Rotational dynamics of hexaamminecobalt(III) bound to oligomeric DNA: Correlation with cation-induced structural transitions

Abstract

Two common assumptions are that duplex DNA structure shows little sensitivity to ionic conditions and that simple cations bind to DNA in a nonspecific fashion. Here we examine these assumptions using as a model ligand the inorganic cation Co(NH3)6(3+). We find, upon titration with Co(NH3)6(3+), that certain DNA oligonucleotides show pronounced changes in circular dichroism spectra. For oligonucleotides such as d(GGCCGGCC), with contiguous, same-strand guanines, the transition is toward A-DNA characteristics. F…