Dimethyl sulfoxide (dmso)

Calf-thymus DNA (CT-DNA) was purchased from Sigma-Aldrich Ltd (Brazil) and used without previous purification. A 1.078 mM solution of CT-DNA was prepared by dissolving an adequate weight of this macromolecule in a deuterated phosphate buffer. The pH 7.2 phosphate D₂O buffer was prepared by dissolving disodium hydrogen phosphate (Na₂HPO₄.12H₂O, 0.1180 g) and sodium dihydrogen phosphate (NaH₂PO₄.2H₂O, 0.0217 g) in 10.00 mL D₂O (99.9%, Cambridge Isotopes Laboratories, Inc. with pH 7.2) to make a 0.046 M solution. The (CBLAU)( ${\text{BF}}_4^{-}$ ) complex was dissolved in a 5:95% v/v of DMSO (99.8% Cambridge Isotopes Laboratories, Inc.) and deuterated buffer respectively. ${\text{BF}}_4^{-}$ was used as a counter ion together with 5% of DMSO-d6 to increase the solubility of the Ru-complex in aqueous solution. All ¹H NMR and STD-NMR spectra were recorded using a 1:100 (DNA:CBLAU) molar ratio, in a final volume of 500 μL transferred to a 5 mm NMR tube (Norrel, Inc. USA). For the epitope mapping experiment, the final concentration of CBLAU was 5 mM and the concentration for the CT-DNA was 50 μM. On the other hand, for the concentration-dependent STD-NMR experiment, the CBLAU and lawsone concentrations were ranged from 5 to 1 mM. In these experiments, the CT-DNA concentration was fixed in 50 μM. For these studies, 7 independent STD-NMR experiments were acquired for each concentration.