1 suggesting groove binding or partial intercalation of complexes to CT-DNA. The complexes display favorable binding affinity to bovine serum albumin (BSA) protein with binding constant (KBSA) of ∼105 M−1. Both the complexes efficiently cleave supercoiled (SC) DNA to its nicked circular (NC) form at UV-A light of 365 nm at 10 μM via formation of singlet oxygen (1O2) and hydroxyl radical (OH) species under physiological condition in a type-II and photoredox pathway.

Graphical abstractPr(III) and Nd(III) complexes namely, [Ln(dpq)(DMF)2(NO3)3] (Ln = Pr(1) and Nd (2)) of dipyridoquinoxaline as efficient photosensitizer were studied for their crystal structures, interaction with DNA and BSA and ROS-mediated photocleavage of DNA.Figure optionsDownload full-size imageDownload as PowerPoint slide