Covalently Palladated Oligonucleotides Through Oxidative Addition of Pd0.

An 11-mer oligonucleotide incorporating a central (2-iodobenzoylamino)methyl residue has been synthesized and palladated by oxidative addition of Pd2 (dba)3 . UV melting profiles of the duplexes formed by the palladated oligonucleotide with its natural complements were biphasic and the higher melting temperatures (Tm ) exhibited considerable hysteresis. CD spectra, in turn, resembled those of canonical B-type double helices. Two-step denaturation, with the "low-Tm " melting involving only canonical base pairs and the "high-Tm " melting involving also dissociation of a PdII -mediated base pair, appears the most likely explanation for the observed UV melting profiles. As the latter step in all cases takes place at a higher temperature than denaturation of natural duplexes of the same length, the putative PdII -mediated base pairs are stabilizing.