An Ir(III) polypyridyl complex-conjugated 14-mer oligonucleotide (IrIII-DNA) was synthesized and its hybridization properties with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) were evaluated by UV-melting experiments. The stabilities of the duplexes of IrIII-DNA with 14-, 20-, and 26-mer ssDNAs were higher than those of the unconjugated oligonucleotides. The triplex of IrIII-DNA with 14-mer dsDNA was also stabilized. However, the triplexes of IrIII-DNA with 20- and 26-mer dsDNAs, flanked by 3 and 6 base pairs at the both ends of 14-mer dsDNA target, were destabilized. This is presumably because of steric repulsion between the Ir(III) complex and the protruding 3- and 6-mer dsDNA moieties which are inflexible compared to ssDNA.
Keywords: Iridium(III) polypyridyl complex; duplex-forming ability; oligonucleotide conjugates; triplex-forming ability.