Synthesis, characterization and DNA binding affinities of water-soluble benzoheterocycle triosmium clusters

The syntheses of the water-soluble clusters [Os3(CO)9(μ-η2-(LH))(μ-H)L′] (L=3-amino quinoline, L′=Na3[P(C6H4SO3)3] 1; L=3-amino quinoline, L′=[P(OCH2CH2NMe3)3]I3, 2; L=3-(2-phenyl acetimido) quinoline, L′=[P(OCH2CH2NMe3)3]I3, 3; L=phenanthridine, L′=[P(OCH2CH2NMe3)3]I3, 4) are reported. The products have been fully characterized by 1H-, 13C VT-NMR and LC–TOF-MS. The effect of pH and concentration on intermolecular aggregation in water has been investigated. The interactions of these clusters with DNA have been studied using the plasmid super coiled DNA relaxation test in a 1% electrophoresis agarose gel. Band retardation due to cluster binding was observed for the positively charged clusters 2–4, but not for the negatively charged 1. The relative binding affinities were in the order 2<3∼4 and all three showed greater binding affinities than the positively charged cluster [Rh3(μ3-S)2(η5-Me5C5)3](BF4)2. These preliminary results suggest a relationship between the nature of the heterocyclic ligand and the binding affinity of the cluster to DNA.