Erbium(III) coordination compounds with substituted salicylaldehydes: Characterization and biological profile

Abstract

Five erbium(III) complexes with salicylaldehyde (saloH for 1), and mono– (5–X–saloH; X = NO2 and Me for 2 and 3, respectively) or di–substituted salicylaldehydes (3,5–diX–saloH; X = Cl and Br for 4 and 5, respectively) were synthesized and characterized by physicochemical and spectroscopic techniques and single–crystal X–ray crystallography. All five complexes have the general formula [Er(deprotonated salicylaldehyde)3(MeOH)(H2O)]. The structure of complexes [Er(3,5–diCl–salo)3(MeOH)(H2O)]·1.5MeOH (complex 4) and [Er(3,5–diBr–salo)3(MeOH)(H2O)]·1.75MeOH (complex 5) were verified by single–crystal X–ray crystallography. The evaluation of antioxidant activity of the complexes was focused on their ability to scavenge 1,1–diphenyl–picrylhydrazyl and 2,2′–azinobis–(3–ethylbenzothiazoline–6–sulfonic acid) free radicals and to reduce H2O2. The interaction of the complexes with calf–thymus DNA was investigated by UV–vis spectroscopy, viscosity measurements and via competitive studies with ethidium bromide in order to evaluate the possible DNA–binding mode and to determine the corresponding DNA–binding constants. The affinity of the complexes for bovine and human serum albumins was explored by fluorescence emission spectroscopy and the corresponding binding constants were determined.