Phenanthridinium cyclobisintercalands. Fluorescence sensing of AMP and selective binding to single-stranded nucleic acids

Macrocyclic ligands 1 and 2 containing two positively charged phenanthridinium units and aminobisacetylenic bridges, exhibit significantly higher affinity toward single-stranded rather than double-stranded polynucleotides. The ligands bis-intercalate into the former and show non-intercalative interactions with the latter type of nucleic acids. Both ligands differentiate AMP from the GMP or UMP by significant fluorescence emission increase upon complexation of the first nucleotide in water (log Ks of 1:1 and 1:2 complexes 5.8 and 1.4, respectively), while only a slight emission change is observed in titrations with GMP and UMP.