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

Abstract

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 ∼300–350nm 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 ∼104M−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 ∼105M−1. Both the complexes efficiently cleave supercoiled (SC) DNA to its nicked circular (NC) form at UV-A light of 365nm at 10μM via formation of singlet oxygen (1O2) and hydroxyl radical (OH) species under physiological condition in a type-II and photoredox pathway.