3.4. Ethidium Displacement Bromide Assay—Determination of DNA-Binding Constants

The fluorescence of DNA solutions (calf thymus DNA, T4 coliphage DNA, poly(dA-dT)₂ and poly(dG-dC)₂ with the investigated compound (final concentrations 10, 50, 100 μM) was measured by fluorescence spectrophotometer Infinite M200 TECAN at room temperature according to the procedure described above. The determination of DNA-binding constants was described in previous articles. The apparent binding constant was calculated from KEtBr [EtBr] = Kapp [drug], where [drug] = the concentration of the tested compound at 50% reduction of fluorescence and KEtBr and [EtBr] are known [25,47]. The results are reported as a percentage of fluorescence decreases in Table 1. The compounds 1–18 and their DNA-bound complexes showed neither optical absorption nor fluorescence at 595 nm and did not interfere with the fluorescence of unbound ethidium bromide.