NMR-titrations with complexes between ds-DNA and indole derivatives including tryptophane containing peptides

It is shown that NMR titrations can be used on a quantitative basis to derive binding constants and binding modes of ds-DNA ligand complexes from several signals. The results are partially at variance with literature conclusions; they can be interpreted by additive and independent contributions of electrostatic interactions between DNA phosphate and ammonium centers in the side chain of the ligands, and of very weak stacking contributions of the indole rings. While gramine and tryptamine are found to intercalate, tryptophane-containing peptides do so only, if the tryptophane is flanked by at least two lysine units.