| Abstract
| - Substitution of natural nucleobases in PNA oligomers with ligands is a strategy for directing metal ion incorporationto specific locations within a PNA duplex. In this study, we have synthesized PNA oligomers that contain up tothree adjacent bipyridine ligands and examined the interaction with Ni2+ and Cu2+ of these oligomers and of duplexesformed from them. Variable-temperature UV spectroscopy showed that duplexes containing one terminal pair ofbipyridine ligands are more stable upon metal binding than their nonmodified counterparts. While binding of onemetal ion to duplexes that contain two adjacent bipyridine pairs makes the duplexes more stable, additional metalions lower the duplex stability, with electrostatic repulsions being, most likely, an important contributor to thedestabilization. UV titrations showed that the presence of several bipyridine ligands in close proximity of each otherin PNA oligomers exerts a chelate effect. A supramolecular chelate effect occurs when several bipyridines arebrought next to each other by hybridization of PNA duplexes. EPR spectroscopy studies indicate that even whentwo Cu2+ ions coordinate to a PNA duplex in which two bipyridine pairs are next to each other, the two metal−ligand complexes that form in the duplex are far enough from each other that the dipolar coupling is very weak.EXAFS and XANES show that the Ni2+-bipyridine bond lengths are typical for [Ni(bipy)2]2+ and [Ni(bipy)3]2+ complexes.
- Peptide nucleic acid duplexes in which one or more natural nucleobases are substituted with bipyridine (Bpy) can be used as scaffolds for multiple transition metal ions. The coordination and geometry of metal−ligand complexes formed within the duplexes depend on the position and number of substitutions and the identity of the metal ions.
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