Jump to main content
Jump to site search

Issue 46, 2015
Previous Article Next Article

Luminescent europium and terbium complexes of dipyridoquinoxaline and dipyridophenazine ligands as photosensitizing antennae: structures and biological perspectives

Author affiliations

Abstract

The europium(III) and terbium(III) complexes, namely [Eu(dpq)(DMF)2(NO3)3] (1), [Eu(dppz)2(NO3)3] (2), [Tb(dpq)(DMF)2Cl3] (3), and [Tb(dppz)(DMF)2Cl3] (4), where dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 1 and 3), dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 2 and 4) and N,N′-dimethylformamide (DMF) have been isolated, characterized from their physicochemical data, luminescence studies and their interaction with DNA, serum albumin protein and photo-induced DNA cleavage activity are studied. The X-ray crystal structures of complexes 1–4 show discrete mononuclear Ln3+-based structures. The Eu3+ in [Eu(dpq)(DMF)2(NO3)3] (1) and [Eu(dppz)2(NO3)3] (2) as [Eu(dppz)2(NO3)3]·dppz (2a) adopts a ten-coordinated bicapped dodecahedron structure with a bidentate N,N-donor dpq ligand, two DMF and three NO3 anions in 1 and two bidentate N,N-donor dppz ligands and three NO3 anions in 2. Complexes 3 and 4 show a seven-coordinated mono-capped octahedron structure where Tb3+ contains bidentate dpq/dppz ligands, two DMF and three Cl anions. The complexes are highly luminescent in nature indicating efficient photo-excited energy transfer from the dpq/dppz antenna to Ln3+ to generate long-lived emissive excited states for characteristic f → f transitions. The time-resolved luminescence spectra of complexes 1–4 show typical narrow emission bands attributed to the 5D07FJ and 5D47FJ f–f transitions of Eu3+ and Tb3+ ions respectively. The number of inner-sphere water molecules (q) was determined from luminescence lifetime measurements in H2O and D2O confirming ligand-exchange reactions with water in solution. The complexes display significant binding propensity to the CT-DNA giving binding constant values in the range of 1.0 × 104–6.1 × 104 M−1 in the order 2, 4 (dppz) > 1, 3 (dpq). DNA binding data suggest DNA groove binding with the partial intercalation nature of the complexes. All the complexes also show binding propensity (KBSA ∼ 105 M−1) to the bovine serum albumin (BSA) protein. The intensity of the time-gated luminescence spectral bands enhances significantly with the increasing DNA concentration in aqueous buffer medium due to displacement of bound water upon interaction with DNA, thus reducing non-radiative quenching through the O–H oscillator. Complexes 1–4 efficiently cleave supercoiled (SC) ds-DNA to its nicked circular (NC) form on exposure to UV-A light of 365 nm via formation of singlet oxygen (1O2) and hydroxyl radicals (HO˙) as the reactive oxygen species at micromolar concentrations under physiological conditions.

Graphical abstract: Luminescent europium and terbium complexes of dipyridoquinoxaline and dipyridophenazine ligands as photosensitizing antennae: structures and biological perspectives

Back to tab navigation

Supplementary files

Publication details

The article was received on 25 Jul 2015, accepted on 12 Oct 2015 and first published on 12 Oct 2015


Article type: Paper
DOI: 10.1039/C5DT02852C
Author version
available:
Download author version (PDF)
Citation: Dalton Trans., 2015,44, 19844-19855
  •   Request permissions

    Luminescent europium and terbium complexes of dipyridoquinoxaline and dipyridophenazine ligands as photosensitizing antennae: structures and biological perspectives

    S. Dasari and A. K. Patra, Dalton Trans., 2015, 44, 19844
    DOI: 10.1039/C5DT02852C

Search articles by author

Spotlight

Advertisements