Synthesis and Structural Investigation of New Bio-Relevant Complexes of Lanthanides with 5-Hydroxyflavone: DNA Binding and Protein Interaction Studies

Abstract

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(C 15 H 9 O 3 ) 3 (OH) 2 (H 2 O) x ]·nH 2 O, 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 (K b )~10 4 . 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 (K a ) 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.

Cytotoxicity studies, DNA interaction and protein binding of new Al (III), Ga (III) and In (III) complexes with 5‐hydroxyflavone

“…The same band appears very weak in the spectra of the complexes, indicating that 5‐hydroxyflavone is coordinated in its deprotonated form. The ν (C‐O‐C) frequency does not appear shifted in the spectra of the complexes, which confirms that the ring oxygen is not involved in coordination …”

“…The emission spectra of EB‐DNA complex in the absence and presence of increasing concentrations of the ligand and complexes (1) – (3) are shown in Figure , Figure S9. Ksv values (Table ) indicate that the complexes bind to CT‐DNA with binding affinities that vary in the following order: (1) > (2) > (3) > 5‐HOF . (1) – (3) display higher binding affinities than the ligand (note that 5‐HOF is planar in the complexes, whereas free 5‐HOF has a non‐planar conformation), which suggests that the complexes may interact with DNA via intercalation, while another mechanism is probably involved in the 5‐HOF‐binding to DNA (e.g.…”

“…Based on the values of the binding constant, K a , the complexes bind to Tf and HSA with affinities that vary in the following order: (1) > 5‐HOF > (2) > (3 ) and (1) > 5‐HOF > (3) > (2) . K a values for 5‐HOF have been taken from ref …”

Molecular Structure–Affinity Relationship of Flavonoids in Lotus Leaf (Nelumbo nucifera Gaertn.) on Binding to Human Serum Albumin and Bovine Serum Albumin by Spectroscopic Method

“…Human serum albumin (HSA) consists of a non-glycosylated single chain containing 585 amino acids with a molecular weight of 66,500 Da [ 24 ]. Three homologous domains (domains I–III), in turn divided into two subdomains (A and B), with multiple ligand-binding sites localized in each of these subdomains were described [ 20 , 25 ]. Many drugs bind to one of the two primary binding sites located in subdomains IIA and IIIA (Sudlow sites I and II, respectively) [ 26 ].…”

Supramolecular interaction of transition metal complexes with albumins and DNA: Spectroscopic methods of estimation of binding parameters

“…X-ray crystallography [23, 24, 40-48, 50, 136-138, 140-142, 145, 150, 151, 156-214] IR-spectroscopy [37, 41, 51, 54, 137, 140, 142, 145, 148, 149, 156, 158-161, 166-170, 172-174, 178, 179, 181, 182, 184-186, 188, 189, 191-198, 200, 202, 204, 205, 207-210, 215-233] Circular dichroism spectroscopy [8, 33-35, 39, 40, 142, 141, 143, 145-149, 163, 168, 169, 172, 179, 185, 189, 193, 196, 199, 202, 203, 206, 216, 219, 221, 223, 225, 226, 229, 231-239] EPR-spectroscopy [49,51,54,159,167,181,187,197,200,201,209,215,216,219,222,223,240] NMR-spectroscopy [37, 41, 52, 140, 142, 149, 155, 158, 161, 172, 179, 181, 183, 185, 188, 191, 192, 200, 202, 204, 205, 207, 209, 210, 214, 218-221, 223, 225, 227, 229-232, 236, 238, 241-243] Cyclic voltammetry [42-46, 48, 50, 54, 149, 151, 159, 164, 167, 173, 175, 176, 179, 184, 189, 208, 211-213, 221, 230, 240, 241, 244-247] X-ray crystallography, as a rule, is used for corroboration or specification of the structure of coordinated metal complexes themselves, [24,40,42] in particular, new biologically active compounds or earlier unknown coordination structures. [7,41,43,44,248] X-ray photoelectron spectroscopy for C, N, and O is used to obtain the information of the changes in the energy of atom bonds of these elements in the protein during the formation .…”