3.8. Ethidium Bromide Displacement Fluorescence Assay

Fluorescence quenching assay was performed using a Spectrofluorimeter (Horiba Fluoromax 4) equipped with 1.0 cm quartz cells and a thermostat bath. Sperm salmon DNA (100 μM) was diluted in a buffer containing 50 mM ammonium acetate pH 7.5 and treated with ethidium bromide at a DNA:ligand ratio of 50:1 for 30 min at room temperature. In control experiments, we verified that the ethidium efficiently binds the DNA. The quenching was evaluated, adding a certain amount of stock solutions of the Pt complexes dissolved in DMSO (50 mM) in increments to the solution of the DNA−ethidium complex.
In control experiments, the quenching effect of DMSO was evaluated, and the results indicate that there is no affect on the amount of DMSO used on the DNA−ethidium interaction. To follow the quenching, an excitation wavelength of 545 nm was chosen for DNA− ethidium in the absence and in the presence of the Pt complexes.