The substitution inert N7-(dien)Pt(II) complex of 2'-deoxyguanosine has been shown to undergo acidic depurination 200 times less readily than the uncomplexed nucleoside, whereas the corresponding Nl-and N7-complexes of 2'-deoxyadenosine are depurinated almost as rapidly as the nucleoside itself. These observations have been compared to the influences that several substitution labile metal ions exerted on the rate of depurination. Accordingly, the effects of (dien)Pd(II), Co(II), Ni(II), Cu(II), Zn(I1) and Cd(I1) ions on the acidic hydrolysis of 2' -deoxyadenosine and 2'-deoxyguanosine have been accounted for by competitive attachment of protons and metal ions to the Nl and N7 sites. The applicability of metal ions in chemical DNA sequencing is briefly discussed.
Chemical DNA sequence determination according to the method of Maxam and Gilbert' is based on specific base modifications. Alternatively, the reactivity of base residues may be influenced by complexing with metal ions.
Since the complex formation depends on both the chemical nature of the interacting species and pH of the reaction mixture, 2-5 metal ions offer a potential system with which to remove selectively a certain type of nucleic acid base. For example, it has been reported recently' that reaction of DNA with K,[PdCl,] at pH 2.0 followed by a piperidine workup results in a specific cleavage of adenine residue. The increased selectivity of the