In this paper, several rare earth [terbium(III), ytterbium(III) and yttrium(III)] complexes containing 2,9-dimethyl-1,10-phenanthroline (Me2Phen) were successfully synthesized and characterized by means of elemental analysis (CHN), infrared spectroscopy (FT-IR), UV–vis absorption spectroscopy and 1HNMR. To explore the potential medicinal value of these complexes (MMe2Phen), their binding interactions with human serum albumin (HSA) were investigated through UV–vis and fluorescence spectroscopies and also molecular docking examinations. The thermodynamic parameters, binding forces and Förster resonance distance between these complexes and Trp-214 of HSA were estimated from the analysis of fluorescence measurements. The values of estimated binding constants (Kb) ranging for the formation of MMe2Phen:HSA complex were in the order of 105 M−1. The thermodynamic parameters determined by van’t Hoff analysis of Kb (ΔH° < 0 and ΔS° < 0) clearly indicate the major rules of hydrogen bonds and van der Waals interactions in the formation process of MMe2Phen:HSA. The values of Stern–Volmer constant and the evaluation of dynamic quenching constant at various temperatures provided good evidences for static quenching mechanism. Furthermore, the results of molecular docking calculation and competitive binding experiments represent the binding of these complexes to site 3 of HSA located in subdomain IB, containing both polar and apolar residues. The consistency of computational and experimental results, according to the binding sites and the order of binding affinities (TbMe2Phen > YbMe2Phen > YMe2Phen), supports the accuracy of docking calculation.
Rare earth complexes Human serum albumin Binding affinity Fluorescence spectroscopy Molecular docking
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The financial supports of Research Councils of Isfahan University, University of Sistan and Baluchestan and National Elites Foundation (grant number 96013717) are gratefully acknowledged.