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Synthesis and Structural Investigation of New Bio-Relevant Complexes of Lanthanides with 5-Hydroxyflavone: DNA Binding and Protein Interaction Studies
Alexandra-Cristina Munteanu 1 , Mihaela Badea 2 , Rodica Olar 2 , Luigi Silvestro, 3 Constanţa Dulea 3 , Constantin-Daniel Negut 4 , Valentina Uivarosi 1 , Arnaud Gautier
1  Department of General and Inorganic Chemistry, Faculty of Pharmacy, “Carol Davila” University of Medicine and Pharmacy, 6 Traian Vuia Str., 020956 Bucharest, Romania
2  Department of Inorganic Chemistry, Faculty of Chemistry, University of Bucharest, 90-92 Panduri Str., 050663 Bucharest, Romania;(M.B.);(R.O.)
3  PharmaServ. International SRL, 52 Sabinelor Str., 050853 Bucharest, Romania;(L.S.);(C.D.)
4  Horia Hulubei National Institute of Physics and Nuclear Engineering (IFIN-HH), IRASM Radiation Processing Department, Reactorului Str. 30, 077125 Magurele-Ilfov, Romania

Published: 16 December 2016 by MDPI in Molecules
MDPI, Volume 21; 10.3390/molecules21121737
Abstract: In the present work, we attempted to develop new metal coordination complexes of the natural flavonoid 5-hydroxyflavone with Sm(III), Eu(III), Gd(III), Tb(III). The resultant hydroxo complexes have been characterized by a variety of spectroscopic techniques, including fluorescence, FT-IR, UV-Vis, EPR and mass spectral studies. The general chemical formula of the complexes is [Ln(C15H9O3)3(OH)2(H2O)x]·nH2O, where Ln is the lanthanide cation and x = 0 for Sm(III), x = 1 for Eu(III), Gd(III), Tb(III) and n = 0 for Sm(III), Gd(III), Tb(III), n = 1 for Eu(III), respectively. The proposed structures of the complexes were optimized by DFT calculations. Theoretical calculations and experimental determinations sustain the proposed structures of the hydroxo complexes, with two molecules of 5-hydroxyflavone acting as monoanionic bidentate chelate ligands. The interaction of the complexes with calf thymus DNA has been explored by fluorescence titration and UV-Vis absorption binding studies, and revealed that the synthesized complexes interact with DNA with binding constants (Kb) ~ 104. Human serum albumin (HSA) and transferrin (Tf) binding studies have also been performed by fluorescence titration techniques (fluorescence quenching studies, synchronous fluorescence spectra). The apparent association constants (Ka) and thermodynamic parameters have been calculated from the fluorescence quenching experiment at 299 K, 308 K, and 318 K. The quenching curves indicate that the complexes bind to HSA with smaller affinity than the ligand, but to Tf with higher binding affinities than the ligand.
Keywords: Lanthanides, Chelates, density functional calculations, Calf thymus DNA, HSA, Transferrin
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