A Supramolecular Interaction of a Ruthenium Complex With Calf-Thymus DNA: A Ligand Binding Approach by NMR Spectroscopy

Flávio Vinícius Crizóstomo Kock; Analu Rocha Costa; Katia Mara de Oliveira; Alzir Azevedo Batista; Antônio Gilberto Ferreira; Tiago Venâncio

doi:10.3389/fchem.2019.00762

A Supramolecular Interaction of a Ruthenium Complex With Calf-Thymus DNA: A Ligand Binding Approach by NMR Spectroscopy

Front Chem. 2019 Nov 8:7:762. doi: 10.3389/fchem.2019.00762. eCollection 2019.

Authors

Flávio Vinícius Crizóstomo Kock¹, Analu Rocha Costa², Katia Mara de Oliveira², Alzir Azevedo Batista², Antônio Gilberto Ferreira¹, Tiago Venâncio¹

Affiliations

¹ Laboratory of Nuclear Magnetic Resonance, Department of Chemistry, Federal University of São Carlos, São Carlos, Brazil.
² Laboratory of Structure and Reactivity of Inorganic Compounds, Department of Chemistry, Federal University of São Carlos, São Carlos, Brazil.

Abstract

Lawsone itself exhibits interesting biological activities, and its complexation with a metal center can improve the potency. In this context a cytotoxic Ru-complex, [Ru(law)(dppb)(bipy)] (law = lawsone, dppb = 1,4-bis(diphenylphosphino)butane and bipy = 2,2'-bipyridine), named as CBLAU, was prepared as reported. In this work, NMR binding-target studies were performed to bring to light the most accessible interaction sites of this Ru-complex toward Calf-Thymus DNA (CT-DNA, used as a model), in a similar approach used for other metallic complexes with anti-cancer activity, such as cisplatin and carboplatin. Advanced and robust NMR binding-target studies, among them Saturation Transfer Difference (STD)-NMR and longitudinal relaxometry (T₁), were explored. The ¹H and ³¹P -NMR data indicate that the structure of Ru-complex remains preserved in the presence of CT-DNA, and some linewidth broadening is also observed for all the signals, pointing out some interaction. Looking at the binding efficiency, the T₁ values are highly influenced by the formation of the CBLAU-DNA adduct, decreasing from 11.4 s (without DNA) to 1.4 s (with DNA), where the difference is bigger for the lawsone protons. Besides, the STD-NMR titration experiments revealed a stronger interaction (K_D = 5.9 mM) for CBLAU-DNA in comparison to non-complexed lawsone-DNA (K_D = 34.0 mM). The epitope map, obtained by STD-NMR, shows that aromatic protons from the complexed lawsone exhibits higher saturation transfer, in comparison to other Ru-ligands (DPPB and bipy), suggesting the supramolecular contact with CT-DNA takes place by the lawsone face of the Ru-complex, possibly by a spatial π-π stacking involving π-bonds on nucleic acids segments of the DNA chain and the naphthoquinone group.

Keywords: CT-DNA; NMR; anti-cancer; binding interactions; lawsone; ruthenium complex.