Guanine-rich nucleic acids can adopt unusual structures called guanine quadruplexes (G4) based on stacked guanine quartets. Both RNA and DNA backbones are compatible with G4 formation. As RNA and DNA quadruplexes may be recognized by ligands, it is important to understand the rules that govern the stability and specificity of these complexes. We explore the binding of a pyridine dicarboxamide derivative to various oligoribo- and oligodeoxyribo-nucleotides.