New ligand combinations for the efficient stabilization of short nucleic acid hairpins

Short nucleic acid hairpins (one or two base-pair stems) were strongly stabilized by simple chemical modifications. Non-nucleosidic pyrene or naphtalene diimide derivatives were appended at both 3′ and 5′ nearby ends of 2′-OMe RNA hairpins, yielding a very large increase in melting temperatures of the modified structures (from +21 to +55°C). The excimer formation between the two consecutive pyrene units is in favor of end-stacked pyrenyl rings.