A Highly Stabilizing Silver(I)-Mediated Base Pair in Parallel-Stranded DNA

The first parallel-stranded DNA duplex with Hoogsteen base pairing that readily incorporates an Ag+ ion into an internal mispair to form a metal-mediated base pair has been created. Towards this end, the highly stabilizing 6FP-Ag+-6FP base pair comprising the artificial nucleobase 6-furylpurine (6 FP) was devised. A combination of temperature-dependent UV spectroscopy, CD spectroscopy, and DFT calculations was used to confirm the formation of this base pair. The nucleobase 6 FP is capable of forming metal-mediated base pairs both by the Watson-Crick edge (i.e. in regular antiparallel-stranded DNA) and by the Hoogsteen edge (i.e. in parallel-stranded DNA), depending on the oligonucleotide sequence and the experimental conditions. The 6FP-Ag+-6FP base pair within parallel-stranded DNA is the most strongly stabilizing Ag+-mediated base pair reported to date for any type of nucleic acid, with an increase in melting temperature of almost 15 degrees C upon the binding of one Ag+ ion.