Effect of bridging ligand structure on the thermal stability and DNA binding properties of iron(ii) triple helicates

Triple helical di-iron complexes, readily prepared through interaction of iron(ii) ions with imine-based ligands, are cylinder-shaped tetracations comparable in size and shape to common protein DNA recognition units. They have a strong tendency to coil DNA, and have recently been found to induce formation of three-way junctions in palindromic oligonucleotides. To introduce potential H bond acceptor units onto the surface of triple-helicates, new iron(ii) complexes have been synthesized in which the central linking unit in the bridging ligand is S or O, instead of CH₂. The DNA binding properties of these new metallo-helicates were studied using UV-vis spectroscopy and circular and linear dichroism. Results show that the three iron triple helicates bind the DNA in a similar way but that the stability of the triple helicate unit is decreased with the O linked bridging ligand.