Abstract/Summary

Λ-[Ru(TAP)2(dppz)]2+ was crystallised with the G-quadruplex-forming heptamer d(TAGGGTT). Surprisingly, the complex is not in contact with any G-quartet surface, even though there are four unique binding sites. Two complexes stabilise cavities formed from terminal TA and TT mismatched pairs. A third shows kinking by a TAP ligand between TT linkages, while the fourth shows intercalation of a dppz ligand at a TT/TA step stabilised by an additional T stacking interaction. Overall, the structure shows an unexpected affinity for thymine, and suggests models for G-quadruplex loop binding.